Systems and methods for generating flat-topped illumination beams based on staggered, incoherent overlapping spots

Abstract

A flat-topped beam generation system may include a beam splitting device that includes one or more beam splitters to split an input beam into three or more sub-beams that propagate along optical paths having different optical path lengths. The system may further include a diffractive optical element (DOE) to diffract the three or more sub-beams into a plurality of diffracted sub-beams. The system may further include one or more optical elements configured to collect the plurality of diffracted sub-beams to provide a flat-topped beam.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 413,631, filed on October 6, 2022, and whose inventor is ChunShen Lee, under 35 U.S.C. §119(e), the entire text of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to generating a light beam having a flat top illumination profile, and more particularly to generating a light beam having a flat top illumination profile by incoherent combination of laser spots. Background Art

[0004] Laser sources typically generate light with a non-uniform spatial profile, such as, but not limited to, a Gaussian profile. However, a uniform spatial profile, often referred to as a flat-top profile, is beneficial for many applications, including, but not limited to, optical inspection.

[0005] There are certain challenges in producing a flat-top illumination profile using coherent light, such as laser light. For example, techniques based on beam shaping may depend heavily on the beam quality and / or shape of the initial beam, and thus may not tolerate variations in such parameters. As another example, interference between different portions of the shaped beam may exhibit speckle, which may produce an unstable non-uniformity distribution.

[0006] Therefore, it is necessary to develop a system and method for solving the above-mentioned deficiencies. Summary of the invention

[0007] According to one or more illustrative embodiments of the present disclosure, a system is disclosed. In an embodiment, the system includes a beam splitting device, the beam splitting device includes one or more beam splitters to split an input beam into three or more sub-beams, the sub-beams propagating along optical paths with different optical path lengths. In an embodiment, the system includes a diffractive optical element (DOE) configured to diffract the three or more sub-beams into diffracted sub-beams. In an embodiment, the system includes one or more optical elements to collect the diffracted sub-beams and provide a flat-top beam.

[0008] According to one or more illustrative embodiments of the present disclosure, a system is disclosed. In an embodiment, the system includes a laser source for generating an input beam. In an embodiment, the system includes a beam splitting device, the beam splitting device includes one or more beam splitters to split the input beam into three or more sub-beams, the sub-beams propagating along optical paths with different optical path lengths. In an embodiment, the system includes a DOE configured to diffract the three or more sub-beams into diffracted sub-beams. In an embodiment, the system includes one or more optical elements to collect the diffracted sub-beams and provide a flat-top beam.

[0009] According to one or more illustrative embodiments of the present disclosure, a method is disclosed. In an embodiment, the system includes using a beam splitting device including one or more beam splitters to split an input beam into three or more sub-beams, the sub-beams propagating along optical paths with different optical path lengths. In an embodiment, the system includes using a DOE to diffract the three or more sub-beams into a plurality of diffracted sub-beams. In an embodiment, the system includes using one or more optical elements to collect the plurality of diffracted sub-beams to provide a flat-top beam.

[0010] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0012] Figure 1A is a block diagram of a beam shaping system according to one or more embodiments of the present disclosure.

[0013] Figure 1B is a simplified schematic diagram of a beam shaping system according to one or more embodiments of the present invention.

[0014] Figure 1C is a first non-limiting configuration of a beam shaping system according to one or more embodiments of the present disclosure.

[0015] Figure 1D is a second non-limiting configuration of a beam shaping system according to one or more embodiments of the present disclosure.

[0016] Figure 1E is a third non-limiting configuration of a beam shaping system according to one or more embodiments of the present disclosure.

[0017] Figure 1Fis a fourth non-limiting configuration of a beam shaping system according to one or more embodiments of the present disclosure.

[0018] Figure 2 is a simplified spatial intensity plot of a top-hat beam in a plane of interest according to one or more embodiments of the present disclosure.

[0019] Figure 3 is a flow chart illustrating steps performed in a method for generating a flat-top beam according to one or more embodiments of the present disclosure.

[0020] Figure 4A Depicts a cross-sectional distribution of an array of temporally coherent light beams in accordance with one or more embodiments of the present disclosure.

[0021] Figure 4B Describes a method of scanning according to one or more embodiments of the present disclosure. Figure 4A Cross-sectional distribution of the effective total intensity obtained for the array in .

