Abstract:
A system and method for aligning a microfilter in an optical circuit and thereby providing sub-beam impingement intensity control from a set of highly proximate sub-beams generated from a parallel process laser system removing a portion from a workpiece (exit holes in inkjet nozzle plates). The energy of laser-generated sub-beams to the target (cutting) point is attenuated to a level sufficient for maintaining operation of a charge-coupled-device camera below saturation when the sub-beams are incident on the camera, the CCD camera monitors the sub-beams and directs output to either a monitor or control computer. The microfilter is then adjusted to provide an optimal sub-beam pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/398,529, filed on Jul. 25, 2002. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to laser drilling and laser milling and particularly relates to microfilter alignment in a laser drilling system. 
     BACKGROUND OF THE INVENTION 
     Material ablation by pulsed light sources has been studied since the invention of the laser. Etching of polymers by ultraviolet (UV) excimer laser radiation in the early 1980s led to further investigations and developments in micromachining approaches using lasers—spurred by the remarkably small features that can be drilled, milled, and replicated through the use of lasers. A recent article entitled “Precise drilling with short pulsed lasers” (X. Chen and F. Tomoo, High Power Lasers in Manufacturing, Proceedings of the SPIE Vol. 3888, 2000) outlines a number of key considerations in micromachining. Other recent patents of interest include the following: 
     U.S. Pat. No. 6,266,198, “Consolidated laser alignment and test station,” describes a consolidated laser alignment and test station. In exemplary embodiments, equipment sufficient to perform complete dynamic testing and alignment of a laser transceiver unit is provided in one compact arrangement. As a result, cavity-box efficiency testing, dynamic open-interferometer alignment, dynamic open-case alignment, closed-case laser boresighting, and complete laser functionality and diagnostic testing can be carried out efficiently at a single location. Real-time diagnostic feedback relating to beam quality, radiometry, and temporal behavior is provided so that high-precision laser alignments and repairs can be made quickly and cost effectively. Customized test fixtures provide easy access to every level of the transceiver unit under test, and two cameras provide far-field, near-field, wide-field and receiver-field beam viewing. One camera is combined with a pin-hole lens and a quad step-filter optic attenuator to provide a wide-field beamfinder assembly enabling an operator to quickly align the laser under test to the narrower field of the second (diagnostic) camera. The second camera provides near-field and far-field beam viewing, while a radiometer and a pulse detector provide additional diagnostic information. The beamfinder assembly also provides receiver-field laser viewing for receiver-path boresight adjustments. In an exemplary embodiment, the beamfinder assembly includes a quad step-filter constructed from circular wedge filters. 
     U.S. Pat. No. 6,122,106, “Displaced aperture beamsplitter for laser transmitter/receiver opto-mechanical system,” describes a single aperture opto-mechanical system for transmitting two small-aperture laser beams and a single received laser beam. The two pencil-thin transmitted beams are co-aligned within 150 micro-radians in the same direction but have optical axes that are displaced laterally. An in-coming beam is received along a path that is essentially parallel with the path of the transmitted beams within 500 micro-radians. The small-aperture transmitted beams each pass through a hole in a metal mirror beamsplitter that is positioned to reflect the received light energy at a 90 E angle through a narrow band-pass filter and focused by an aspheric glass lens that directs the received beam energy onto a receiver detector. The beamsplitter has indexing features that provide self-alignment of the beamsplitter to the laser mount. 
     U.S. Pat. No. 5,991,015, “Beam monitoring assembly,” describes a beam monitoring assembly that provides near-field imaging, far-field imaging and power measurements of a laser beam in real-time for alignment and performance verification purposes. The monitoring assembly includes a holographic beam splitter that splits the laser beam from the laser resonator cavity into a series of separate split beams having varying beam powers. One of the split beams is directed to a power meter to measure the power of the beam. One of the split beams is directed to a near-field camera that provides a near-field image of the beam. Another one of the split beams is directed to a heat dump that absorbs and removes the beam&#39;s energy from the assembly. Another one of the split beams is directed to a far-field lens that focuses the split beam onto a far-field camera that provides a far-field image of the beam. The near-field and far-field images of the beam are displayed on an operator control panel in real time. Suitable computer electronics and camera electronics are provided to process the electrical signals from the power meter and the cameras. 
