DOE-BASED SYSTEMS AND DEVICES FOR PRODUCING LASER BEAMS HAVING MODIFIED BEAM CHARACTERISTICS

Abstract: Novel methods are disclosed for designing and constructing miniature optical systems and devices employing light diffractive optical elements (DOEs) for modifying the size and shape of laser beams produced from commercial-grade laser diodes, over an extended range hitherto unachievable using conventional techniques. The systems and devices of the present invention have uses in a wide range of applications, including laser scanning, optical-based information storage, medical and analytical instrumentation, and the like. In the illustrative embodiments, various techniques are disclosed for implementing the DOEs as holographic optical elements (HOEs), computer-generated holograms (CGHs), as well as other diffractive optical elements.

Description: DOR-RASED SYSTEMS AND DRVTCRS FOR PRODUCTNG T .ASRR BEAMS HAVTNG MODTFTED REAM CHARACTERISTICS BACKGROUND OF THE TNVRNTTON Technical Field The present invention relates generally to diffractive optical element (DOE) based optical systems of ultra-compact design capable of modifying the inherent elliptical, divergent, eccentric and astigmatic characteristics of laser beams produced from laser diode sources, such as visible laser diodes (VLDs). Brief Description of the Prior Ar Laser diodes or visible laser diodes (VLD) are often used as light sources in many scientific _and engineering applications. While laser diodes offer significant advantages over other laser sources, e.g. gas lasers, in terms of efficiency, size, and cost, they nevertheless suffer from several undesirable optical characteristics, namely: high beam divergence, elliptical beam profile, and astigmatism. In order to use laser diodes in many communication, datastorage, scanning, and imaging applications, these inherent deficiencies i n laser diodes must be corrected. While complex refractive-optics type systems (employing anamorphic lenses and the like) have been developed for the purpose of correcting for laser diode characteristics, such systems are generally bulky and expensive, and thus ill-suited for use in numerous applications. US Patent Nos. 5,247,162 and Bl 4,816,660 disclose the use of a lens an d aperture-stop to shape the laser beam produced from a VLD for use in laser scanners. While this technique provides an inexpensive way of shaping the cross-section of a VLD laser beam, it does so at the expense of a substantial loss in beam power. Moreover, this "pinhole" technique is incapable of correcting for astigmatism in laser beams produced by VLDs. In recent years, alternative approaches to VLD beam shaping an d correction have been developed. Such alternative techniques include, for example, the use of: integrated-optics lenses; computer-generated hologram (CGH) gratings; micro-Fresnel lenses; waveguide optics; and holographic optical elements (HOEs). The use of HOEs for beam collimation, shaping/profiling an d astigmatism-correction has received great attention, as such devices can b e made inexpensively and small in size to be used in CD-ROM players, consumer- products and analytical instruments employing VLDs and the like. Examples of prior art laser diode beam-correction techniques employing HOEs are disclosed in the following journal articles: "Efficient Beam-Correcting Holographic Collimator For Laser Diodes" by A. Aharoni, et al., published in Vol. 17, No. 1 8 , OPTICS LETTERS, September 15, 1992, at pages 1310-1312; "Beam-Correcting Holographic Doublet For Focusing Multimode Laser Diodes" by A. Aharoni, et al., published in Vol. 18, No. 3, OPTICS LETTERS, February 1, 1993, at pages 179-181 ; and "Design of An Optical Pickup Using Double Holographic Lenses" by Hiroyasu Yoshikawa, et al., published in SPIE, Vol. 2652, 1996, at pages 334- 340. While the above-cited prior art publications disclose dual-HOE optics systems for beam-collimation, beam-shaping and astigmatism correction, such prior art design methods do not enable the design and construction of laser beams having any degree of astigmatism, focal-distance, spot-size, focused-spot aspect-ratio, and zero dispersion. These are critical requirements in many laser scanning bar code reading applications. Prior art HOE-based systems do not address the fact that commercial VLDs suffer from beam eccentricity (i.e. poor beam pointing characteristics). Consequently, it has not been possible to successfully carry out many design objectives by virtue of the fact that assumptions made during system design are not satisfied during design realization. Accordingly, there is a great need in the art for an improved method of designing and constructing optical systems for modifying the elliptical, divergent, eccentric and astigmatic characteristics of laser beams inherently produced from commercial-grade laser diodes, while avoiding the shortcomings and drawbacks of prior art systems, devices, and methodologies. DISCLOSURE OF THE PRESENT INVENTION Thus, it is a primary object of the present invention to provide a n improved method of designing optical systems for modifying the inherent elliptical, divergent, eccentric and astigmatic characteristics of a laser diodes, while avoiding the shortcomings and drawbacks of prior art systems, devices, and methodologies. Another object of the present invention is to provide a novel laser beam modification system employing a plurality of diffractive optical elements (DOEs) for modifying the size and shape of a laser beam produced from a commercial-grade laser diode, such as a VLD, over an extended range which has hitherto been impossible to achieve using conventional techniques, while avoiding the introduction of dispersion in the output laser beam which is commonly associated with prior art HOE doublets and the like. Another object of the present invention is to provide such a DOE-based laser beam modifying system, wherein the inherent astigmatism characteristics associated with a VLD are eliminated or minimized. Another object of the present invention is to provide a DOE-based laser beam modifying system, wherein beam dispersion is minimized, or normal dispersion or reverse dispersion characteristics are provided for any given beam compression or expansion ratio, by selecting the proper angle between the two DOEs of the system. Another object of the present invention is to provide a DOE-based laser beam modifying system, wherein beam dispersion is minimized for the system acting alone, or fine-tuned to compensate for the dispersion of other elements preceding it or following the system. Another object of the present invention is to provide a laser beam modifying system capable of producing a laser beam having a desired spot-size over a specified depth of field, achieved by focusing the laser beam with a lens (or variable DOE of a selected type), and then reshaping the laser beam using a pair of DOEs. Another object of the present invention is to provide a laser beam producing system employing a set of beam-modifying DOEs which produce zero dispersion while simultaneously providing any desired aspect-ratio for the beam leaving (exiting) the second DOE. Another object of the present invention it to provide a HOE-based laser beam modifying system adapted for use in a broad range of applications employing VLDs, which includes, but is not limited to, laser scanning applications. Another object of the present invention it to provide a CGH-based laser beam modifying system adapted for use in a broad range of applications employing VLDs, which includes, but is not limited to, laser scanning applications. Another object of the present invention is to provide an ultra-compact DOE-based device capable of collimating or focusing laser beams produced from astigmatic VLDs while minimizing dispersion beam dispersion an d correcting for beam ellipticity. A further object of the present invention is to provide an ultra-compact optics module for modifying the aspect-ratio of laser beams produced by VLDs, while eliminating beam astigmatism introduced by virtue of the inherent astigmatic difference in the VLD, and minimizing dispersion in the output laser beam created by wavelength-dependent variations in the spectral output of the VLD, such as superluminescence, multi-mode lasing, and laser mode hopping. Another object of the present invention is to provide a novel optical- bench module which enables easy mounting and alignment of selected components of the laser beam producing systems of the present invention so that the inherently elliptical beam produced from commercial VLDs is simply aligned on the optical axis of the system. Another object of the present invention is to provide a novel DOE-based laser beam producing device, wherein refractive optics (LI) having an axially symmetric surface profile characteristics are disposed between the laser diode source (VLD) and the diffractive optics (e.g. DOEs Dl and D2), to enable the use the DOEs to modify (e.g. correct or eliminate) astigmatism in the output laser beam, while simplifying the manufacture of the refractive optics (LI) an d diffractive optics ( DOEs Dl and D2), reducing the cost of optical elements, an d simplifying parameter alignment during the assembly process. Another object of the present invention is to provide a novel optics module employing a pair of DOEs configured in the beam compression mode, wherein the total expansion factor (M) of the DOE combination is less than one, so that the size of the laser beam in the plane of diffraction is compressed without changing the beam size in the dimension perpendicular to the plane of diffraction. Another object of the present invention is to provide a novel optics module employing a pair of DOEs configured in the beam expansion mode, wherein the total expansion factor (M) of the DOE combination is greater than one, so that the size of the laser beam in the plane of diffraction is expanded without changing the beam size in the dimension peφendicular to the plane of diffraction. A further object of the present invention is to provide a novel light diffractive optics module for incorporation into small laser scanning devices, such as laser scan-engines, as well as replacing conventional prisms an d anamorphic lenses used in VLD-based optical systems such as optical storage devices, CD-ROM players and recorders, and like systems and devices. Another object of the present invention is to provide a DOE-based optics module for modifying the aspect-ratio of a VLD beam while simultaneously controlling beam dispersion to minimize the overall dispersion of the optical system in which it is being used. Another object of the present invention is to provide such an optics module, wherein beam astigmatism inherently associated with VLDs is eliminated or minimized. Another object of the present invention is to provide a novel method for designing a dual-HOE laser beam modifying system, in which a pair of equations are solved under a given set of conditions which ensures that beam dispersion is eliminated and a desired expansion factor (M) is obtained. Another object of the present invention is to provide such an optical design method, wherein analytical and spreadsheet-type programs are combined in an i ntegrated fashion to allow for easy design and analysis of the optics module under consideration. Another object of the present invention is to provide a dual-DOE optics module particularly designed for replacing "pinhole" type beam shaping modules used i n laser scanning bar code symbol readers . Another object of the present invention is to provide a novel system for precisely and rapidly aligning the parameters of the optics modules of the present invention to enable the inexpensive mass production of such optical systems and devices for widespread use in diverse fields of endeavor. Another object of the present invention is to provide such a parameter alignment system, wherein micro-adjustment of the optical components of the laser beam producing modules of the present invention are carried out in a fully automated manner under microcomputer control, thereby allowing (i.e. enabling) mass-production of DOE-based laser beam producing modules which satisfy high quality-control (QC) measures. Another object of the present invention is to provide a novel method of designing an ultra-compact HOE-based device for producing a laser beam having a selected set of beam characteristics obtained by modifying the astigmatic, elliptical light beams produced from inexpensive VLDs. Another object of the present invention is to provide a hand-held laser scanner, wherein the laser beam producing system of the present invention is embodied to enable the production of laser beams for bar code scanning operations. Another object of the present invention is to provide a body-wearable laser scanner, wherein the laser beam producing system of the present invention is embodied to enable the production of laser beams for bar code scanning operations. Another object of the present invention is to provide a laser scanning- engine, wherein the laser beam producing system of the present invention is embodied to enable the production of laser beams for bar code scanning operations. Another object of the present invention is to provide in-counter scanners, projection scanners, pass-through (passive) scanners, laser pointers, and the like, wherein the laser beam producing system of the present invention is embodied. Another object of the present invention is to provide a holographic laser scanner, wherein one or more laser beam producing modules of the present invention are embodied to enable the production of a plurality of laser beams for bar code scanning operations. Another object of the present invention is to provide a CD-ROM playing unit, wherein the laser beam producing system of the present invention is embodied to enable the production of laser beams for reading information digitally recorded within a CD-ROM or like recording device. Another object of the present invention is to provide a laser-based instrument, wherein the laser beam producing system of the present invention is embodied to enable the production of laser beams for diagnosis or detection of various conditions. These and other objects of the present invention will become apparent hereinafter and in the Claims to Invention. BRIEF DESCRIPTION OF THR DRAWINGS In order to more fully understand the Objects of the Present Invention, the following Best Modes For Carrying Out The Present Invention should b e read in conjunction with the accompanying Figure Drawings, wherein: Fig. 1 is a schematic representation of a general model for the DOE-based laser beam producing system of the present invention, showing its laser source and the DOE-based laser beam modifying subsystem; Fig. 1A is a schematic representation of the dual-DOE optical subsystem used in the various illustrative embodiments of the laser beam producing system of the present invention, identifying the geometrical optical parameters employed in the design of this subsystem; Fig. 2A is a geometrical optics model of the first illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2B is a geometrical optics model of the second illustrative embodiment of the DOE-based laser beam producing subsystem according t o the principles of the present invention, realized using a transmission-type DOE for both DOE1 and DOE2; Fig. 2B1 is a geometrical optics model of the second illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention, realized using reflection-type DOEs for both DOE1 and DOE2; Fig. 2B2 is a geometrical optics model of the second illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention, realized using a transmission-type DOE for DOE1 and a reflection-type DOE for DOE2; Fig. 2B3 is a geometrical optics model of the second illustrative embodiment of t he DOE-based laser beam producing subsystem according to the principles of the present invention, realized using a reflection-type DOE for DOE1 and a transmission-type DOE for DOE2; Fig. 2C is a geometrical optics model of the third illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2D is a geometrical optics model of the fourth illustrative embodiment of the DOE-based laser beam producing subsystem according t o the principles of the present invention; Fig. 2E is a geometrical optics model of the fifth illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2F is a geometrical optics model of the sixth illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2G is a geometrical optics model of the seventh illustrative embodiment of the DOE-based laser beam producing subsystem according t o the principles of the present invention; Fig. 2H is a geometrical optics model of the eighth illustrative embodiment of the DOE-based laser beam producing subsystem according t o the principles of the present invention; Fig. 21 is a geometrical optics model of the ninth illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2J is a geometrical optics model of the tenth illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2K is a geometrical optics model of the eleventh illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2L is a geometrical optics model of the twelfth illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2M is a geometrical optics model of the thirteenth illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Fig. 2N is a geometrical optics model of the fourteenth illustrative embodiment of the DOE-based laser beam producing subsystem according to the principles of the present invention; Figs. 3A1 through 3A3 set forth a flow chart illustrating the steps involved in carrying out the method of designing DOE-based laser beam producing systems according to the present invention, wherein astigmatism can be tolerated and adjustment of the focal-length of the resulting stigmatic beam is not required; Figs. 3B1 through 3B3 set forth a flow chart illustrating the steps involved in carrying out the method of designing DOE-based laser beam producing systems, wherein astigmatism correction is desired and adjustment of the focal-length of the resulting stigmatic beam is not required; Figs. 3C1 through 3C3 set forth a flow chart illustrating the steps involved in carrying out the method of designing DOE-based laser beam producing systems, wherein astigmatism correction and adjustment of the focal-length of the resulting stigmatic beam are required; Figs. 3D1 through 3D3, taken together show a flow chart, set forth a flow chart illustrating the steps involved in carrying out the method of designing DOE-based laser beam producing systems, wherein astigmatism correction is desired and adjustment of the focal-length of the resulting stigmatic beam an d delta-focusing are not required; Fig. 3E is a "central-ray" type geometrical optics model of the DOE-based laser beam modifying subsystem employed within each of the illustrative embodiments of the laser beam producing systems of the present invention; Figs. 3F1 through 3F3 set forth a flow chart illustrating the steps involved in carrying out the method of designing the DOE-based laser beam modifying subsystem of the present invention so that pre-selected design criteria is satisfied; Fig. 4A sets forth a flow chart illustrating a preferred method of converting the design p arameters of a HOE into its construction parameters expressed at the construction wavelength; Fig. 4B is a schematic diagram showing apparatus for recording HOEs to be used in the dual-HOE subsystem specified in Fig. 4A; Figs. 4C1 and 4C2 collectively set forth a flow chart illustrating the basic steps involved in constructing a CGH implementation of the DOE-based laser beam modifying subsystem hereof; Fig. 4D is a schematic diagram showing apparatus for generating an d recording master CGHs, and producing copies thereof for use in DOE-based subsystems in accordance with the principles of the present invention; Fig. 5A is a schematic diagram of an optical arrangement for analyzing dispersion in the laser beam output from the DOE-based laser beam modifying subsystem of the present invention; Fig. 5B is a generalized graphical representation of two different dispersion characteristics of a laser beam producing system of the present invention when operated in different modes of operation, shown plotted as a function of output wavelength; Fig. 5B1 is a graphical representation of the dispersion characteristics of an exemplary laser beam producing system of the type shown in Figs. 2A and 7A-7C, showing a negative (concave down) curvature when plotted as a function of output wavelength; Fig. 5B2 is a graphical representation of the dispersion characteristics of a laser beam producing system of the type shown in Figs. 2A and 7A-7C if the direction of propagation of the laser beam is reversed, thereby exhibiting a positive (concave upward) curvature, plotted as a function of output wavelength; Fig. 6A is a first perspective view of a first illustrative embodiment of a laser beam producing module according to the present invention, wherein its VLD laser source is adjustable relative to its imaging lens (LI) and pair of stationary-mounted HOEs and beam directing mirror so that the elliptical beam produced from the VLD is aligned relative to the optical axes of the HOEs i n order to minimize laser beam dispersion and to control the aspect-ratio of the output laser beam in a desired manner; Fig. 6B is a second perspective view of the laser beam producing module shown in Fig. 6A; Fig. 6C is a plan view of the laser beam producing module shown in Fig. 6A; Fig. 7A is a perspective view of a second illustrative embodiment of the laser beam producing module of the present invention, wherein its VLD laser source is adjustable relative to its imaging lens (LI) and pair of stationary- mounted HOEs so that the inherently off-axis elliptical beam produced from the VLD is aligned relative to the optical axes of the HOEs in order to minimize beam dispersion and control the aspect ratio of the output laser beam in a desired manner; Fig. 7B is an exploded view of the laser beam producing module of the present invention shown in Fig. 7A, showing its heat-sink plate, VLD, VLD-yoke, lens LI, HOES HI and H2, optics module base, and cover plate; Fig. 7C is a plan view of the laser beam producing module shown in Fig. 7A; Fig. 8A is a perspective view of a miniature laser scanning module for use in connection with laser beam producing modules of the present invention; Fig. 8B is an exploded view of the laser beam scanning module of the present invention shown in Fig. 8A, showing its scanning element, mounting plates, electromagnet, support base, and cover plate; Fig. 9 is a plan view of the laser beam producing module of the present invention shown in Fig. 7A configured for cooperation with the laser beam scanning module shown in Fig. 8A; Fig. 10A is perspective view of the third illustrative embodiment of the laser beam producing module of the present invention, wherein a laser beam scanning mechanism is integrated therein and its VLD laser source is adjustable relative to its imaging lens (LI) and pair of stationary-mounted HOEs so that the inherently off-axis elliptical beam produced from the VLD is aligned relative to the optical axes of the HOEs in order to minimize laser beam dispersion, and control the aspect-ratio of the output laser beam in a desired manner; Fig. 10B is an exploded view of the laser beam producing module shown in Fig. 10A, showing its heat-sink plate, VLD, VLD-yoke, lens LI, HOES HI an d H2, optics module base, scanning element, mounting plates, electromagnet, and cover plate; Fig. IOC is a cross-section view of the laser beam producing module taken along line I OC- IOC; Fig. 10D is an exploded perspective view of the laser beam producing module of Fig. 10A mounted within a miniature housing of a laser beam scanning engine; Fig. 11A is a perspective view of a fourth illustrative embodiment of the laser beam producing module of the present invention, wherein its VLD laser source is adjustable relative to its imaging lens (LI) and so that the inherently off-axis elliptical beam produced from the VLD is aligned relative to the optical axes of the HOEs in order to minimize laser beam dispersion, control the aspect-ratio of the output laser beam in a desired manner, and correct for astigmatism in the output laser beam, the focal length of the second lens (L2) is adjustable to fine-tune the focal-length of the output laser beam as required b y the application to which the laser beam producing system is put; Fig. 11B is an exploded view of the laser beam producing module shown in Fig. 11 A, showing its sub-components and mechanisms enabling the adjustment of the position of the VLD relative to the lens LI and the position of HOE H2 relative to HOE HI ; Fig. 11C is a cross-section view of the laser beam producing module taken along line 11C-11C shown in Fig. 1 1 A; Fig. 12A is a perspective view of the fifth illustrative embodiment of the laser beam producing module of the present invention, wherein a laser beam scanning mechanism is integrated therein and its VLD laser source is adjustable relative to its imaging lens (LI) so that the inherently off-axis elliptical beam produced from the VLD is aligned relative to the optical axes of the HOEs i n order to minimize laser beam dispersion, and control the aspect-ratio of the output laser beam in a desired manner, correction for astigmatism in the output laser beam; Fig. 12B is an exploded view of the laser beam producing module shown in Fig. 12A showing its subcomponents and mechanisms enabling the adjustment of the position of the VLD relative to the lens LI, the position of HOE H2 relative to HOE HI, and the focal length of lens L2 which can b e realized as a compound lens system; Fig. 12C is a cross-section view of the laser beam producing module taken along line 12C-12C shown in Fig. 12A; Fig. 13 is a schematic representation of a parameter adjustment system for aligning the optical components within the various types of laser beam producing modules of the present invention disclosed herein; Fig. 14 is a schematic diagram of the laser beam producing module of Fig. 7A installed upon the parameter adjustment system of Fig. 13, for aligning optical components in the module so that laser beam dispersion is minimized and the aspect-ratio of the output laser beam is controlled in a desired manner; Fig. 15 is a schematic diagram of the laser beam producing module shown in Fig. 11 A installed upon the parameter adjustment system of Fig. 13 , for aligning optical components of the module so that laser beam dispersion is minimized, the aspect-ratio of the output laser beam is controlled in a desired manner, and astigmatism in the output laser beam is corrected, e.g. eliminated; Fig. 16 is a schematic diagram of the laser beam producing module shown in Fig. 12A installed upon the parameter adjustment system of Fig. 13 , for aligning the optical components of the module so that laser beam dispersion is minimized, the aspect-ratio of the output laser beam is controlled in a desired manner, astigmatism in the output laser beam is corrected, an d adjustment of the focal-length of the resulting stigmatic beam is achieved; Fig. 17 is a schematic diagram of the laser beam producing module shown in Fig. 12A installed upon the parameter adjustment system of Fig. 1 3 , for aligning the optical components of the module so that laser beam dispersion is minimized, and astigmatism in the output laser beam is corrected, without focus control or focal length adjustment; Fig. 18 is a schematic representation of a hand-supportable laser scanning system constructed in accordance with the present invention, wherein one or more DOE-based laser beam producing systems of the present invention are configured and driven by a synchronized driver circuit for producing a 2-D laser scanning pattern suitable for omni-directional or raster scanning of bar code symbols; Fig. 19 is a schematic representation of a fixed-type projection laser scanning system, wherein a laser beam producing subsystem of the present invention is used to produce a laser beam having desired beam characteristics for omni-directional laser scanning; Fig. 20 is a schematic representation of a body-wearable laser scanning system which embodies an DOE-based laser beam producing module of the present invention within its finger-mounted scanning module; Fig. 21 is a schematic representation of a holographic laser beam scanning system, wherewith a plurality of laser beam producing modules of the present invention cooperate with a holographic laser scanning disc and a plurality of wavelength-compensation gratings to produce an omni-directional scanning pattern within a 3-D scanning volume; Fig. 22 is a schematic representation of a CD-ROM player in which a laser beam producing module according to the present invention is integrated; Fig. 23 is a schematic representation of a laser beam pointing device, wherein a laser beam producing module according to the present invention is embodied; an d Fig. 24 is a schematic representation of an analytical instrument, i n which a laser beam producing module according to t he present invention is employed for detection or diagnosis of a particular condition. BEST MODES FOR CARRYING OUT THE PRESENT INVENTION In accordance with one broad aspect of the present invention, illustrated in Fig. 1, novel apparatus 1 employs a light-diffractive optical subsystem 2 for modifying the inherent beam characteristics of a laser beam 3 generated from a laser diode source 4 (e.g. visible laser diode or VLD). Preferably, the laser diode source 4 has the so-called heterostructure or double-heterostructure, o r multi-quantum well construction. The laser beam output from the laser diode source 4 is modified by optical subsystem 2, and the modified beam characteristics associated therewith, are suited by design for use in particular applications. Hereinafter, apparatus according to this first aspect of th e present invention, adapted for modifying the characteristics of laser beams produced from laser diode sources, shall be referred to as "a laser beam modifying subsystem" . Each embodiment of the laser beam-modifying system of the present invention is designed using the beam characteristics of the particular laser source 4 employed in the system. As shown in Fig. 1A, the optical subsystem 2 comprises: a lens element (LI); and at least two light diffractive optical elements (DOEs), indicated by Dl and D2, respectively, in Fig. 1A. The primary function of optical subsystem 2 is to modify the laser beam produced from the laser diode source 4 so that the resulting laser beam 5 output from DOEs D l and D2 has predetermined (modified) beam characteristics that are suited b y design for use in particular applications. Hereinafter, apparatus according to this second aspect of the present invention, adapted for producing laser beams having predetermined beam characteristics, shall be referred to as "laser beam producing system". In defining the laser beam modifying (optics) subsystem 2, the angle of incidence of the laser beam from the lens LI onto the front surface of the first diffractive optical element (DOE) Dl is specified by θ n , whereas the angle of diffraction therefrom is specified by θ d l . The angle of incidence of the laser beam from the first DOE Dl onto the front surface of second fixed DOE D2 is specified by θ i2 , whereas the angle of diffraction therefrom is specified by θ d2 . The angle p between the surfaces of the two DOEs Dl and D2 as: p=θ d l - θ i2 These five parameters θ , θ d l , θ i2 , θ d2 , and p completely define the dual-DOE subsystem, and thus provide four degrees of freedom within the geometrical optics model thereof. Hereinbelow, a number of illustrative embodiments of the laser beam producing system according to the present invention will now be described i n great detail. In such illustrative embodiments shown in the figures of the accompanying Drawings, like structures and elements shall be indicated by like reference numerals. Description Of Illustrative Svstem Embodiments Of The Laser Beam-Producing Svstem Of The Present Invention In each of the fourteen illustrative embodiments described below, the laser beam is produced from a VLD 4 having the so-called heterostructure o r double-heterostructure, or multi-quantum well construction. In a typical VLD, the beam divergence will be less in the direction parallel to the VLD junction. Also, in all commercially produced VLDs, the electric field (E-field) of the laser beam is oriented (i.e. polarized) in a direction parallel to the narrow divergence direction of the beam, which is generally parallel to the junction of the VLD. In order to understand the operation of commercial VLDs which inherently produce astigmatic beams, it will be helpful to construct a model thereof, as done in copending Application Serial No. 08/573,949 filed December 18, 1995, incorporated herein by reference. According to this model, the laser beam exiting the diode source is deemed to be generated from a combination of sources, namely: a S "source" and a P "source" coaxially located inside the VLD, but separated by a distance referred to as the astigmatic difference or simply the astigmatism of the VLD. Each wave source in this model creates an independent cylindrical wavefront which interacts with the other wave source to create an effect on the resulting wavefront that results in the astigmatism. In the case where the astigmatism is zero, the two cylindrical sources coincide and the resultant wavefront is spherical. The P source is considered the source of origin of the narrow divergence portion of the beam (and thus P shall hereinafter refer to the direction parallel to the VLD junction). The S source is considered the source of origin of the wide direction of the beam (and thus S —derived from the German word "Senkrecht" meaning "perpendicular"— shall hereinafter refer to the direction perpendicular to the VLD junction). Ideally, to ensure the highest diffraction efficiency of the laser beam transmitted through the DOEs Dl and D2, the diffracted laser beam at angle θ d l should be in the "plane of incidence" of the incoming beam at DOE D1. In accordance with standard definitions, the "plane of incidence" shall mean the plane containing the incident light ray at DOE Dl and the normal to the surface of DOE Dl at the point of incidence thereon. It is not possible to define a plane of incidence for a cone of rays incident the surface of lens LI. Also, the diffracted laser beam at angle θ d2 relative to DOE D2 should be in the "plane of incidence" of the incident beam at DOE D2, and the plane of incidence at DOE Dl should be coplanar with the plane of incidence at DOE Dl (i.e. disposed within a common plane), to ensure the highest possible light diffraction efficiency as the laser beam passes through the dual-DOE beam modifying subsystem 6. Regardless of how the DOEs are implemented (e.g. as HOEs, CGHs, surface-relief holograms, etc), the fringe structure of the DOEs must b e arranged perpendicular to the (common) plane of incidence at the DOEs i n order to achieve maximum light diffraction efficiency through this subsystem. With this general arrangement, it is noted that all modifications to the laser beam exiting the VLD (e.g. compression or expansion) will occur within the "common plane of incidence" passing through DOEs Dl and D2. Depending on the application at hand, there may be a need to compress or expand a particular dimension of the astigmatic laser beam exiting from the VLD. In order to perform such beam modifying functions upon this laser beam, the individual expansion ratios for DOEs Dl and D2, designated by M γ and M 2 , respectively, will be selected by the optical system designer so that the beam-shaping factor (e.g. expansion ratio) of the DOE-subsystem, M=M,M 2 , is greater than unity when beam expansion is required, and less than unity when beam compression is required. In the DOE subsystem, the individual expansion ratios are given by the following formulas: M,=D 0Utputl /D inputl an d M 2 =D 0Utput2 /D input2 , wherein D represents dimension of the beam in the compression/expansion direction (i.e. common plane of incidence of DOEs D 1 and D2). There are four general cases of laser beam modification that may b e carried out by any particular embodiment of the laser beam producing system of the present invention. These cases will now be briefly described below to provide an overview of the system of t he present invention. In the first general case of beam modification, the wider dimension of the laser beam requires compression by the DOE-based subsystem. In this case, the DOEs Dl and D2 are designed so that the beam-shaping factor M thereof is less than unity and the narrower dimension of the laser beam exiting the VLD is oriented perpendicular to the "common" plane of incidence passing through DOEs Dl and D2. As this latter condition is satisfied by orienting the VLD junction (and thus its narrower b eam dimension and polarization direction) perpendicular to the common plane of incidence, the laser beam incident o n DOE D1 is said to be "S-polarized" or "S-incident" on the surface of DOE D 1 , that is the E-field of the incident laser beam is perpendicular to the common plane of incidence. In this configuration, the wider dimension of the laser beam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam compression results as desired by the design, while the narrower beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that no beam compression results along this dimension as desired by the design. In this case, an elliptical laser beam can be made less elliptical o r circular. In the second general case of beam modification, the narrower dimension of the laser beam requires compression by the DOE-based subsystem. In this case, the DOEs Dl and D2 are designed so that the beam- shaping factor M thereof is less than unity and the narrower dimension of the laser beam exiting the VLD is oriented parallel to the "common" plane of incidence passing through DOEs Dl and D2. As this latter condition is satisfied by orienting the VLD junction (and thus its narrower beam dimension an d polarization direction) parallel to the common plane of incidence, the laser beam incident on DOE Dl is said to be "P-polarized" or "P-incident" on the surface of DOE D1, that is the E-field of the incident laser beam is parallel to the common plane of incidence. In this configuration, the narrower dimension of the laser beam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam compression results as desired by the design, while the wider beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that no beam compression results along this dimension as desired by the design. In this case, an elliptical laser beam can be made more elliptical. In the third general case of beam modification, the wider dimension of the laser beam requires expansion by the DOE-based subsystem. In this case, the DOEs Dl and D2 are designed so that the beam-shaping factor M thereof is greater than unity and the narrower dimension of the laser beam exiting the VLD is oriented perpendicular to the "common" plane of incidence passing through DOEs Dl and D2. As this latter condition is satisfied by orienting the VLD junction (and thus its narrower beam dimension and polarization direction) perpendicular to the common plane of incidence, the laser beam incident on DOE Dl is said to be "S-polarized" or "S-incident" on the surface of DOE D1, that is the E-field of the incident laser beam is perpendicular to the common plane of incidence. In this configuration, the wider dimension of the laser b eam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam expansion results as desired by the design, while the narrower beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that no beam expansion results along this dimension as desired by the design. In this case, an elliptical laser beam can b e made more elliptical. In the fourth general case of beam modification, the narrower dimension of the laser beam requires expansion by the DOE-based subsystem. In this case, the DOEs Dl and D2 are designed so that the beam-shaping factor M thereof is greater than unity and the narrower dimension of the laser beam exiting the VLD is oriented parallel to the "common" plane of incidence passing through DOEs Dl and D2. As this latter condition is satisfied by orienting the VLD junction (and thus its narrower beam dimension and polarization direction) parallel to the common plane of incidence, the laser beam incident on DOE D 1 is said to be "P-polarized" or "P-incident" on the surface of DOE DI, that is the E-field of the incident laser beam is parallel to the common plane of incidence. In this configuration, the narrower dimension of the laser beam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam expansion results as desired by the design, while the wider beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that no beam expansion results along this dimension as desired by the design. In this case, an elliptical laser beam can be made less elliptical or circular. Using the above-described principles, numerous embodiments of the laser beam producing system of the present invention can be designed an d constructed using various types of enabling technologies. Below, fourteen different illustrative embodiments of the laser beam producing system hereof shall be described in detail. In each of these illustrative embodiments of the present invention, the angles of incidence and diffraction at the DOEs are the only parameters that determine whether the incident laser beam is compressed or expanded. For a fixed set of DOE angles, the polarization direction of the laser beam will determine whether the aspect ratio of the elliptical beam is increased or decreased. This is due to the direct relationship that exists between the narrow dimension and the polarization direction of the laser beam exiting a VLD. In each of the beam compression embodiments, an S-polarized beam as well as a P-polarized beam incident DOE Di will be compressed. The difference between such cases is that the elliptical S-polarized beam will become less elliptical while the P-polarized beam will become more elliptical. In many instances where beam compression is desired or required, an S-polarized beam will be preferred as its beam aspect ratio will be reduced while its beam cross- section is made smaller. In each of the beam expansion embodiments, an S-polarized beam as well as a P-polarized beam incident DOE Dl will be expanded. The difference between such cases is that the elliptical S-polarized beam will become more elliptical while the P-polarized beam will become less elliptical. In many instances where beam expansion is desired or required, a P-polarized beam will be preferred as its beam aspect ratio will be reduced while its beam cross- section is made larger. First Illustrative System Embodiment Of The Laser Beam Producing Svstem Of The Present Invention In Fig. 2A, the first illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 1") comprises: a laser beam source, such as a visible laser diode (VLD), (e.g. Sony Model SLD1122VS) for producing a laser beam from its junction typically having divergent and elliptical beam characteristics; a collimating lens (LI), realizable as a refractive lens e.g. a 4/35 mm lens, a HOE, other type of DOE, a grin lens, one or more zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by D 1 having a beam expansion factor M γ ; and a fixed spatial-frequency diffractive optical element (DOE) indicated by D2, having a beam expansion factor M 2 . Collectively, the collimating lens (LI), the fixed spatial-frequency DOE HI an d the fixed spatial-frequency DOE D2 comprise a laser beam-modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a computer- generated hologram (CGHs), a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. Notably, there will be many cases in which the beam shaping factor is less than unity, including, for example: where M1<1 and M2<1; where M l = l and M2<1; and where M1<1 and M2=l . In the Beam Compression Mode, one of the cross-sectional dimensions of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. Typically, although not necessarily, the wider cross-sectional dimension of the laser beam will b e the one that is compressed. For example, if the beam is S-polarized at DOE D 1 , then the widest cross-sectional dimension of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. If the beam is P-polarized, then the narrowest dimension of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension, thereby making the laser beam even more elliptical in cross-section. In the laser beam producing system shown in Fig. 2A, the aspect-ratio of the output laser beam is controlled and dispersion in the output laser beam produced therefrom eliminated for the central ray (and minimized for off- center rays) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for th e two DOEs Dl and D2 indicated by θ π , θ d θ i2 and θ d2 which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment, the (x,y,z) position of the VLD is adjustable relative to lens LI during the parameter alignment stage of the system assembly process in order to set the focal length of the output laser beam to the desired value and to align the VLD to the optical axis of lens LI. The (x,y,z) position of the VLD has no effect o n dispersion except insofar as the x, y position effects the angle of incidence θ π at HI. If the laser beam output from the VLD is not aligned along the optical axis of LI, then dispersion may not be zeroed or minimized as the beam will n ot pass through the DOEs are designed. In this embodiment, astigmatism in the output laser beam is not minimized or otherwise controlled. Consequently, there will be a number of applications to which this system embodiment can b e put with satisfactory result. Notably, in the embodiment of the laser beam producing system shown in Fig. 2A, the convergence of the beam leaving collimating lens LI must b e adjusted to provide the proper image distance to the focal point of the system, and therefore it cannot be used to control or eliminate the astigmatism that is inherent in the laser beam leaving the VLD. In the case of Scan-Engine and like type applications, where the laser scanning device is realized within an ultra- small volume, laser beam astigmatism is not a problem as the increase (i.e. elongation) in spot-size in the non-scan-dimension helps reduce the problems associated with paper noise, described in US Patent No. 4,748,316, incorporated herein by reference. Second Tlhistrative Svstem Embodiment Of The Laser Beam Producing System Of The Present Inventi on In Fig. 2B, the second illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 2") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction having divergent and elliptical characteristics; a collimating lens (LI), realizable as a refractive lens e.g. a 4/35 mm lens, a HOE, other type of DOE, a grin lens, one or more zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl having a beam expansion factor Mj . ; and a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by D2, having a beam expansion factor M 2 ; and a focusing lens L2, realizable as a refractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like, disposed after DOE D2 for focusing the output laser beam to a desired or required point in space. Collectively, the collimating lens LI, the fixed spatial-frequency DOE D1, the fixed spatial-frequency DOE D2, an d focusing lens L2, comprise a laser beam modifying subsystem in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, o r other diffractive optical element. In this embodiment, the total beam-shaping factor for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, an d thus the laser beam leaving the collimating lens (LI) is compressed in on e dimension. Notably, there will be many cases in which the beam shaping factor is less than unity, including, for example: where M1<1 and M2<1 ; where M l = l and M2<1; and where M1<1 and M2=l . In the Beam Compression Mode, one of the cross-sectional dimensions of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. Typically, although not necessarily, the wider cross-sectional dimension of the laser beam will b e the one that is compressed. In this embodiment, the total beam-shaping factor for the laser beam subsystem is less than unity (1), and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. In the laser beam producing system shown in Fig. 2B, the aspect-ratio of the output laser beam can be controlled and dispersion in the output laser beam produced therefrom can be eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ l θ d l , θ l2 and θ d2 which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD can be either adjusted o r eliminated by choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y,z) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI and to align the VLD to the optical axis of lens LI . Also, the position of lens L2 is adjustable along its optical axis relative to DOE D2 during the alignment stage of the system assembly process in order to set the focal length of the output laser beam to the desired value. In the illustrative embodiment described hereinabove, DOEs Dl and D2 are realized using transmission-type light diffractive optical elements (e.g. and/or transmission-type volume HOEs). It is understood, however, that this illustrative embodiment of the present invention can be realized using reflection-type volume DOEs (e.g. reflection-type HOEs and/or CGHs) as well. In such alternative realizations of this embodiment of the present invention, each DOE can be realized using a reflective-type DOE. The only requirement i n either case is that the angle of diffraction be different than the angle of incidence for each light diffractive element of the DOE-based device. In general, this requirement can be met using either a transmissive holographic optical element (HOE) or a reflective HOE. As shown in Fig. 2B1, the second illustrative embodiment of the DOE- based laser beam producing subsystem hereof is shown realized using reflection-type DOEs (e.g. HOEs) for both DOE Dl and DOE D2. In this alternative realization, DOE Dl and DOE D2 both have a fixed spatial frequency and, when combined together with the VLD, lenses LI and L2 as shown in Fig. 2B1, produce a system which is the functional equivalent of the system shown in Fig. 2B, and operates in the Beam Compression Mode. As shown in Fig. 2B2, the second illustrative embodiment of the DOE- based laser beam producing subsystem hereof is shown realized using a transmission-type DOE (e.g. transmission-type HOE HI) for DOE Dl and a reflection-type DOE (e.g. reflection-type HOE H2) for DOE D2. In this alternative realization, DOE Dl and DOE D2 both have a fixed spatial frequency and, when combined together with the VLD, lenses LI and L2 as shown in Fig. 2B2, produce a system which is the functional equivalent of the system shown in Fig. 2B, and operates in the Beam Compression Mode. As shown in Fig. 2B3, the second illustrative embodiment of the DOE- based laser beam producing subsystem hereof is shown realized using a reflection-type DOE (e.g. reflection-type HOE HI) for DOE Dl and a reflection- type DOE (e.g. reflection-type HOE H2) for DOE D2. In this alternative realization, DOE Dl and DOE D2 both have a fixed spatial frequency and, when combined together with the VLD, lenses LI and L2 as shown in Fig. 2B3, produce a system which is the functional equivalent of the system shown i n Fig. 2B, and operates in the Beam Compression Mode. Third Illustrative System Embodiment Of The Laser Beam Producing System Of The Present Invention In Fig. 2C, the third illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 3") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction ; a collimating lens (LI), realizable as a refractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like, for collimating the laser beam as it is transmitted t hrough collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl having a beam expansion factor M, ; and a variable spatial-frequency diffractive optical element (DOE) indicated by D2, having a beam expansion factor M 2 . Collectively, the collimating lens LI, the fixed spatial-frequency DOE Dl and the variable spatial-frequency DOE D2 comprise a laser beam-modifying (sub)system in accordance with t he present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor (M=MιM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, an d thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. There will be many cases in which the beam shaping factor is less than unity, including, for example: where M1<1 and M2<1 ; where Ml=l an d M2<1; and where M1<1 and M2=l. In the Beam Compression Mode, one of the cross-sectional dimensions of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. Typically, although n ot necessarily, the wider cross-sectional dimension of the laser beam will be the one that is compressed. In the laser beam producing system shown in Fig. 2C, the aspect-ratio of the output laser beam can be controlled and dispersion in the output laser beam produced therefrom is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated b y θπ, θ d l , θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD is adjusted or eliminated b y choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI. The z position of visible laser diode (VLD) is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to align the VLD with respect to the optical axis of lens LI. Also, the position of DOE D2 is adjustable along its optical axis relative to DOE Dl during the alignment stage of the system assembly process in order to set the focal length of the output laser beam to the desired value. Fourth Illustrative System Embodiment Of The Laser Beam Producing System Of The Present Invention In Fig. 2D, the fourth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 4") comprises: a laser beam source, such as a visible laser diode (VLD), for producing an elliptical divergent laser beam from its junction; a collimating lens (LI), realizable as a refractive lens, a HOE, or other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI an d through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; a variable spatial-frequency diffractive optical element (DOE) indicated by D2 an d adjustably mounted to enable, during the alignment stage of the system adjustment process, the principal plane of DOE D2 to be translated along its optical axis relative to the principal plane of DOE Dl without modifying the tilt angle therebetween; and a focusing lens (L2), realizable as a refractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like, disposed after the second DOE D2 and having a focal length which is can be adjusted to enable the focusing of the output laser beam to some predetermined focal point in space, during the alignment stage of the system assembly process. Collectively, the collimating lens LI, the fixed spatial-frequency DOE D1, the variable spatial- frequency DOE D2, and the focusing lens L2 comprise a laser beam-modifying subsystem in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this illustrative embodiment of the o ptical system of the present invention, focusing lens L2 is disposed after the second focusing DOE D2 i n order to provide additional optical power to the exiting laser beam. In general, lens L2 can be as a single lens whose position can be adjusted relative to th e second DOE D2, or as a compound lens system having a focal length that can be adjusted so as to adjust the focal length of the output laser beam. This second optical arrangement L2 would be useful in applications where, for example, multiple focusing HOEs as are commonly arranged on a holographic scanning disc (disclosed in Application Serial No. 08/573,949) or where several different single HOEs of differing optical power were available to be placed i n the system. One of these HOEs on the disc could be presented to the laser beam producing system hereof in the position of DOE D2 and effectively vary the focal distance of the output laser beam about an average focal point established by the lens L2, a process which shall be referred to hereinafter as "delta-focusing". This delta-focusing feature yields the benefits of reduced spot aberrations due to the optical power of DOE D2 as well as increased modularity of the system. In this embodiment, the total beam-shaping factor (M=MjM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. There will be many cases in which the beam shaping factor is less than unity, including, for example: where M1<1 and M2<1 ; where Ml=l an d M2<1; and where M1<1 and M2=l . In the Beam Compression Mode, one of the cross-sectional dimensions of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. Typically, although n ot necessarily, the wider cross-sectional dimension of the laser beam will be the one that is compressed. In the laser beam producing system shown in Fig. 2D, the aspect-ratio of the output laser beam can be controlled and dispersion in the output laser beam eliminated (or minimized) for any given beam expansion or beam compression ratio at each of the DOEs, by selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated b y θ ϋ , θ d b θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD is adjusted or eliminated b y choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI. The z position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to align the VLD relative to the optical axis of lens LI. Also, the position of second lens L2 is adjustable along its optical axis relative to DOE D2 during the alignment stage of the system assembly process. The function of this second lens L2 is to set the average focal length of the output laser beam to the desired value for use by the delta-focusing subsystem. Fifth Illustrative Svstem Embodiment Of The Laser Beam Producing System Of The Present Invention In Fig. 2E, the fifth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 5") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating (non-focusing) lens (LI), realizable as a refractive lens, a HOE or other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; and a fixed spatial-frequency diffractive optical element (DOE) indicated by D2. Collectively, the collimating lens LI, the fixed spatial-frequency DOE Dl and the fixed spatial-frequency DOE D2 comprise a laser beam-modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can b e realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor for the laser beam modifying subsystem is greater than unity (1), that is M1*M2>1 , and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. There will be many cases in which the beam shaping factor is greater than unity, including, for example: where M1>1 and M2>1 ; where Ml=l and M2>1; and where M1>1 and M2=l . In the Beam Expansion Mode, one of the cross-sectional dimensions of the laser beam from the VLD is expanded at the output of the system to a predetermined dimension. Typically, although not necessarily, the narrower cross-sectional dimension of the laser beam will be the one that is expanded. In the laser beam producing system shown in Fig. 2E, the aspect-ratio of the output laser beam can be controlled and dispersion in the output laser beam produced therefrom is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated b y θii > θ d l , θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment, the (x,y) position of the VLD is adjustable relative t o lens LI during the parameter alignment stage of the system assembly process in order to set the focal length of the output laser beam to the desired value. The z position of the VLD is adjustable relative to lens LI during the parameter alignment stage of the system assembly process in order to align the VLD to the optical axis of lens LI. Notably, in the embodiment of the laser beam producing system shown in Fig. 2E, the convergence of the beam leaving collimating lens LI must b e adjusted to provide the proper image distance to the focal point of the system, and therefore it cannot be used to control or eliminate the astigmatism that is inherent in the laser beam leaving the VLD. In the case of Scan-Engine and like type applications, where the laser scanning device is realized within an ultra- small volume, laser beam astigmatism is not a problem as the increase (i.e. elongation) in spot-size in the non-scan-dimension helps reduce the problems associated with paper noise, described in US Patent No. 4,748,316, supra. Sixth Illustrative Svstem Embodiment Of The Laser Beam Producing System Of The Present Invention In Fig. 2F, the sixth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 6") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI), realizable as a refractive lens, a HOE or other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; a fixed spatial-frequency diffractive optical element (DOE) indicated by D2; and a focusing lens (L2), realizable as a refractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like, disposed after the second DOE D2 for focusing the output laser beam to some point i n space. Collectively, the collimating lens LI, the fixed spatial-frequency DOE Dl, the fixed spatial-frequency DOE D2, and focusing lens L2 comprise a laser