Abstract:
An apparatus and method for two-dimensional wavelength beam combining of a plurality of laser sources. In one embodiment, an external cavity multi-wavelength laser comprises an array of laser gain elements, two optical transform lenses, two dispersive elements, an imaging system, a deflective array, and an output coupler. First and second optical transform lenses spatially overlap optical beams in first and second dimensions forming regions of overlap at the first and second dispersive elements. The deflective array comprises a plurality of mirrors wherein each mirror deflects and rearranges the optical beams from a common row. The dispersive elements introduce wavelength discrimination that when combined with the output coupler, provide the required feedback gain. The output coupler creates a single output port for the plurality of external optical cavities established in unison with the plurality of laser emitters. The output coupler transmits a multi-wavelength output beam comprising spatially overlapped coaxial optical beams.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the priority of U.S. Patent Application Ser. No. 61/595,838 filed Feb. 7, 2012, which application is incorporated in its entirety herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to the field of lasers and in particular to methods and apparatus for configuring two-dimensional multi-wavelength laser source arrays into composite coaxial beams having higher laser power. 
         [0003]    Laser systems that use multiple laser sources or multiple laser gain medium, are utilized in a variety of applications including cutting, machining, welding, material processing, laser pumping, fiber optic communications, free-space communications, illumination, imaging and numerous medical procedures. Many of these applications can be significantly benefitted with higher laser power. In support of achieving higher laser power, the input energy is typically increased. However, simply increasing the input energy may introduce additional thermal management considerations. For example, thermal conditions and heat load within the laser gain medium typically contribute to internal aberrations and corresponding beam quality reductions in the emitted radiation. Additionally, unaddressed internal heating may also lead to internal damage of the laser components themselves. In general, issues like these place practical limits on the achievable laser power for a given laser system design approach. In many cases the most cost effective method for further power scaling is achieved by combining the optical outputs from more than one laser or laser gain medium. 
         [0004]    The ability to focus a laser beam into a small spot is generally characterized by its beam quality which is in part, a measure of its usefulness in a many applications. Ideally, laser power scaling through beam combining of multiple laser sources or multiple laser gain medium would be done in a manner that minimizes the reduction in the beam quality of the combined beam. When considered in combination, both laser power and laser beam quality contribute to what is typically termed beam brightness. When either or both laser beam power and laser beam quality are improved, the brightness of the laser beam is said to be improved. Beam brightness, being a measure of the combination of the power and focusability of a laser beam, is a fundamental measure of a laser beam&#39;s overall utility in many high power applications. 
         [0005]    Historically, many methods have been used to advance the above objectives with varying degrees of success. These methods can be organized into three broad categories of design approaches, namely coherent, incoherent and polarization approaches. Methods characterized by coherent approaches have the ability to power scale significantly but require a high degree of mutual coherence between the laser sources. They generally employ real time beam phasing techniques between the laser sources or laser gain medium that are complex and costly to implement. Polarization approaches are simple to implement but, by themselves, do not scale beyond a factor of two, one for each available polarization. There are many approaches that do not use either mutual coherence or polarization to combine beams. These fall within the category of incoherent approaches. In general, incoherent approaches are easier to implement then coherent approaches. 
         [0006]    One of the simplest incoherent approaches employs side-by-side beam combining whereby the laser sources or laser gain medium are arranged side-by-side, propagate nominally parallel to one another, are not overlapping or coaxial, and are not phased to each other. This incoherent side-by-side combined beam can be focused but does not produce an optimal focused spot for the given diameter of the side-by-side combined beam. In this case, the beam quality is said to be reduced. Incoherent approaches that both power scale and also maintain good beam quality generally employ specified and unique wavelengths for each laser source or laser gain medium as a fundamental aspect in the combining process. This technique is often called wavelength or spectral beam combining. Examples of components often employed in these systems are dispersive prisms, dialectic wavelength filters, volume Bragg gratings, and diffraction gratings. Naturally, this approach leads to combined beams having many wavelengths, or put another way, a large laser linewidth. In some laser applications, having a large laser linewidth may not be a desirable feature, but for many other laser applications, a large laser linewidth may be inconsequential and may even be advantageous in still other laser applications. 
