Apparatus for forming a homogeneous intensity distribution with bright or dark edges - Patent 7323633

Abstract

A beam homogenizer (30) for modifying a beam of laser radiation into a flat-top intensity distribution with brighter or darker edges comprises a first lens array (32), a second lens array (14), and a positive lens (16). The first lens array (32) includes a plurality of lens elements (20) separated by gaps (34) having no optical power. The brighter or darker edges are produced by selecting a distance between the first and second lens arrays that is less than or greater than the focal length of the lens elements in the second lens array.

Description

[Technical field]

[0001] This application claims priority to U.S. Provisional Application No. 62 / 817,331, filed March 12, 2019, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates generally to shaping light from a laser, and more particularly to shaping light from one or more lasers into a beam of radiation having a uniform cross-section with brighter or darker edges. [Background technology]

[0003] Lasers have become an essential source for uniform illumination in a wide range of applications including surface inspection of semiconductor materials, thermal annealing of display screen glass, metal hardening, and rapid assay of biomedical fluids. A common requirement is an elongated beam of laser radiation that uniformly illuminates a line on a flat surface or plane within a volume of a transparent material. Such an elongated beam of laser radiation is generally referred to as a "line beam."

[0004] Diode lasers are efficient devices for converting electrical power into coherent optical power. For high power applications, diode laser bars with multiple diode laser emitters provide a convenient way to scale the optical power available from a single diode laser emitter. The diode laser emitters are spaced apart and arranged in a linear array. Diode laser bars inherently have an elongated emission cross section, but need to overcome the non-uniform intensity distribution resulting from emission from multiple spatially distributed diode laser emitters.

[0005] An optical device for modifying a laser beam to make the intensity uniform across the cross section of the transformed beam is generally referred to as a "beam homogenizer". A beam homogenizer often includes one or two "microlens arrays" with multiple lenslets, each of which is much smaller than the incident beam. Each microlens is an illumination source that contributes to the transformed beam. The "pitch" of the beam homogenizer is the distance between the centers of adjacent microlenses. Additional optics are required to collect and shape the multiple beams emanating from all the microlenses that intercept the incident beam. A linear array of microlenses can be used as a beam homogenizer for an elongated beam of laser radiation emitted by a diode laser bar. One example of such a beam homogenizer is described in U.S. Pat. No. 7,265,908.

[0006] Diode-pumped solid-state lasers, including fiber lasers, typically produce a Gaussian intensity distribution. A Gaussian laser beam can be converted to a nearly uniform intensity distribution by a Powell lens or equivalent optics and then homogenized using a lens array. Collimated laser beams from multiple such diode-pumped solid-state lasers can be combined and homogenized using a lens array.

[0007] Slab lasers are diode-pumped solid-state lasers, gas discharge CO 2 Lasers include excimer lasers. Slab lasers essentially produce a line beam. However, the line beam may not be uniform in cross section and the cross-sectional intensity distribution may be unstable. Lens arrays are used to homogenize the line beam from slab lasers and to combine the line beams from multiple slab lasers.

[0008] In processes involving heating a portion of a workpiece by laser illumination, a perfectly uniform cross-sectional intensity distribution may not produce uniform laser processing due to heat transfer away from the illuminated portion. Illumination with a laser beam having a higher intensity at the edge of the intensity distribution may be preferred to ensure uniform heating. In other processes requiring multiple passes of a line beam to illuminate many areas on a workpiece, adjacent passes with some overlap will ensure complete exposure but may result in differences in processing between portions illuminated once and portions illuminated twice. Illumination with a laser beam having a lower intensity at the edge of the intensity distribution may be preferred to prevent overexposure.

[0009] A need exists for a beam shaping device for shaping a laser beam having an otherwise uniform cross-sectional intensity distribution with brighter or darker edges. Preferably, the optical device would have the precision, simplicity, and compactness of a lens array homogenizer. Summary of the Invention [Means for solving the problem]

[0010] In one aspect, a beam homogenizer according to the present invention comprises a first lens array having a plurality of identical lens elements, each lens element of the first lens array having a focal length F 1 Adjacent lens elements of the first lens array are separated by gaps, each gap having a common width. A second lens array is provided. Each lens element of the second lens array has a focal length F 2 The first lens array and the second lens array have F 2 A positive lens is provided and located on the optical axis. The positive lens has a focal length F 3 In order, the first lens array, the second lens array, and the positive lens are arranged along the optical axis.