beam-modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor (M=M,M 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1 *M2>1 , and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. There will be many cases in which the beam shaping factor is greater than unity, including, for example: where M1>1 and M2>1 ; where Ml=l and M2>1; and where M1>1 and M2=l . In the Beam Expansion Mode, one of the cross-sectional dimensions of the laser beam from the VLD is expanded at the output of the system to a predetermined dimension. Typically, although not necessarily, the narrower cross-sectional dimension of the laser beam will be the one that is expanded. In the laser beam producing system shown in Fig. 2F, aspect-ratio control is achieved and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence, and diffraction for the two DOEs Dl and D2 indicated by θ π , θ dl , θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD is either adjusted or eliminated by choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process in order to adjust the divergence or convergence of the beam leaving lens LI. The z position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process in order to align the VLD to the optical axis of lens LI. Setting the focal length of output laser beam is achieved by adjusting the position of lens L2 relative to DOE D2 during the alignment stage of the assembly process. Seventh Illustrative System Embodiment Of The Laser Beam Producing Svstem Of The Present Inventi on In Fig. 2G, the seventh illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 7") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI), realizable as a refractive lens, HOE o r other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; and a variable spatial-frequency diffractive optical element (DOE) indicated by D2, which can be translated along the optical axis relative to the principal plane of DOE Dl during the alignment stage of the system assembly process. Collectively, the collimating lens LI, the fixed spatial-frequency DOE Dl and the variable spatial-frequency DOE D2 comprise a laser beam-modifying (sub)system in accordance with th e present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type DOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor (M=M^ 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1 *M2>1 , and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. There will be many cases in which the beam shaping factor is greater than unity, including, for example: where M1>1 and M2>1; where Ml=l and M2>1 ; and where M1>1 and M2=l . In the Beam Expansion Mode, one of the cross-sectional dimensions of the laser beam from the VLD is expanded at the output of the system to a predetermined dimension. Typically, although not necessarily, the narrower cross-sectional dimension of the laser beam will be the one that is expanded. In the laser beam producing system shown in Fig. 2G, aspect-ratio control is achieved and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ n , θ d l , θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD is either adjusted or eliminated by choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system - assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI. The z position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process in order to align the VLD to the optical axis of lens LI. Also, the position of DOE D2 is adjustable along its optical axis relative to DOE D 1 during the alignment stage of the system assembly process in order to set the focal length of the output laser beam to the desired value. Eighth Illustrative Svstem Embodiment Of The Laser Beam Producing Svstem Of The Present Invention In Fig. 2H, the eighth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 8") comprises: a laser beam source, such as a visible laser diode (VLD); a collimating lens (LI ) realizable as a refractive lens, a HOE, a CGH or other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; a variable spatial-frequency diffractive optical element (DOE) indicated by D2, adjustably mounted relative to DOE D1; and a focusing lens (L2), realizable as a refractive lens, a HOE, a DOE, grin lens, zone plate(s) or the like, disposed after the second DOE D2, and adjustably mounted relative thereto, for focusing the output laser beam to some point in space. Collectively, the collimating lens LI, the fixed spatial-frequency DOE D1, the variable spatial-frequency DOE D2 and focusing lens L2 comprise a laser beam- modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this illustrative embodiment of the optical system of the present invention, focusing lens L2 is disposed after the second focusing DOE D2 in order to provide additional optical power to the exiting laser beam. This optical arrangement would be useful in applications employing delta-focusing. This delta-focusing yields the benefits of reduced spot aberrations due to the optical power of DOE D2 as well as increased modularity of the system. In this embodiment, the total beam-shaping factor (M=MjM 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1 *M2>1 , and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. There will be many cases in which the beam shaping factor is greater than unity, including, for example: where M 1>1 and M2>1; where Ml=l and M2>1; and where M1>1 and M2=l. In the Beam Expansion Mode, one of the cross-sectional dimensions of the laser beam from the VLD is expanded at the output of the system to a predetermined dimension. Typically, although not necessarily, the narrower cross-sectional dimension of the laser beam will be the one that is expanded. In the laser beam producing system shown in Fig. 2H, aspect-ratio control is achieved and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ l θ dl , θ l2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD is either adjusted or eliminated by choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI. The z position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to align the VLD to the optical axis of lens LI. Also, the position of lens L2 is adjustable along its o ptical axis relative to DOE D 2 during the alignment stage of the system assembly process in order to set the average focal length of the output laser beam to the desired value for use b y the delta-focusing system. Ninth Tlhistrative Svstem Embodiment Of The Laser Beam Producing System Of The Present Invention In Fig. 21, the ninth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 9") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI), realizable as a refractive lens, a HOE, CGH or other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in an S- incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; a fixed spatial-frequency diffractive optical element (DOE) indicated by D2; and a focusing lens (L2), realizable as a refractive lens, holographic optical element (HOE), diffractive optical element (DOE), grin lens, zone plate(s) or the like, disposed between DOE Dl and DOE D2 and adjustably translatable along its optical axis for focusing the output laser beam to some point in space. Collectively, the collimating lens LI, the fixed spatial-frequency DOE D1, the fixed spatial-frequency DOE D2, an d focusing lens L2 comprise a laser beam-modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, o r other diffractive optical element. In this embodiment, the total beam-shaping factor (M=MjM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, an d thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. Notably, there will be many cases in which the beam shaping factor is less than unity, including, for example: where M1<1 and M2<1; where M l = l and M2<1; a nd where M1<1 and M2=l. In the Beam Compression Mode, one of the cross-sectional dimensions of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. Typically, although not necessarily, the wider cross-sectional dimension of the laser beam will b e the one that is compressed. In the laser beam producing system shown in Fig. 21, aspect-ratio control is achieved and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion or b eam compression ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ n , θ d l , θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated b y P- In this embodiment of the laser beam producing system, lenses LI an d L2 are chosen such that the desired focus is achieved and the inherent astigmatism of the laser beam leaving the VLD is either adjusted or eliminated. Neither lens LI nor L2 independently set the astigmatism nor the focus. Rather the combined set of lenses produce the combined result. The (z) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI to produce a predetermined amount of astigmatism at a predetermined distance. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, i n order to align the VLD to the optical axis of lens LI. Also, the position of lens L2 is adjustable along its optical axis between DOE Dl and DOE D2 during the alignment stage of the system assembly process in order to set the desired focus as well as the desired amount of astigmatism of the output laser beam. Tenth Tlhistrative System Embodiment Of The Laser Beam Producing System Of The Present Invention In Fig. 2J, the tenth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 10") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI), realizable as a refractive lens, a HOE, CGH o r other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; a variable spatial-frequency diffractive optical element (DOE) indicated by D2, adjustably translatable relative to the principal plane of DOE Dl during the alignment stage of the system assembly process; and a focusing lens (L2), realizable as a refractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like, disposed between DOE Dl and DOE D2 an d adjustably translatable along its optical axis during the parameter alignment stage of the system assembly process for focusing the output laser beam to some point in space. Collectively, the collimating lens LI, the fixed spatial- frequency DOE Dl, the variable spatial-frequency DOE D2, and focusing lens L2 comprise a laser beam-modifying (sub)system in accordance with t he present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this illustrative embodiment of the optical system of the present invention, focusing lens L2 is disposed between DOE Dl and DOE D2 in order to provide additional optical power to the exiting laser beam. This optical arrangement would be useful in applications employing delta-focusing. This delta-focusing yields the benefits of reduced spot aberrations due to the optical power of DOE D2 as well as increased modularity of the system. In this embodiment, the total beam-shaping factor for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, an d thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. Notably, there will be many cases in which the beam shaping factor is less than unity, including, for example: where M1<1 and M2<1 ; where M l = l and M2<1 ; and where M1<1 and M2=l . In the Beam Compression Mode, one of the cross-sectional dimensions of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. Typically, although not necessarily, the wider cross-sectional dimension of the laser beam will b e the one that is compressed. In the laser beam producing system shown in Fig. 2J, beam aspect-ratio control is achieved and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion or beam compression ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ π , θ d b θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD can be either adjusted o r eliminated by choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI . The (z) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to align the VLD to the optical axis of lens LI. Also, the position of lens L2 is adjustable along its optical between DOE D l and DOE D2 during the alignment stage of the system assembly process in order to set the average focal length of the output laser beam to the desired value for use by the delta-focusing system. Eleventh Illustrative Svstem Embodiment Of The Laser Beam Producing System Of The Presen Invention In Fig. 2K, the eleventh illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 11") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI), realizable as a refractive lens, a HOE or other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P- incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; a fixed spatial-frequency diffractive optical element (DOE) indicated by D2; and a focusing lens (L2), realizable as a refractive lens, holographic optical element (HOE), diffractive optical element (DOE), grin lens, zone plate(s) or the like, between DOE Dl and DOE D2 an d adjustably translatable along its optical axis during the alignment stage of the system assembly process for focusing the output laser beam to some point in space. Collectively, the collimating lens LI, the fixed spatial-frequency DOE Dl, the fixed spatial-frequency DOE D2, and the focusing lens L2 comprise a laser beam-modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission- type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor (M=M r M 2 ) for the laser beam modifying s ubsystem is greater than unity (1), that is M1 *M2>1 , and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. There will be many cases in which the beam shaping factor is greater than unity, including, for example: where M 1 > 1 and M2>1; where Ml=l and M2>1; and where M1>1 and M2=l. In the Beam Expansion Mode, one of the cross-sectional dimensions of the laser beam from the VLD is expanded at the output of the system to a predetermined dimension. Typically, although not necessarily, the narrower cross-sectional dimension of the laser beam will be the one that is expanded. In the laser beam producing system shown in Fig. 2K, beam aspect-ratio is controlled and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ π , θ d l , θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, lenses LI an d L2 are chosen such that the desired focus is achieved and the inherent astigmatism of the laser beam leaving the VLD is either adjusted or eliminated. Neither lens LI nor L2 independently set the astigmatism nor the focus. Rather the combined set of lenses produce the combined result. The (z) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI to produce a predetermined amount of astigmatism at a predetermined distance. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to align the VLD to the optical axis of lens LI. Also, the position of lens L2 is adjustable along its optical axis between DOE Dl and DOE D2 during the alignment stage of the system assembly process in order to set the desired focus as well as the desired amount of astigmatism of the output laser beam . Twelfth Illustrative Svstem Embodiment Of The Laser Beam Producing System Of The Presen Tnvention In Fig. 2L, the twelfth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 12") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI), realizable as a refractive lens, a HOE, CGH or other DOE, a grin lens, zone plate(s), etc., for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; a variable spatial-frequency diffractive optical element (DOE) indicated by D2, adjustably translatable relative to the principal plane of DOE Dl during the alignment stage of the system assembly process; and a focusing lens (L2), realizable as a refractive lens, a HOE, a CGH or other a DOE, a grin lens, zone plate(s) or the like, disposed between DOE Dl and DOE D2 and adjustably translatable along its optical axis during the parameter alignment stage of the system assembly process for focusing the output laser beam to some point in space. Collectively, the collimating lens (LI), the fixed spatial-frequency DOE (D l ) and the variable spatial-frequency DOE (D2) comprise a laser beam-modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this illustrative embodiment of the optical system of t he present invention, focusing lens L2 is disposed between DOE Dl and DOE D2 in order to provide additional optical power to the exiting laser beam. This optical arrangement would be useful in applications employing delta-focusing. This delta-focusing yields the benefits of reduced spot aberrations due to the optical power of DOE D2 as well as increased modularity of the system. In this embodiment, the total beam-shaping factor (M=M,M 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1 *M2>1 , and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. There will be many cases in which the beam shaping factor is greater than unity, including, for example: where M1>1 and M2>1; where Ml=l and M2>1; and where M1>1 and M2=l. In the Beam Expansion Mode, one of the cross-sectional dimensions of the laser beam from the VLD is expanded at the output of the system to a predetermined dimension. Typically, although not necessarily, the narrower cross-sectional dimension of the laser beam will be the one that is expanded. In the laser beam producing system shown in Fig. 2L, beam aspect-ratio control is achieved and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ n , θ d θ l2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In this embodiment of the laser beam producing system, the inherent astigmatism of the laser beam leaving the VLD can be either adjusted o r eliminated by choosing proper divergence or convergence of the laser beam leaving the collimating lens LI. The (x,y) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to adjust the divergence or convergence of the beam leaving lens LI. The (z) position of visible laser diode VLD is adjustable relative to the lens LI during the parameter adjustment stage of the system assembly process, in order to align the VLD to the optical axis of lens LI. Also, the position of lens L2 is adjustable along its optical axis between DOE Dl and DOE D2 during the alignment stage of the system assembly process in order to set the average focal length of the output laser beam to the desired value for use by the delta-focusing system. Thirteenth Tlhistrative System Embodiment Of The Laser Beam Producin g System Of The Present Invention In Fig. 2M, the thirteenth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 13") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; an imaging lens (LI), realizable as a refractive lens, a HOE o r other DOE, a grin lens, zone plate(s), etc., for imaging the laser source to the focal distance as it is transmitted through imaging lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl; and a fixed spatial- frequency diffractive optical element (DOE) indicated by D2. Collectively, the collimating lens LI, the fixed spatial-frequency DOE Dl and the fixed spatial- frequency DOE D2 comprise a laser beam-modifying (sub)system in accordance with the present invention. Each of the DOEs in this system embodiment can b e realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor (M=MιM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1 *M2<1, an d thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. Notably, there will be many cases in which the beam shaping factor is less than unity, including, for example: where M1<1 and M2<1 ; where M l = l and M2<1 ; and where M1<1 and M2=l. In the Beam Compression Mode, one of the cross-sectional dimensions of the laser beam from the VLD is compressed at the output of the system to a predetermined dimension. Typically, although not necessarily, the wider cross-sectional dimension of the laser beam will b e the one that is compressed. In the laser beam producing system shown in Fig. 2M, beam aspect-ratio control is achieved and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs Dl and D2 indicated by θ.j, θ d l , θ l2 and θ d2 , which, in turn, determine the proper angle between the two DOEs previously defined hereinabove. Notably, in this embodiment of the laser beam producing system, the convergence of the beam leaving focusing lens LI need not be adjusted to provide the proper image distance to the focal point of the system, an d therefore it can be used to control or eliminate the astigmatism that is inherent in the laser beam leaving t he VLD. This embodiment of the laser beam producing system will be useful in applications where astigmatism inherent i n the laser beam leaving the VLD must be corrected or eliminated, and there is no need to focus the output laser beam to any particular focal distance using the optics associated with the laser beam producing system. Fourteenth Illustrative em Embodiment Of The Laser Beam Producin g Svstem Of The Present Invention In Fig. 2N, the fourteenth illustrative embodiment of the laser beam producing system hereof ("System Embodiment No. 14") comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a focusing (non-collimating) lens (LI), realizable as a refractive lens, a HOE, CGH or other DOE, a grin lens, zone plate(s), etc., for focusing the laser beam as it is transmitted through focusing lens LI an d through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE), i.e. diffraction grating, indicated by Dl ; an d a fixed spatial-frequency diffractive optical element (DOE) indicated by D2. Collectively, the focusing lens LI, the fixed spatial-frequency DOE Dl and the fixed spatial-frequency DOE D2 comprise a laser beam-modifying subsystem in accordance with the present invention. Each of the DOEs in this system embodiment can be realized as a transmission-type HOE, a CGH, a surface-relief hologram, or other diffractive optical element. In this embodiment, the total beam-shaping factor for the laser beam modifying subsystem is greater than unity (1), that is M1 *M2>1 , and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. There will be many cases in which the beam shaping factor is greater than unity, including, for example: where M1>1 and M2>1 ; where Ml=l and M2>1 ; and where M1>1 and M2=l. In the Beam Expansion Mode, one of the cross-sectional dimensions of the laser beam from the VLD is expanded at the output of the system to a predetermined dimension. Typically, although not necessarily, the narrower cross-sectional dimension of the laser beam will be the one that is expanded. In the laser beam producing system shown in Fig. 2N, beam aspect-ratio control and dispersion in the output laser beam is eliminated (or minimized) for any given beam expansion ratio at each of the DOEs, by way of selecting the right combination of angles of incidence and diffraction for the two DOEs D 1 and D2 indicated by θ π , θ d b θ i2 and θ d2 , which, in turn, determine the proper angle between the two DOEs, indicated by p. In System Embodiment No. 14 shown in Fig. 2N, the convergence of the beam leaving focusing lens LI need not be adjusted to provide the proper image distance to the focal point of the system, and therefore it can be used to control or eliminate the astigmatism that is inherent in the laser beam leaving the VLD. This embodiment of the laser beam producing system will be useful i n applications where astigmatism inherent in the laser beam leaving the VLD must be corrected or eliminated, and there is no need to focus the output laser beam to any particular focal distance using the optics associated with the laser beam producing system. In each of the fourteen illustrative embodiments described hereinabove, it is preferred that optical elements LI and L2 have axially symmetric optical properties (i.e. lenses LI and L2 are stigmatic optical elements). In the preferred embodiments, where LI and L2 are both refractive lenses, the lens surface profiles should be axially symmetric in order to allow for the use of both spheric and aspheric lenses. In most cases, the sub-system consisting of the VLD and lens LI, performs outside of the realm of paraxial optics; therefore lens LI will typically be aspheric in order to minimize the spherical aberration common in non-paraxial systems. Also in most cases, the use of lens L2 typically satisfies the requirements of paraxial analysis; therefore, use of a spheric lens for this optical element is usually acceptable. A major advantage of using an optical element with axial symmetry to realize lens LI is that it is then be possible to use diffractive optics to modify (e.g. correct or eliminate) astigmatism in the output laser beam. Notably, if one were to realize lens LI using an optical element not having axial symmetry , then diffractive elements (e.g. DOEs Dl and D2) could no longer be used to eliminate or correct astigmatism in the output laser beam, and that cylindrical or toroidal lenses would be required for astigmatism control or elimination. Notably, there are number of important advantages obtained when using diffractive optics (rather than astigmatic refractive optics) to correct o r eliminate astigmatism in the output laser beam astigmatism, namely: ( 1 ) simplification of the manufacture of the refractive optics (LI) as well as the diffractive optics (Dl and D2); (2) reduction in the cost of optical elements; and (3) simplification of parameter alignment during the assembly process. Methods Fnr Desi gning Laser Beam Producing Systems Of The Tllustrative System Embodiments Of The Present Invention Where Focus Control Is Desired But Neither Asti gmatism Correction Nor Delta-Focusing Are Required: System Embodiments Nos. (1 ) & C 5 System Embodiment Nos. (1) and (5) of the laser beam producing system of the present invention can be designed using the below-described design methodology, wherein the steps thereof are set forth in Figs. 3A1 through 3 A3. As indicated at Block A in Fig. 3A, the first step in the design method involves e stablishing end-user requirements for the laser beam producing module under design. In bar code symbol scanning applications, where t h e laser beam output from the system under design is to be used to scan th e elements of bar code symbols, such end-user requirements will typically include, for example, the working distance from the scanner, the depth of field of the scanning system, the type of bar code symbols that the laser beam mu s t read, the minimal width of the elements in the bar code symbols, etc. As indicated at Block B, the second step in the design method involves determining the necessary spot-size, aspect-ratio and waist dimensions of th e output laser beam in order to scan the desired bar code determined duri ng step ( 1 ) described at Block A. As indicated at Block C, the third step in the design method involves determining the module focal distance, f mo u i e> t at will provide the desired depth of field for the end-user scanning system at the desired working distance. As indicated at Block D in Fig. 3A1 , the fourth step in the design metho d involves using a Gaussian beam propagation model to determine the required beam size and aspect-ratio leaving the laser beam producing system. Notably, the steps at Blocks B, C and D are somewhat interconnected inasmuch as th e spot-size, depth-of-field, and focal distance of the output laser beam, are all aspects of Gaussian beam propagation. The values of each of these parameters have an effect on the other parameters. Therefore, it is understood that t h e order in which such parameters are determined, may be different from embodiment to embodiment. As indicated at Block E in Fig. 3A2, the fifth step in the design me'«:hod involves choosing an acceptable laser source (e.g. a VLD). In an ideal world, criteria for acceptability may include limits on beam divergence and amount of astigmatism, as well as aspect ratio, wavelength, and bandwidth. However, i n practice, such criteria will be satisfied by ensuring that the aspect ratio of the beam leaving the VLD is not too large for compression by the DOE-based subsystem. As indicated at Block F in Fig. 3A2, the sixth step in the design method involves determining an appropriate value for the beam-shaping factors of DOEs Dl and D2 which ensures that the aspect-ratio of the beam entering the laser beam-modifying subsystem (Dl and D2) from the VLD is sufficiently modified so that output laser beam has the desired aspect ratio determined at Block D described above. Notably, the beam-shaping factor M (also called the expansion ratio), defined as provides beam compression within the laser beam modifying subsystem when M<1, and provides beam expansion within the laser beam modifying subsystem when M>1. As indicated at Block G in Fig. 3A2, the seventh step in the design method involves using the beam-shaping factor determined at Block F, to determine the design angles, θ π , θ d l , θ i2 and θ d2 (expressed at the reconstruction/design wavelength, λ R ) for the two DOEs Dl and D2, which provides an optical subsystem wherein t he laser beam output from the second DOE D2 thereof has (1) effectively zero net beam dispersion, and (2) the desired aspect-ratio determined at Block B in Fig. 3A1. Notably, this step of the design method involves designing the dual-DOE laser beam modifying subsystem using either of the optical design procedures described in detail hereinbelow, As indicated at Block H in Fig. 3A3, the eighth step in the design method involves determining the theoretical distance from the VLD to the first lens element LI that produces an output laser beam having the desired beam size determined at Block D. Notably, this computation is carried out assuming a VLD beam having an elliptical spot aligned along the optical axis of lens LI. As indicated at Block I in Fig. 3A3, the ninth step in the design method involves determining the focal length of lens element LI that produces a n output laser beam having the desired focus determined at Block C in Fig. 3A1. Methods Fnr Designing Laser Beam Producing Systems Of The Illustrative System Rmhodiments Of The Present Invention Where Rocus Control And Astigmatism Correction Are Desired And Delta-FoCUSJng Is Not Required: System Embodiments Nos. (2). (3). (6). (7). (9). & H 1 ) System Embodiment Nos. (2), (3), (6), (7), (9) and (1 1) of the laser beam producing system of the present invention can be designed using the below- described design methodology, wherein the steps thereof are set forth in Figs. 3B1 through 3B2. As indicated at Block A in Fig. 3B1, the first step in the design method involves establishing end-user requirements for the laser beam producing module under design. In bar code symbol scanning applications, where the laser beam output from the system under design is to be used to scan the elements of bar code symbols, such end-user requirement will typically include, for example, the working distance from the scanning system, the depth of field of the scanning system, the type of bar code symbols that the laser beam must read, the minimal width of the elements in the b ar code symbols, etc. As indicated at Block B, the second step in