[0022] Figure 4C Describes one or more embodiments of the present disclosure. Figure 4B 1D cross section of the effective total intensity of the lines shown in .

[0023] Figure 5 is a simplified schematic diagram of an optical system including a beam shaping system for providing a flat-top beam according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0024] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments set forth herein are to be considered illustrative and not restrictive. It will be apparent to those skilled in the art that various changes and modifications may be made in form and details without departing from the spirit and scope of the present disclosure.

[0025] Embodiments of the present disclosure relate to systems and methods for providing a flat-top illumination profile of light from a coherent input beam. In an embodiment, a coherent input beam is split into a plurality of sub-beams that are delayed in time relative to each other. The time-delayed sub-beams are then each diffracted by a diffractive optical element (DOE) to produce a number of diffracted sub-beams, which are then collected by a lens to produce an output beam. In this configuration, the diffracted sub-beams may partially overlap so that the output beam as a whole may have a flat-top illumination profile. In addition, since the diffracted sub-beams are delayed in time relative to each other, speckle may be prohibited or at least mitigated to below a selected tolerance. In other words, the diffracted sub-beams may provide interleaved, incoherent overlapping spots (IIOS), wherein the intensity distribution of the resulting output beam may be associated with a simple summation of the intensities of the diffracted sub-beams, rather than with a sum of field amplitudes, which would otherwise result in interference and speckle generation.

[0026] Reference Figures 1A to 5 , according to one or more embodiments of the present disclosure, systems and methods for providing flat top illumination from a coherent input light beam are described in more detail.

[0027] Figure 1A is a block diagram of a beam shaping system 100 according to one or more embodiments of the present disclosure.

[0028] In an embodiment, the beam shaping system 100 includes a beam splitting subsystem 102 that splits a coherent input beam 104 into three or more sub-beams 106 that propagate along different optical paths having different optical path lengths to a diffractive optical element (DOE) 108. The DOE 108 may then diffract the sub-beam 106 into a plurality of diffracted sub-beams 110, and one or more collection optics 112 are configured to collect the diffracted sub-beams 110 to form a flat top beam 114 having a flat top illumination profile. In this configuration, the different optical path lengths of the sub-beams 106 before the DOE 108 ensure that the various diffracted sub-beams 110 that form the flat top beam 114 are mutually incoherent (e.g., uncorrelated) with respect to each other, and therefore do not interfere to form a speckle pattern. Thus, the various diffracted sub-beams 110 may be arranged in a partially overlapping configuration such that the overall intensity distribution of the flat top beam 114 may be uniform within a selected tolerance.

[0029] Figure 2 is a simplified spatial intensity plot of the top hat beam 114 in a plane of interest in accordance with one or more embodiments of the present disclosure.

[0030] In an embodiment, the intensity profile of the flat-top beam 114 may be characterized by a transition region 202 where the intensity is substantially uniform and a central region 204 where the intensity transitions sharply downward to zero or a nominally low intensity.

[0031] As used herein, the term flat top illumination profile or flat top distribution is used to indicate a uniform spatial intensity profile within the central region 204 measured in a cross-sectional plane orthogonal to the propagation direction. Additionally, the spatial intensity profile may be uniform according to any selected metric.

[0032] For example, the intensity profile of the flat top beam 114 in the plane of interest may have a peak-to-valley difference 206 that is below a selected tolerance. As another example, a statistical measure describing the variation of the intensity profile of the flat top beam 114 in the plane of interest, such as, but not limited to, a mean, a variance, a standard deviation, or a root mean square (RMS) value, may have a value that is below a selected tolerance.

[0033] Reference again Figure 1A , the beam splitting subsystem 102 may include any combination of optical elements configured to split the input light beam 104 into sub-beams 106, and further provide the various sub-beams 106 to propagate along different optical paths with different optical path lengths to the DOE 108, so that the resulting diffracted sub-beams 110 can be incoherently combined to form a flat-top beam 114. For example, the beam splitting subsystem 102 may include one or more beam splitters 116 with any splitting ratio to generate the sub-beams 106. As another example, the beam splitting subsystem 102 may include various optical elements suitable for providing different optical path lengths for the sub-beams 106, such as, but not limited to, one or more mirrors, one or more optical fibers, or one or more transparent optical elements with selected thicknesses. As another example, the beam splitting subsystem 102 may include various beam manipulation optical devices, such as, but not limited to, lenses, mirrors, polarizers, or wave plates.