         [0007]    Within the prior art, two dispersive methods of wavelength beam combining employing angular dispersion have been disclosed that achieve the challenging task of combining two-dimensional laser emitter arrays while maintaining beam quality. In both of these dispersive methods, a plurality of wavelength dependent dispersive elements are used sequentially in two essentially orthogonal directions to combine the two-dimensional array of beams into a single composite beam. In the first method, the orthogonal dispersive elements include a first-order diffraction grating or prism and an Echelle diffraction grating operating in several high diffracting orders simultaneously. In a second method, the orthogonal dispersive elements include a first-order diffraction grating or prism and a first-order diffraction grating stack made up of a plurality of individual first-order diffraction gratings each having a different amount of angular dispersion. An example of a two-dimensional wavelength beam combining system that includes the use of high-order Echelle gratings is disclosed in U.S. Pat. No. 6,327,292 to Sanchez-Rubio et al. filed on Jun. 21, 1999. Two different examples of two-dimensional wavelength beam combining systems employing the use of a first-order diffraction grating stack are disclosed in U.S. Pat. No. 8,179,594 to Tidwell et al. filed on Jun. 30, 2008 and U.S. Patent Application No. US 2011/0222574 A1 to Chann et al. filed on Mar. 9, 2010. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention addresses the above and other needs by providing a method and apparatus for two-dimensional wavelength beam combining of laser sources or laser gain medium in which a first-order diffraction grating and a deflective array of mirrors are used instead of a first-order diffraction grating stack or an Echelle diffraction grating used in multiple are used for generating high-power, high-brightness, multi-wavelength laser systems and laser beams using two-dimensional arrays of laser emitters by wavelength beam combining. 
         [0009]    In accordance with one aspect of the invention, since the system can be constructed using a significantly reduced number of diffraction gratings and without need for a first-order diffraction grating stack, embodiments of the present invention may be simpler to implement and may make use of less costly off-the-shelf diffraction gratings. In addition, since the system can be constructed without higher-order Echelle diffraction gratings, embodiments of the system may have high wavelength beam combining efficiency. 
         [0010]    In accordance with another aspect of the invention, there is provided a multi-wavelength laser system comprising a plurality of laser emitters. In another embodiment, a laser emitter is comprised of a laser source producing optical radiation and having a wavelength and having a linewidth and having an optical axis. In another embodiment, a laser emitter is comprised of a laser gain medium capable of amplifying optical radiation at a specified wavelength and over a specified linewidth and having an optical axis. In another embodiment, a laser emitter has a fast-axis collimating optical arrangement. In another embodiment, a laser emitter has a slow-axis collimating optical arrangement. In yet another embodiment, a laser emitter has both a fast-axis and a slow-axis collimating optical arrangement. 
         [0011]    In accordance with yet another aspect of the invention, there is provided a multi-wavelength laser comprising an array of laser emitters arranged in a two-dimensional pattern, a first dispersive element producing wavelength dependent angular dispersion in a first dimension, a deflective array comprising a plurality of mirrors or optical wedges and arranged in a second dimension and producing deflection in a first dimension, and a second dispersive element producing dispersion in a second dimension. The multi-wavelength laser further includes second dimension imaging optics positioned between the deflective array and the array of laser emitters and configured to reimage in at least one dimension a scaled image of the optical field near the laser emitter array to a location near a deflective array. The multi-wavelength laser further includes a first optical transform lens and a second optical transform lens. The first optical transform lens produces focus power in a first dimension and positioned approximately a focal length from the array of laser emitters and configured to spatially overlap the optical beams in a first dimension forming a first region of overlap at the first dispersive element. The second optical transform lens produces focus power in a second dimension and positioned between the second dispersive element and the first dispersive element and configured to receive the optical beams from the first dispersive element and to spatially overlap the optical beams in the second dimension forming a second region of overlap at the second dispersive element. The second dispersive element transmits a multi-wavelength output beam comprising the spatially overlapped and coaxial optical beams from the array of laser emitters. 