the design method involves determining the necessary spot-size, aspect-ratio and waist dimensions of the output laser beam in order to scan the desired bar code determined during step (1) d escribed in Block A. As indicated at Block C, the third step in the design method involves determining the module focal distance, f modu ie> that will provide the desired depth of field for the end-user scanning system. As indicated at Block D in Fig. 3B1, the fourth step in the design method involves using a Gaussian beam propagation model to determine the required beam-size and aspect-ratio leaving the laser beam producing system. Notably, the steps at Blocks B, C and D are somewhat interconnected inasmuch as the beam spot-size, depth-of-field, and focal distance are all aspects of Gaussian beam propagation. The values of each of these parameters have an effect o n the other parameters. Therefore, it is understood that the order in which such parameters are determined may be different, from embodiment to embodiment. As indicated at Block E in Fig. 3B2, the fifth step in the design method involves choosing an acceptable laser source (e.g. a VLD). Criteria for acceptability may include limits on beam divergence and amount of astigmatism, as well as aspect ratio, wavelength, and bandwidth. As indicated at Block F in Fig. 3B2, the sixth step in the design method involves determining an appropriate value for the beam-shaping factor of DOEs Dl and D2 which ensures that the aspect-ratio of the beam entering the laser beam-modifying subsystem (Dl and D2) from the VLD is sufficiently modified so that output laser beam has the desired aspect-ratio determined at Block D described above. Notably, the beam-shaping factor M (also called the expansion ratio), defined as M=M)M 2 , provides beam compression within th e laser beam modifying subsystem when M<1, and provides beam expansion within the laser beam modifying subsystem when M>1. As indicated at Block G in Fig. 3B2, the seventh step in the design method involves using the beam-shaping factor determined at Block F, to determine the design angles, θ π , θ d l , θ i2 and θ d2 (expressed at the reconstruction wavelength, λ R ) for the two DOEs Dl and D2, which provides an optical subsystem wherein the laser beam output from the second DOE D2 thereof has (1) effectively zero net beam dispersion, and (2) the desired aspect-ratio determined at Block B in Fig. 3A1. Notably, this step of the design method involves designing the dual-DOE laser beam modifying subsystem using either of the optical design procedures described in detail hereinbelow. As indicated at Block H in Fig. 3B3, the eighth step in the design method involves determining the distance from the VLD to the first lens element LI that produces an output laser beam having the desired beam size determined at Block D. Notably, this calculation is carried out assuming that the elliptical beam produced from the VLD 4 is aligned along the optical axis of lens LI. The remaining design procedure diverges for the present embodiments ((2), (3), (6), (7), (9) and (11)); therefore, the remaining steps will be handled below on a by embodiment basis. System Embodiment Nos. (2) & (6): For System Embodiment Nos. (2) and (6), the ninth step in the design method involves determining the focal length of lens LI so that, when the correct amount of separation exists between the VLD and lens LI, the resulting convergence/divergence of the laser beam will eliminate astigmatism upon passing through both DOEs Dl and D2. The tenth step in the design method for embodiments (2) and (6) involves determining the focal length of lens L2 in order to focus the beam at the desired focal point determined at Block C in Fig. 3B 1. System Embodiment Nos. (3) & C7): For System Embodiment Nos. (3) and (7), the ninth step in the design method involves determining the focal length of lens LI so that, when the correct amount of separation exists between the VLD and lens LI, the resulting convergence/divergence of the laser beam will eliminate astigmatism upon passing through DOE Dl only. The tenth step in the design method for embodiments (3) and (7) involves determining the design parameters of DOE D2 in order to focus the beam at the desired focal point determined at Block C in Fig. 3B1. In these embodiments, DOE D2 is a stigmatic element. System Embodiment Nos. (9) & H H : For System Embodiment Nos. (9) and (11), the ninth step in the design method involves determining the focal length of lens LI so that, when the correct amount of separation exists between the VLD and lens LI, the resulting convergence/divergence of the laser beam will produce a predetermined amount of astigmatism upon passing through DOE Dl only. The tenth step in the design method for embodiments (9) and ( 1 1 ) involves determining the focal length of lens L2 in order to focus the beam at the desired focal point determined at Block C in Fig. 3B1. The known astigmatic beam entering lens L2 will be focused through DOE D2 resulting in a focused, stigmatic spot. Methods For Designing Laser Beam Producing Systems Of The Illustrative System Embodiments Of The Present Invention Where Focus Control . Astigmatism Correction And Delta-Focusing Tn Output Laser Beam Are Desired : System Embodiments Nos. (4). C8). H O) M 2) System Embodiment Nos. (4), (8), (10) and (12) of the laser beam producing system hereof can be designed using the below-described design methodology, wherein the steps thereof are set forth in Figs. 3C1 through 3C. As indicated at Block A in Fig. 3C1, the first step in the design method involves establishing end-user requirements for the laser beam producing module under design. In bar code symbol scanning applications, where the laser beam output from the system under design is to be used to scan the elements of bar code symbols, such end-user requirement will typically include, for example, the working distance from the scanning system, the depth of field of the scanning system, the type of bar code symbols that the laser beam must read, the minimal width of the elements in the bar code symbols, etc. As indicated at Block B, the second step in the design method involves determining the necessary spot-size, aspect-ratio and waist dimensions of the output laser beam in order to scan the desired bar code determined during step (1) described above. As indicated at Block C, the third step in the design method involves determining the module focal distance, f modu ι e> that will provide the desired depth of field for the end-user scanning system at the desired working distance. As indicated at Block D in Fig. 3C1, the fourth step in the design method involves using a Gaussian beam propagation model to determine the required beam-size and aspect-ratio leaving the laser beam producing system. Notably, the steps at Blocks B, C and D are somewhat interconnected inasmuch as the beam spot-size, depth-of-field, and focal distance are all aspects of Gaussian beam propagation. The values of each of these parameters have an effect o n the other p arameters. Therefore, it is understood that, from embodiment to embodiment, the order of determination of such parameters may be different. As indicated at Block E in Fig. 3C2, the fifth step in the design method involves choosing an acceptable laser source (e.g. a VLD). Criteria for acceptability may include limits on beam divergence and amount of astigmatism, as well as aspect ratio, wavelength, and bandwidth. As indicated at Block F in Fig. 3C2, the sixth step in the design method involves determining an appropriate value for the beam-shaping factors of DOEs Dl and D2 which ensures that the aspect-ratio of the beam entering the laser beam-modifying subsystem (Dl and D2) from the VLD is sufficiently modified so that output laser beam has the desired aspect-ratio determined at Block D described above. Notably, the beam-shaping factor M (also called the expansion ratio), defined as M=M]M 2 , provides beam compression within the laser beam modifying subsystem when M<1, and provides beam expansion within the laser beam modifying subsystem when M>1. As indicated at Block G in Fig. 3C2, the seventh step in the design method involves using the Beam Shaping Factor determined at Block F, to determine the design angles, θ π , θ d ι, θ i2 and θ d2 , (expressed at the reconstruction wavelength, λ R ) for the two DOEs Dl and D2, which provides an optical subsystem wherein the laser beam output from the second DOE D2 thereof has (1) effectively zero net beam dispersion, and (2) the desired aspect-ratio determined at Block B in Fig. 3A1. Notably, this step of the design meth od involves designing the dual-HOE laser beam modifying subsystem using either of the optical design procedures described in detail hereinbelow. As indicated at Block H in Fig. 3C3, the eighth step in the design method involves determining the distance from the VLD to the first lens element LI that produces an output laser beam having the desired beam size determined at Block D. As indicated in Block I in Fig. 3C2, the ninth step in the design method involves determining the focal length of lens LI so that, when the correct amount of separation exists between the VLD and lens LI, the resulting convergence/divergence of the laser beam will eliminate astigmatism up on passing through DOE Dl only. As indicated at Block J in Fig. 3C3, the tenth step of the design method is to assume DOE D2 to be a stigmatic optical element with no optical power (it is not, in general, for System Embodiment Nos. 4, 8, 10, 12) and then determine the focal length of the final lens element L2 in the system such that the desired "average" focal distance of the output laser beam is achieved. As indicated at Block K in Fig. 3C3, the eleventh step of the design method involves determining the design parameters of HOE D2 that produce the desired delta-focus of the laser beam through the lens L2. Methods For Desi gning Laser Beam Producin g Systems Of The Tllustrati ve Svstem Embodiments Of The Present Invention Where Astigmatism Correcti on Ts Desired But Neither Focus Control Nor Delta-Focusing Are Required: System Embodiments Nos. ( 13) & ( 1 4 ) System Embodiment Nos. (13) and ( 14) of the laser beam producing system of the present invention can be designed using the below-described design methodology, wherein the steps thereof are set forth i n Figs. 3 D 1 through 3D3. As indicated at Block A in Fig. 3D1, the first step in the design method involves establishing end-user requirements for the laser beam produci ng module under design. These embodiments are similar in structure to System Embodiment Nos. (1 ) and (5). However, since the design goal here is different, the use will be different as will the end-user requirements. For the sake of this discussion, the chosen requirements will be a set final aspect ratio and b eam spot size. Notably for this discussion, the beam-shaping that occurs will necessarily be aspect-ratio reduction. It is understood that one skilled in the art could adjust this design procedure to meet a different combination of end- user requirements . As indicated at Block B i n Fig. 3D1 , the second step in the design method involves using a Gaussian beam propagation model to determine the required beam aspect-ratio leaving the laser beam producing system in order t o produce the specified aspect-ratio at focus. As indicated at Block C in Fig. 3D1 , the third step in the design metho d involves choosing an acceptable laser source (e.g. a VLD). Criteria for acceptability may include limits on beam divergence and amount of astigmatism, as well as aspect ratio, wavelength, and bandwidth . As indicated at Block D in Fig. 3D1 , the fourth step in the design metho d involves determining an appropriate value for the beam-shaping factors of DOEs Dl and D2 which ensures that the aspect-ratio of the beam entering t h e laser beam-modifying subsystem (Dl and D2) from the VLD is sufficiently modified so that output laser beam has the desired aspect ratio determined a t Block B described above. Notably, the beam-shaping factor M (also called the expansion ratio), defined as M=M ! M 2 , provides beam compression within the laser beam modifying subsystem when M<1, and provides beam expansion within the laser beam modifying subsystem when M>1. As indicated at Block E in Fig. 3D2, the fifth step in the design method involves using the beam-shaping factor d etermined at Block D, to determine the design angles, θ u , θ d ι, θ i2 and θ d2 , (expressed at the reconstruction wavelength, X R ) for the two DOEs Dl and D2, which provides an optical subsystem wherein the laser beam output from the second DOE D2 thereof has (1) effectively zero net beam dispersion, and (2) the desired aspect-ratio determined at Block B. Notably, this step of the design method involves designing the dual-DOE laser beam modifying subsystem using either of the optical design procedures described in detail hereinbelow. As indicated at Block F in Fig. 3D2, the sixth step in the design method involves determining the convergence of the beam leaving lens LI that will adjust or eliminate the astigmatism produced by the VLD. Specifically for this discussion it is known that the beam will converge. Once the convergence is known, the focus location can be calculated. As indicated at Block G in Fig. 3D2, the seventh step in the design method involves using a Gaussian beam propagation model to determine the required beam spot size leaving the laser beam producing system in order to produce the focused spot size determined at Block A. As indicated at Block H in Fig. 3D2, the eighth step in the design method involves determining the distance from the VLD to the first lens element LI that produces an output laser beam having the desired beam size determined at Block G. As indicated at Block I in Fig. 3D3, the ninth step in the design method involves determining the focal length of lens element LI that produces a beam with the convergence determined in Block F. A First Procedure F r Determining The Desi gn Angles For The Diffractive Optical Elements Within The Laser Beam Modifying Subassemhlv Of The System Of The Present In venti on In order to determine the design angles for DOEs Dl and D2 within th e dual-DOE laser beam modifying subsystems hereof, it is necessary to construct a geometric optics model thereof. For the sake of simplification, each DOE i n each subsystem is represented using a "central-ray" m odel, as shown in Fig. 3E. Using this reasonable modeling assumption, DOE Dl can be represented as a first fixed spatial-frequency hologram having fringe-spacing dl , whereas DOE D2 can be represented as a second fixed spatial-frequency hologram having fringe-spacing d2. This central-ray model provides a perfect description for the central ray of the laser beam, in all cases herein considered, but less than a perfect description for non-collimated rays (i.e. rays not parallel to the center ray of the laser beam). If the beam passing through DOEs Dl and D2 has a relatively large f/#, then the effect of the non-collimated rays will be negligible. In defining the laser beam modifying (optics) subsystem, the angle of incidence of the laser beam from lens LI o nto the front surface of first fixed- spatial-frequency DOE (Dl) is specified by θ 11 ; whereas the angle of diffraction therefrom is specified by θ d b as illustrated in Fig. 3E. The angle of incidence of the laser beam from the first fixed spatial-frequency DOE Dl onto the front surface of second fixed spatial-frequency DOE D2 is specified by θ l2 , whereas the angle of diffraction therefrom is specified by θ d2 . These four parameters θ ll3 θ d l , 9, 2 and θ d2 , completely define the dual-DOE subsystem hereof, and thu s provides four degrees of freedom within the geometrical optics model thereof. Applying the well known "diffraction grating" equation to the first and second DOEs, Dl and D2, respectively, the following two system equations are obtained : sinθ,, + sinθ d l (Eq. 1 ) d, ' — = sιnθ l2 + sιnθ d2 (Eq. 2 ) wherein the parameter λ R is the design (i.e. reconstruction) wavelength of the laser beam used during reconstruction, and parameters d t and d 2 are the surface spacing of the fringes within the first and second DOEs Dl and D2, respectively. Using simple geometry, the following expression is obtained: P=θ d I - θ l2 (Eq. 3 ) wherein p, the DOE tilt angle, is the angle formed between the surfaces of the two DOEs Dl and D2 within the laser beam modifying subsystem under design. Notably, parameter p has been previously defined in the geometrical optics model used to design the laser beam production modules disclosed i n Applicant's copending US Patent Application Serial No. 08/573,949 filed December 18, 1995, incorporated herein by reference. The above-described geometrical optics model will be used to determine the optimum configuration of the dual-DOE subsystem which produces a n output laser beam h aving minimum beam dispersion and prescribed beam aspect-ratio. Notably, correction for laser beam astigmatism is not addressed in this modeling procedure; however, this does not preclude the ability t o control astigmatism when this procedure is used. The dual-DOE subsystem contains four degrees of design freedom, wherein two of those degrees of freedom are removed by requiring minimum dispersion and a specific beam expansion. This leaves two additional degrees of freedom in the design process to meet some additional design goals. Specifying The Design Criteria For The Laser Beam Modifying Subsystem Of The Present Invention In the illustrative embodiments, the dual-DOE laser beam modifying subsystem must satisfy two design constraints, namely: (1) for an input laser beam having a first specified beam aspect-ratio, produce an output laser beam having a second specified beam aspect-ratio; and (2) produce an output laser beam, wherein the dispersion characteristics or "dispersion" thereof (defined by dθ d2 /dλ) are minimized over the spectral bandwidth of the VLD beam. The first design constraint is achieved by compressing or expanding one dimension of the laser beam incident upon the first DOE Dl . Thus, this design constraint is best described as the beam-shaping factor (e.g. expansion ratio), M, which is equal to the product of the individual expansion ratios for DOEs D 1 and D2, designated by M, and M 2 , respectively, wherein Mι = D 0Utpu , ι /D ιnput l an d 2 =D 0Utput2 /D ιnput2 , and D represents dimension of the beam in the compression/expansion direction (i.e. common plane of incidence of DOEs D 1 and D2). In order to meet this design constraint, the following equations must be satisfied: The second constraint (i.e. relating to minimizing dispersion) is achieved by satisfying the following equation: d 2 cosθ l2 =d ! Cθsθ d l (Eq. 6 ) wherein parameters d [ and d 2 are the surface spacing of the fringes within the first and second DOEs Dl and D2, respectively. A First Procedur For Desi gning The. Dual-DOE Subsystem So That The Prespecified Design Constraints Are Satisfied An optimal design for the dual-DOE laser beam modifying subsystem hereof, which satisfies the above-specified design constraints, can b e determined using the following procedure in conjunction with the geometrical optics model described above. As indicated at Block A in Fig. 3F1, the first step of the design procedure involves choosing values for the beam compression/expansion ratios M, and M 2 such that the total desired Beam Shaping Factor M satisfies the expression M=M[M 2 . Also, at this stage of the design method, the design (i.e. reconstruction) wavelength λ R , and the angle of incidence θ.x, are chosen b y the DOE-subsystem designer. As indicated at Block B in Fig. 3F1, the second step of the "design procedure involves solving for the angle of diffraction θ d l at DOE Dl using Equation No. (4) set forth above. As indicated at Block C in Fig. 3F1, the third step of the design procedure involves solving for the fringe structure (surface) spacing d , of DOE Dl, using Equation No. (1) set forth above. As indicated at Block D in Fig. 3F1, the fourth step of the design procedure involves solving for the angle of i ncidence θ l2 at DOE D2, using the following equation: θ,2 = arctan -{ M\K - K + — (Eq.7) 2 l 2 K d,cosθdi where K = As indicated at Block E in Fig. 3F1, the fifth step of the design procedure involves solving for the DOE tilt angle p, using Equation No. (3). As indicated at Block F in Fig. 3F2, the sixth step of the design procedure involves solving for the angle of diffraction θ d2 at DOE D2, using Equation No. (5). As indicated at Block G in Fig. 3F2, the seventh step of the design procedure i nvolves solving for the fringe surface spacing d 2 within DOE D2, using Equation No. (2). The above described parameters specify the design parameters for the dual-DOE subsystem at the reconstruction wavelength λ R which typically b e specified by the characteristic wavelength of the VLD used to realize the laser beam producing system under design. A Second Procedure For Determining The Design Angles For The Diffractive Optical Elements Within The Laser Beam Modifying Subassemhlv Of The System Of The Present Invention According to the second design procedure, the two equations for (1) zero beam dispersion and (2) the desired beam aspect-ratio are solved and then graphed (i.e. plotted) to determine the intersection of the two functions which yields the design point at which both design requirements are simultaneously satisfied. Typically, a few iterations of the solutions of the equations will b e required to determine the design point to an acceptable level of precision. This procedure has been described in detail in Applicant's copending Application Serial No 08/573,949, incorporated herein by reference. Notably, the graphical approach described hereinabove provides additional information about the residual dispersion that will exist when the wavelength of the VLD laser beam differs from the design wavelength. The graphical approach also provides information regarding the rate of change of dispersion as a function of laser beam wavelength, which is useful in particular applications. Such information can also be obtained from the model employed in the First Procedure described above using Equation (8) which will b e described in greater detail hereinafter. Considerations When Desi gning The DOE-Based Suhsystem Of The Presen t Invention When designing a DOE-based laser beam modifying subsystem hereof using either of the design procedures set forth above, the following factors should be considered. First, it is desirable to select angles of incidence and diffraction that are not too large or too different in magnitude. This will make the construction of the DOEs simpler. This is an example of a supplementary goal that can be met by exercising the aforementioned unused degrees of freedom in the laser beam modifying subsystem design. Second, it is desirable to have the angular separation between the incident beam at DOE Dl and the diffracted beam at DOE D2 greater than zero so as to avoid interference between the zero-order beam from DOE Dl and the diffracted beam from DOE D2. As this may b e difficult to do, it may be necessary to provide a blocking plate or surface between the two DOEs as shown in illustrative embodiments of " the present invention in Figs. 6C, IOC and l lC. Notably, in such illustrative embodiments, the blocking plate is provided as an integral part of the module housing. Considerations On Aspect-Ratio Control And Beam Disp sio Minimization /Elimination Provided that the desired parameters are reasonable, the system an d assembly methods of the present invention enable the construction of optical systems capable of producing output laser beams having (1) a desired beam aspect-ratio and (2) zero or minimum beam dispersion. These design objectives can be accomplished over a fairly wide range of beam aspect-ratios, angles of incidence and diffraction, and angles between the two DOES. For all of the system embodiments herein, beam dispersion correction is perfect only for the center ray in the system. However, if the angle of the cone of rays passing through the laser beam modifying subsystem is relatively small, then beam dispersion correction, while not perfect, will be acceptable in many applications. In bar code scanning applications where, for example, the f- number of the focusing cone of light rays is generally on the order of 200 o r more (so that the full angle subtended by the cone of light rays (i.e. the full cone angle) is less than 0.3 degrees), beam dispersion correction will be more - than adequate for all rays within the light cone incident on the DOEs Dl and D2. Considerations On Astigmatism Correction When proceeding to eliminate astigmatism in the output laser beam from the laser beam producing module, the resulting pair of designed DOEs does not change in any way. In accordance with the principles of the present invention, astigmatism correction is accomplished by adjusting the separation between the VLD and the first lens LI during the alignment stage of the system assembly process of the present invention. The amount of adjustment is dependent on the fixed parameters of t he DOE pair (e.g. diffraction angles an d angle between DOEs Dl and D2) and the beam characteristics of each VLD used in the construction of each laser beam producing system. Notably, it is possible to specifically design the laser beam modifying subsystem to eliminate a specific amount of astigmatism for a given desired focus as accomplished, for example, in System Embodiment Nos. (13) and ( 14). When designing such systems, the beam-shaping factor, M, can be specifically chosen to eliminate astigmatism. In all of the other system embodiments disclosed herein the beam shaping factor M is used to control aspect-ratio. However, when designing a system to eliminate astigmatism, it is understood that aspect-ratio control will be sacrificed in order to reduce astigmatism. The specific system embodiments disclosed herein can be modified using such teachings to provide numerous other types of system designs in accordance with the principle of the present invention.. The inherent astigmatism of the laser beam produced from the VLD is modified or eliminated by adjusting the convergence or divergence of the beam incident on the dual-DOE laser beam-modifying subsystem hereof. If the laser beam-modifying subsystem is used to expand the narrower dimension of the VLD beam or to compress the wider dimension of the VLD beam (i.e. aspect-ratio reduction), then the astigmatism is minimized by using a converging beam incident on the laser beam-modifying subsystem. If the laser beam-modifying subsystem is used to compress t he narrower dimension of the VLD beam or to expand the wider dimension of the VLD beam (i.e. aspect-ratio enlargement), then the astigmatism is minimized by using a diverging beam incident on the laser beam-modifying subsystem. Considerations On Adiustment Of The Focal Length Of The Stigmatic Output Laser Beam Relatively simple optics following the laser beam-modifying subsystem, as shown in Fig. 2H, 2J, and 2L, can be used to focus the astigmatism-free (stigmatic) beam produced by the subsystem. By placing a second lens L2 after the variable spatial-frequency DOE D2, as in System Embodiment Nos. 4 and 8 , or before the variable spatial-frequency DOE D2, as in System Embodiments Nos. 10 and 12, the laser beam producing system is provided with a means for adjusting (i.e. fine-tuning) the focal length the stigmatic output laser beam. This feature is advantageous in applications where, for example, the laser beam producing system functions as an optical subsystem within a larger optical system, and the laser beam output therefrom is to be further modified in terms of focal length and the like. For example, if the DOE-based subsystem hereof is used to compress the laser beam produced from the subsystem comprising the VLD and lens LI, as i n the illustrative embodiments shown in Figs. 2A, 2B, 2C, 2D, 21, 2J, and 2M, then the minimum dispersion curve for the laser beam output from the resulting laser beam producing system will have a negative curvature (i.e. its graphical representation is concave downward), as illustrated in Figs. 5 and 5B1. If the DOE-based system hereof is used to expand the laser beam produced from the subsystem comprising the VLD and lens LI, as in the illustrative embodiments shown in Figs. 2E, 2F, 2G, 2H, 2K, 2L, and 2N, then the minimum dispersion curve for the laser beam output from the resulting laser beam producing system will have a positive curvature (i.e. its graphical representation is concave upward), as illustrated in Figs. 5 and 5B2. If DOE-based subsystem hereof neither expands nor compresses the input laser beam (i.e. the Beam Shaping Factor M of the subsystem is unity), then the dispersion curve for the output laser beam will be perfectly flat, as illustrated in Fig. 5B. This unique case occurs only when the two DOEs Dl an d D2 of the subsystem are arranged parallel to each other and the laser beam entering the DOE Dl is parallel to the beam leaving the DOE D2. Various Options Available For Implementing The DOE-Based Laser Beam Modifying Subsystem Of The Present Invention In general, there are a variety of different techniques available for implementing (i.e. realizing) the DOEs of the DOE-based subsystem 2 described in great detail hereinabove. One technique known in the art would involve the use of conventional "optically-based" holographic recording techniques, wherein each designed DOE of the subsystem is realized as a volume transmission hologram (HOE) constructed by the interference of a laser "object" beam and a laser "reference" beam within a photosensitive recording medium. Another technique known in the art would involve the use of computer generated holographic techniques, wherein each designed DOE of the Analv/ing The Dispersion Associated With The Laser Beam Output From Th e Laser Ream Producing Svstem Desi gned In Accordance With The Principles Of The Present Inventi on Having designed a laser beam producing system using the above- described design procedure, the dispersion characteristics thereof can b e analyzed by using the following equation : θ<n[λg) - arcsin ■ a (Eq. 8 ) Equation (8) can be used to plot the deflection (i.e. diffraction) angle of each wavelength component in the laser beam output from any laser b eam producing system designed and constructed in accordance with the principles of the present invention. A geometrical optics model is presented in Fig. 5A for dispersion analysis of the output laser beam. A graphical representation of dispersion analysis is provided in Fig. 5B, showing a plot of diffraction angle