     Japanese Patent JP62,273,503, “Laser alignment measuring instrument,” describes a laser alignment detector including a screen with scale marks, lighting device, partially transmitting mirror which partially transmits rays of light, image pickup element placed on the reflecting optical axis of the mirror, and box body which intercepts outside light and houses the screen, mirror, lighting device, and image pickup element. An incident laser beam passes through an optical filter for adjusting light quantity and reaches a half mirror, which is a partially transmitting mirror. The transmittance of the half mirror is about 30% and a non-reflective coating is performed on one side of the mirror for preventing the ghost of the laser beam. About 50% quantity of the laser beam reflected by the half mirror is absorbed into a box body, which is plated to a black color. The transmitted laser beam hits a screen with scale marks and the laser pattern is monitored by a CCD camera through the half mirror. An optical filter for adjusting light quantity is provided in front of the CCD camera containing an image pickup element and LEDs are provided beside the screen as lighting devices for illuminating the scale marks, so that the scale marks on the screen can be seen with the CCD camera. Therefore, the compact laser alignment-measuring instrument can be obtained. 
     Ultrafast lasers generate intense laser pulses with durations from roughly 10 −11  seconds (10 picoseconds) to 10 −14  seconds (10 femtoseconds). Short pulse lasers generate intense laser pulses with durations from roughly 10 −10  seconds (100 picoseconds) to 10 −11  seconds (10 picoseconds). Along with a wide variety of potential applications for ultrafast and short pulse lasers in medicine, chemistry, and communications, short pulse lasers are also useful in milling or drilling holes in a wide range of materials. In this regard, hole sizes in the sub-micron range are readily drilled by these lasers. High aspect ratio holes are also drilled in hard materials; applications in this regard include cooling channels in turbine blades, nozzles in ink-jet printers, and via holes in printed circuit boards. 
     Parallel processing of laser-milled holes is a key technique for increasing throughput in laser micromachining. Beamsplitting devices (beamsplitters) such as diffractive optical elements (DOEs) are used in laser micromachining to divide a single beam into multiple beams and thereby achieve parallel machining. However, such use of beamsplitters introduces technical challenges in hole geometry requirements and in the ability to produce consistent, repeatable results. Such challenges need to be overcome in order to maintain consistency and repeatability in laser milling. 
     The primary advantage of a parallel process laser drilling system over a single beam laser drilling system is the efficiency gain in processing time. Parallel process drilling systems drill many holes in the same amount of time that a single beam laser drilling system drills just one hole. The repeatability and quality of the parallel-processed holes is important to create a product that meets the required specifications. Any variation in beam intensity or in alignment between sub-beams causes a parallel process laser drilling system to drill misshapen holes, creating a product that does not meet specifications. 
     Alignment of microfilters to the sub-beam pattern is critical in producing a drilled workpiece that meets final specification. The microfilter needs to be adjusted in terms of position and focus to achieve these specifications. However, current methods for adjusting microfilters are complex and time consuming, and therefore not cost efficient. 
     What is needed is a way to increase the performance of a parallel process laser drilling system by being able to rapidly and optimally align a microfilter within a parallel process laser drilling system when alignment is required. Fullfilling this need requires a way to simultaneously align a plurality of beams with a microfilter in a parallel process laser drilling system and also a way to determine the degree and nature of misalignment of the sub-beams. The present invention provides a solution to these needs. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a laser drilling system includes an imaging device illuminated by at least two sub-beams of the laser drilling system, including a first sub-beam and a second sub-beam, a microfilter intersecting beam paths of the first sub-beam and the second sub-beam, and a display communicating an image from the imaging device to an operator of the laser drilling system. 
     A number of advantages are provided with the invention. For example, equalizing the sub-beam intensity and aligning sub-beams through a microfilter increases the performance of a parallel process laser drilling system. A way is also provided to align and confirm alignment of a microfilter in such a drilling system toward an optimal alignment of the sub-beams. Another advantage of the present invention relates to determining the degree and nature of misalignment in a microfilter respective to the sub-beams of a parallel process laser drilling system. The present invention also provides a way to align beams outside of the visible-spectrum (e.g., infrared beams). 
     The ability to align a microfilter with the sub-beams of a parallel process laser drilling system without disturbing the optical alignment of the other system elements is yet another benefit. Finally, the basic invention provides a way to align a microfilter with the sub-beams of a parallel process laser drilling system with a CCD camera without damaging the CCD camera with the high power laser beams. 