[0011] In another aspect, a beam homogenizer according to the present invention includes a first lens array having a plurality of identical lens elements, each lens element of the first lens array having a flat central portion and a curved outer portion, the central portion having no optical power and the outer portion having a focal length F 1 A second lens array is provided, each lens element of the second lens array having a focal length F 2 The first lens array and the second lens array have F 2 A positive lens is provided, which is located on the optical axis and has a focal length F 3 In order, the first lens array, the second lens array, and the positive lens are arranged along the optical axis.

[0012] In yet another aspect, the laser radiation propagates sequentially through the lens elements and gaps of the first lens array, through the second lens array, and through the positive lens onto the illumination plane. The illumination plane is a distance F from the positive lens. 3 Laser radiation propagating through the lens elements of the first lens array has a different magnification at the illumination plane than laser radiation propagating through the gaps of the first lens array.

[0013] In yet another aspect, the laser radiation propagates sequentially through the first lens array, through the second lens array, and through the positive lens onto the illumination plane, the illumination plane being a distance F from the positive lens. 3 The laser radiation on the illumination plane is transformed into a homogenized intensity distribution with brighter or darker edges in an otherwise uniform intensity distribution. The present invention provides, for example, the following: (Item 1) 1. A beam homogenizer comprising: A first lens array, the first lens array having a plurality of identical lens elements, each lens element of the first lens array having a focal length F 1 a first lens array having adjacent lens elements of the first lens array separated by gaps, each gap having a common width; A second lens array, each lens element of the second lens array having a focal length F 2 The first lens array and the second lens array have F 2 a second lens array separated by a distance unequal to Focal length F3 a positive lens located on an optical axis having a first lens array, a second lens array, and a positive lens arranged along the optical axis, in that order; A beam homogenizer comprising: (Item 2) The first lens array and the second lens array are F 2 2. The beam homogenizer of claim 1, separated by a distance greater than (Item 3) The first lens array and the second lens array are F 2 2. The beam homogenizer of claim 1, separated by a distance that is less than (Item 4) The first lens array and the second lens array are spaced apart by a distance F 2 It is separated only into ±δ, and δ is F 2 2. The beam homogenizer according to claim 1, wherein the optical axis of the beam homogenizer is less than 10% of the optical axis of the beam homogenizer. (Item 5) δ is F 2 5. The beam homogenizer according to claim 4, wherein the optical axis of the beam homogenizer is less than 5% of the optical axis of the beam homogenizer. (Item 6) 6. The beam homogenizer of any one of claims 1 to 5, wherein the gaps between adjacent lens elements of the first lens array are empty gaps or air gaps. (Item 7) 6. The beam homogenizer of any one of claims 1 to 5, wherein the gaps between adjacent lens elements of the first lens array are made from the same material as the lens elements of the first lens array. (Item 8) 8. The beam homogenizer of claim 7, wherein the material from which the gaps and the lens elements of the first array are made is transparent glass or polymer. (Item 9) 9. The beam homogenizer of any one of claims 1 to 8, wherein the gaps between adjacent lens elements of the first lens array fixedly connect the adjacent lens elements. (Item 10) 10. The beam homogenizer of any one of items 1 to 9, wherein the gaps between adjacent lens elements of the first lens array have no optical power. (Item 11) Item 11. The beam homogenizer of item 10, wherein the gaps between adjacent lens elements of the first lens array are in the form of slabs having plane-parallel faces. (Item 12) Item 11. The beam homogenizer of item 10, wherein the gaps between adjacent lens elements of the first lens array are in the form of wedges having non-parallel planar surfaces. (Item 13) The gap between adjacent lens elements of the first lens array is F 1 6. The beam homogenizer according to any one of claims 1 to 5, wherein the beam homogenizer is occupied by an optical element having a focal length at least 5 times longer than the focal length of the first optical element. (Item 14) A distance F from the second lens array 2 An image having a repeating pattern of wider and narrower bands located in an image plane at a distance F from the positive lens. 3 14. The beam homogenizer according to any one of items 1 to 13, wherein the beam homogenizer is imaged onto an illumination plane located at. (Item 15) Item 15. The beam homogenizer of any one of items 1 to 14, wherein the first lens array is configured and arranged to be translated longitudinally parallel to the optical axis. (Item 16) 1. A beam homogenizer comprising: A first lens array having a plurality of identical lens elements, each lens element of the first lens array having a flat central portion and a curved outer portion, the central portion having no optical power and the outer portions having a focal length F 1 A first lens array having A second lens array, each lens element of the second lens array having a focal length F 2 The first lens array and the second lens array have F 2 a second lens array separated by a distance unequal to Focal length F 3 a positive lens located on an optical axis having a first lens array, a second lens array, and a positive lens arranged along the optical axis, in that order; A beam homogenizer comprising: (Item 17) Item 17. The beam homogenizer of item 16, wherein the first lens array is constructed and arranged to be translated longitudinally parallel to the optical axis. (Item 18) 1. A beam homogenizer for laser radiation, comprising: a first lens array having a plurality of identical lens elements, adjacent lens elements of the first lens array being separated by gaps, each gap having a common width; A second lens array, each lens element of the second lens array having a focal length F 2 The first lens array and the second lens array have F 2 a second lens array separated by a distance unequal to Focal length F 3 wherein the laser radiation propagates sequentially through lens elements and gaps of the first lens array, through the second lens array, through the positive lens, and onto an illumination plane, the illumination plane being a distance F from the positive lens. 3 A positive lens located at wherein laser radiation propagating through the lens elements of the first lens array has a different expansion at the illumination plane than laser radiation propagating through the gaps in the first lens array. (Item 19) The first lens array and the second lens array are F 2 19. The beam homogenizer of claim 18, wherein the laser radiation propagates through lens elements of the first lens array by a distance greater than 100 nm, and the laser radiation propagates through the lens elements of the first lens array thereby having a smaller magnification than laser radiation propagating through the gaps of the first lens array. (Item 20) The first lens array and the second lens array are F 2 20. The beam homogenizer of claim 18, wherein the laser radiation propagates through lens elements of the first lens array by a distance that is less than 100 nm, and the laser radiation propagates through the lens elements of the first lens array, thereby having a greater magnification than laser radiation propagating through the gaps of the first lens array. (Item 21) 1. A beam homogenizer for laser radiation, comprising: a first lens array having a plurality of identical lens elements, adjacent lens elements of the first lens array being separated by gaps, each gap having a common width; A second lens array, each lens element of the second lens array having a focal length F 2 The first lens array and the second lens array have F 2 a second lens array separated by a distance unequal to Focal length F 3 wherein the laser radiation propagates sequentially through the first lens array, through the second lens array, through the positive lens, and onto an illumination plane, the illumination plane being a distance F from the positive lens. 3 and a positive lens, which converts the laser radiation on the illumination plane into a homogenized intensity distribution with brighter or darker edges in an otherwise uniform intensity distribution. A beam homogenizer comprising: [Brief description of the drawings]