         [0012]    In one example, the dispersive element is a first-order diffraction grating. In another example, the dispersive element is a prism. In one example, the deflective array is a set of mirrors, each having specified angles and positions. In another example, the deflective array is a set of optically transparent wedges, each having specified angles and positions. In one example, the first dimension is perpendicular to the second dimension. In another example, the imaging optics comprise a first lens element and a second lens element. In another example, the imaging optics comprise a first, a second and a third lens element. In another example a first optical transform lens is positioned between the first lens element and the second lens element. In another example a first optical transform lens is positioned between the array of laser emitters and the first lens element. In another example a first optical transform lens is positioned between the second lens element and the deflective array. In another example, the array of laser emitters comprises a plurality of laser emitters arranged in first number of rows, and deflective array in first number of mirrors. In another example, each deflective array mirror is constructed and arranged to deflect a group of laser emitter beams from a common row of emitters comprising first dimension spatially overlapped optical beams. In another example, each deflective array mirror is constructed and arranged to deflect a group of laser emitter beams from a common row of emitters comprising first dimension non-spatially overlapped optical beams. In another example, the deflective array is positioned between the first dispersive element and the second optical transform lens. In another example, the deflective array is positioned between the second lens element of the imaging optics and the first dispersive element. 
         [0013]    In another example, the laser emitters are laser gain media and an output coupler and is positioned after the second dispersive element wherein the output coupler reflects a fraction of the optical radiation form a plurality of beams and transmits a multi-wavelength output beam comprising the spatially overlapped and coaxial optical beams from the array of laser emitters. In another example, the laser emitters are laser sources each having a specified wavelength and linewidth. 
         [0014]    Another embodiment is directed to a method of two-dimensional wavelength beam combining in a laser system. The method includes acts of spatially overlapping in a first dimension, optical beams from a plurality of laser emitters using a first dispersive element and a deflective array comprising a plurality of mirrors or transparent optical wedges, reproducing in at least one dimension a scaled image of the optical field near the laser emitter array to a location near a deflective array, and spatially overlapping in a second dimension the optical beams from the first dispersive element at the second dispersive element to generate a multi-wavelength output beam. 
         [0015]    In one example of the method, reproducing in at least one dimension a scaled image of the optical field near the laser emitter array to a location near a deflective array includes acts of imaging the optical beams with second dimension imaging optics positioned between the deflective array and the plurality of laser emitters. In another example, spatially overlapping in the first dimension the optical beams from the plurality of laser emitters includes spatially overlapping the optical beams in the first dimension using a first optical transform lens to form a first region of overlap at the first dispersive element. The method may further comprise an act of transmitting the multi-wavelength output beam from a second dispersive element. In one example, spatially overlapping in the second dimension the optical beams from the first dispersive element includes spatially overlapping the optical beams in the second dimension using a second optical transform lens to form a second region of overlap at the second dispersive element. 
         [0016]    Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments, are discussed in detail below. Any embodiment disclosed herein may be combined with any other embodiment in any manner consistent with at least one of the objects, aims, and needs disclosed herein, and references to “an embodiment,” “some embodiments,” “an alternate embodiment,” “various embodiments,” “one embodiment” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment. The accompanying drawings are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0017]    Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. Where technical features in the figures, detailed description or any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures, detailed description, and claims. Accordingly, neither the reference signs nor their absence are intended to have any limiting effect on the scope of any claim elements. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. The figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the invention. In the figures: 
           [0018]      FIG. 1  is a schematic diagram of two examples of two-dimensional laser emitter array according to aspects of the present invention; 
           [0019]      FIG. 2  is a schematic diagram of one example of a laser emitter array according to aspects of the present invention; 
           [0020]      FIG. 3  is a schematic diagram of one example of a two-dimensional laser system in a laser emitter source configuration according to aspects of the invention; 
           [0021]      FIG. 4  is a illustrative schematic representation of one example of first dimension beam combining according to aspects of the invention; 
           [0022]      FIG. 5  is another illustrative schematic representation of one example of first dimension beam combining according to aspects of the invention; 
           [0023]      FIG. 6  is a schematic diagram of one example of a deflective array according to aspects of the invention and a schematic diagram of one example of first dimension beam combining according to aspects of the invention; 
           [0024]      FIG. 7  is a schematic diagram of one example of two-dimensional laser system in a laser emitter gain medium configuration according to aspects of the invention; 
       
    
    
       [0025]    Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
         [0027]    It is to be appreciated that embodiments of the methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and apparatuses are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, elements and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiments. Furthermore, although the following discussion may refer primarily to lasers as an example, the aspects and embodiments discussed herein are applicable to any type of electro magnetic source that is wavelength-selectable, including, but not limited to, semiconductor lasers, diode lasers and fiber lasers, laser amplifier, and master oscillator power amplifier systems. 