     In a preferred form of the invention, a further benefit of using a microfilter with a reflective coating is that a way is provided to optimize the contrast between the sub-beams&#39; incidence location upon the transmissive disks of the microfilter and the sub-beams&#39; incidence location upon the reflective coating of the microfilter, thus providing an improved alignment means in a parallel process laser drilling system. In a preferred use, print resolution in inkjet printers is also realized when the inkjet nozzles of the printer are manufactured with the benefit of the invention. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 presents a schematic of a laser drilling system; 
     FIG. 2 shows shows an aligning system according to the present invention; 
     FIG. 3 (FIGS. 3A and 3B) shows a misaligned sub-beam pattern and an aligned sub-beam pattern; 
     FIG. 4 illustrates a method for aligning a microfilter with the sub-beams of a parallel process laser drilling system; 
     FIG. 5 shows an example of misalignment of a microfilter from shifting one sub-beam; 
     FIG. 6 provides a perspective view showing major constituent components of an ink-jet printer; 
     FIG. 7 provides a schematic cross-sectional view of an ink-jet head. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Microfilters are used to correct for inconsistencies in sub-beam intensity to help resolve the technical challenges referenced above. However, the introduction of any new element to a laser drilling system requires careful alignment to ensure drilling quality. When aligning hundreds of sub-beams in a regular pattern to a patterned microfilter, there is a chance that any given sub-beam will be mis-aligned to the wrong part of the transmissive pattern. This type of error is not detected in a single-beam alignment procedure, in which, as long as a sub-beam is transmitted through a transmissive filter of the microfilter, it is difficult to discern if the individual sub-beam is aligned with its intended individual transmissive filter. However, when a set of sub-beams are to be aligned, the alignment issue between sub-beam and pattern can be avoided by measuring the alignment of all sub-beams simultaneously. A secondary benefit of simultaneous alignment is that the decreased time spent aligning the microfilter translates to a decreased operating cost and increased throughput of the laser drilling system. 
     In overview, the preferred embodiments provide a microfilter alignment system that simultaneously aligns a microfilter using all the sub-beams filtered by it in a parallel process laser drilling system. The aligning system includes a charge-coupled-device having a size large enough to capture images of all sub-beams simultaneously (hereinafter referred to as a large-format CCD camera), a microfilter, a PZT scan mirror, a diffractive optical element to split a single beam into a plurality of sub-beams, an image transfer lens, and at least one attenuator. The large-format CCD camera captures images of the sub-beams as they are moved in a pattern by the PZT scan mirror and transmitted through the microfilter. The sub-beams are aligned as a simultaneously transmitted group. The alignment approach includes reducing beam intensity with a second attenuator, placing a CCD camera in the imaging plane of the microfilter, guiding the sub-beams using the PZT mirror, measuring the alignment of the guided sub-beams upon the large-format CCD camera, and realigning the microfilter based on the measurement from the camera. 
     In a further embodiment, a highly reflective coating on the microfilter provides up to a twenty times higher contrast for sharply defining the edges of the transmissive filters pattern. 
     Turning now to specific details in the preferred embodiments, FIG. 1 shows a simplified schematic of a laser drilling system  100 , including a laser  105 , a beam  107 , a shutter  110 , an attenuator  115 , a beam expander  120 , a spinning half-wave plate  125 , a first mirror  108 , a second mirror  117 , a third mirror  121 , a fourth mirror  122 , a piezo electric transducer (PZT) scan mirror  130 , a diffractive optical element (DOE)  135 , a plurality of sub-beams  137 , a plurality of sub-beams  138  a scan lens  140 , a microfilter  145 , an image transfer lens  150 , and a workpiece  155 , arranged as shown. All elements of laser drilling system  100  are conventional in laser micromachining. 
     Laser  105  is a conventional laser used for laser drilling. In one embodiment, laser  105  is a picosecond laser. However, laser  105  may be generalized for use with other lasers, such as excimer, CO 2 , and copper vapor laser systems. 
     PZT scan mirror  130  implements a laser milling algorithm (not described here, but which should be apparent), and guides beam  107  to achieve the desired shape in workpiece  155 . The specifications of PZT scan mirror  130  are selected in coordination with scan lens  140  according to the size and shape of the holes to be milled and the material of workpiece  155 . In one embodiment, PZT scan mirror  130  is a high-resolution, small-range PZT tip-tilt mirror in the 1-3 mrad scan range. 