[0034] The diffracted beamlets 110 may be arranged in any one-dimensional (1D) or two-dimensional (2D) distribution, such that the top-hat beam 114 may have any corresponding 1D or 2D top-hat distribution. In an embodiment, the beamlets 106 are directed to the DOE 108 at different incident angles (e.g., different azimuthal and / or polar incident angles). In this configuration, the DOE 108 may diffract each beamlet 106 into an array (e.g., a 1D or 2D array) of diffracted beamlets 110, wherein the various arrays of diffracted beamlets 110 are interleaved to form the top-hat beam 114.

[0035] The input light beam 104 may be generated by any suitable illumination source 118 configured to generate coherent light (e.g., spatially and / or temporally coherent light). In an embodiment, the illumination source 118 includes a laser source, such that the input light beam 104 is a laser beam. The input light beam 104 may further have any spectral or temporal profile. In an embodiment, the input light beam 104 is a continuous wave (CW) light beam having a relatively narrow bandwidth. In an embodiment, the input light beam 104 is a pulsed light beam having any pulse duration or spectral bandwidth.

[0036] The DOE 108 may include any optical element or combination of optical elements suitable for splitting the incident beamlet 106 into a plurality of diffracted beamlets 110. For example, the DOE 108 may include an optical element that includes a 1D or 2D distribution of features (e.g., diffraction features) that is suitable for diffracting the incident beamlet 106 into a desired distribution of diffraction orders (e.g., a desired angular distribution) that form the diffracted beamlets 110. The diffraction features may generally be characterized by any number of characteristic pitches (or spatial frequencies) along any number of directions. As an illustration, the diffraction features may include a sinusoidal diffraction grating characterized by a single pitch (e.g., a single spatial frequency) along a particular direction. More generally, however, the diffraction features may include any complex distribution of features, where any complex distribution of spatial frequencies is suitable to produce any desired spatial distribution in the near field or far field. In an embodiment, the diffraction features of the DOE 108 are arranged to provide two or more diffracted sub-beams 110 with controlled beam shapes and angular distributions. For example, the diffraction features of the DOE 108 may be arranged to provide two or more diffracted sub-beams 110 with equal intensity. As another example, the diffraction features of the DOE 108 may be arranged to provide two or more diffracted sub-beams 110 with selected unequal intensity distributions. In addition, each diffracted sub-beam 110 may have any selected beam profile, such as, but not limited to, a Gaussian beam profile or a flat-top beam profile.

[0037] Any suitable technique may be used to fabricate the diffractive features of the DOE 108. For example, the diffractive features may correspond to refractive index modulations within the volume of a transparent material, surface relief features, or reflective features (e.g., patterned metal features). Additionally, the DOE 108 may be formed as a transmissive optical device such that the diffracted beamlets 110 may exit on an opposite plane relative to the incident beamlet 106, or as a reflective optical device such that the diffracted beamlets 110 may exit on a common plane as the incident beamlet 106.

[0038] Reference Figures 1B to 1F , according to one or more embodiments of the present disclosure, the operation of the beam shaping system 100 is described in more detail.

[0039] Figure 1B is a simplified schematic diagram of a beam shaping system 100 according to one or more embodiments of the present disclosure.

[0040] In an embodiment, the beam splitting subsystem 102 splits the input beam 104 into three or more sub-beams 106 and directs the sub-beams 106 to the DOE 108 along different optical paths with different optical path lengths such that the sub-beams 106 are not temporally correlated with each other. Figures 1C to 1F The design of the beam splitting subsystem 102 is described in more detail.

[0041] In an embodiment, Figure 1B , the beam splitting subsystem 102 can direct various sub-beams 106 to a common location on the DOE 108, but at different angles of incidence. It is contemplated herein that directing the sub-beams 106 to a common location on the DOE 108 at different angles can beneficially provide a staggered array of diffracted sub-beams 110 that exit from the DOE 108. In particular, because each of the sub-beams 106 is incident on a common portion of the DOE 108 that includes a common set of diffractive features, the DOE 108 can diffract each incident sub-beam 106 into an identical 1D or 2D array of diffracted sub-beams 110, wherein the arrays are angularly shifted relative to each other based on the relative angles of incidence of the sub-beams 106.