         [0028]    Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to embodiments or elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality of these elements, and any references in plural to any embodiment or element or act herein may also embrace embodiments including only a single element. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, first dimension and second dimension, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. 
         [0029]    The present invention is directed to a two-dimensional wavelength beam combining implementation including two-dimensional laser sources, two dispersive elements, and a deflective array as a technique to enhance power and brightness. As discussed above, prior art two-dimensional wavelength beam combining systems rely on first and second dimension dispersive elements. The prior art teaches the use of a first-order diffraction grating or prism as the angle and wavelength dependent dispersive element in a second dimension, and either an Echelle diffraction grating operating in high diffracting orders or a first-order diffraction grating stack, as the angle and wavelength dependent dispersive element in a first dimension. 
         [0030]    By contrast to prior art, one embodiment of the present invention also includes the use of two-dimensional dispersive elements but is distinguished from prior art by its use of a first-order diffraction grating or prism as the angle and wavelength dependent dispersive element in both the first and second dimension and the use of a deflective array of mirrors or optically transmitting wedges, as discussed further below. When compared to prior art teachings instructing the use of Echelle diffraction gratings operating in high order diffraction orders, which generally have low diffraction efficiency, the present invention, which can employ all first-order diffraction gratings and which may have significantly higher diffraction efficiency, may have a higher beam combining efficiency than embodiments employing prior art. Furthermore, since the total number of dispersive elements employed in the present invention is reduced to two, the present invention may be simpler to implement than prior art employing a diffraction grating stack. Additionally, since the present invention does not employ the prior art teaching of a diffraction grating stack made up of an array of diffraction gratings having either different period or different angle, the present invention may potentially make use of less expensive off-the-shelf diffraction gratings. 
         [0031]      FIG. 1  shows examples of two examples of embodiments of two-dimensional laser emitter arrays  10  comprising a plurality of laser emitters  14  (e.g., laser source or laser gain medium) arranged in rows as laser emitter rows  12 . The emitters  14  may be any type of source of electromagnetic radiation whereby the wavelength and linewidth can be specified. Electromagnetic radiation emerging from laser emitter  14  may be generated from a device or system not shown. Each laser emitter  14  may be a laser source that emits optical radiation at a predetermined wavelength, and may be self wavelength-stabilized using an internal grating, external volume Bragg grating, an amplifier seed from a master oscillator or by some other self wavelength-stabilizing method. 
         [0032]    The laser emitters  14  may be a laser gain medium whereby electromagnetic amplification of optical radiation may take place at a specified wavelength and over a specified linewidth. Each laser emitter row  12  is comprised of two or more laser emitters  14  and collectively form a row group. The laser emitters  14  within a laser emitter row  12  are positioned in a nominally linear fashion and may be positioned on equal or unequal center-to-center spacing in either a first or second or combination of first and second dimensions. It is to be appreciated that the laser emitters  14  in a laser emitter row  12  may or may not be on a straight line, depending on the specifics of other components used by an embodiment. It is also to be appreciated that laser emitter rows  12  may or may not be on parallel lines, depending on the specifics of other components in used by an embodiment. 
         [0033]    The laser emitters  14  may include, for example, a plurality of discrete single-mode or multi-mode semiconductor amplifiers or a plurality of fiber amplifiers, and may preferably have sufficient gain and sufficient gain bandwidth to overcome optical losses at the desired lasing wavelengths. Furthermore, a plurality of the laser emitters  14  in the two-dimensional wavelength beam combining laser emitter array  10  has a linewidth which can be defined as Full Width Half Max (FWHM) of the laser emitter&#39;s wavelength. The wavelength and linewidth of a laser emitter  14  are specified such that the range of wavelengths within each laser emitter  14  are not produced by more than one of the laser emitters  14 . As a result, embodiments of the present invention employ these wavelength differences as a means to direct each beam from each laser emitter  14  through the optics of an embodiment in a unique way that is dependent on its wavelength and linewidth. 
         [0034]    In one example, the wavelengths of the laser emitters  14  within each laser emitter row  12  of the laser emitter array  10  are monotonically changing in a nearly linear manner from laser emitter  14  to laser emitter  14  across laser emitter rows  12 , and continuing from laser emitter row  12  to laser emitter row  12  in a raster scan manner across all of the laser emitters  14  with the longest and shortest wavelengths associated with two corner laser emitter  14  at opposite laser emitter end one  15   a  and at opposite laser emitter end two  15   b  of the laser emitter array  10 . 