     DOE  135  acts as a highly efficient beamsplitter and beam array pattern generator enabling picosecond laser drilling system  100  to drill parallel holes in workpiece  155 . The pattern of sub-beams  137  output by DOE  135  is pre-determined by the specifications of the holes to be drilled in workpiece  155 . In one embodiment, DOE  135  splits the single incident laser beam from laser  105  into 152 beams in the forms of 4 rows with 38 beams in each row. (This excimer/kinoform information is from Holmér and Hård&#39;s 1995 paper “Laser-machining experiment with an excimer laser and a kinoform” in Applied Optics which is hereby incorporated by reference herein). 
     Scan lens  140  determines the spot size of sub-beams  137  upon workpiece  155 . The size of beam  107  that enters scan lens  140  is less than or equal to the pupil size of scan lens  140 . Telecentricity is required to keep the incident angle between sub-beams  137  and workpiece  155  essentially perpendicular, a necessary angle for drilling parallel holes in workpiece  155 . In a preferred embodiment, scan lens  140  is an f-theta telecentric (scan) lens. In alternate embodiments, where the axes of the holes do not need to be parallel to each other, a non-telecentric scan lens is used. 
     Microfilter  145  equalizes the uniformity of sub-beams  137  emitted from picosecond laser  105  through DOE  135 . Microfilter  145  is made of dielectric coatings on a glass substrate and is custom designed and fabricated according to the intensity patterns of the sub-beams  137  from DOE  135 . In one embodiment, microfilter  145  has two transmission values, 100% and 98%, in a pattern of 152 individual filters of 4 rows with 38 filters in each row that corresponds to the example given to DOE  135  above. In order to increase the contrast for better alignment, the background area of microfilter  145  is 100% reflective such that sub-beams  137  are only passed through the transmissive filters area. This 100% reflective coating improves the signal-to-noise ratio by at least a factor of twenty over a microfilter with an uncoated background for realizing the misalignment. In this embodiment, each of the individual transmissive filters is circular in shape with a diameter of 250 microns. 
     Image transfer lens  150  maintains image quality, spot size, and telecentricity, while preventing the blowback of ablated particles from workpiece  155  onto microfilter  145  by distancing workpiece  155  more than two additional focal lengths away from microfilter  145 . These ablated particles damage microfilter  145  due to the proximity between microfilter  145  and workpiece  155  if image transfer lens  150  is not used. In one embodiment, image transfer lens  150  has two telecentric scan lenses, identical to scan lens  140 , placed back to back, with the pupil planes of the two scan lenses coinciding in the middle. 
     Workpiece  155  is the target for picosecond laser drilling system  100 . In one embodiment, workpiece  155  is a stainless steel inkjet nozzle foil; however, the present invention may be generalized to a variety of workpiece materials, such as polymers, semiconductor metals, or ceramics. In alternate embodiments, a picosecond laser drilling system  100  can drill holes of a wide variety of shapes and tapers in workpiece  155 . 
     In operation, laser  105  emits beam  107  along the optical path identified in FIG.  1 . Beam  107  propagates along the optical path to be incident upon first mirror  108 . First mirror  108  redirects beam  107  along the optical path to be incident upon shutter  110 . Shutter  110  opens and closes to selectively illuminate workpiece  155 . Beam  107  exits shutter  110  and propagates along the optical path to attenuator  115 . Attenuator  115  filters the energy of picosecond laser  105  in order to precisely control ablation parameters. Beam  107  exits attenuator  115  and propagates along the optical path to be incident upon second mirror  117 . Second mirror  117  redirects beam  107  along the optical path to be incident upon beam expander  120 . 