[0014] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

[0015] [Figure 1A] 1A is a plan view diagrammatically illustrating a prior art beam homogenizer having a first lens array, a second lens array, and a positive lens. Collimated laser radiation propagating parallel to the optical axis is incident on the first lens array and propagates through the beam homogenizer.

[0016] [Figure 1B] Figures 1B and 1C are plan views that diagrammatically illustrate imaging through the beam homogenizer of Figure 1 A. Inverted and magnified images of each lens element in the first lens array are formed and superimposed at the illumination plane. [Figure 1C] Figures 1B and 1C are plan views that diagrammatically illustrate imaging through the beam homogenizer of Figure 1 A. Inverted and magnified images of each lens element in the first lens array are formed and superimposed at the illumination plane.

[0017] [Figure 2A] 2A-2C are plan views diagrammatically illustrating one preferred embodiment of a beam homogenizer according to the present invention. The beam homogenizer of the present invention comprises a first lens array, a second lens array, and a positive lens. Each lens element of the first lens array is separated by a gap having no optical power. The distance between the first lens array and the second lens array is slightly greater than the focal length of each lens element of the second lens array. [Figure 2B]2A-2C are plan views diagrammatically illustrating one preferred embodiment of a beam homogenizer according to the present invention. The beam homogenizer of the present invention comprises a first lens array, a second lens array, and a positive lens. Each lens element of the first lens array is separated by a gap having no optical power. The distance between the first lens array and the second lens array is slightly greater than the focal length of each lens element of the second lens array. [Figure 2C] 2A-2C are plan views diagrammatically illustrating one preferred embodiment of a beam homogenizer according to the present invention. The beam homogenizer of the present invention comprises a first lens array, a second lens array, and a positive lens. Each lens element of the first lens array is separated by a gap having no optical power. The distance between the first lens array and the second lens array is slightly greater than the focal length of each lens element of the second lens array.