         [0035]    Illustrated in  FIG. 2  is a laser emitter array  10  and shows a multi-wavelength beam  27  comprising the optical beams generated by the laser emitters  14  within the laser emitter array  10 , according to aspects of the present invention. A multi-wavelength row beam  29  comprises the optical beams generated by the laser emitters  14  within a common laser emitter row  12 , according to aspects of the present invention. 
         [0036]    A first embodiment of a two-dimensional multi-wavelength beam combining system in a laser emitter source configuration  11   a  is shown in  FIG. 3 . The system  11   a  includes the laser emitter array  10 . The laser emitter array  10  may be comprised of a plurality of laser emitters  14  and may be arranged in rows as laser emitter rows  12 . Each laser emitter  14  may emit a beam of optical radiation at a unique wavelength and over a specified linewidth as discussed above. In the laser emitter source configuration  11   a,  and each laser emitter  14  emits at a predetermined wavelength. The center of each beam emitted from each laser emitter  14  travels along an optical path that defines an optical axis. In the example shown in  FIG. 3 , an optical axis for a laser emitter  14  within a first laser emitter row  12  is shown as a solid line optical axis  17   a.  Optical axes for laser emitters  14  within subsequent laser emitter rows  12  are shown as long and short dashed line optical axis  17   b  and  17   c,  respectively. As shown in the example illustration of  FIG. 3 , the laser emitter array  10  may be used as the input beam to a two-dimensional wavelength beam combining system. 
         [0037]    In the example of the present invention illustrated in  FIG. 3 , two dispersive elements  18 ,  22  are shown as first first-order diffraction grating  18 , and second first-order diffraction grating  22 . The first and second first-order diffraction gratings  18  and  22  are shown with first and second parallel diffraction grating lines  40 ,  42 , respectively, and are arranged in two orthogonal first and second dimensions, respectively. For ease of explanation, the first dispersive element  18  is said to have second dimension (depicted as vertical) diffraction grating lines  40  and having first dimension (depicted as horizontal) dispersive effects, and the second dispersive element  22  is said to have first dimension (depicted as horizontal) diffraction grating lines  42  and having second dimension (depicted as vertical) dispersive effects. The first or second dispersive element  18 ,  22  may comprise a reflection diffraction grating or comprise a transmission diffraction grating or may comprise an optical prism or may comprise any other device having angular dispersion that is dependent on the wavelength of the beam impinging the dispersive element  18 ,  22 . For ease of illustration in  FIG. 3 , only the beams of interest are shown emerging from first and second dispersive elements  18 ,  22 . Other beams may or may not emerge from the dispersive elements  18 ,  22  in additional diffraction orders and would not contribute to the energy of the combined beam and would contribute to an energy loss and reduced system efficiency. 
         [0038]    The system  11   a  may further include imaging optics  24 . In this example, the imaging optics  24  are comprised of a first lens element  23 , and a second lens element  25  that form an optical imaging telescope and placed somewhere between the laser emitter array  10  and the deflective array  26 . In this example the first and second lens elements  23 ,  25  are comprised of cylindrical optics with optical power in the second dimension as shown. Other examples of imaging optics  24  can be comprised of one, two, three or more optical lenses, and have optical power in either or both the first or second dimension. In this example the imaging optics  24  image in the second dimension an object plane at or near the laser emitter array  10  onto an image plane at or near a deflective array  26 . The deflective array  26  is comprised of an array of deflective elements  31 . Furthermore, in the imaging process of this example, the imaging optics  24  are configured to reimage in the second dimension a scaled image of the optical field (both intensity and phase) near the laser emitter array  10  to a location near the deflective array  26 . In this example, the imaging optics  24  have little impact on the beam propagation properties of the two-dimensional multi-wavelength beams in the first dimension. Also in this example, the imaging optics  24  image between object plane and image plane with magnification m Y  in the second dimension and also reproduce at the image plane, the propagation angles in the second dimension of each beam at the object plan with magnification 1/m Y . 