     Beam expander  120  increases the size of beam  107  to match the pupil size of scan lens  140 . Beam  107  exits beam expander  120  and propagates along the optical path to be incident upon third mirror  121 . Third mirror  121  redirects beam  107  along the optical path to be incident upon fourth mirror  122 . Fourth mirror  122  redirects beam  107  along the optical path to be incident upon spinning half-wave plate  125 . Spinning half-wave plate  125  changes the polarization of beam  107 . Upon exiting spinning half-wave plate  125 , beam  107  propagates along the optical path to be incident upon PZT scan mirror  130 . PZT scan mirror  130  moves in a pre-defined pattern using a drilling algorithm (not shown) to drill the holes in workpiece  155 . PZT scan mirror  130  redirects beam  107  along the optical path to be incident upon DOE  135 . DOE  135  splits beam  107  into a plurality of sub-beams  137 , which allow parallel drilling of workpiece  155 . Sub-beams  137  exit DOE  135  and propagate along the optical path, where they are incident upon scan lens  140 . Scan lens  140  determines the spot size of sub-beams  137  upon microfilter  145 . Microfilter  145  equalizes the intensities of sub-beams  138 . Sub-beams  138  exit microfilter  145  and propagate along the optical path, where they are incident upon image transfer lens  150 . Image transfer lens  150  re-images the focal spots of sub-beams  138  onto workpiece  155 . Sub-beams  138  ablate workpiece  155  in a pattern according to the pre-defined milling algorithm. 
     Turning now to further details in the present invention, a microfilter alignment system and method of using a large format charge-coupled device (CCD) camera with a display screen align a microfilter within a parallel process laser drilling system. The system includes a large format CCD camera and a laser drilling system (e.g., laser drilling system  100 ) with a PZT scan mirror, a DOE used to split a single beam into a plurality of sub-beams, an image transfer lens, and at least one attenuator. The method utilizes a CCD camera to image the drilling pattern and determine corrections for the microfilter alignment. Microfilter alignment is completed prior to drilling a workpiece with a parallel process laser drilling system (e.g., laser drilling system  100 ). In this regard, FIG. 2 presents the system for aligning a microfilter with the sub-beams of a parallel laser drilling system. 
     FIG. 2 shows an aligning system  200  including PZT scan mirror  130 , beam  107 , DOE  135 , sub-beams  137 , sub-beams  138 , scan lens  140 , microfilter  145 , image transfer lens  150 , a second attenuator  252 , a CCD camera  253 , and a display screen  254 . 
     Second attenuator  252 , CCD camera  253 , and display screen  254  are used, as shown in aligning system  200 , to perform the alignment of sub-beams  137  and microfilter  145 , and are subsequently removed, without disturbing the alignment of the laser drilling system  100 , to perform drilling. Aligning system  200  is identical to the elements shown in laser drilling system  100 , except that workpiece  155  has been replaced with second attenuator  252 , CCD camera  253  (at the target spot where cutting is normally performed), and display screen  254  in order to perform alignment of microfilter  145  prior to drilling. 
     Beam  107 , DOE  135 , sub-beams  137 , sub-beams  138 , scan lens  140 , microfilter  145 , and image transfer lens  150  function as described in laser drilling system  100 . 
     PZT scan mirror  130  guides beam  107  in a pattern identical to the perimeter of the workpiece geometry eventually (after completing the alignment of microfilter  145 ) to be drilled in workpiece  155 . In one embodiment, where microfilter  145  is aligned for use in laser drilling system  100  as it drills conical holes in an inkjet nozzle foil, PZT scan mirror  130  guides beam  107  in a circular pattern with a diameter equal to the entrance diameter of the conical hole to be drilled. 
     Microfilter  145  is placed near to, but outside, the focal plane of sub-beams  137 , for two primary purposes. The first purpose is to ease the measurement of sub-beams  137  with CCD camera  253 . Sub-beams  137  are larger in diameter outside the focal plane. When the distance offset is chosen properly, the effective coverage of the beam track matches the size and shape of the transmissive filters patterned on microfilter  145 , and thus the alignment accuracy is greatly enhanced. The second purpose is to eliminate possible damage to microfilter  145  caused by sub-beams  138 . Microfilter  145  is fastened to a translation stage with an X-Y-Z translation plus rotation (not shown but which should be apparent) enabling microfilter  145  to be moved and aligned within the optical path between scan lens  140  and image transfer lens  150 . In one embodiment, microfilter  145  is glued to a manual rotational stage which is in turn mounted on an X-Y-Z translational stage. In another embodiment, microfilter  145  is fastened to a computer-controlled rotational and X-Y-Z translational stage that systematically adjusts the alignment of microfilter  145  based on alignment data received from CCD camera  253 . In an alternate embodiment, microfilter  145  has a 100% reflective coating to enhance the contrast for realizing the edges of the transmissive filters pattern. 