[0018] [Figure 3A] Figures 3A and 3B are plan views diagrammatically illustrating another preferred embodiment of a beam homogenizer according to the present invention, which is similar to the embodiment of Figures 2A-2C, but in which the distance between the first lens array and the second lens array is slightly less than the focal length of each lens element of the second lens array. [Figure 3B] Figures 3A and 3B are plan views diagrammatically illustrating another preferred embodiment of a beam homogenizer according to the present invention, which is similar to the embodiment of Figures 2A-2C, but in which the distance between the first lens array and the second lens array is slightly less than the focal length of each lens element of the second lens array.

[0019] [Figure 4A] FIG. 4A diagrammatically illustrates the intensity distribution in the illumination plane for a beam of laser radiation propagating through the beam homogenizer of FIGS. 2A-2C.

[0020] [Figure 4B]FIG. 4B diagrammatically illustrates the intensity distribution in the illumination plane for a beam of laser radiation propagating through the beam homogenizer of FIGS. 3A and 3B.

[0021] [Figure 5A] 5A and 5B are plan views that diagrammatically illustrate the effect of diffraction on a beam of laser radiation propagating through the beam homogenizer of FIGS. 2A-2C. [Figure 5B] 5A and 5B are plan views that diagrammatically illustrate the effect of diffraction on a beam of laser radiation propagating through the beam homogenizer of FIGS. 2A-2C.

[0022] [Figure 6A] FIG. 6A diagrammatically illustrates a camera image of the intensity distribution in the illumination plane for a beam of laser radiation propagating through the example beam homogenizer of FIGS. 3A and 3B.

[0023] [Figure 6B] FIG. 6B is a graph that diagrammatically illustrates the intensity distribution along line AA in FIG. 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring now to the drawings, in which like components are designated by like numerals, Figure 1A diagrammatically illustrates a prior art beam homogenizer 10 having a first linear lens array 12, a second linear lens array 14, a positive lens 16, and an optical axis 18. Each identical lens element 20 of lens array 12 has a focal length F 1 and each identical lens element 22 in the lens array 14 has a focal length F 2 and the lens 16 has F 3 Each lens element 20 and 22 has a common width d. Lens array 12 and lens array 14 are spaced apart by a distance F. 2The drawing depicts rays 24 of laser radiation propagating through the beam homogenizer 10. In this example, the laser radiation incident on the lens array 12 is collimated and propagating parallel to the optical axis 18.

[0025] 1B and 1C diagrammatically illustrate imaging through beam homogenizer 10. An inverted, magnified image 26 of the laser radiation incident on each lens element 20 is formed in illumination plane 28, which is a distance F from lens 16. 3 The inverted magnified images 26 of all illuminated lens elements 20 are superimposed in an illumination plane 28 and have a width D. FIG. 1B depicts the imaging of light rays emanating from the center of each lens element 20. FIG. 1C depicts the imaging of light rays emanating from the center of each lens element 20 at a distance X 1 These rays are displaced a distance X from the optical axis 18. 2 The image is projected onto a location in the illumination plane 28 displaced by a factor of 1. [ka] It is.

[0026] The lens array 12 does not directly affect the homogenization and has a focal length F 1 does not determine the magnification. The purpose of the lens array 12 is to increase the acceptance angle for the rays 24 incident on the beam homogenizer 10. Although the incident rays 24 are depicted parallel to the optical axis 18, they can be incident at a maximum angle relative to the optical axis while still projecting overlapped images onto the illumination plane 28. At the maximum acceptance angle, the peripheral rays focused by each lens element 20 can be incident on the edge of the corresponding lens element 22. There is a compromise between this maximum acceptance angle and the area of ​​each lens element 22 that is illuminated. F 2 For F 1 Reducing φ increases this area, thereby reducing the vulnerability of lens element 22 to optical damage, while also reducing the maximum acceptance angle.