         [0039]    In this embodiment of the system  11   a  is comprised a first optical transform lens  16 . In this example, a first optical transform lens  16  employs optical power in a first dimension with focal length f 1  and is placed between a laser emitter array  10  and a first dispersive element  18 , and is used to spatially overlap beams in a first dimension at a first dispersive element  18 . The distance between a first dispersive element  18  and a first optical transform lens  16  is nominally equal to the focal length of a first optical transform lens  16 . The distance between a laser emitter array  10  and a first transform lens  16  is nominally equal to the focal length of a first optical transform lens  16 . 
         [0040]    The system  11   a  may further include a second optical transform lens  20 . In this example, a second optical transform lens  20  employs optical power in a second dimension with focal length f 2  and is placed between the first dispersive element  18  and the second dispersive element  22 , and is used to spatially overlap beams in a second dimension at the second dispersive element  22 . The separation of the first dispersive element  18  and the second optical transform lens  20  is preferably equal to the focal length of a second optical transform lens  20 . The separation of the second optical transform lens  20  and the second dispersive element  22  is also preferably equal to the focal length of a second optical transform lens  20 . 
         [0041]    Several aspects of the geometry of the laser emitter array  10  are shown in  FIGS. 4 and 5 . In order to rearrange the beams from each laser emitters  14  such that each is presented at a unique second dimension location, laser emitter rows  12  may be specified to be non-parallel (or rotated) with respect to a first dimension in order to obtain a non-zero displacement in an orthogonal second dimension, thereby producing a laser emitter spacing projected component ΔY e  between adjacent laser emitters  14 . Additionally, each group of laser emitters  14  formed by a laser emitter row  12  has nominal second dimension row spacing projected component ΔY g  between adjacent laser emitter rows  12  as shown in  FIG. 4  and  FIG. 5 . Furthermore, the first dimension laser emitter spacing projected component ΔX e  between adjacent laser emitters  14  is also shown in  FIG. 4  and  FIG. 5 . An example of a method to alter the magnitude of the second dimension laser emitter spacing projected component ΔY e  is through rotation of the laser emitter array  10  about an axis in a third dimension that is orthogonal to the first two orthogonal dimensions. First dimension beam combining is conceptualized by representative first dimension combining arrows  13 . Each representative first dimension combining arrow  13  points to a corresponding beam location in the plane of a first dispersive element  18  and after having passed through the imaging optics  24  having second dimension magnification m Y . The imaging optics  24  invert the image plane with respect to the object plane, a fact that can be ignored for simplicity of explanation and is not illustrated in  FIG. 4  or  FIG. 5 . The imaging optics  24  alter the apparent size of the second dimension laser emitter spacing projected component ΔY e  and the apparent size of the second dimension laser row spacing ΔY g  by the magnification factor m Y  resulting in a second dimension laser emitter image spacing m Y ΔY e  and a second dimension row image spacing m Y ΔY g . The collection of beam images at or near the plane of a first dispersive element  18  and originating from laser emitters  14  within a common laser emitter row  12  are described collectively as a row group  19 . A first optical transform lens  16  (see  FIG. 3 ) having optical power in a first dimension may cause each beam from each laser emitter  14  to be first dimension spatially overlapping at or near a plane of the first dispersive element  18  thereby generating a first dimension overlapped beam  21  whereby each laser emitter  14  beam has a common first dimension location. 