     Second attenuator  252  is used to reduce the laser energy of sub-beams  138  before sub-beams  138  are incident upon CCD camera  253 . Second attenuator  252  is necessary to prevent the laser energy of sub-beams  138  (e.g., the energy level normally used by sub-beams  138  for drilling) from saturating or damaging CCD camera  253 . If CCD camera  253  becomes saturated, alignment details are not discernable. Second attenuator  252  is a piece of Schott glass of fixed optical density placed after image transfer lens  150 , against CCD camera  253 . Second attenuator  252  is placed directly against the CCD camera  253  to block ambient light from being detected simultaneously. 
     CCD camera  253  is a large-format CCD camera with a pixel array (used for image capturing) equal to or larger than the target pattern of the laser drilling system upon workpiece  155 . In one embodiment of drilling inkjet nozzles, the target pattern is 13 mm by 12 mm. CCD camera  253  is used to measure the alignment of all sub-beams  138  simultaneously. CCD camera  253  is a large-format CCD camera such as those manufactured by Apogee Instruments, Incorporated. The individual pixel size of CCD camera  253  must be small enough to resolve the circular path of the individual sub-beams  138  and should, therefore, be roughly equivalent to the diameter of sub-beams  138 . In one embodiment, sub-beams  138  have a 10-micron diameter, and CCD camera  253  has a corresponding pixel size of 9 microns. 
     Display screen  254  is a conventional computer monitor. Display screen  254  is used to image sub-beams  138  as they are incident upon CCD camera  253 . In one embodiment, a “frame-grabber interface card” transports pixel-to-pixel images from CCD camera  253  to a computer (not shown), and the computer digitally processes the image and displays the result on display screen  254 . Ability to digitally zoom-in, zoom-out, and process the images is essential to fully utilize the resolution of the large area CCD camera  253 . In an alternate embodiment, in which a computer adjusts microfilter  145  systematically, display screen  254  is not a required element. 
     In operation, shutter  110  of drilling laser  105  is opened and beam  107  propagates along an optical path through optical elements in a laser drilling system (e.g., laser drilling system  100 ) until it is incident upon PZT scan mirror  130 . PZT scan mirror  130  directs beam  107  in a pattern along the optical path towards DOE  135 . Beam  107  propagates along the optical path to be incident upon DOE  135 . DOE  135  splits beam  107  into sub-beams  137 , to allow for the parallel drilling of workpiece  155 . Sub-beams  137  exit DOE  135  and propagate along the optical path, where they are incident upon scan lens  140 . Scan lens  140  determines the final spot size of sub-beams  137  upon workpiece  155 . Sub-beams  137  exit scan lens  140  and propagate along the optical path, where they are incident upon microfilter  145 . Microfilter  145  equalizes the intensities of sub-beams  138 . Sub-beams  138  exit microfilter  145  and propagate along the optical path, where they are incident upon image transfer lens  150 . Image transfer lens  150  re-images the focal spots of sub-beams  138  onto second attenuator  252 . Second attenuator  252  reduces the laser energy of sub-beams  138 . Sub-beams  138  exit second attenuator  252  and are incident upon CCD camera  253 . The pattern of sub-beams  138  is captured by CCD camera  253  and shown on display screen  254 . Based on the pattern and appearance of patterning sub-beams  138 , the position and alignment of microfilter  145  is adjusted to ensure alignment of microfilter  145  and all sub-beams  138 . The spatial movement (X-Y-Z direction and rotation) required to align microfilter  145  with sub-beams  138  is discernable from the pattern of sub-beams  138  as captured by CCD camera  253  and shown on display screen  254 . This concept is illustrated in FIGS. 3A and 3B below. 
     FIG. 3A shows an example of using aligning system  200  in which sub-beams  138  are shaped as circles, travel through misaligned microfilter  145 , are captured by CCD camera  253 , and are displayed on display screen  254 . In FIG. 3A, a plurality of clipped circular images  356  show that sections of the circled pattern of sub-beams  138  have been “clipped” by the edges of the transmissive disk patterns in microfilter  145 ; therefore, microfilter  145  is not aligned with sub-beams  138 . Microfilter  145  is then translated and rotated until microfilter  145  is aligned with sub-beams  138  to create a plurality of complete circular images  357  on display screen  254 , as shown in FIG.  3 B. 