[0042] As an illustration, Figure 1B A configuration is depicted in which the beamlets 106 all propagate within the YZ plane of the figure and are incident on the DOE 108 at different angles of incidence, so that the DOE 108 generates an array of three diffracted beamlets 110 (e.g., associated with +1 order diffraction, 0 order diffraction, and -1 order diffraction) for each incident diffracted beamlet 110. In addition, the array of diffracted beamlets 110 is staggered.

[0043] In an embodiment, one or more collection optics 112 may collect the diffracted sub-beams 110 from the DOE 108 to form a flat top beam 114. The collection optics 112 may include any type or combination of optical elements configured to receive the diffracted sub-beams 110 and direct them along a parallel optical path to form the flat top beam 114, such as, but not limited to, one or more lenses or one or more mirrors. For example, the diffracted sub-beams 110 may diverge at an angle from the DOE 108, such that the collection optics 112 are required to collect and parallelize the diffracted sub-beams 110. The one or more collection optics 112 may further direct the diffracted sub-beams 110 as the flat top beams 114 to a target plane 120 where a flat top illumination distribution is desired. The target plane 120 may be located at any location. By way of illustration, Figure 1BA configuration is depicted in which the collection optics 112 (e.g., a lens) collimates the diffracted sub-beams 110 so that they propagate in parallel and form a collimated flat-top beam 114. In this manner, the target plane 120 can correspond to any plane after the lens up to an infinite distance so that the flat-top beam 114 can have a flat-top distribution at any location after the collection optics 112. Inset 122 depicts a simplified diagram of overlapping diffracted sub-beams 110 at the target plane 120, while inset 124 depicts a simplified diagram of the total intensity distribution of the flat-top beam 114 at the target plane 120 based on the overlapping diffracted sub-beams 110.

[0044] However, it should be understood that the diffracted sub-beams 110 may have some non-zero divergence. Therefore, the term collimated is used herein to describe light that is collimated within a tolerance suitable for a particular application. As another illustration, although not shown, the one or more collection optics 112 may focus the diffracted sub-beams 110 to a target plane 120 such that the top hat beam 114 may have a top hat illumination profile at least at the target plane 120.

[0045] In an embodiment, the various components of the beam shaping system 100 are configured together to provide the flattened beam 114 with a flattened distribution at least at the target plane 120. In particular, since the diffracted sub-beams 110 are not temporally correlated, the intensity distribution of the flattened beam 114 in the target plane 120 may correspond to the sum of the intensity distributions of the diffracted sub-beams 110. In contrast, the temporal correlation between the diffracted sub-beams 110 may result in interference effects, such as, but not limited to, speckle, which may negatively impact the intensity uniformity across the central region 204 of the flattened beam 114.

[0046] For example, the various components of the beam shaping system 100 may be configured to provide partial overlap of the diffracted sub-beams 110 in the target plane 120 such that the sum of the intensities is uniform within a selected metric, as previously described herein.

[0047] It is contemplated herein that the distribution of the diffracted sub-beams 110 required to provide a flat-top distribution may depend on the exact intensity distribution (e.g., beam profile) of the diffracted sub-beams 110 and related parameters such as peak intensity or beam size. As an illustration, in a configuration in which the diffracted sub-beams 110 each have a Gaussian profile, the tails of the Gaussian profiles may overlap to provide a flat-top distribution.

[0048] It is further contemplated herein that the distribution or pattern of the diffracted beamlets 110 (e.g., the spacing between the diffracted beamlets 110) may be controlled via parameters associated with the beamsplitting subsystem 102, the DOE 108, the collection optics 112, and / or the input beam 104. For example, the pattern of diffracted beamlets 110 generated by the DOE 108 based on each incident beamlet 106 may be based on a characteristic pitch (or spatial frequency) in the DOE 108, the wavelength of the input beam 104, or the angle of incidence of the beamlets 106 on the DOE 108. As another example, the array of diffracted beamlets 110 and the spatial separation (e.g., staggering) of the various beamlets 106 may further depend on the distribution of the angles of incidence of the beamlets 106 on the DOE 108. As another example, because the diffracted beamlets 110 can diverge from the DOE 108, the separation between the various diffracted beamlets 110 (e.g., the density of the diffracted beamlets 110) can be controlled in part by the separation distance 126 between the DOE 108 and the collection optics 112. In this way, the distribution of the diffracted beamlets 110 within the flat-top beam 114 can be tailored based on the combined selection and / or configuration of the beamsplitting subsystem 102, the DOE 108, the collection optics 112, and / or the input beam 104 to provide a flat-top distribution.