[0027] 2A-2C diagrammatically illustrate one preferred embodiment of a beam homogenizer 30 according to the present invention. The beam homogenizer 30 has adjacent lens elements 20 of a first lens array 32 separated by the same gap 34, and the separation between the first lens array 32 and the second lens array 14 is a distance F 2 Each lens element 20 has a common width d 1 Each gap 34 has a common width d 2 and each lens element 22 has a common width d=d 1 +d 2 The distance δ is the focal length F 2 For example, δ is preferably small compared to F 2 More preferably, δ is less than 20% of F 2 and most preferably less than 10% of F 2 It is less than 5% of the total.

[0028] The gaps 34 are depicted as empty gaps or "air gaps." The gaps 34 may also be made of transparent glass or polymer. The gaps 34 are most preferably made of the same material as the lens elements 20, have plane-parallel surfaces, and therefore have no refractive power. In general, it may be practical to mill or mold the lens array 32 from a single piece of material, with each gap fixedly connecting neighboring lens elements. FIG. 2A depicts a ray 24 of laser radiation propagating through the lens elements 20. FIG. 2B depicts a ray 36 of laser radiation propagating through the gap 34. FIG. 2C has a close-up view of both the ray 24 (solid lines) and the ray 36 (dashed lines) around the illumination plane 28 and around the lens array 32.

[0029] To explain imaging through the beam homogenizer 30 of the present invention, it is useful to consider ray matrix analysis, or ABCD matrix analysis, as is known in the optical arts. First, referring to FIG. 1C, the ray matrix for focusing by lens 16 and propagation between lens 16 and illumination plane 28 is:

number

number

number

number

number

[0030] When δ=0, which corresponds to an “ideal imaging” of the beam homogenizer 10, Equation 5 simply becomes:

number

[0031] 2A, inverted images 26 of all illuminated lens elements 20 are superimposed in an illumination plane 28. The images 26 are [ka] Therefore, the width [ka] 2B, the inverted images 40a and 40b of all illuminated gaps 34 are also superimposed in the illumination plane 28. The two gap images are split according to the lens elements 22 of the lens array 14 on which the respective light rays are incident. Both gap image 40a and gap image 40b have [ka] Therefore, each gap image is magnified by [ka] 2C, the smaller absolute magnification of image 26 produces dark gaps between image 26 and gap images 40a and 40b.

[0032] It is insightful to consider the beam homogenizer 30 in terms of the ideal imaging described above. Within the beam homogenizer 30, a distance F 2 An image plane 38 located at is precisely imaged onto the illumination plane 28 by the lens array 14 and the lenses 16. The image plane 38 is illuminated by converging light rays 24 focused by the lens elements 20 and parallel light rays 36 propagating through the gap 34. The illumination of the image plane 38 is a repeating pattern of wider and narrower bands, which is depicted in FIG. 2C. The illumination of the image plane 38 is [ka] , is projected and superimposed by lens array 14 and lens 16 onto illumination plane 28 with a magnification of .

[0033] The two presented descriptions of the beam homogenizer 30, one using a ray matrix and the other in terms of ideal imaging, are equivalent. The homogenizer produces a uniform or "flat-top" intensity distribution in the illumination plane, with reduced intensity towards the edges of the otherwise uniform intensity distribution. The relative location and width of the dark gaps in the intensity distribution depend on the focal length F. 1 , gap width d 2 , and the distance δ.

[0034] 3A and 3B diagrammatically illustrate another preferred embodiment of a beam homogenizer 50 according to the present invention. The beam homogenizer 50 has a smaller separation distance F between the lens array 32 and the lens array 14. 2 The beam homogenizer 50 is similar to the beam homogenizer 30 except that the beam homogenizer 50 has a ray matrix analysis identical to that for the beam homogenizer 30. The image 26 is [ka] The width is expanded by [ka] , on the other hand, width [ka] 3B. Thus, for ray 24 incident on lens element 20, the absolute magnification is greater than for ray 36 incident on gap 34. This greater magnification creates an overlap between image 26 and gap images 40a and 40b. The overlap creates two bright peaks toward the edge of the otherwise uniform intensity distribution. For convenience of illustration, the image on illumination plane 28 is depicted in FIG. 3B with the rays propagating through lens element 20 and the rays propagating through gap 34 differentiated by their respective left and right offsets.