θ d2 as a function of wavelength component of the output laser beam. Inasmuch a s the sole objectives for the DOE-subsystem design process described hereinabove are shaping the laser beam without introducing dispersion, t h e values for the expansion factors M, and M 2 and angle of incidence θ,, specified at Block A in Fig. 3E1 can be varied to obtain virtually any acceptable solution (provided that the Beam Shaping Factor M=M,M 2 is satisfied). Using the Beam Dispersion Equation (Eq. 8) set forth above, one c an predict the behavior of the laser beam producing system, as well as design a system that will perform in the manner required by any particular application at hand. Unlike conventional optical elements, the dispersion of the DOE-based laser beam-modifying subsystem can be adjusted so that the function θ d2 (λ) exhibits a minimum or a maximum value reflected in a graphical representation thereof. The maximum or minimum point is the precise design point of zero dispersion. If desired or required by any particular application, the dispersion characteristics can be modified in a variety of ways. subsystem is realized as a copy of computer-generated hologram (CGH) b y computer modeling the interference pattern and producing the same through printing techniques to produce a hologram having performance characteristics specified during the design process. Other techniques, while less preferred, could involve the use of micro-etching of optical structures to produce "surface-relief holograms" having performance characteristics specified during the design process of the present invention. For purposes of illustration, techniques for producing HOE, CGH and surface-relief implementations of the DOE-based subsystem hereof will be described in greater detail hereinbelow. Implementing The DOE-Based Subsystem Using Optical-Based Holographic Recording Techniques: Two Cases To Consider Prior to teaching particular procedures for making fixed spatial frequency and variable spatial frequency HOEs, it will be helpful to provide a brief overview on these different holographic construction techniques. Case 1 : Constructing Fixed Frequency HOEs When constructing a fixed frequency hologram (HOE), the object an d reference beams must have the same radius of curvature. In most applications, this is accomplished by collimating the two beams so that we have two wavefronts at the hologram recording medium. The angle between the two beams will determine the spatial frequency of the fixed frequency hologram. The greater the angle, the greater the spatial frequency. The actual spatial frequency of the hologram is, more precisely, a function of the angles of incidence of the two beams at the hologram recording medium and the wavelength of the two beams. The spatial frequency is established by the well known grating equation: d= wavelength/(sinO + sinR), where O is the angle of incidence of the object beam and R is the angle of incidence of the reference beam. Case TT: Constructing Variable Frequency HOEs When constructing a variable frequency hologram (HOE), the object an d reference beams must have different radii of curvature. In most applications, this is accomplished by collimating one of the beams and making the other beam a diverging beam. We will choose to call the collimated beam the reference beam. The diverging beam, which we will choose to call the object beam, is generally created by transmitting the object beam portion of the laser beam through a positive lens, such as a microscope objective. The focal point of the converging beam leaving the positive lens then becomes the center of curvature of the object beam. If this positive lens is a spherical lens, the object beam wavefront at the hologram recording medium will be spherical. If the lens is cylindrical lens, with optical power in only one dimension, the object beam wavefront at the hologram recording medium will be cylindrical. In the case of cylindrical wavefront, some additional spherical optics is generally employed to expand the cylindrical beam along the axis of the cylinder withou t modifying the wavefront in that direction. That is, in the direction parallel to the cylindrical axis of the wavefront the beam will appear to be collimated. As in the fixed frequency hologram, the wavelength of the beams an d the angles of incidence of the two beams at the hologram recording medium will determine the spatial frequency of the hologram. However, in this case, the angle of incidence of the object is not constant since the beam has spherical (or cylindrical) wavefront. The angle of incidence of any beam at the point of incidence of any surface is the angle between the normal to the surface and the incoming ray at the point of incidence. And the incoming ray, by definition, is just the normal to the wavefront. But for a spherical, o r cylindrical, wavefront, the normal to the wavefront will not be constant across the wavefront. The angle of incidence for* the object beam will be the angle between the normal to the surface and the line running from the point of incidence to the center of curvature of the object beam. Since this angle will vary with position on the hologram recording medium, then, from the grating equation, the spatial frequency will also vary with position on the hologram recording medium. That is, we will have a variable frequency hologram. The spatial frequency of this variable frequency hologram will vary i n both (x and y) dimensions of the plane of the hologram recording medium when the object beam is a spherical wavefront. The spatial frequency of this variable frequency hologram will vary in only one dimension of the plane of the hologram recording medium when the object beam is a cylindrical wavefront. Having provided an overview on these different construction techniques, it is now appropriate to disclose hereinbelow preferred procedure of constructing both fixed and variable spatial frequency HOEs. A Procedure For Constructing Fixed And Variable Spatial Frequency HOEs As indicated at Block A in Fig. 4A, the design parameters θ i; , θ d ] , θ i2 an d θ d2 and f 2 (i.e. focal length of DOE D2 in the case of variable spatial frequency DOEs) expressed at the reconstruction wavelength λ R are converted into construction parameters expressed at the construction wavelength λ c namely: object and reference beam angles θ 0 ι and Θ R1 for HOE HI at construction wavelength λ c ; and object and reference beam angles θ 02 andθ R2 , respectively, for HOE H2. This parameter convention process can be carried out using, for example, the conversion method described on Pages 163-164 and Figs. 28 A 1 - through 28D and Fig. 29 of International Publication No. WO/9722945, based on corresponding US Application Serial Nos. 08/573,949 and 08/726,522, each of which is incorporated herein by reference. Notably, instances where the design (reconstruction) wavelength λ R is equal to the construction wavelength λc and there is no need for wavelength correction or conversion, then the design parameters can be used for the construction parameters in a manner well known in the art. As indicated at Block B in Fig. 4A, it will be necessary, in the case of variable spatial frequency DOEs, to use computer ray-tracing analysis in order to determine the distances of the object and reference sources relative to the recording medium (as well as the distances of any aberration-correcting lenses therefrom) which are employed during the holographic recording process, schematically depicted in Fig. 4B for the case of a variable spatial frequency HOE. In the case of fixed spatial frequency DOEs, computer ray-tracing analysis is not necessary. Notably, in this case, the location of the object an d reference sources relative to the recording medium will be effectively located at infinitely (e.g. realized by the use of collimating mirrors or the like). Having computed the construction parameters for HOE HI and HOE H2, the HOEs can then be constructed using the holographic recording system illustrated in Fig. 4B, using the volume holographic recording techniques detailed in International Publication No. WO/9722945, supra. Regarding, non- VLD type astigmatism, the method used to construct HOE HI should seek t o minimize the astigmatism that would normally occur when a widely diverging - beam is incident on a glass plate with parallel surfaces. This type of astigmatism can be minimized in many instances if, for example, the HOE is constructed using: (1) the same type of laser as is used in the end-user scanning system; and (2) the same illumination geometry as is used in the end- user scanning system. While applying the above conditions is helpful in many instances, it is understood that it is not always necessary, nor is it always possible to do so. Implementing The DOE-Based Subsystem Using Computer-Generated Holographic CCGH) Recording Techniques The values obtained for design p arameters θ π , θ d I , θ i2 and θ d2 , d l 5 d 2 an d f 2 (focal length of variable frequency DOE) associated with the dual-DOE subsystem can be used to derive construction parameters necessary to construct a dual-CGH implementation thereof. A suitable procedure for this type of implementation will be described below. As indicated at Block A in Fig. 4C1, the first step of the method involves formulating, within a digital computer system 170, a mathematical description of the object and reference beam wavefronts at the design wavelength λ R . Typically, standard diffraction integrals, such as the Kirchhoff integral, can b e used to produce mathematical descriptions of these wavefronts. Such mathematical descriptions can be derived from the design parameters {e.g., for DOE Dl, such parameters include θ (1 , θ d l , θ l2 and θ d2 , the image produced b y DOE Dl (i.e. reference source point) and image produced from DOE D2 (i.e. object source point)}. In particular, a mathematical description for the object and reference beam wavefronts at the design wavelengths λ R for DOE Dl can b e formulated as Kirchhoff integrals using the design parameters for DOE D 1 , expressed at the reconstruction (i.e. design) wavelength λ R . Also, a mathematical description for the object and reference beam wavefronts at the design wavelength for DOE D2can be formulated as Kirchhoff integrals using the design parameters for DOE D2, expressed at the reconstruction wavelength λ R . Notably, using the CGH implementation technique, there typically will b e no need to make any corrections for the construction wavelength as the CGH has been previously constructed for aberration-free performance at the reconstruction wavelength (which is specified by the commercial-g r ade VLD selected for use in constructing the laser beam producing system). As indicated at Block B in Fig. 4C1, the second step of the method involves using the digital computer system 170 to formulate a mathematical description of the "interference pattern" that is generated by mathematically superimposing the mathematical model of the object beam wavefront (e.g. represented by Kirchoff integrals) with the mathematical model of the reference beam wavefront (also represented by Kirchoff integrals). The mathematical description of the interference pattern generated by the computer system 170 provides a "spatial function" of the interference pattern. In cases where only fixed-spatial frequency DOEs are used to construct the laser beam modifying subsystem, the interference pattern generated by the reference and object wavefronts will be mathematically represented by a one- dimensional sinusoidal function, expressed in the form of D=A+Bsinfx, where A is a bias level; B is a modulation factor always less than A; and f is the spatial frequency. In cases where a variable spatial frequency DOE is used to construct the laser beam modifying subsystem, the interference pattern generated by the reference and object wavefronts can be mathematically represented by an infinite series of one-dimensional sinusoidal functions. As indicated at Block C in Fig. 4C1, the third step of the method involves using the digital computer system 170 to sample the spatial function of the computer generated/represented interference pattern along the x and y directions in order to produce a large set of sampled values of varying light transmission associated with the computer generated interference pattern (represented within the computer system 170). These sampled values correspond to either the light transmittance of the computer generated/represented interference pattern over its x,y spatial extent. As indicated at Block D in Fig. 4C2, the fourth step of the method involves transferring the sampled light transmittance values from the computer system 170 to the drivers of a graphical plotter or plotting tool 1 7 1 shown in Fig. 4C2. As indicated at Block E in Fig. 4C2, the plotting system 171 uses the set of sampled amplitude transmittance values to plot the two-dimensional sampled interference pattern on paper or other recording medium 172, thereby creating a graphical representation thereof 173 consisting of fine (sampled) dots of particular density, in a way similar to that produced by a digital printing process. In general, the two-dimensional amplitude transmittance function 173 plotted on paper or other recording medium 1 72 by the plotting tool 171 is usually quite large (i.e. several orders larger than the final CGH master). The two-dimensional plot produced from this step of the method provides a graphical representation of the CGH under construction. For fixed spatial frequency DOEs, the 2-D plot provides a graphical representation of a CGH which functions as a planar diffraction grating. For variable spatial frequency DOEs, the 2-D plot provides a graphical representation of a CGH which functions with some degree of focal power. As indicated at Block F in Fig. 4C2, two-dimensional amplitude transmittance function 173 plotted on paper at Block E can then b e photographically reduced on some light transmissive or reflective recording medium, generally photographic film 175 using photographic reduction equipment 174. The output of this system is a master of the CGH which can b e then bleached to improve its diffraction efficiency. However, its diffraction efficiency will always be low because the CGH is a surface relief hologram, not a volume hologram as produced by the optically-based Holographic Recording Method described above. As normal photographic film will often be the medium used for the first recording of the CGH (at Block F), it is expected that resolution of the CGH will not be very high. As required by most embodiments of the DOE-based subsystem hereof, - the CGH master obtained at Block F can be copied onto some higher efficiency medium, such as DCG, photoresist, or suitable surface relief material 177 using conventional copying apparatus 176 well known in the art. While such copying techniques enable the production of DOEs having greater diffraction efficiencies, these techniques are not without their problems, as explained below. For example, copies of a CGH master can be made with high diffraction efficiency in surface relief material by standard pressing operations provided that the aspect ratio of the surface relief structure (groove depth / groove spacing) is on the order of one. However, it is very difficult to make such copies when the aspect ratio of the surface relief structure is that large. Using photoresist CGH copies directly is also difficult because the material is susceptible to damage during handling. Also, sealing the photoresist CGH copies between glass will be required in many applications. However, this will drastically reduce the diffraction efficiency of the photoresist CGH copies if an index matching fluid is used to minimize reflection losses. Making DCG copies of the CGH masters at the 488 nm Argon wavelength is a much better method, as the "nearly-contact" copy process will always faithfully reproduce the surface fringe structure of the master, regardless of the wavelength of the copying laser light source. Consequently, the copy holograms will be aberration-free at the wavelength at which the CGH masters were constructed (for use with conventional VLDs). The CGH HOEs will b e essentially the same as the photographic plate masters. Notably, however, the CGH fabrication technique described above will have little advantage over the optically-based Holographic Recording Method. In fact, this technique will have the significant disadvantage of producing holograms having a much lower resolution. In typical applications, the DOEs will require a resolution of at least 2000 cycles per mm. While the DCG copying method is capable of producing HOE having a resolution better than 2000 cycles per mm, the resolution of the DCG copy can be n o greater than that of the CGH master, which, for normal photographic film, will be much less than 2000 cycles per mm. Consequently, when using the CGH implementation technique described hereinabove, it will be desirable (if not necessary) to first record the CGH master in a photographic medium having a very high resolution in order to produce CGH masters having diffraction efficiencies suitable for use in the DOE-based subsystem hereof. Having produced a master CGH in the manner described above, copies thereof can be made using various copying techniques known in the art. If the illuminating beam transmitted through the CGH copy (during reconstruction) is identical to the reference beam (modeled at Block A), then the object beam (modeled at Block A) will be reconstructed by the interference pattern embodied within the CGH copy. If the illuminating beam transmitted - through the CGH copy (during reconstruction) is identical to the object beam (modeled at Block A), then the reference beam (modeled at Block A) will b e reconstructed by the interference pattern embodied within the CGH copy. Additional details regarding CGH implementation process can found with reference to: Chapter 19 of the book entitled "Optical Holography" by Collier, Burckhardt and Lin (1971), published by Academic Press, incorporated herein by reference. Applications Of The Laser Beam Producing System Of The Present Tnvention In general, each illustrative embodiment of the laser beam producing system described above can be realized in a variety of different ways. For example, in Figs. 6A through 10D, several laser beam production modules of the present invention are disclosed for producing a laser beam having a pre- specified beam aspect-ratio, zero beam dispersion and a predetermined focus. In Figs. 11A through 11C, a laser beam production module of the present invention is shown for producing a laser beam, wherein a pre-specified beam aspect-ratio is achieved, its beam dispersion is zero (or minimized), its focus set to a predetermined distance, and its astigmatism corrected. In Figs. 12A through 112C, a laser beam production module of the present invention is shown for producing a laser beam wherein its aspect-ratio is controlled, its beam dispersion is zero (or minimized), its astigmatism corrected, its focus set to a predetermined distance, and its focal length adjusted. With reference to modified system designs shown in Figs. 7A through 7C, several laser beam production modules of the present invention are disclosed for producing a laser beam having a pre-specified beam aspect-ratio, zero beam dispersion an d astigmatism control. For purposes of illustration, HOE-based implementations of these illustrative system embodiments will be described hereinbelow. Equivalent CGH-based implementations thereof can be readily made using the principles disclosed hereinabove. Laser Beam Production Module Of The First Illustrative Svstem Embodiment For Producing A Stigmatic Laser Beam Having Zero Beam Dispersion. Predetermined Aspect Ratio And Preset Focus fCASE D In Figs. 6A, 6B and 6C, a first illustrative embodiment of the laser beam production system of Figs. 2M and 2N (System Embodiment Nos. 13 and 14) is disclosed. As shown, this optical system is realized in the form of a miniature laser beam producing module 10 comprising an assembly of subcomponents, namely: a module housing 11 made of lightweight plastic and serving as a n optics bench for the optical components within the laser beam producing system; a VLD 12, press-fit mounted through a metal heat sinking plate 26; a VLD, mounting bracket (i.e. Yoke) 13, having side projecting 13A and 13B slidable within spaced apart recesses 11A and 11B respectively formed in the rear portion of the module housing: connected to the terminal 14 of the VLD, for applying a supply voltage and driving the VLD to produce a laser beam having elliptical, divergent, eccentric, and astigmatic characteristics, and a oversized aperture 27 for receiving the case portion (or beam emitting) portion of the VLD and allowing x, y positioning thereof relative to the VLD mounting bracket 13; a flexible circuit 15; a focusing lens LI 16 for focusing the laser beam produced from the VLD; fixed spatial-frequency HOE HI 17, securely mounted within a first mounting slot 1 8 formed in the module housing 11, for modifying the beam characteristics of the laser beam output from focusing lens LI 16; fixed spatial-frequency HOE H2 19, securely mounted within a second mounting slot 20 formed in the module housing 11, for modifying the beam characteristics of the laser beam produced from HOE HI to produce the output laser beam; a beam folding mirror 21, mounted on side wall surface 22 of the module housing, for directing the output laser beam through the beam output window 23 formed in the side wall of the module housing; a first radiation- absorbing wall surface 24 formed in the module housing, aligned with the zeroeth-order diffraction beam from HOE HI, and absorbing the zeroeth-order diffraction beam produced from HOE HI; and second radiation-absorbing wall surface 25 formed in the module housing, aligned with the zeroeth-order diffraction beam from HOE H2, and absorbing the zeroeth-order diffraction beam produced from HOE H2. In an illustrative embodiment of this system design, the VLD 12 can b e realized using a SONY Model SLD1122VS laser diode, and the focusing lens LI 16 can be realized as a 4.35 mm lens made of an optically transparent plastic. The HOEs HI 17 and H2 19 can be made using DCG recording material of about 5 microns thick, a construction wavelength of 488 nanometers. These volume transmission holograms can be mounted between a pair of ultra-small plates made from float glass. It is understood, however, that other embodiments of this system design can be made using different types of components an d materials, having different design parameters selected or determined for the particular application at hand . As shown in Fig. 6C, during the alignment stage of the assembly process for the laser beam producing module 10, t he distance between VLD 12 and lens LI 16 is adjusted by sliding the VLD mounting bracket 13 within the pair of recesses 11A and 11B. As will be explained in greater detail hereinafter, this parameter adjustment mechanism is employed while the system is mounted o n a special design fixture specifically crafted for aligning such parameters. When the x, y position of the VLD is properly aligned relative to lens LI, by a translation of the VLD/heat-sinking plate subassembly relative to VLD mounting bracket 13 during the alignment stage of the module assembly process, then the output laser beam from the module will have the desired beam aspect-ratio and minimized (or zero) beam dispersion minimized i n accordance with the design criteria for this laser beam producing module. Also, the (z) axis position of the VLD is relative to lens LI can be adjusted during the alignment stage by sliding VLD mounting bracket 13 within recesses 11A and 11B in the module housing until beam astigmatism is eliminated. This parameter alignment process will be described in greater detail hereinafter. Laser Beam Producing Module Of The Second Tllustrative System Embodiment For Producing A Laser Beam Having Focus Control. Controlled Aspect-Ratio An d Zero Beam Dispersion: CASE A In Figs. 7A, 7B and 7C, a second illustrative embodiment of the laser beam production System Embodiment No. 1) of Fig. 2M is disclosed. As shown, this optical system is realized in the form of a miniature laser beam producing module 30 comprising an assembly of subcomponents, namely: a module housing 31 made of lightweight plastic and serving as an optical bench for the optical components within the laser beam producing system; a VLD 3 2 mounted to a VLD heat-sinking plate 33 through aperture 33A and producing a visible laser beam having elliptical, divergent and astigmatic beam characteristics in response to a voltage source applied VLD terminal 34 by way of a flexible circuiter like connectors (not shown) well known in the art; a mounting bracket 36 having an aperture 36A for receiving the barrel portion of the casing of the VLD 32 and a mounting surface 36B for affixing the associated heat-sinking plate 33 and premounted VLD 32 thereto, and also having side projections 36C and 36D for slidable receipt within s paced apart recesses 37C and 37D formed in the rear portion of the module housing; a collimating lens LI 38 for focusing the laser beam produced from the VLD; fixed spatial-frequency HOE HI 39, securely mounted within a first mounting slot 40 formed in the module housing 31, for modifying the beam characteristics of the laser beam output from focusing lens LI 38; fixed spatial- frequency HOE H2 41, securely mounted within a second mounting slot 4 2 formed in the module housing 31, for modifying the beam characteristics of the laser beam produced from HOE HI to produce the output laser beam; a radiation-absorbing wall surface 43 formed in the module housing, aligned with the zeroeth-order diffraction beam from HOE HI, and absorbing the same during operation of the device; and a housing cover plate 44 for attachment to the top portion of the module housing 31 and securing HOEs HI and H2 therein. In the illustrative embodiment, the VLD 32 can be realized using a SONY Model SLD1122VS laser diode, and the collimating lens LI 38 can be realized as a 4.35 mm lens made of an optically transparent plastic. The HOEs HI 39 an d H2 41 can be made using DCG recording material of about 5 microns thickness, at a construction wavelength of 488 nanometers. These volume transmissions holograms can be mounted between a pair of ultra-small plates made from float glass. It is understood, however, that other embodiments of this system design can be made using different types of components and materials, having different design parameters selected or determined for the particular application at hand . When the proper x, y position of the VLD 32 relative to the optical axis of lens LI 38 is set during the alignment stage of the module assembly process, then the output laser beam from the module will have the desired beam aspect- ratio and minimized (or zero) beam dispersion in accordance with the design criteria for this laser beam producing module. As shown in Fig. 7C, during assembly and construction of the laser beam producing module 30, the distance between VLD 32 and lens LI 38 (i.e. "d") is adjusted by sliding the VLD mounting bracket 36 within the pair of recesses 37C and 37D in the module housing. As will be explained in greater detail hereinafter, this parameter adjustment m echanism is employed while the system is mounted o n an optical bench specially crafted for aligning such parameters. Laser Beam Scanning Module Adapted For Use With The Laser Beam Produci ng Modules Of The Present Invention In Figs. 8A and 8B, a laser b eam scanning module is disclosed for use with any of the laser beam producing modules of the present invention. As shown, the laser beam scanning module 50 comprising an assembly of subcomponents, namely: a module housing 51 made of lightweight plastic an d serving as an optical bench for the optical components within the laser beam scanning system; an electromagnetic coil 52 mounted within recess 53 in the module housing, for producing a magnetic force field FM in response to electrical current supplied to the input terminals thereof 52A; a scanning element 54 supporting a light deflecting element (e.g. mirror, hologram, refractive element, etc.) 55 on the front surface of its free end, and a permanent magnetic element 56 on the rear surface of its free end; a pair of mounting plates 57 and 58 having projections 57A, 57B, and matching holes 58A, 58B respectively for clamping the base portion 54A of the scanning element 54, and securely mounting the same within recess 59 formed within the module housing 5 1 , as shown in Fig. 8B and 9; and a housing cover plate 60 for attachment to the top surface 61 of the module housing 51, an d securing the scanning mechanism components therewithin, while forming a scanning window 62 through which a laser beam produced from a laser beam producing module hereof can pass to the scanning element and be deflected therefrom out through the scanning window across the scan field of the resulting scanning system. Details regarding the design and construction of the scanning mechanism formed by the electromagnet 52, the scanning element 54 and the scanning element anchoring mechanism (formed by plates 57 and 58, and recess 56) are disclosed in copending Application Serial No. 08/931,694 filed September 16, 1997, and incorporated herein by reference in its entirety. It is understood, however, that there are other scanning mechanisms that may be embodied within the module housing 51 described above, for use in conjunction with the laser beam producing modules of the present invention. As shown in Fig. 8A, when scanning element mounting plates 57 and 5 8 are inserted within the mounting recess 59 in the module housing, the top projections 57C and 58C thereof protrude slightly above the top surface of the module housing and through aperture 63 in the housing cover plate. Screws (not shown for clarity of illustration) can then be passed through holes formed in holes 64 and 65 in the cover plate 60 and inserted into threaded holes 66 and 67 in the module housing 51. In this assembled configuration, the scanning window 62 is completely formed and provides access to the scanning element disposed within the housing. In alternative embodiments, a transparent plate can be mounted over the scanning window to prevent dust, dirt and the like from entering the scanning mechanism embodied within the module housing. Miniature Laser Beam Scanning Svstem Formed Bv Arranging A Laser Beam Producing Module Of The Present Invention With A Laser Beam Scannin g Module In Fig. 9, there is shown a miniature laser beam