     FIG. 4 illustrates a method  400  of aligning microfilter  145  with sub-beams  137  of a parallel process laser drilling system (e.g., laser drilling system  100 ), including the following steps: 
     In step  410 , providing laser drilling system, a laser drilling system with a specific set of minimally required elements is provided. The minimally required elements, as shown in aligning system  200 , include PZT scan mirror  130 , beam  107 , DOE  135 , sub-beams  137 , sub-beams  138 , scan lens  140 , microfilter  145 , image transfer lens  150 , second attenuator  252 , CCD camera  253 , and display screen  254 . 
     Shutter  110  of drilling laser  105  is opened, and attenuator  115  is adjusted to a proper level. Microfilter  145  is placed and roughly aligned using an infrared viewer (not shown but which should be apparent) within aligning system  200 . In one example, microfilter  145  is aligned to a range of 100 microns with this infrared viewer. 
     In step  420 , reducing beam intensity with second attenuator, second attenuator  252  reduces the intensity of sub-beams  138  to prevent sub-beams  138  from saturating CCD camera  253  such that the images would be unusable for alignment purposes, and also to prevent damage to CCD camera  253 . 
     In step  430 , placing CCD camera in imaging plane of microfilter, CCD camera  253  is placed in the imaging (or conjugate) plane of microfilter  145 . CCD camera  253  must be placed in the imaging plane of microfilter  145  to capture the boundaries of circular sub-beams  138  generated from microfilter  145 . This placement serves as an initial “rough” focusing to be improved later in method  400 . In one embodiment, the rough focusing of CCD camera  253  using laser drilling system  100  is typically accurate to within 1 mm of the true imaging plane at this step. 
     In step  440 , circling beam with PZT scan mirror, PZT scan mirror  130  moves in such a manner as to circle beam  107  as it propagates through laser drilling system  100 . PZT scan mirror  130  is programmed with a computer (not shown) to circle beam  107  until alignment is complete. The rate of circling is fast enough that a single exposure on CCD camera  253  reveals complete circles when alignment is achieved. In one embodiment, the rate is set to five circles per second while the CCD is exposed for 2 seconds for each frame. 
     In a general embodiment, PZT scan mirror  130  circles beam  107  to create a circular pattern with a diameter greater than or equal to the size of the hole to be drilled in workpiece  155  to ensure that, when drilling to create a specified workpiece geometry, none of sub-beams  138  will be clipped by the edges of the individual filters in microfilter  145 . 
     In a specific embodiment, PZT scan mirror  130  circles sub-beam  137  (with a 30-micron diameter) in a 100-micron diameter circle through the 250-micron individual filters in microfilter  145 . 
     In step  450 , viewing display screen image, a laser system operator uses display screen  254  to view the images of circling sub-beams  137  that successfully pass through microfilter  145  and are incident upon CCD camera  253 . Frames with two-second exposure time are transferred to display screen  254  to view the circular tracks of sub-beam  137  In an alternate embodiment where microfilter  145  is adjusted systematically by a computer, step  450  is not required. 
     FIG. 5 presents an example of misalignment of a microfilter from shifting of one sub-beam. Sub-beam A is blocked by the microfilter while other sub-beams pass through the microfilter apertures. In step  460 , decision as to microfilter alignment based on image, the laser system operator analyzes the images on display screen  254  and determines whether microfilter  145  is in alignment with sub-beams  138 . The system operator monitors possible interval shifts for patterns with some regularity. For hole patterns where the holes are regularly spaced, situations can happen where the microfilter is shifted by an integer number of holes from the beam pattern, but the majority of the laser beams still pass the microfilter. As an example (see FIG.  5 ), a row of regularly spaced laser sub-beams labeled A, B, C, D, . . . are correctly aligned when they pass the corresponding regularly spaced microfilter apertures labeled A′, B′, C′, D′, . . . . However, a situation may happen where the sub-beams are misaligned and shifted by one hole, i.e., sub-beam B passes A′, sub-beam C passes B′, sub-beam D passes C′, etc., but sub-beam A is blocked by the microfilter, as shown in FIG.  5 . This misalignment can only be detected by zooming out to view the entire hole pattern on display screen  254  and by counting the number of sub-beams to make sure the the correct number of sub-beams are present. 