[0035] From an ideal imaging perspective, the image plane 38 is located in the path of the light rays 24 incident on the lens elements 20 and the light rays 36 incident on the gaps 34, prior to the lens array 32. Again, for ease of illustration, the illumination of the image plane 38 by the light rays 24 and 36 are distinguished by their respective left and right offsets. The image plane 38 is uniformly illuminated, but the portion of the plane illuminated by the light rays 36 (right offset) is imaged through both the lens elements 20 and the gaps 34. For example, the dashed light rays 52 depicted on the lens elements 20 result from the portion of the image plane illuminated by the light rays 36. The portion imaged through both the lens elements and the gaps appears brighter when projected onto the illumination plane 28. The beam homogenizer 50 thereby produces a uniform intensity distribution in the illumination plane with increased intensity towards the edges.

[0036] 4A diagrammatically illustrates a nominally uniform intensity distribution in illumination plane 28 with dark gaps towards the edges of the intensity distribution produced by beam homogenizer 30. The overall intensity distribution is depicted with thick lines, and the lower intensity distribution produced by the light rays propagating through lens element 20 and gap 34 is depicted with thinner lines. Similarly, FIG. 4B diagrammatically illustrates a nominally uniform intensity distribution in illumination plane 28 with bright peaks towards the edges of the intensity distribution produced by beam homogenizer 50. The overall width D of the intensity distribution is the width of the gap d 2 Note that D is independent of the distance δ. 1 +2D 2 Therefore, dark gaps appear in the intensity distribution of FIG. 4A. <D 1 +2D 2 , a bright peak appears in the intensity distribution of FIG. 4B.

[0037] A beam homogenizer having a lens array 32 constructed and arranged to be translated longitudinally parallel to the optical axis 18 can be adjusted to produce a continuum of intensity distributions with darker edges (as in FIG. 4A ) or lighter edges (as in FIG. 4B ) or completely uniform intensity. These intensity distributions have a constant overall width D and a constant distance D at the edges.2 Mechanical devices for precise linear translation of optical systems are commercially available, and a detailed description of such devices is not necessary for understanding the principles of the present invention. The intensity distribution with the darker edges is similar to that with the dark gap distance D. 1 The intensity distribution with brighter edges may have a slightly higher intensity over the distance D between the bright peaks. 1 The lens array 32 may have a slightly lower intensity over the width d 1 Small width d compared to 2 These intensity differences are relatively small when the gap 34 has a ratio [ka] is less than 0.12, or the ratio [ka] is less than 0.06.

[0038] 5A and 5B diagrammatically illustrate some effects of diffraction on the beam homogenizer 30 of FIGS. 2A-2C. Diffraction can occur at the edges of each lens element 20 of the lens array 32 (this is the depicted example). Light rays propagating through the gaps 34 and near neighboring lens elements 20 become angularly dispersed. Light rays passing very close to the lens elements 20 become dispersed over a circumferential angle φ. Note that the edge intensity distribution caused by diffraction is not uniform, rather, the diffracted intensity decreases with increasing angle. The circumferential angle φ is differentiated here to illustrate this effect of diffraction. Also, note that the diffracted light rays can be directed toward one of two lens elements 22, either the lens element 22 corresponding to the diffractive lens element 20 or another lens element 22 in the neighborhood of the corresponding lens element. Both of these lens elements 22 are located within the circumferential angle φ.

[0039] FIG. 5A depicts only the diffracted rays propagating through corresponding lens elements 22 of lens array 14. These rays are projected onto the same range of locations in illumination plane 28 as in the absence of diffraction. FIG. 5B depicts only the diffracted rays propagating through neighboring lens elements 22. These rays are projected onto a range of locations in illumination plane 28 that would be outside of the nominally uniform intensity distribution in the absence of diffraction. Overall, diffraction reduces the distance D inside each edge of the nominally uniform intensity distribution. 2 The illumination is slightly reduced over a distance D outside each edge of the intensity distribution. 2 Therefore, the edge contrast is reduced due to diffraction.

[0040] FIG. 6A diagrammatically illustrates a camera image of an intensity distribution obtained using the experimental beam homogenizer 50. The image is expanded in the vertical dimension relative to the horizontal dimension. The beam homogenizer was partially illuminated with a collimated beam from an excimer laser. The lens array 32 has 25 lens elements 20, and most of these lens elements were illuminated. The lens array 32 is proportionally [ka] and width d=d 1 +d 2 was a few millimeters. FIG. 6B is a graph illustrating diagrammatically the measured intensity distribution along line AA superimposed on FIG. 6A. FIGS. 6A and 6B are shown to the same horizontal scale. The measured intensity distribution has bright peaks at each edge and relatively uniform intensity between the bright peaks. By translating the lens array 32 vertically and varying the distance δ, we demonstrated a continuous evolution from a perfectly uniform intensity distribution when δ was about 0 mm to an intensity distribution that can be described as having bright edges when δ was about 9 mm.