scanning system formed by arranging the laser beam producing module 70 shown in Fig. 7 with the laser scanning module 50, shown in Fig. 8A. This novel arrangement provides a laser scanning system for use in laser scanning engines of the general type disclosed, for example, in copending Application Serial No 08/292,237 filed August 17, 1994, incorporated herein by reference. As shown in Fig. 9, the output laser beam 71 from the laser beam producing module 70 is directed onto the mirror on the light deflecting element (e.g. mirror) 55 within the laser scanning module 50. As the scanning element oscillates about its anchored base portion, the laser beam 71A reflected off the mirror element 55 is scanned over the scanning region of the scanning system. Modules 70 and 50 can b e mounted upon optical bench of various types employed, for example, for bar code symbol scanning systems, and the like. Integrated Laser Beam Producing And Scanning Module According To A First Illustrative System Embodiment Of The Present Tnvention In Figs. 10A, 10B and 10C, a laser scanning device is shown, wherein the laser scanning subsystem shown in Fig. 8A is integrated with a laser beam producing subsystem of Fig. 7A. As shown, integrated scanning device 8 0 comprises an assembly of subcomponents, namely: a module housing 81 made of lightweight plastic and serving as an optical bench for the optical components within the laser beam producing and scanning systems alike; a VLD 82 mounted to a VLD heat- sinking plate 83 t hrough aperture 83A an d producing a visible laser beam having elliptical, eccentric, divergent, an d astigmatic beam characteristics in response to a voltage source applied to terminals 82A by way of a flexible circuit or other conductive structures well known in the art; a mounting bracket 84 having an aperture 84A for receiving a portion of the casing of the VLD 82 and a plane surface 84B affixing the associated heat-sinking plate 83 thereto, and also having side projections 84D and 84E for slidable receipt within spaced apart recesses 85B and 85C formed in the rear portion of the module housing 81 ; a collimating lens LI 86 for focusing the laser beam produced from the VLD; fixed spatial-frequency HOE HI 88, securely mounted within a first mounting slot 89 formed in the module housing 81, for modifying the beam characteristics of the laser beam output from collimating lens LI 86; fixed spatial-frequency HOE H2 90, securely mounted within a second mounting slot 91 formed in the module housing 8 1 , for modifying the beam characteristics of the laser beam produced from HOE HI to produce the output laser beam; a radiation-absorbing wall surface 9 2 formed in the module housing, aligned with the zeroeth-order diffraction beam from HOE HI, and absorbing the zeroeth-order diffraction beam produced from HOE HI; electromagnetic (i.e. coil) 52 mounted within recess 93 in the module housing, for producing a magnetic force field in response to electrical current supplied to the input terminals thereof; scanning element 5 4 supporting light deflecting element (e.g. mirror, hologram, refractive element, etc.) 55 on the front surface of its free end, and permanent magnetic element 56 on the rear surface of its free end; mounting plates 57 and 58 for clamping the base portion of the scanning element 54, and mounting the same within recess 94 formed within the module housing 81 ; and a housing cover plate 9 5 for attachment to the top surface 96 of the module housing 81, and securing the laser beam producing and scanning mechanism components therewithin, while forming a scanning window 97 through which a scanned laser beam can be projected out into a scan field for scanning. In Fig. 10D, the subcomponents of integrated scanning engine are shown mounted within a miniature housing 99 having a base portion 99A and cover plate 99C. Typically, the length, and width dimensions of the housing 99 will be substantially smaller than a matchbox and can be realized as small as a sugar-cube using presently available enabling technology. As shown, a plastic window or filter 100 can be mounted over the scanning window to protect entry of dust, dirt and the like into the interior of the scan engine where there are optical components. Module housing 81 can be mounted to the bottom half of the scan engine housing 99A shown in Fig. 10D. The scan engine can include a photodetector, analog and digital signal processing circuits 1 0 1 realized or printed circuit boards 102 and 103, as taught in copending Application Serial No. 08/292, 237 filed on August 17, 1994. Laser Beam Producing Module For Producing A Stigmatic Laser Beam Havin g Focus Control. Controlled Aspect-Ratio and Zero Beam Dispersion CCASE ^ In Figs. 11 A, 11B and 11C, an illustrative embodiment of the laser beam production System Embodiment Nos. 2 and 6 of Figs. 2B and 2F) is disclosed. It is understood, however, that designs according to System Embodiments 3, 7, 9 and 11 may be used as well in the construction of this class of laser beam producing module. As shown in Figs. 11A through 11C, this optical system is realized in the form of a miniature laser beam producing module 110 comprising an assembly of subcomponents, namely: a module housing 111 made of lightweight plastic and serving as an optical bench for the optical components within the laser beam producing system; a VLD 112 mounted to a VLD heat sinking plate 1 1 3 through aperture 113A and producing a visible laser beam having elliptical, eccentric, divergent and astigmatic beam characteristics in response to a voltage source applied to terminals 112A by way of a flexible circuit or like structure well known in the art; a mounting bracket 114 having an oversized aperture 114A for receiving a portion of the casing of the VLD 112 and planar surface 114B for affixing the associated heat-sinking plate 113 thereto, an d also having side projections 114C and 114D for slidable receipt within spaced apart recesses 115C and 115D formed in the rear portion of the module housing; a focusing lens LI 116 for focusing the laser beam produced from the VLD; a bore 117 formed in module housing 111 for mounting lens LI 1 1 6 therein; fixed spatial-frequency HOE HI 118, securely mounted within a first mounting slot 119 formed in the module housing 111, for modifying the beam characteristics of the laser beam output from focusing lens LI 116; fixed spatial-frequency HOE H2 120, fixedly mounted within a second mounting slot 121, formed in the module housing 111, for modifying the beam characteristics of the laser beam produced from HOE HI; a focusing lens L2 122 mounted within a lens-support bracket 123, slidably mounted within a third mounting slot 124 formed in the module housing, for adjustable movement of lens L2 122 along the optical axis of HOE H2 120 to adjust the focal-length of output laser beam; a radiation-absorbing wall surface 1 26 formed in the module housing, aligned with the zeroeth-order diffraction beam from HOE HI, and absorbing the zeroeth-order diffraction beam produced from HOE HI; and a housing cover plate 127 for attachment to the top portion of the module housing 111 and securing HOEs HI and H2 and focusing lens L2 therein. In an illustrative embodiment of this system design, VLD 112 can b e realized using a SONY Model SLD1122VS laser diode, the focusing lens LI 1 1 6 can be realized using a 4.35 mm lens, and the focusing lens L2 122 can b e realized using a 250 mm lens, to provide an output focal distance of about 1 0 inches from the module. The HOEs HI and H2 can be made using DCG recording material, of 5 microns film thickness, at a construction wavelength of 480 nanometers. These volume transmission holograms can be mounted between a pair of ultra-small plates made from float glass. It is understood, however, that other embodiments of this system design can be made using different types of components and materials, having different design parameters selected or determined for the particular application at hand . As shown in Fig. 11C, during assembly and alignment of the laser beam producing module 110, the distance between VLD 112 a nd lens LI 116 is adjusted by sliding the VLD mounting bracket 114 within the pair of recesses 115C and 115D in the module housing, and the distance between the lens L2 122 and HOE H2 120 is adjusted by sliding lens-support bracket 124 within the recess 1 24 in module housing along the optical axis of HOE H2. As will b e explained in greater detail hereinafter, these parameter adjustment mechanisms are employed while the optics system is mounted on an optical bench specially crafted for aligning such parameters. Laser Beam Producing Module For Producing A Stigmatic Laser Beam Having Focus Control. Controlled Aspect-Ratio. Zero Beam Dispersion, and Adjustable Focal -Length (CASE C In Figs. 12A, 12B and 12C, an illustrative embodiment of the laser beam production System Embodiment Nos. 4 and 8 of Figs. 2D and 2H) is disclosed. It is understood, however, that such a design can be realized using System Embodiment Nos. 10 and 12, as well. As shown in Figs. 12A, 12B and 12C, this optical system is realized i n the form of a miniature laser beam producing module 130 comprising a n assembly of subcomponents, namely: a module housing 135 made of lightweight plastic and serving as an optical bench for the optical components within the laser beam producing system; a VLD 131 mounted to a VLD heat sinking plate 132 through aperture 132A and producing a visible laser beam having elliptical, divergent, eccentric, and astigmatic beam characteristics i n response to a voltage source applied to terminal 131 A by way of a flexible circuit or like conductive elements well known in the art; a mounting bracket 133 having an aperture 133 A for receiving a portion of the casing of the VLD 131 and, a planar surface 133B for affixing the associated heat-sinking plate 132 thereto, and also having side projections 133C and 133D for slidable receipt within spaced apart recesses 135C and 135D formed in the rear portion of the module housing; a focusing lens LI 136 for focusing the laser beam produced from the VLD; a bore 137 for mounting lens 136 within the module housing; fixed spatial-frequency HOE HI 138, securely mounted within a first mounting slot 139 formed in the module housing 135, for modifying the beam characteristics of the laser beam output from focusing lens LI 136; fixed spatial-frequency HOE H2 140, mounted within a HOE-support bracket 141 that is slidably mounted within a second mounting slot 142 formed in the module housing 135, for adjustable movement relative to HOE HI 138 (during assembly/alignment) in order to modify the beam characteristics of the laser beam produced from HOE HI; a focusing lens L2 143 mounted within a lens- support bracket 144 that is slidably mounted within a third mounting slot 1 45 formed in the module housing, for adjustable movement along the optical axis of the system; a radiation-absorbing wall surface 146 formed in the module housing, aligned with the zeroeth-order diffraction beam from HOE HI, an d absorbing the zeroeth-order diffraction beam produced from HOE HI; and a housing cover plate 147 for attachment to the top portion 148 of the module housing 135 and securing HOEs HI and H2 and focusing lens L2 therein. In an illustrative embodiment, the VLD can be realized using a SONY Model SLD1122VS laser diode, the focusing lens LI can be realized using a 4.35 mm lens, and the focusing lens L2 is realized using a 250 mm lens. The HOEs HI and H2 can be made using DCG recording material, of about 5 microns thickness, at construction wavelength 488 nanometers. These volume transmission holograms can be mounted between a pair of ultra-small plates made from float glass. It is understood, however, that other embodiments of this system design can be made using different types of components an d materials, having different design parameters selected or determined for the particular application at hand. As shown in Fig. 12C, during assembly and alignment of the laser beam producing module 130, the distance between VLD 131 and lens LI 136 is adjusted by sliding the VLD mounting bracket 133 within the pair of recesses 135C and 135D in the module housing, and the distance between the lens L2 and HOE H2 140 is adjusted by sliding lens-support bracket 144 within the recess 145 in module housing, and the distance between HOE H2 and HOE HI is adjusted by sliding HOE support bracket Ml within recess 142 in the module housing. As will be explained in greater detail hereinafter, these parameter adjustment mechanisms are employed while the system is mounted on a n optical bench specially crafted for aligning such parameters. The design methods of the present invention provide a way of determining the design and construction parameters for the laser beam producing system of the present invention. However, by virtue of the fact that properties of the VLD are not easily ascertainable in practice, such methods cannot be used to compute the distance between the VLD and lens LI which results in an output laser beam having zero dispersion and a desired aspect ratio. The Parameter Adiustment Svstem Used During The Module Assembly an d Alignment Procedure Of The Present Invention In Fig. 13, a computer-controlled parameter adjustment system of the present invention is shown. For purposes of illustration only, this system is shown in Fig. 13 with a laser beam producing module of Figs. 12A- 12C (embodying System Embodiment No. 4 for illustration only) mounted to the fixtures of the system. This case was selected because this module requires th e maximum number of parameters to be adjusted, thus implicating all of the functions of t he parameter adjustment system. As will be illustrated, however, the parameter adjustment system can be used to adjust the parameters of any one of the illustrated embodiment of the present invention in a rapid, highly efficient manner, thereby making the laser beam producing modules hereof suitable for mass production. As shown in Fig. 13, the parameter adjustment system 150 comprises a number of subsystems and subcomponents, namely: a module support platform 151 for supporting and translating (in the z direction during the "loading stage") the module housing (e.g. 135) of each laser beam producing module (being assembled and adjusted); a VLD support platform 154 for adjustably supporting the VLD (and its mounting structure) along three- coordinate axes relative to the stationary module housing support platform 151 and lens LI; a lens L2 support platform 155 for supporting and translating second lens L2 of the laser beam producing module along one-coordinate axis relative to the stationary module housing support platform 151 ; a HOE support platform 156 for supporting and translating HOE H2 of the laser beam producing module along one-coordinate axis (i.e. optical axis) relative to the module housing support platform 151 (i.e. along the optical axis of the system); a beam profiler 157 (such as, for example, Model 0180-XYS Beam Scan from Photon, Santa Clara, California) having a beam scan display monitor 1 5 8 connected thereto; a quadrant detector 159 having a quadrant detector display 160 connected thereto; a first computer-controlled translation mechanism 161 A for translating the VLD support platform 154 relative to module housing support platform 151 during analysis of the laser beam output from the HOE- based subsystem of the laser beam producing module 153 using the beam scanner 157 and quadrant detector 159 ; a second computer-controlled translation mechanism 161B for translating the lens L2 support platform 1 55 relative to module housing support platform 151 during analysis of the laser beam output from t he HOE-based subsystem of the laser beam producing module 153 using the beam scanner 157 and the quadrant detector 159; and a third computer-controlled translation mechanism 161 C for translating the HOE support platform 156 relative to module housing support platform 151 during analysis of the laser beam output from the HOE-based subsystem of the laser beam producing module 153 using the beam scanner 157 and the quadrant detector 159. As will be explained hereinafter, certain of these subsystems are not e mployed when adjusting the parameters of particular laser beam producing modules of the present invention, while other of these subsystem are employed when aligning the components of other types of laser beam producing modules. Such details will be described below. Method Of Assembling And Aligning The ubc mpon nts Of Laser Beam Producing Systems Of The Illustrative Svstem Embodiments Of The Present Invention Design For Instances Where Focusing Control Is Desired An d Astigmatism Correction And Delta-Focusing Al£ N_oi Desired (System Rmhodiments Nos. (1 ) And (5V. CASE A In general, when assembling a laser beam producing module based o n System Embodiments Nos. 1 and 5, the below described parameter adjustment procedure can be used in conjunction with the p arameter adjustment system of Fig. 13. The procedure comprises a pre-alignment stage and an alignment stage. During the prealignment stage, the various optical components of the laser beam producing module are installed within their respective mounting locations within the module housing, or within support structure associated with the parameter adjustment system 150. During the alignment stage, the VLD and lens LI are aligned in order to achieve the performance characteristics considered during the design stage. Referring to Fig. 14, the details of each of these stages will be described below for System Embodiment Nos. 1 and 5. In Fig. 14, the module of Figs. 7A-7C is shown mounted within the fixture of the parameter adjustment system as it embodies System Embodiment Nos. 1 and 5 in their entirety. Pre-Alignment Stage Of The Assembly Procedure For System Embodiment Nos. 1 And 5 The first step of the pre-alignment stage of the system assembly procedure involves press fitting the VLD 32 into VLD heat-sink plate 33 so that the VLD junction is arranged in a predetermined orientation relative to the VLD heat-sink plate. The second step of the prealignment stage involves mounting HOE H 1 (39) and HOE H2 (41) into their appropriate mounting slots 40 and 42 formed within module housing 31. Thereafter, the HOEs can be glued or otherwise fixed in position. The third step of the prealignment stage involves inserting lens LI into the lens recess (e.g. pocket) formed within the module housing. Thereafter, the lens LI can be glued or otherwise fixed in position. The fourth step of the prealignment stage involves placing the VLD mounting bracket (i.e. yoke) 36 into appropriate recesses 37C and 37D formed in the module housing. Notably, the VLD mounting bracket is held within such recesses by frictional fit and can only be translated along (z) axis of the parameter alignment system (i.e. the x and y directions being fixed by the geometry of these recesses. The fifth step of the prealignment stage involves placing the module housing 31 onto the module housing support platform 151 so that pins on the bottom surface of the housing module 31 align with corresponding holes formed on the housing module support platform 151. When housing module 31 is installed in the m anner described above, the module housing 31 is then clamped to the module housing support platform 151 by way of screws, pressurized clamps or other releasable fastening devices. The sixth step of the prealignment stage involves clamping the yoke 3 6 to affixed holder 164. The seventh and last step of the prealignment stage involves attaching the VLD 32 to VLD support platform 154 of the parameter alignment system. In the preferred embodiment, this step can be achieved by sliding the leads of the VLD into a connector provided on the VLD support platform and secured by clamping, etc. The VLD support platform 154 is capable of movement along the x, y and z axes of the parameter adjustment system 150. The Alignment Stage Of The Assembly Procedure For Svstem Embodiments Nos. 1 And 5 The first step of the alignment stage of the system assembly procedure involves sliding the module housing support platform 151 towards VLD support platform 151 under the control of microcontroller 161 until the VLD 32 is positioned within oversized aperture 36A formed within the VLD support 36 positioned within the recesses of the module housing. Notably, at this "load" position, the VLD 32 is free to move within the x and y plane by virtue of the oversized aperture in the VLD m ounting yoke, and also along the z axis by virtue of clearance provided between the premounted lens LI and the outer face of the VLD mounting yoke. As will become apparent hereinafter, such clearance enables the optical axis of each loaded VLD to be aligned with the optical axis of lens LI as well as attaining the required distance which achieves the desired focus (for System Embodiment Nos. 1 and 5) or control of astigmatism (for all System Embodiments except Nos. 13 and 14) as specified during the design stage described in detail above. The second step of the alignment stage of the procedure involves locking the position the module housing support platform 151 relative to the underlying optical bench 151 (arranged in its "loaded" configuration). This locking operation can be carried out using a computer-controlled locking mechanism 163 known in the art. The third step of the alignment stage of the procedure involves locking the VLD heat-sink plate 32 to the VLD support platform 154 locking using mechanism 162 so that the VLD heat-sink plate is prevented from undergoing rotation in the x-y plane during alignment of the VLD relative to the lens LI during the subsequent steps of the alignment procedure. This condition will ensure that the VLD junction is prevented from rotation during the alignment procedure, which may involve translation of the VLD junction in the x, y and/or z axes of the system in order to secure the performance parameters of the module established during the design stage. The fourth step of the alignment stage of the procedure involves applying a biasing force on the VLD support yoke 36 (in the direction of the VLD heat-sink plate 33) so that the plate-like portion of the VLD support yoke gently engages the VLD heat-sink plate 33 in order that the surface of the VLD heat-sink plate and planar portion of the VLD support yoke assume the same z coordinate position during x, y alignment operations, while permitting relative movement between these two plate-like structures along the x-y plane of the system. The fifth step of the alignment stage of the procedure involves supplying electrical power to the VLD 32 so that it produces a laser beam which is transmitted through lens LI and HOEs HI and H2. The sixth step of the alignment stage of the procedure involves translating the VLD support platform 154 in the x-y plane until the output laser beam strikes the center of the quadrant detector 159, which has been prealigned relative to the locked-in-position module housing 31 so that first diffraction order beam from HOE H2 (i.e. the optical axis thereof disposed i n the plane of diffraction at diffraction angle θ d2 ) passes through the center of the quadrant-type photodetector 159. When the output laser beam strikes the center of the quadrant-type photodetector, then the design geometry will b e achieved, resulting in minimum beam dispersion and the desired amount of beam shaping by design. Also optimal output power will be transmitted from the module along the optical axis of the system. This condition is based on the reasonable assumption that the diffraction efficiency of HOEs HI and H2 will be maximum along the first diffraction order by design, and characteristic wavelength of the VLD is substantially the same as the reconstruction wavelength of HOEs HI and H2. Notably, this on-center aligned position can b e visually detected when the indicator dot on the quadrant detector display unit 160 is aligned with the crosshair thereof. Completion of this step of the procedure will ensure that output power from the laser beam producing module will be as close to the output of the VLD as is practically possible, as well as ensuring that the design requirements have been satisfied. The seventh step of the alignment stage of the procedure involves gluing or otherwise permanently securing the x-y position of the VLD heat- sinking plate 33 and VLD support bracket 36 in the position determined during the step above. Thereafter, the biasing force applied during the above step of the procedure can be removed. The eighth step of the alignment stage of the procedure involves adjusting the position of the subassembly (comprising the VLD 32, the VLD heat-sink plate 32 and the VLD support yoke 36) along the z axis of the parameter adjustment system while monitoring the output laser spot at the desired focal length of the module using a beam profiler (i.e. profiling instrument) 157, as identified above. When the spot size of the output laser beam at the desired focal length is minimum (along either the x or y axis of the system, not both), then VLD support yoke 36 is glued or otherwise fixed in position relative to the module housing 31. Thereafter, the housing cover plate 44 is fastened upon the module housing and then the aligned laser beam producing module is removed from the parameter adjustment system and is ready for use in the system 150 for which it has been designed. Method Of Assembly And Aligning The Subcomponents Of Laser e m Producing Systems Of The Illustrative Svstem Embodiments Of The Present Invention Designed For Instances Where Astigmatism Correction And Focus Control Are Desired. But Not The Adiustment Of The Laser Beam Focal Length : Svstem Embodiment Nos. (2 (3). (6). (7). (9) And (1 1 ): CASE B In general, when assembling a laser beam producing m odule based o n System Embodiments Nos. 2 and 6, the parameter adjustment procedure of the present invention can be carried out on the module design shown in Figs. 1 1 A- 11C supported upon the parameter adjustment system of Fig. 13. When assembling a laser beam producing module based on System Embodiments Nos. 9 and 11, the parameter adjustment procedure of the present invention can b e carried out on the module design similar to that shown in Figs. 11A-11C (but with lens L2 disposed between HI and h2) supported upon the parameter adjustment system of Fig. 13. Also, when assembling a laser beam producing module based on System Embodiments Nos. 3 and 7, the parameter adjustment procedure of the present invention can be carried out on the module design similar to the module shown in Figs. 12A through 12C (without lens L2) supported upon the parameter adjustment system of Fig. 13. For each of these groups of system embodiments, the assembly procedure comprises a prealignment stage and an alignment stage. During the prealignment stage, the various optical components of the laser beam producing module are installed within their respective mounting locations within the module housing, or within support structure associated with the parameter adjustment system 150. During the alignment stage, the VLD an d lens LI are aligned, as well as HOE H2 relative to HOE HI (and L2 where applicable) in order to achieve the performance characteristics specified during the design stage. Details of each of these stages will be described below for System Embodiment Nos. 2 and 6, 9 and 11, 3 and 7, with reference to Fig. 15. Pre-Alignment Stage Of The Assembly Procedure For Svstem Embodiment Nos. 2 And 6 The first step of the prealignment stage of the system assembly procedure involves press fitting the VLD 112 into VLD heat- sink plate 113 so that the VLD junction is oriented in it predetermined orientation relative to the VLD heat-sink plate. The second step of the prealignment stage involves mounting HOE H 1 and HOE H2 into their appropriate mounting slots 115C and 115D formed within module housing 111. Thereafter, the HOEs can be glued or otherwise fixed in position. The third step of the prealignment stage involves inserting lens LI into the lens recess (e.g. bore) 117 formed within the module housing. Thereafter, the lens LI can be glued or otherwise fixed in position. The fourth step of the prealignment stage involves placing the VLD mounting yoke 114 into appropriate recesses 115C and 115D formed in the module housing. Notably, the VLD mounting yoke is held within recesses 1 15C and 115D by frictional fit and can only be translated along z axis of the parameter alignment system (i.e. the x and y directions being fixed by the geometry of the recesses. The fifth step of t he prealignment stage involves placing the module housing 11 1 into the module housing support platform 151 so that pins on the bottom surface of the housing module align with corresponding holes formed on the housing module support platform 151. When housing module 111 is installed in the manner described above, the module housing is then clamped to the module housing support platform 151 by way of screws, pressurized clamps or other releasable fastening devices. The sixth step of the prealignment stage involves placing the mounting yoke 114 on its support platform and clamping the same in place. The seventh and last step of the prealignment stage involves attaching the VLD 112 to VLD support platform 151 of the parameter alignment system. In the preferred embodiment, this step can be achieved by sliding the leads of the VLD into a connector provided on the VLD support platform. The VLD support platform 154 is capable of movement along the x, y and z axes of the parameter adjustment system 150. Alignment Stage Of The Assembly Procedure For Svstem Embodiment Nos. 2. And 6 The first step of the alignment stage of the system assembly procedure involves sliding the module housing support platform 151 towards VLD support platform 154 under the control of microcontroller 161 until the VLD is positioned within oversized aperture 1 14A formed within the VLD support yoke 1 14 positioned within the recesses of the module housing. Notably, at this "load" position, the VLD is free to move within the x and y plane by virtue of the oversized aperture in the VLD mounting yoke, and also along the z axis by virtue of clearance provided between the premounted lens LI and the outer face of the VLD mounting yoke. As will become apparent hereinafter, such clearance enables the optical axis of each loaded VLD to be aligned with respect to the optical axis of lens LI . The second step of the alignment stage of the procedure involves locking the position the module housing support platform 151 relative to the underlying optical b ench (arranged in its "loaded" configuration). This