         [0042]      FIG. 6  shows an example of how a first optical transform lens  16  may spatially overlap laser emitter  14  beams in a first dimension at or near a first dispersive element  18  into a first dimension overlapped beam  21  similar to the beams shown in  FIGS. 4 and 5 . In this example, beams originating from laser emitters  14  within a common row  12  each impinge a first dispersive element  18  at a unique angle after traveling through a first optical transform lens  16 . The angle difference between two adjacent beams within a common row is nominally given by the ratio of the first dimension laser emitter spacing projected component ΔX e  to the first dimension focal length of the first optical transform lens  16 , namely ΔX e /f 1 . The wavelength dependent angular dispersion of the first dispersive element  18  is represented by (dα 1 /dλ) and when this term is multiplied by the difference in wavelength Δλ e  between two adjacent laser emitters  14  within a common row  12 , the product represents an angle, namely (dα 1 /dλ)Δλ e . When systems are constructed whereby these two quantities are equal to each other, namely ΔX e /f 1. =(dα 1 /dλ)Δλ e , then each beam from each laser emitter  14  within a common row  12  will emerge from the first dispersive element  18  both overlapped in a first dimension and propagating with a common angle in a first dimension as those shown in  FIG. 6  as row group first dimension combined beams  32 . It is to be appreciated that in this embodiment of the present invention, not all laser emitter  14  beams emerging from the first dispersive element  18  emerge at the same first dimension angle. However, all laser emitter  14  beams originating from within a common laser emitter row  12  will emerge form the first dispersive element  18  at the same angle and form row group first dimension combined beams  32  as shown. This forms the process of beam combining for laser emitter  14  beams within rows and is only a part of the process required for beam combining all beams in a first dimension according to aspects of the present invention. The process of further combining each row group first dimension combined beam  32  into an all beam first dimension combined beam  34  may be accomplished with a deflective array  26  through appropriately chosen deflections at appropriately chosen locations along the optical path, nominally one deflection for each row group first dimension combined beam  32 . One example of a deflective array  26  is illustrated in  FIG. 6  as an arrangement of mirrors  30 , one mirror  30  for each row group first dimension combined beam  32 . Since the optical field at an object plane at or near the laser emitter array  10  is imaged in a second dimension by the imaging optics  24  into a scaled copy at an image plane at or near the deflective array  26 , each beam is distinguishable and not overlapping in a second dimension at or near the deflective array  26 . This allows each mirror  30  of the deflective array  26  to address the beams within each row group first dimension combined beam  32  and minimizing undesired cross talk between row group first dimension combined beams  32 . In other embodiments of the present invention not shown here, a deflective array  26  may reside between the second lens element  25  of the imaging optics  24  and a first dispersive element  18 . Still other embodiments of the present invention not shown here, the deflective array  26  may reside at other locations between the input laser emitter array  10  and a second dimension dispersive element  22 . 
         [0043]    In addition to the first dimension beam combining discussed above, embodiments of the present invention, employ second dimension beam combining. In the example shown in  FIG. 3 , a second optical transform lens  20  having optical power in a second dimension causes each beam originating from each laser emitter  14  to be spatially overlapped at or near a second dimension dispersive element  22  and to impinge the second dimension dispersive element  22  at a unique angle in the second dimension. As discussed and shown above, this example includes the plurality of laser emitter  14  beams exiting the deflective array  26  as combined in a first dimension and spatially separated in a second dimension with laser emitter spacing projected component spacing m Y ΔY e  and a plurality of row group first dimension combined beams  32  with second dimension row group spacing projected component m Y ΔY g . As in a way similar to first dimension beam combining, second dimension beam combining holds to a pair of relationships, namely f 2 (dα 2 /dλ)=m Y ΔY e /Δλ e =m Y ΔY g /Δλ g  whereby (dα 2 /dλ) is the angular wavelength dependent dispersion of the second dispersive element  22 , f 2  is the second dimension focal length of the second optical transform lens  20 , Δλ e  is the wavelength difference between two adjacent laser emitters  14  within a laser emitter row  12  and Δλ g  is the wavelength difference between two adjacent row groups  19  of row group first dimension combined beams  32 . When systems are constructed whereby these two pairs of relationships are maintained, namely f 2 (dα 2 /dλ)=m Y ΔY e /Δλ e =m Y ΔY g /Δλ g , then each beam from each laser emitter  14  will emerge from a second dispersive element  22  both overlapped in both a first and second dimension and propagating with a common angle in both a first and second dimension as a multi-wavelength output beam  28 , as shown in  FIG. 3 . 
         [0044]    In this example, the optical elements: imaging optics  24 ; first optical transform lens  16 ; first dispersive element  18 ; deflective array  26 ; second optical transform lens  20 ; and second dispersive element  22 , may be used in one example of a laser emitter source configuration  11   a  as shown in  FIG. 3  and further illustrated in  FIGS. 4-6 , and in a manner described above, to combine a plurality of laser emitters  14  comprised of laser sources each having a unique and specified wavelength into a single combined multi-wavelength output beam  28  whereby a plurality of laser emitter  14  beams are overlapped in both dimensions and propagating in the same direction in both dimensions. 