[0041] Although gaps in the first lens array having no refractive power have been illustrated and described herein, a requirement for producing an intensity distribution with dark gaps or bright peaks is a "gap" 34 in the first lens array having a refractive power substantially less than the refractive power of the lens elements 20 in the first lens array 32. For example, the gap 34 may be occupied by a weaker lens element, the weaker lens element having a focal length F of the lens elements 20. 1 Increasing the focal length of the weaker lens element increases the contrast between the dark gaps or bright peaks and the uniform parts of the intensity distribution.

[0042] The gaps 34 in the first lens array, which has no refractive power, may have the form of a slab with plane-parallel faces. Such a slab may not modify the angle of the light rays propagating through it. Alternatively, the gaps 34 may have the form of a wedge, which has a plane but is not parallel. The wedge angle may be another variable that may be selected to position dark gaps or bright peaks in an otherwise uniform intensity distribution, either toward or away from the optical axis.

[0043] Yet another preferred embodiment of a beam homogenizer apparatus for producing the intensity distribution depicted in Figures 4A and 4B may be similar to the beam homogenizer of Figures 3A and 2A, but with the first lens array 32 replaced by a different inventive lens array. This different inventive lens array may be fabricated from the prior art lens array 12 by machining flat a central portion of each lens element. The resulting lens array may have a plurality of identical lens elements, each of which may have a flat central portion and a curved outer portion. The central portion may have no optical power, and the outer portions may have a focal length F. 1The light rays passing through the flat portion may be imaged onto the illumination plane with a different magnification than the light rays passing through the curved portion. An advantage of this beam homogenizer embodiment is that the first lens array may be fabricated by simply grinding and polishing a prior art lens array that is commercially available. For example, Thorlabs (Newton, New Jersey). A disadvantage of this embodiment is that it has a smaller acceptance angle for the light rays incident on the beam homogenizer.

[0044] The ray matrix analysis presented herein above assumes thin lenses and uses the paraxial approximation. Analysis using these assumptions is sufficient to explain the principles and operation of the present invention. Those skilled in the art will recognize that precise calculations must properly account for the geometry of the optical elements, and will recognize when to include these additional parameters.

[0045] In summary, a beam of laser radiation can be converted into a homogenized intensity distribution having brighter or darker edges within an otherwise uniform intensity distribution using the beam homogenizer of the present invention. The beam homogenizer includes a first lens array having a plurality of identical lens elements separated by gaps having a common width. The second lens array has a focal length F 2 The first and second lens arrays have a plurality of identical lens elements having F 2 are separated by a distance close to, but not equal to, F 2 A separation distance of less than F produces a bright peak. 2 A separation distance greater than 0.05 produces dark gaps, which are located towards the edges of the intensity distribution.

[0046] The present invention is described above in terms of preferred and alternative embodiments. However, the present invention is not limited to the embodiments described and depicted herein. Rather, the present invention is limited only by the claims appended hereto.

Claims

1. 1. A beam homogenizer, comprising: A first lens array, the first lens array having a plurality of identical lens elements, each lens element of the first lens array having a focal length F １ a first lens array having adjacent lens elements of the first lens array separated by gaps, the gaps having no optical power, and each gap having a common width; A second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F ２ and the first lens array and the second lens array are spaced apart by a distance F ２ a second lens array separated by ±δ; a positive lens disposed on the optical axis, the positive lens having a focal length F ３ the first lens array, the second lens array, the positive lens, and the illumination plane are arranged in sequence along the optical axis, and the illumination plane is a distance F from the positive lens. ３ A positive lens is placed at the Equipped with F １ , F ２ , F ３ , δ is the distance X from the center of the lens element of the first lens array １ A ray of light incident on the lens element at a position of a distance X from the optical axis ２ is selected to be projected onto the illumination plane at a position X ２ teeth, [Number 100] and δ≠0.

2. The first lens array and the second lens array are F ２ Distance F is greater than ２ 2. The beam homogenizer of claim 1, wherein the first and second radians are separated by +δ.

3. The first lens array and the second lens array are F ２ Distance F smaller than ２ 2. The beam homogenizer of claim 1, separated by −δ.