locking operation can be carried out using locking mechanism 162 known under computer control. The third step of the alignment stage of the procedure involves locking the VLD heat-sink plate to the VLD s upport platform 154 so that the VLD heat- sink plate is prevented from undergoing rotation in the x-y plane during alignment of the VLD relative to the lens LI during the subsequent steps of the alignment procedure. This condition will ensure that the VLD junction is prevented from rotation during the alignment procedure, which may involve translation of the VLD junction in the x, y and/or z axes of the system in order to secure the performance parameters of the module established during the design stage. The fourth step of the alignment stage of the procedure involves applying a biasing force on the VLD support yoke 114 (in the direction of the VLD heat-sink plate 113) so that the plate-like portion of the VLD support yoke gently engages the VLD heat-sink plate 113 in order that the surface of the VLD heat-sink plate and planar portion of the VLD support yoke assume the same z coordinate position during x, y alignment operations, while permitting relative movement between these two plate-like structures along the x-y plane of the system. The fifth step of the alignment stage of the procedure involves supplying electrical power to the VLD 112 so that it produces an output laser beam which is transmitted through lens LI and HOEs HI and H2. The sixth step of the alignment stage of the procedure involves translating the VLD support platform 154 in the x-y plane until the output laser beam strikes the center of the quadrant photodetector 159, which has been prealigned relative to the locked-in-position module housing 111 so that first diffraction order beam from HOE H2 (i.e. the optical axis thereof disposed in the plane of diffraction at diffraction angle θ d2 ) passes through the center of the quadrant-type photodetector. When the output laser beam strikes the center of the quadrant-type photodetector, then the design geometry will b e achieved, resulting in minimum beam dispersion and the desired amount of beam shaping by design. Also optimal output power will be transmitted from the module along the optical axis of the system. This condition is based on the reasonable assumption that the diffraction efficiencies of HOEs HI and H2 1 20 will be maximum along the first diffraction order by design, and characteristic wavelength of the VLD is substantially the same as the reconstruction wavelength of HOEs HI and H2. Notably, this on-center aligned position can b e visually detected when the indicator dot on the quadrant detector display unit 160 is aligned with the cross-hair on the display surface thereof. Completion of this step of the procedure will ensure that the output power of the laser beam producing module will be as close to the output of the VLD as is practically possible, as well as ensuring that the design requirements have been satisfied. The seventh step of the alignment stage of the procedure involves gluing or otherwise permanently securing the x-y position of the VLD plate an d VLD support yoke in the position determined during the step above. Thereafter, the biasing force applied during the above step of the procedure can be removed. The eighth step of the alignment stage of the procedure involves adjusting the position of the subassembly (comprising the VLD 112, the VLD heat-sink plate 113 and the VLD support yoke 114) along the z axis of the parameter adjustment system while monitoring the output laser at the desired focal length of the module using beam profiling (scanning) instrument 157. When the spot size of the output laser beam (at some unknown location along the optical axis HOE H2) is minimum in both the x and y dimensions, then VLD support yoke 114 is glued or otherwise fixed in position relative to the module housing 111. Notably, the beam profiling instrument will have to be moved along the optical axis of HOE H2 to detect this condition, in which the output laser beam is free of astigmatism. While the output beam may still have elliptical cross-sectional characteristics along its direction of propagation, its beam cross-section will be minimum for both dimensions at this detected point which, by definition, is a stigmatic beam. Thereafter, the VLD support yoke is glued or otherwise fixed to the module housing 1 1 1 . The ninth step of the alignment stage of the procedure involves inserting lens support bracket 123, containing prespecified lens L2, into recess 124 formed within the front end of the module housing 1 1 1 . The tenth step of the alignment stage of the procedure involves adjusting the focal length of the module by translating lens L2 along the optical axis (or adjusting the combined focal length of a lens pair) while monitoring the output laser beam (at the desired focal length of the module set during design) until the spot size of the laser is minimum. In one illustrative embodiment, this is achieved by sliding lens L2 relative to HOE H2. In instances where multiple lens elements are used to construct L2, the spacing if such lenses can be varied to impart the desired focal length to the lens system L2. Notably, in some instances, it may also be desirable or necessary to adjust the (x,y) position of the L2 along the optical axis of the system. Thereafter, the lens L2 mounting bracket is glued or otherwise fixed relative to the module housing. Then the housing cover plate 127 is then fastened upon the top of the module housing a nd then the aligned laser beam producing module is removed from the parameter adjustment system and is ready for use in the system for which it has been designed. Pre-Alignment/Ali gnment Stage Of The Assembly Procedure For Svstem Embodiment Nos. 9 And 1 1 The prealignment stage for System Embodiments Nos. 9 and 11 is similar to that described for System Embodiments 1, 5, 13 and 14 above with several exceptions. Foremost, in System Embodiment Nos. 9 and 11, second lens L2 is disposed between HI and H2. Thus, a module similar to that shown in Figs. 11A-11C, but with second lens L2 disposed between HOEs HI and H2, could be used to realize such a system design. Notably, the design of such a module will enable the second lens L2 to be installed within its m odified module housing after completing the alignment procedure described above. When the second lens L2 is installed within the module housing, the focal length of the output laser beam can be set by translating lens L2 along the optical axis (or adjusting the focal-length of second lens L2 in appropriate cases). Pre-Ali gnment And Alignment Stages Of The Assembly Procedure For Svstem Embodiment Nos. 3 and 7 The prealignment stage of the assembly procedure for System Embodiment Nos. 3 and 7 is different than that described for System Embodiment Nos. 2 and 6 above, in two significant ways. First, HOE H2 is a variable spatial-frequency HOE (having focusing power) which is mounted in a HOE support bracket enabling its principal plane to be translated along its optical axis relative to the principal plane of HOE HI without modifying the tilt angle P therebetween. Secondly, in System Embodiment Nos. 3 and 7, there is no second lens L2 as required in System Embodiments Nos. 2 and 6. While such structural differences simplify the prealignment stage of the assembly process, they do not alter the procedure for aligning the VLD junction along the x and y axes of the system to minimize beam dispersion, or along the z axis to eliminate beam astigmatism. Notably, after eliminating beam dispersion an d correcting for astigmatism, HOE H2 can be translated along its optical axis to set the focal length (i.e. focus) of the output laser beam to that specified during design. Method Of Assembling And Aligning The Subcomponents Of Laser Beam Producing Systems Of The Illustrative Svstem Embodiments Of The Present Invention Designed For Tnstances Where Focus Control. Astigmatism Correction And Delta-Focusing Are Desired: Svstem Embodiments Nos. (4). (8). (10) And (12); Case C In general, when assembling a laser beam producing module based o n System Embodiments Nos. 4 and 8, the parameter adjustment procedure of the present invention can be carried out on the module design shown in Figs. 1 1A- 11C supported upon the parameter a djustment system of Fig. 13. When assembling a laser beam producing module based on System Embodiments Nos. 10 and 12, the parameter adjustment procedure of the present invention can be carried out on the module design similar to that shown in Figs. 1 1A- 1 1 C (but with lens L2 disposed between HI and H2) supported upon the parameter adjustment system of Fig. 1 3 . For each of these groups of system embodiments, the assembly procedure comprises a prealignment stage and an alignment stage. During the prealignment stage, various optical components of the laser beam producing module are installed within their respective mounting locations within the module housing, or within support structure associated with the parameter adjustment system 150. During the alignment stage, the VLD and lens LI are aligned relative to each other, the focusing lens L2 is aligned relative to HOE H2, and the HOE H2 is aligned relative to HOE HI, in order to achieve the performance characteristics specified during the design stage. Details of each of these stages will be described below for System Embodiment Nos. 4, 8, 1 0 and 12, with reference to Fig. 16. Pre-Alignment Stage Of The Alignment Procedure For Svstem Embodiment Nos. 4 And 8 The first step of the prealignment stage of t he system assembly procedure involves press fitting the VLD 131 into VLD heat-sink plate 132 so that the VLD junction is oriented in it predetermined orientation relative to the VLD heat-sink plate. The second step of the prealignment stage involves mounting HOE H I and HOE H2 (supported in its mounting bracket 141) into their appropriate mounting slots 139 and 142 formed within module housing 135. Thereafter, HOE HI can be glued or otherwise fixed in position, while HOE H2 is permitted to moved along its along its optical axis within the module housing. The third step of the prealignment stage involves inserting lens LI into the lens recess (e.g. pocket) formed within the module housing, so that the planar side of the lens LI is mounted incident the VLD 1 31. Thereafter, the lens LI can be glued or otherwise fixed in position. The fourth step of the prealignment stage involves placing the VLD mounting bracket 133 into appropriate recesses 133C and 133D formed in the module housing. Notably, the VLD mounting yoke is held within recesses 133C and 133D by frictional fit and can only be translated along z axis of the parameter alignment system (i.e. the x and y directions being fixed by the geometry of the recesses. The fifth step of the prealignment stage involves placing the module housing 135 into the module housing support platform 151 so that pins on the bottom surface of the housing module align with corresponding holes formed on the housing module support platform 151. When housing module 135 is installed in the manner described above, it is then clamped to the module housing support platform 151 by way of screws, pressurized clamps or other releasable fastening devices. The sixth step of the prealignment stage involves placing the mounting yoke 114 on its support and clamping the same. The seventh and last step of the prealignment stage involves attaching the VLD 131 to VLD support platform 154 of the parameter alignment system. In the preferred embodiment, this step can be achieved by sliding the leads of the VLD into a connector provided on the VLD support platform. The VLD support platform 154 is capable of movement along the x, y and z axes of the parameter adjustment system 150. Alignment Stage Of The Assembly Procedure For System Embodiment Nos. 4 and 8 The first step of the alignment stage of the procedure involves sliding the module housing support platform 151 towards VLD support platform 1 54 under the control of microcontroller 161 until the VLD is positioned within oversized aperture 133A formed within the VLD support bracket 1 33 positioned within the recesses of the module housing. Notably, at this "load" position, the VLD is free to move within the x and y plane by virtue of the oversized aperture in the VLD mounting yoke, and also along the z axis b y virtue of clearance provided between the premounted lens LI and the outer face of the VLD mounting yoke. As will become apparent hereinafter, such clearance enables the optical axis of each loaded VLD to be aligned with respect to the optical axis of lens LI in a manner required to achieve minimal beam dispersion and the desired aspect-ratio specified during the design stage described above. The second step of the alignment stage of the procedure involves locking the position the module housing support platform 151 relative to the underlying optical bench 152 (arranged in its "loaded" configuration). This locking operation can be carried out using locking mechanism 162 computer control. The third step of the alignment stage of the procedure involves locking the VLD heat-sink plate 132 to the VLD support platform 154 so that the VLD heat-sink plate is prevented from undergoing rotation in the x-y plane during alignment of the VLD 131 relative to the lens LI during the subsequent steps of the alignment procedure. This condition will ensure that the VLD junction is prevented from rotation during the alignment procedure, which may involve translation of the VLD junction in the x, y and/or z axes of the system in order to secure the performance parameters of the module established during the design stage. The fourth step of the alignment stage of the procedure involves applying a biasing force on the VLD support bracket 133 (in the direction of the VLD heat-sink plate) so that the plate-like portion of the VLD support yoke gently engages the VLD heat-sink plate 132 in order that the surface of the VLD heat-sink plate and planar portion of the VLD support bracket 133 assume the same z coordinate position during x, y alignment operations, while permitting relative movement between these two plate-like structures along the z-x plane of the system. The fifth step of the alignment stage of the procedure involves supplying electrical power to the VLD 131 so that it produces an output laser beam which is transmitted through lens LI and HOEs HI and H2. The sixth step of the alignment stage of the procedure involves translating the VLD support platform 154 in the x-y plane until the output laser beam strikes the center of the quadrant photodetector 159, which has been prealigned relative to the locked-in-position module housing 135 so that first diffraction order beam from HOE H2 (i.e. the optical axis thereof disposed ft in the plane of diffraction at diffraction angle d2 ) passes through the center of the quadrant-type detector 159. When the output laser beam strikes the center of the quadrant-type photodetector, then the design geometry will be achieved, resulting in minimum beam dispersion and the desired amount of beam shaping by design. Also optimal output power will be transmitted from the module along the optical axis of the system. This condition is based on the reasonable assumption that the diffraction efficiencies of HOEs HI and H2 will be maximum along the first diffraction order by design, a nd characteristic wavelength of the VLD is substantially the same as the reconstruction wavelength of HOEs HI and H2. Notably, this on-center aligned position can b e visually detected when the indicator dot on the quadrant detector display unit 160 is aligned with the cross-hair on the display surface thereof. Completion of this step of the procedure will ensure that output power of the laser beam producing module will be as close to the output power of the VLD as is practically possible, as well as ensuring that the design requirements have been satisfied. The seventh step of the alignment stage of the procedure involves gluing or otherwise permanently securing the x-y position of the VLD heat-sink plate 132 and VLD support bracket (yoke) 133 in the position determined during the step above. Thereafter, the biasing force applied during the above step of the procedure can be removed. The eighth step of the alignment stage of the procedure involves adjusting the position of the subassembly (comprising the VLD 131, the VLD heat-sink plate 132 and the VLD support yoke 133) along the z axis of the parameter adjustment system while monitoring the output laser at the desired focal length of the module using beam profiling instrument 157. When the spot size of the output laser beam (at some unknown location along the optical axis HOE H2) is minimum in both the x and y dimensions, then VLD support yoke 133 is glued or otherwise fixed in position relative to the module housing 135. Notably, the beam profiling instrument will have to be moved along the optical axis of HOE H2 to detect this condition, in which the output laser beam is free of astigmatism. While the output beam may still have elliptical cross- sectional characteristics along its direction of propagation, its beam cross- section will be minimum for both dimensions at this detected point which, b y definition, is stigmatic beam. Thereafter, the VLD support yoke is glued o r otherwise fixed to the module housing 1 35. The ninth step of the alignment stage of the procedure involves adjusting the position of HOE H2 relative to HOE HI while monitoring the beam cross-section at a focal point determined during the process) using beam profiling instrument 157. When the output laser beam is focused to a predetermined focal point, then the position of HOE H2 is glued or otherwise fixed relative to HOE HI . The tenth step of the alignment stage of the procedure would involve inserting lens support bracket 144, containing prespecified lens L2 143, into recess 145 formed within the front end of the module housing 135. In the illustrative embodiment, lens mounting bracket 144 can be manually adjusted by a small adjustment screw or like mechanism embodied within the module housing. This adjustment mechanism allows the end-user to fine-tune the resulting focal length of the laser beam producing module as required o r desired by the application at hand. In some instances, it is contemplated that the laser beam producing module will be installed within a larger system, i n which the output stigmatic laser beam from the module will be further modified for a particular application (e.g. scanning). In such cases, it is understood that the laser beam producing module may be first removed from the module housing support platform 151 of the parameter adjustment system described above, and then installed within the larger system. Thereafter, the resulting larger system can be mounted to a parameter adjustment system of the general type described above in order to set the focal length of the laser beam producing module so that the focal length of the resulting system is achieved. Clearly, there will be may ways in which to fine-tune the focal length of the laser beam producing module of System Embodiment Nos. 4 and 8. Then the housing cover plate 147 is fastened upon the top of the module housing, and thereafter the aligned laser beam producing module is removed from the parameter adjustment system and is ready for use in the system 150 for which it has been designed. Pre-Alignment And Alignment Stages Of The Assembly Procedure For System Embodiment Nos. 1 and 1 2 The prealignment stage of the assembly procedure for System Embodiment Nos. 10 and. 12 is different than that described for System Embodiment Nos. 4 and 8 above, in one significant way. In particular, i n System Embodiment Nos. 10 and 12, the second lens L2 is disposed between the HOEs HI and H2, rather than beyond the HOE H2, as shown in Figs. 2J an d 2L. Such structural differences alter the prealignment stage of the assembly process slightly, as well as the procedure for aligning the VLD junction along the x and y axes of the system to minimize beam dispersion, or along the z axis to eliminate beam astigmatism. In particular, beam dispersion is minimized while an "alignment HOE" with no optical power installed in the position of HOE H2, when the position-adjustable lens L2 is not yet installed within the module housing. Astigmatism is corrected by adjusting the position of the VLD relative to fixed lens LI 136. Then a n average focal distance for the laser beam producing module is set by inserting lens L2 and adjusting its position within its mounting recess. At this stage, the alignment HOE is removed and HOE H2 is put into place and can be adjusted while on the module housing platform t o set a finely tuned focal distance for the laser beam producing module, o r alternatively, first installed within a larger optical system, and thereafter adjusted to fine tune the focal length of the module to achieve a particular design objective for the larger optical system, as described hereinabove. Method Of Assembly And Aligning The Subcomponents Of Laser Beam Producing Systems Of The Illustrative Svstem Embodiments Of The Present Invention Designed For Instances Where Astigmatism Correction Ts Desired But Neither Focus Control Nor Delta-Focusing Are Required: System Embodiment Nos. (13) And (14V CASE D In general, when assembling a laser beam producing module based o n System Embodiments Nos. 13 and 14, the parameter adjustment procedure of the present invention can be carried out on the module design similar to that shown in Figs. 7A-7C (but with lens LI being a focusing lens) supported up on the parameter adjustment system of Fig. 13, as shown in Fig. 17. For this group of system embodiments, the assembly procedure comprises a prealignment stage and an alignment stage. During the prealignment stage, various optical components of the laser beam producing module are installed within their respective mounting locations within the module housing, or within support structure associated with the parameter adjustment system 150, as described in connection with System Embodiment Nos. 1 and 5. During the alignment stage, the (x,y) position of the VLD is aligned relative to the focusing lens LI in order to achieve zero beam dispersion for the central ray of the beam and minimized for all others, using the (x,y) alignment procedure described hereinabove. Thereafter, the position of the VLD is adjusted along the z axis in order to eliminate astigmatism in the, output laser beam using the z axis alignment procedure described above. Notably, in this System Embodiment, astigmatism elimination is achieved at the expense of the focus control, while minimizing beam dispersion and achieving a limited degree of aspect-ratio control. Exemplary Systems and Devices Within Which The Laser Beam Producin g Svstem Of The Present Invention Can Be Embodied The laser beam producing system of the present invention described i n detail hereinabove may, in all of its various embodiments, be embodied within an infinite variety of systems requiring the production of a laser beam having predetermined beam characteristics, substantially free of dispersion. Hereinbelow are just a few exemplary systems and devices within which the laser beam production system can be embodied in accordance with the principles of the present invention. As such, each such system provides a further embodiment of the present invention. As illustrated in Fig. 18, any one of the laser beam producing devices of the present invention can be incorporated in a hand-supportable laser scanning device As illustrated in Fig. 19, any one of the laser beam producing devices of the present invention can be incorporated a fixed-projection type laser scanning system. As illustrated in Fig. 20, any one of the laser beam producing devices of the present invention can be incorporated a body-wearable laser scanning system, as well as a finger-mounted laser scanning system. As illustrated in Fig. 21 , any one of the laser beam producing devices of the present invention can be incorporated a holographic laser scanning system. As illustrated in Fig. 22, any one of the laser beam producing devices of the present invention can be incorporated a CD-ROM disc playback system. As illustrated in Fig. 23, any one of the laser beam producing devices of the present invention can be incorporated a laser pointing device. As illustrated in Fig. 24, any one of the laser beam producing devices of the present invention can be incorporated a medical laser sculpturing system. Any of the hand-supportable, body-wearable, or other scanning systems described hereinabove may embody one or more of the following functionalities: the spatially overlapping object detection and laser scan fields taught in U.S. Patent No. 5,468,951 ; the long-range/short-range modes of programmable scanning operation taught in U.S. Patent No. 5,340,971 ; the power-conserving system-control architecture taught in U.S. Patent No. 5,424,525; and the RF signal transmission functionalities and acoustical acknowledgement signaling taught in copending U.S. Patent Application Serial No. 08/292,237, each of which is commonly owned by Metrologic instruments, Inc. of Blackwood. Some Modifications That Readily Come To Mind While each of the previous module designs has two DOE's, it is possible to design a module with three or more DOE's if desired or required by a particular application. One possible reason for desiring additional DOEs might be a need for more beam shaping than can reasonably be provided by only two DOE's. While three or more DOEs would be acceptable, one DOE would not b e acceptable, due to the excessive amount of dispersion produced by diffractive optics. This is not a problem for multiple DOE's because they can b e specifically designed to have a net dispersion of zero when combined together. While the illustrative embodiments described hereinabove make reference to using DCG material to fabricate the DOEs within modules, devices an d systems of the present invention, it is understood that other types of recording materials such as photo-polymer recording materials (e.g. photo-polymer DMP 128 from DuPont and other vendors) can be used with excellent results. One advantage of using a photo-polymer recording material (e.g. photo-polymer DMP 128from Dupont) to fabricate the DOEs is that, unlike DCG material, photo-polymer recording materials are easier to handle and less sensitive to moisture. In general, the refractive optical elements LI and L2 employed in the illustrative embodiments disclosed hereinabove can be realized using an y suitable optically-transparent material including glass and plastic. In applications having insignificant temperature changes and where manufacturing cost is a n issue, it will be preferred to make lens LI entirely from plastic material. However, in many applications, wherein the ambient temperature is expected to cycle over a substantial temperature range, it wiii be preferable to construct such lens from glass material rather than a plastic material, as glass material is less susceptible to thermal variations than plastic material. Consequently, the focal length of lens LI (which is typically quite short) will not change nearly as much in response to a given temperature change, as compared to a lens LI made from a plastic material. In order to make inexpensive aspheric lens (e.g. LI) which is less sensitive to thermal changes, it is possible to mount an aspherical surface element made from a material other than glass (e.g. molded plastic) onto a spherical lens made from glass. Mounting of the aspherical surface element can be carried out using a suitable optical cement. In general, thermal-related effects in such optical components are proportional to the Temperature Coefficient of Expansion (TCE) and Temperature Coefficient of Refractive Index (TCRI) of the optical material being used. Both of these constants are much greater for plastic than for glass. Thermal-related effects are also a function of ths thickness of the material and the relative optical power of the optical element. Most of the thickness and thus most of the optical power provided by a two-part lens device (LI) as described above is contained in the glass element component thereof. In this two-part lens device, the plastic aspheric element is made very thin and contains, theoretically, only the amount of aspherical component needed to provide correction of spherical aberration in the incident laser beam. Thus, the plastic aspheric component mounted to the glass component will have very little optical power. Therefore, the overall two- part lens LI will have thermal properties much closer to a pure glass lens that to a pure plastic lens. Alternatively, in applications having significant a mbient temperature changes and where the cost of manufacture of the lens LI is not critical design constraint, it will be preferred to make lens LI entirely from glass material. In the second illustrative embodiment shown in Figs. 2B, 2B1, 2B2 an d 2B3 and described hereinabove (i.e. System Embodiment No. 2), Applicants have taught how DOEs Dl and D2 employed therein can be realized using either transmission-type and/or reflection-type volume holograms (HOEs) for DOE1 and DOE2. It is understood, however, that the other illustrative embodiments of the present invention (System Embodiments Nos. 1 and 3- 14) disclosed herein can be realized as well using reflection-type and/or transmission-type volume HOEs. In such alternative realizations of these system embodiments, the only requirement is that the angle of diffraction b e different than the angle of incidence for each light diffractive element of the DOE-based device. In general, this requirement can be met using either a transmissive DOE (e.g. transmission HOE) or a reflective DOE (e.g. reflection HOE). The various embodiments of the laser beam producing system hereof have been described in connection with linear (1-D) and 2-D code symbol scanning applications. It should be clear, however, that the apparatus an d methods of the present invention are equally suited for use in other applications including, for example, scanning alphanumeric characters (e.g. textual information) in optical character recognition (OCR) applications. Several modifications to t he illustrative embodiments have been described above. It is understood, however, that various other modifications to the illustrative embodiment of the present invention will readily occur to persons with ordinary skill in the art. All such modifications and variations are deemed to be within the scope and spirit of the present invention as defined b y the accompanying Claims to Invention.