     Returning to FIG. 4, if microfilter  145  is misaligned, the image of sub-beams  138  shows clipped circular paths  356 , as shown in FIG. 3A, and method  400  proceeds to step  470 . If the image of sub-beams  138  on display screen  254  shows complete circular paths  357  with all sub-beams  138  present, as shown in FIG. 3B, microfilter  145  is in alignment with all sub-beams  138 , and method  400  ends. 
     In step  470 , translating and/or rotating microfilter, the laser system operator translates and/or rotates the rotational stage of microfilter  145  into a position closer to alignment based on the pattern of clipped circular paths  356  on display screen  254 . In one embodiment, the system operator manually adjusts the position of microfilter  145  by turning a knob(s) on a manual rotational stage that holds microfilter  145 . In an alternate embodiment, a computer (not shown) adjusts a mechanical rotational stage holding microfilter  145  based on the alignment data captured by CCD camera  253 . The computer receives data from CCD camera  253  regarding the pattern of clipped circular paths  356  incident upon CCD camera  253 , and adjusts the position of microfilter  145  based on that data. 
     In step  480 , focusing CCD camera, CCD camera  253  is moved forward or backward within the optical path to compensate if there is no focusing mechanism within CCD camera  253 . If CCD camera  253  does contain a focusing lens or other focusing mechanism, CCD camera  253  is not moved, but focused either manually or electronically. 
     The system and method of the present invention are used to align a microfilter article that is specifically designed to equalize intensity of sub-beams within a parallel process laser drilling system. 
     The system and method of the present invention are also used to produce an inkjet nozzle article with improved workpiece geometry, uniformity, and repeatability via use of the aligned microfilter designed to equalize intensity of sub-beams within a parallel process laser drilling system. In this regard, a nozzle plate of an ink-jet head may be constructed with the laser drilling system of the present invention as further detailed in FIGS. 6 and 7. 
     As shown in FIG. 6, an ink-jet printer  640  has an ink-jet head  641  capable of recording on a recording medium  642  via a pressure generator. Ink droplets emitted from ink-jet head  641  are deposited on the recording medium  642 , such as a sheet of copy paper, so that recording can be performed on the recording medium  642 . 
     The ink-jet head  641  is mounted on a carriage  644  capable of reciprocating movement along a carriage shaft  643 . More specifically, the ink-jet head  641  is structured such that it can reciprocate in a primary scanning direction X in parallel with the carriage shaft  643 . The recording medium  642  is timely conveyed by rollers  645  in a secondary scanning direction Y. The ink-jet head  641  and the recording medium  642  are relatively moved by the rollers  645 . 
     Turning now to FIG. 7, further details in in-jet head  641  are shown. Pressure generator  704  is preferably a piezoelectric system, a thermal system, and/or equivalent system. In this embodiment, the pressure generator  704  corresponds to a piezoelectric system which comprises an upper electrode  701 , a piezoelectric element  702 , and an under electrode  703 . 
     A nozzle plate  714  (an instance of workpiece  155 ) comprises a nozzle substrate  712  and a water repellent layer  713 . The nozzle substrate  712  is made of metal, resin and/or equivalent material. The water repellant layer is made of fluororesin or silicone resin. In this embodiment, the nozzle substrate  712  is made of stainless steel and has a thickness of 50 um, and the water repellent layer is made of a fluororesin and has a thickness of 0.1 um. 
     The ink-jet ink is filled in an ink supplying passage  709 , a pressure chamber  705 , an ink passage  711 , a nozzle  710 . Ink droplets  720  are ejected from nozzle  710  as pressure generator  704  pushes on pressure chamber element  706 . 
     As a result of the present invention, very good nozzles are formed without flash and foreign matter (carbon etc) in the nozzle plate. Further, the accuracy of the nozzle outlet diameter is 20 um±1.5 um (a preferred predefined acceptable threshold value for tolerance between the perimeter and the excision edge of the 20 um diameter nozzle outlet). 
     From the foregoing it will be understood that the present invention provides an alignment system and method for aligning a microfilter which is then used in a system cutting a workpiece with a laser cutting tool with a high degree of precision in the quality of the conformance of the dimensions of the removed portion to the dimensions of the design used in the cutting operation with special value in using a laser to mill exit holes in inkjet nozzles. While the invention has been described in its presently preferred form, it will be understood that the invention is capable of certain modification without departing from the spirit of the invention as set forth in the appended claims.