4. δ is F ２ 2. The beam homogenizer of claim 1, wherein the .lambda.-dimension is less than 10% of the .lambda.-dimension.

5. δ is F ２ 5. The beam homogenizer of claim 4, wherein the .lambda.-dimension is less than 5% of the .lambda.-dimension.

6. The beam homogenizer of any one of claims 1 to 5, wherein the gaps between adjacent lens elements of the first lens array are empty gaps or air gaps.

7. 6. The beam homogenizer of claim 1, wherein the gaps between adjacent lens elements of the first lens array are made from the same material as the lens elements of the first lens array.

8. 8. The beam homogenizer of claim 7, wherein the material from which the gap and the plurality of lens elements of the first lens array are made is a transparent glass or polymer.

9. The beam homogenizer of any one of claims 1 to 8, wherein the gaps between adjacent lens elements of the first lens array fixedly connect the adjacent lens elements.

10. 10. The beam homogenizer of claim 1, wherein the gaps between adjacent lens elements of the first lens array are in the form of slabs having plane-parallel faces.

11. 10. The beam homogenizer of claim 1, wherein the gaps between adjacent lens elements of the first lens array are in the form of wedges having non-parallel planar faces.

12. A distance F from the second lens array ２ 12. The beam homogenizer according to claim 1, wherein an image having a repeating pattern of wider and narrower bands arranged in an image plane at is imaged onto the illumination plane.

13. A beam homogenizer according to any preceding claim, wherein the first lens array is constructed and arranged to be translated longitudinally parallel to the optical axis.

14. 1. A beam homogenizer comprising: A first lens array, the first lens array having a plurality of identical lens elements, each lens element of the first lens array having a flat central portion and a curved outer portion, the central portion having no optical power, and the outer portions having a focal length F １ A first lens array having A second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F ２ The first lens array and the second lens array have a structure of F ２ a second lens array separated by a distance not equal to a positive lens disposed on the optical axis, the positive lens having a focal length F ３ a positive lens, wherein the first lens array, the second lens array, and the positive lens are sequentially arranged along the optical axis; A beam homogenizer comprising:

15. 15. The beam homogenizer of claim 14, wherein the first lens array is constructed and arranged to be translated longitudinally parallel to the optical axis.

16. 1. A beam homogenizer for laser radiation, the beam homogenizer comprising: A first lens array, the first lens array having a plurality of identical lens elements, each lens element of the first lens array having a focal length F １ a first lens array having adjacent lens elements of the first lens array separated by gaps, the gaps having no optical power, and each gap having a common width; A second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F ２ and the first lens array and the second lens array are spaced apart by a distance F ２ a second lens array separated by ±δ; Focal length F ３ wherein the laser radiation propagates through the lens elements and the gaps of the first lens array, through the second lens array, and through the positive lens onto an illumination plane, the illumination plane being a distance F from the positive lens. ３ A positive lens is placed at the Equipped with laser radiation propagating through the lens elements of the first lens array has a different magnification at the illumination plane than laser radiation propagating through the gaps of the first lens array; F １ , F ２ , F ３ , δ is the distance X from the center of the lens element of the first lens array １ A ray of light incident on the lens element at a position of a distance X from the optical axis ２ is selected to be projected onto the illumination plane at a position X ２ teeth, [Number 101] and δ≠0.

17. The first lens array and the second lens array are F ２ Distance F is greater than ２ 20. The beam homogenizer of claim 16, wherein the beams are separated by +δ.

18. The first lens array and the second lens array are F ２ Distance F smaller than ２ 17. The beam homogenizer of claim 16, separated by -δ.

19. 1. A beam homogenizer for laser radiation, comprising: a first lens array having a plurality of identical lens elements, adjacent lens elements of the first lens array being separated by gaps, each gap having a common width; A second lens array, the second lens array having a plurality of identical lens elements, each lens element of the second lens array having a focal length F ２ The first lens array and the second lens array have a structure of F ２ a second lens array separated by a distance not equal to Focal length F ３ wherein the laser radiation propagates through the lens elements and the gaps of the first lens array, through the second lens array, and through the positive lens onto an illumination plane, the illumination plane being a distance F from the positive lens. ３ and a positive lens, the positive lens being disposed at a position such that the laser radiation on the illumination plane is transformed into a homogenized intensity distribution having lighter or darker edges and a uniform intensity distribution between the lighter or darker edges. A beam homogenizer comprising:

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