Claims: CLATMS TO TNVENTTON 1. A laser beam modification system comprising: a plurality of diffractive optical elements (DOEs) for modifying the size and shape of a laser beam produced from a commercial-grade laser diode, such as a VLD, over an extended range while avoiding the introduction of dispersion in the output laser beam. 2. The laser beam modifying system of claim 1 , wherein the inherent astigmatism characteristics associated with said VLD are eliminated o r minimized. 3. A DOE-based laser beam modifying system comprising: a plurality of diffractive optical elements (DOEs) for modifying the size and shape of a laser beam produced from a commercial-grade laser diode, such as a VLD, wherein beam dispersion is minimized, or normal dispersion or reverse dispersion characteristics are provided for any given beam compression o r expansion ratio, by selecting the proper a ngle between said DOEs. 4. A DOE-based laser beam modifying system, wherein beam dispersion is minimized for the system acting alone, or fine-tuned to compensate for the dispersion of other elements preceding it or following the system. 5. A method of producing a laser beam having a desired spot-size over a specified depth of field, comprising the steps of: (a) focusing said laser beam with a lens; an d (b) reshaping said laser beam using a pair of diffractive optical elements. 6. The method of claim 5, wherein said lens is realized as refractive element having symmetric surface profile characteristics. 7. The method of claim 5, wherein said lens is realized as variable DOE of a selected type. 8. A laser beam producing system comprising: a set of first and second beam-modifying holograms which produce zero dispersion while simultaneously providing any desired aspect-ratio for the beam leaving (exiting) said second beam-modifying hologram. 9. An ultra-compact DOE-based device comprising: means for collimating or focusing a laser beam produced from a n astigmatic VLD while minimizing dispersion beam dispersion and correcting for beam ellipticity. 10. An ultra-compact optics module comprising: means for modifying the aspect-ratio of a laser beams produced by a VLD; means for eliminating beam astigmatism introduced by virtue of the inherent astigmatic difference in said VLD, an d means for minimizing dispersion in the output laser beam created b y wavelength-dependent variations in the spectral output of the VLD. 11. An optics module comprising: a pair of DOEs configured in the beam compression mode, wherein the total expansion factor (M) of the DOE combination is less than one, so that the size of the laser beam in the plane of diffraction is compressed without changing the beam size in the dimension perpendicular to the plane of diffraction. 12. An optics module employing a pair of DOEs configured in the beam expansion mode, wherein the total expansion factor (M) of the DOE combination is greater than one, so that the size of the laser beam in the plane of diffraction is expanded without changing the beam size in the dimension perpendicular to the plane of diffraction. 13. A light diffractive optics module for incorporation into small laser scannin g devices, such as laser scan-engines, as well as replacing conventional prisms and anamorphic lenses used in VLD-based optical systems such as optical storage devices, CD-ROM players and recorders, and like systems and devices. 14. A DOE-based optics m odule comprising: means for modifying the aspect-ratio of a VLD beam while simultaneously controlling beam dispersion to minimize the overall dispersion of the optical system in which it is being used. 15. The DOE-based optics module of claim 14, wherein beam astigmatism inherently associated with said VLD is eliminated or minimized. 16. A method for designing a dual-DOE laser beam modifying system, in which a pair of equations are solved under a given set of conditions which ensures that beam dispersion is eliminated and a desired expansion factor (M) is obtained. 17. An optical design method, wherein analytical and spreadsheet-type programs are combined in an integrated fashion to allow for easy design an d analysis of the optics module under consideration. 18. An optics module comprising: one or more light absorbing surfaces for absorbing one or more zeroeth-order beams diffracted from two or more DOEs employed in said DOE-based optics module. 19. A system for precisely and rapidly aligning the p arameters of the optics modules of the present invention to enable the inexpensive mass production of such optical systems and devices for widespread use in diverse fields of endeavor. 20. A parameter alignment system, comprising: means for micro-adjustment of the optical components of HOE-based laser beam producing modules under microcomputer control, thereby enabling mass-production of laser beam producing modules which satisfy high quality- control (QC) measures. 21. A method of producing a laser beam comprising the steps of: (a) producing an astigmatic elliptical light beam from a VLD; an d (b) modifying said light beam so that it has a selected set of beam characteristics. 22. A hand-held laser scanner, wherein a DOE-based laser beam producing system is embodied for producing a laser beam for bar code scanning operations. 23. A body-wearable laser scanner, wherein a DOE-based laser beam producing system is embodied for producing a laser beam for bar code scanning operations. 24. A laser scanning-engine, wherein a DOE-based laser beam producing system is embodied for producing a laser beam for bar code scanning operations. 25. A holographic laser scanner wherein a DOE-based laser beam producing system is embodied for producing a laser beam for bar code scanning operations. 26. A CD-ROM playing unit, wherein a DOE-based laser beam producing system is embodied to enable the production of laser beams for reading information digitally recorded within a CD-ROM or like recording device. 27. A laser-based instrument, wherein a DOE-based laser beam producing system is embodied to enable the production of laser beams for diagnosis o r detection of various conditions. 28. A DOE-based subsystem comprising: a laser diode source for producing a laser beam; an d a pair of DOEs (Dl and D2) designed to satisfy a condition wherein that the beam-shaping factor M of said DOEs is less than unity and the narrower dimension of the laser beam exiting said laser diode source is oriented perpendicular to a common plane of incidence passing through said DOEs D 1 and D2. 29. The DOE-based subsystem of claim 28, wherein said condition is satisfied by orienting the junction of said laser diode source (and thus its narrower beam dimension and polarization direction) perpendicular to the common plane of incidence, and the E-field of the incident laser beam perpendicular to the common plane of incidence, so that the wider dimension of the laser beam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam compression results, while the narrower beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that n o beam compression results along said narrower beam dimension. 30. A DOE-based subsystem comprising: a laser diode source for producing a laser beam; and a pair of DOEs (Dl and D2) designed to satisfy a condition wherein the beam-shaping factor M for said DOEs is less than unity and the narrower dimension of the laser beam exiting said laser diode source is oriented parallel to the common plane of incidence passing through said DOEs Dl and D2. 31. The DOE-based subsystem of claim 30, wherein said condition is satisfied by orienting the junction of said laser diode source (and thus its narrower beam dimension and polarization direction) parallel to the common plane of incidence, and the E-field of the incident laser beam parallel to the common plane of incidence, so that the narrower dimension of the laser beam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam compression results, while the wider beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that no beam compression results along said wider beam dimension . 32. A DOE-based subsystem comprising: a laser diode source for producing a laser beam; an d a pair of DOEs (Dl and D2) designed to satisfy a condition wherein the beam-shaping factor M thereof is greater than unity and the narrower dimension of the laser beam exiting the VLD is oriented perpendicular to the common plane of incidence passing through said DOEs Dl and D2. 33. The DOE-based subsystem of claim 32, wherein said condition is satisfied by orienting the VLD junction (and thus its narrower beam dimension an d polarization direction) perpendicular to the common plane of incidence, ari the E-field of the incident laser beam perpendicular to the common plane of incidence, so that the wider dimension of the laser beam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam expansion results, while the narrower beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that no beam expansion results along said narrower beam dimension. 34. A DOE-based subsystem comprising: a laser diode source for producing a laser beam; an d a pair of DOEs (Dl and D2) designed to satisfy a condition wherein the beam-shaping factor M of said DOEs is greater than unity and the narrower dimension of the laser beam exiting said laser diode source is oriented parallel to the common plane of incidence passing through DOEs Dl and D2. 35. The DOE-based of claim 34, wherein said condition is satisfied by orienting the junction of said laser diode source (and thus its narrower beam dimension and polarization direction) parallel to the common plane of incidence, and the E-field of the incident laser beam parallel to the common plane of incidence, so that the narrower dimension of the laser beam is disposed within the common plane of incidence (wherein diffraction occurs) so that beam expansion results, while the wider beam dimension is disposed perpendicular thereto (wherein no diffraction occurs) so that no beam expansion results along said wider beam dimension. 36. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD) for producing a laser beam from its junction typically having divergent and elliptical beam characteristics; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl having a beam expansion factor M^ an d a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2, having a beam expansion factor M 2 . 37. The laser beam producing system of claim 36, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 38. The laser beam producing system of claim 36, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief h ologram, and other diffractive optical element. 39. The laser beam producing system of claim 36, wherein the total beam- shaping factor (M=MιM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 40. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction having divergent and elliptical characteristics; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl having a beam expansion factor M, ; a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2, having a beam expansion factor M 2 ; an d a focusing lens L2, realizable as a refractive lens, a HOE, a DOE, a grin lens, or zone plate(s), disposed after DOE D2 for focusing the output laser beam to a desired or required point in space. 41. The laser beam producing system of claim 40, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 42. The laser beam producing system of claim 40, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGH), a surface-relief hologram, and other diffractive optical element. 43. The laser beam producing system of claim 40, wherein the total beam- shaping factor (M=M]M 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1 *M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 44. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction ; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl having a beam expansion factor Mj; an d a variable spatial-frequency diffractive optical element (DOE) denotable by D2, having a beam expansion factor M 2 . 45. The laser beam producing system of claim 44, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s), and wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 46. The laser beam producing system of claim 44, wherein the total beam- shaping factor for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 47. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a n elliptical divergent laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl ; a variable spatial-frequency diffractive optical element (DOE) denotable by D2 and adjustably mounted to enable, during the alignment stage of the system adjustment process, the principal plane of DOE D2 to be translated along its optical axis relative to the principal plane of DOE Dl without modifying the tilt angle between said DOEs Dl and D2; an d a focusing lens (L2) disposed after the second DOE D2 and having a focal length which is can be adjusted to enable the focusing of the output laser beam to some predetermined focal point in space, during the alignment stage of the system assembly process. 48. The laser beam producing system of claim 47, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 49. The laser beam producing system of claim 47, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 50. The laser beam producing system of claim 47, wherein said focusing lens (L2) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a DOE, a grin lens, and zone plate(s). 51. The laser beam producing system of claim 47, wherein the total beam- shaping factor (M=MιM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1 *M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 52. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl; an d a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2. 53. The laser beam producing system of claim 52, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 54. The laser beam producing system of claim 52, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 55. The laser beam producing system of claim 52, wherein the total beam- shaping factor (M=M]M 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1*M2>1, and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. 56. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl ; a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2; an d a focusing lens (L2) disposed after the second DOE D2 for focusing the output laser beam to some point in space. 57. The laser beam producing system of claim 56, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 58. The laser beam producing system of claim 56, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGH), a surface-relief hologram, and other diffractive optical element. 59. The laser beam producing system of claim 56, wherein said focusing lens (L2) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like, disposed after said second DOE D2, for focusing the output laser beam to some point i n space. 60. The laser beam producing system of claim 56, wherein the total beam- shaping factor (M=M T M 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1 *M2>1, and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. 61. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl; an d a variable spatial-frequency diffractive optical element (DOE) denotable by D2, which can be translated along the optical axis relative to the principal plane of DOE Dl during the alignment stage of the system assembly process. 62. The laser beam producing system of claim 61, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 63. The laser beam producing system of claim 61, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 64. The laser beam producing system of claim 61, wherein each of said DOEs is realized by an optical element selected from the group consisting of a DOE, a CGH, a surface-relief hologram, and other diffractive optical element. 65. The laser b eam producing system of claim 61, wherein the total beam- shaping factor (M=M,M 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1*M2>1, and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. 66. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD); a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl ; a variable spatial-frequency diffractive optical element (DOE) denotable by D2, adjustably mounted relative to DOE Dl; an d a focusing lens (L2) disposed after the second DOE D2, and adjustably mounted relative thereto, for focusing the output laser beam to some point in space. 67. The laser beam producing system of claim 66, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 68. The laser beam producing system of claim 66, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 69. The laser beam producing system of claim 66, wherein the total beam- shaping factor (M=M]M 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1*M2>1, and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. 70. The laser beam producing system of claim 66, wherein each of said DOEs is realized by an optical element selected from the group consisting of a HOE, a CGH, a surface-relief hologram, and other diffractive optical element. 71. The laser beam producing system of claim 66, wherein said focusing lens (L2) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a DOE, a grin lens, and zone plate(s). 72. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in an S-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl ; a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2; an d a focusing lens (L2) disposed between DOE Dl and DOE D2 and adjustably translatable along its optical axis for focusing the output laser beam to some point in space. 73. The laser beam producing system of claim 72, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE. a CGH, other type of DOE, a grin lens, and one or more zone plate(s) . 74. The laser beam producing system of claim 72, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 75. The laser beam producing system of claim 72, wherein the total beam- shaping factor (M=MιM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1 *M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 76. The laser beam producing system of claim 72, wherein each of said DOEs is realized by an optical element selected from the group consisting of a HOE, a CGH, a surface-relief hologram, and other diffractive optical element. 77. The laser beam producing system of claim 72, wherein said focusing lens (L2) is realized by an optical element selected from the group consisting of a refractive lens, holographic optical element (HOE), diffractive optical element (DOE), grin lens, and zone plate(s). 78. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a S-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl ; a variable spatial-frequency diffractive optical element (DOE) denotable by D2, adjustably translatable relative to the principal plane of DOE Dl during the alignment stage of the system assembly process; an d a focusing lens (L2) disposed between DOE Dl and DOE D2 and adjustably translatable along its optical axis during the parameter alignment stage of the system assembly process for focusing the output laser beam to some point i n space. 79. The laser beam producing system of claim 78, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 80. The laser beam producing system of claim 79, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 81. The laser beam producing system of claim 79, wherein the total beam- shaping factor (M=M]M 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 82. The laser beam producing system of claim 79, wherein each of the DOEs is realized by an optical element selected from the group consisting of a HOE, a CGH, a surface-relief hologram, and other diffractive optical element. 83. The laser beam producing system of claim 79, wherein said focusing lens (L2) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a DOE, a grin lens, and zone plate(s). 84. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable by Dl ; a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2; and a focusing lens (L2) disposed between DOE Dl and DOE D2 and adjustably translatable along its optical axis during the alignment stage of the system assembly process for focusing the output laser beam to some point in space. 85. The laser beam producing system of claim 84, wherein said collimating lens (LI) is realized by an optical element selected from t he group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 86. The laser beam producing system of claim 84, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 87. The laser beam producing system of claim 84, wherein each of said DOEs is realized by an optical element selected from the group consisting of a HOE, a CGH, a surface-relief hologram, and other diffractive optical element. 88. The laser beam producing system of claim 84, wherein the total beam- shaping factor (M=M,M 2 ) for the laser beam modifying subsystem is greater than unity (1), t hat is M1*M2>1, and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. 89. The laser beam producing system of claim 84, wherein said focusing lens (L2) is realized by an optical element selected from the group consisting of a refractive lens, holographic optical element (HOE), diffractive optical element (DOE), grin lens, and zone plate(s) or the like. 90. A laser beam producing system comprises: — a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a collimating lens (LI) for collimating the laser beam as it is transmitted through collimating lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl ; a variable spatial-frequency diffractive optical element (DOE) denotable by D2, adjustably translatable relative to the principal plane of DOE Dl during the alignment stage of the system assembly process; and a focusing lens (L2) disposed between DOE Dl and DOE D2 and adjustably translatable along its optical axis during the parameter alignment stage of the system assembly process for focusing the output laser beam to some point i n space. 91. The laser beam producing system of claim 90, wherein said collimating lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 92. The laser beam producing system of claim 90, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 93. The laser beam producing system of claim 90, wherein each of said DOEs is realized by an optical element selected from the group consisting of a HOE, a CGH, a surface-relief hologram, and other diffractive optical element. 94. The laser beam producing system of claim 90, wherein the total beam- shaping factor (M=M^ 2 ) for the laser beam modifying subsystem is greater than unity (1), that is M1*M2>1, and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. 95. A laser beam producing system of claim 90, wherein said focusing lens (L2) is realized by an optical element selected from the group consisting of as a refractive lens, a HOE, a CGH or other a DOE, a grin lens, and zone plate(s). 96. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; an imaging lens (LI) for imaging the laser source to the focal distance as it is transmitted through imaging lens LI and through the system in a S- incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable by Dl; an d a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2. 97. The laser beam producing system of claim 96, wherein said imaging lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 98. The laser beam producing system of claim 96, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, and other diffractive optical element. 99. The laser beam producing system of claim 97, wherein the total beam- shaping factor (M=MιM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1 *M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 100. The laser beam producing system of claim 98, wherein each of the DOEs is realized by an optical element selected from the group consisting of a HOE, a CGH, a surface-relief hologram, and other diffractive optical element. 101. The laser beam producing system of claim 99, wherein the total beam- shaping factor (M=MιM 2 ) for the laser beam modifying subsystem is less than unity (1), that is M1*M2<1, and thus the laser beam leaving the collimating lens (LI) is compressed in one dimension. 102. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a focusing lens (LI) for focusing the laser beam as it is transmitted through focusing lens LI and through the system in a P-incident manner; a fixed spatial-frequency diffractive optical element (DOE) denotable b y Dl; an d a fixed spatial-frequency diffractive optical element (DOE) denotable b y D2. 103. The laser beam producing system of claim 102, wherein said focusing lens (LI) is realized by an optical element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 104. The laser beam producing system of claim 102, wherein each said DOE is realized by an optical element selected from the group consisting of a HOE, a computer-generated hologram (CGHs), a surface-relief hologram, or other diffractive optical element. 105. The laser beam producing system of claim 102, wherein the total beam- shaping factor for the laser beam modifying subsystem is greater than unity (1), that is M1*M2>1, and thus the laser beam leaving the collimating lens (LI) is expanded in one dimension. 106. The laser beam producing system of claim 102, wherein each of said DOEs is realized by an optical element selected from the group consisting of a HOE, a CGH, a surface-relief hologram, and other diffractive optical element. 107. A laser beam production module for producing a laser beam having a pre- specified beam aspect-ratio, zero beam dispersion and a predetermined focus. 108. A laser beam production module for producing a laser beam, comprising: means for achieving a pre-specified beam aspect-ratio; means for achieving zero or minimum beam dispersion; means for focusing said laser beam to a predetermined distance; an d means for correcting the astigmatism in said laser beam exiting said module. 109. A laser beam production module for producing a laser beam, wherein its aspect-ratio is controlled, its beam dispersion is zero (or minimized), its astigmatism corrected, its focus set to a predetermined distance, and its focal length adjusted. 110. A laser beam production modules for producing a laser beam having a pre-specified beam aspect-ratio, zero beam dispersion and astigmatism control. 111. A laser beam producing device, comprising: a laser diode source, such as a visible laser diode (VLD), for producing a laser beam from its junction; a first diffractive optical element (DOE) denotable by Dl; an d a second diffractive optical element (DOE) denotable by D2, disposed adjacent said first DOE Dl ; refractive optics (LI) having an axially symmetric surface profile characteristics, and being disposed between said laser diode source and said first and second diffractive optic elements (DOEs Dl and D2), so that said DOEs modify (e.g. correct or eliminate) astigmatism in the output laser beam from said device. 112. The laser beam producing device of claim 11 1, wherein said reflective optics comprises an refractive lens (LI). 113. The laser beam producing device of claim 112, which further comprises means for adjusting the x, y and z position of said laser diode source, relative to said refractive lens, during assembly of said laser beam producing device, for minimizing dispersion in the output laser beam from said laser beam producing device and for eliminating or minimizing astigmatism in said output laser beam, or focusing said output laser beam to a desired focus. 114. A laser beam producing system comprises: a laser beam source, such as a visible laser diode (VLD), for producing a laser beam from its junction typically having divergent and elliptical beam characteristics; a collimating lens (LI) for collimating said laser beam as said laser beam is transmitted through said collimating lens LI; a first diffractive optical element (DOE) denotable by Dl; an d a second diffractive optical element (DOE) denotable by D2; wherein said DOE Dl and DOE D2 are arranged as a light diffractive subsystem, and collimating lens LI is disposed between said VLD and said light diffractive subsystem so as to modify said laser beam as said laser beam passes from said VLD through said lens LI and thence through said DOE Dl and DOE D2. 115. The laser beam producing system of claim 114, wherein said collimating lens LI is realized by an element selected from the group consisting of a refractive lens, a HOE, a CGH, other type of DOE, a grin lens, and one or more zone plate(s). 116. The laser beam producing system of claim 114, wherein said collimating lens LI is realized by a multi-part optical device comprising a spherical component made from a glass or glass-like material, and an aspherical component mounted onto said spherical component an d made from a plastic or plastic-like material. 117. The laser beam producing system of claim 114, wherein said DOE Dl and said DOE D2 are both realized using transmission-type DOEs. 118. The laser beam producing system of claim 117, wherein said transmission-type DOEs are transmission-type HOEs. 119. The laser beam producing system of claim 114, wherein said DOE Dl an d said DOE D2 are both realized using reflection-type DOEs. 120. The laser beam producing system of claim 119, wherein said reflection- type DOEs are reflection-type HOEs. 121. The laser beam producing system of claim 114, wherein said DOE Dl is realized using a transmission-type DOE and said DOE D2 is realized using a reflection-type DOE. 122. The laser beam producing system of claim 122, wherein said transmission-type DOE is transmission-type HOE, said reflection-type DOE is a reflection-type HOE. 123. The laser beam producing system of claim 114, wherein said DOE Dl is realized using a reflection-type DOE and said DOE D2 is realized using a transmission-type DOE. 124. The laser beam producing system of claim 122, wherein said transmission-type DOE is transmission-type HOE, said reflection-type DOE is a reflection-type HOE.

Inventors: AMUNDSEN THOMAS C, CARULLO THOMAS, DICKSON LEROY, GOOD TIMOTHY A, GROOT JOHN, KNOWLES C HARRY, AMUNDSEN, THOMAS, C., CARULLO, THOMAS, DICKSON, LEROY, GOOD, TIMOTHY, A., GROOT, JOHN, KNOWLES, C., HARRY
Applicants: AMUNDSEN THOMAS C, CARULLO THOMAS, DICKSON LEROY, GOOD TIMOTHY A, GROOT JOHN, KNOWLES C HARRY, METROLOGIC INSTR INC, AMUNDSEN, THOMAS, C., CARULLO, THOMAS, DICKSON, LEROY, GOOD, TIMOTHY, A., GROOT, JOHN, KNOWLES, C., HARRY, METROLOGIC INSTRUMENTS, INC.
Application year: 1999
Main classification: G02B
IPC codes: G02B5, G02B27, H01S5