         [0045]      FIG. 7  shows an embodiment of the present invention in a laser emitter gain medium configuration  11   b  which is similar to the laser emitter source configuration  11   a  shown in  FIG. 3  and discussed above. A first differences between these two embodiments is that of the type laser emitter  14 . In the example of a laser emitter gain medium configuration  11   b  the laser emitters  14  are laser gain medium, which is in contrast to the example laser emitter source configuration  11   a  where the laser emitters  14  are laser sources. As discussed above, each laser gain medium has optical gain at a specified wavelength and over a specified linewidth and can made to lase (amplify radiation) at a specified wavelength with external cavity optics that provide optical feedback at the specified wavelength. The optical elements: imaging optics  24 ; first optical transform lens  16 ; first dispersive element  18 ; deflective array  26 , second optical transform lens  20 , and second dispersive element  22  may be arranged, in similar manners to those disclosed above, to provided optical wavelength discrimination at specified wavelengths. An optical feedback element may be added to this arrangement whereby, collectively, they provide both the necessary optical feedback and the necessary wavelength discrimination for a laser system to operate as a plurality of external laser cavities. 
         [0046]    In an example of the present invention in a laser emitter gain medium configuration  11   b,  an optical feedback element in the form of an output coupler  38  having partial reflectivity at a plurality of wavelengths over the wavelength range of the laser emitters  14  is placed along the multi-wavelength beam  27  path emerging from the second dispersive element  22  to return a fraction of the multi-wavelength beam  27  emerging from the second dispersive element  22  toward the plurality laser emitters  14 , as shown in the example illustrated in  FIG. 6 . In this embodiment, each laser emitter  14  can be made to automatically stabilize its wavelength and lase (amplify radiation) as an independent eternal cavity operating at a unique center wavelength and over a unique range of wavelengths determined by the circulating feedback wavelength dependent gain of the external cavity. In this embodiment of the present invention, a multi-wavelength output beam  28  emerges from the output coupler  38  whereby a plurality of laser emitter  14  beams produced by a plurality of external cavities are overlapped in both dimensions and propagating in the same direction in both dimensions. 
         [0047]    In other embodiments of the present invention, the output coupler  38  may be positioned at other locations along the path of the multi-wavelength beam  27  to provide optical feedback to the plurality of laser emitters  14 . For example, locations whereby a plurality of laser emitter  14  beams are propagating at angles that are parallel to one another, are locations whereby a flat surface can be positioned normal to the optical axis of the laser emitter  14  beams and can provide wavelength discriminating optical feedback from an output coupler  38  having a flat surface and placed there. Additionally, in another example, locations whereby a plurality of laser emitter  14  beams are propagating toward a point, are locations whereby a surface having spherical curvature can be specified and positioned so that a plurality of laser emitter  14  beams are propagating at angles that are normal to the surface, and can provide wavelength discriminating optical feedback from an output coupler  38  having the specified spherical curvature and positioned there. 
         [0048]    For example, according this invention placing the output coupler  38  at a location after the deflective array  26  and the first dispersive element  18  and before the second optical transform lens  20  can be made to provide optical feedback at the specified wavelengths to generate optical gain for the plurality of laser emitters  14  from the laser emitter array  10  and cause a multi-wavelength output beam  28  to emerge from the second dispersive element  22  in a laser emitter gain medium configuration  11   b.  In another example, separate output couplers  38  may be placed at different angles and along each multi-wavelength row beam  29  path and between the first dispersive element  18  and the deflective array  26  to provide the wavelength discriminating optical feedback for a plurality of laser emitters  14  within a laser emitter row  12  as well as the plurality of laser emitters  14  within the laser emitter array  10 . 
         [0049]    Thus, there has been described at least two embodiments of two-dimensional wavelength beam combining of two-dimensional laser emitter arrays  10  according to aspects of the intention. The invention may be used as a technique to enhance the power and/or brightness of a two-dimensional array of laser emitters  14 . 
         [0050]    Any of the above discussed embodiments of a wavelength beam combining system may be incorporated into an associated laser system. Such a laser system may include, for example, a wavelength beam combining system, electrical, thermal, mechanical, electro-optical and opto-mechanical laser control equipment, associated software and/or firmware, and an optical power delivery subsystem. Embodiments of the wavelength beam combining laser system, and associated laser systems, can be used in applications that benefit from the high power and brightness of the embodied laser source produced using the wavelength beam combining system. These applications may include, for example, materials processing, such as welding, drilling, cutting, annealing and brazing; marking; laser pumping; medical applications; and directed energy applications. In many of these applications, the laser source formed by the wavelength beam combining system may be incorporated into a machine tool and/or robot to facilitate performance of the laser application. 
         [0051]    While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.