[0049] In addition, it should be understood that providing Figure 1B and the associated descriptions are for illustrative purposes only and should not be construed as limiting the present disclosure. For example, Figure 1B A 1D top-hat beam 114 is depicted based on a 1D distribution of the diffracted beamlets 110 in the YZ plane of the figure. However, the beam shaping system 100 can provide a top-hat beam 114 having any desired 1D or 2D distribution shape based on any number or distribution of diffracted beamlets 110 from any number or distribution of beamlets 106.

[0050] Reference Figures 1C to 1F , various non-limiting configurations of the beam splitting subsystem 102 are described in more detail according to one or more embodiments of the present disclosure. For simplicity and clarity of description, Figures 1C to 1F Depiction Figure 1B A variation of the embodiment of the present invention is shown in which only the internal components of the beam splitting subsystem 102 are changed, while the other components of the beam shaping system 100 and the resulting flat-top beam 114 remain unchanged. However, it should be understood that these descriptions are not limiting.

[0051] The beam splitting subsystem 102 may include any number or combination of components suitable for providing a plurality of sub-beams 106 (temporally uncorrelated sub-beams 106 ) from an incident input beam 104 .

[0052] In an embodiment, beam splitting subsystem 102 includes at least one beam splitter 116 for generating beamlets 106 and one or more optical elements configured to direct beamlets 106 to DOE 108 along optical paths having different optical path lengths such that beamlets 106 are temporally uncorrelated.

[0053] Figure 1C is a first non-limiting configuration of the beam shaping system 100 according to one or more embodiments of the present disclosure.

[0054] In an embodiment, the beam splitting subsystem 102 may include a beam splitter 116 formed as an additional DOE to diffract the input beam 104. In this way, the sub-beams 106 may correspond to diffraction orders of the input beam 104. As an illustration, Figure 1C Three sub-beams 106 associated with the +1 diffraction order, the 0 diffraction order, and the -1 diffraction order are depicted. Such a beam splitter 116 configured as an additional DOE can be configured to provide sub-beams 106 with any intensity. In some configurations, the beam splitter 116 configured as an additional DOE provides sub-beams 106 with equal intensity.

[0055] Figure 1C Further depicted are two lenses 128 configured to collect diverging sub-beams 106 from the beam splitter 116 and direct these sub-beams 106 to a common location on the DOE 108 at different angles of incidence to produce a staggered pattern of diffracted sub-beams 110, as previously described herein. However, it should be understood that the beam splitting subsystem 102 may utilize any number of lenses in any configuration, including but not limited to a single lens.

[0056] The beam splitting subsystem 102 may utilize any number or type of optical components to provide different optical path lengths for the various sub-beams 106. Figure 1C , the beam splitting subsystem 102 includes an optical retarder 130 in the optical path of at least one of the sub-beams 106. The optical retarder 130 may include any component suitable for adjusting the optical path length of light, and may include, but is not limited to, a transparent optical element (e.g., a slab of transparent material transparent to the sub-beams 106 of a selected thickness), an optical fiber of a selected length, or a retro-reflector mounted to a translation stage. As an illustration, Figure 1C A configuration comprising two optical retarders 130 formed as transparent optical elements having different thicknesses associated with two of the three sub-beams 106 is depicted.

[0057] Figure 1Dis a second non-limiting configuration of the beam shaping system 100 according to one or more embodiments of the present disclosure. In an embodiment, the beam splitting subsystem 102 includes two or more beam splitters 116 configured to generate the sub-beams 106. For example, the beam splitting subsystem 102 may include a plurality of beam splitters 116 having a splitting ratio designed to provide sub-beams 106 with equal intensities, but this is not a requirement.

[0058] For example, Figure 1D A configuration is depicted in which the beam splitting subsystem 102 includes a first beam splitter 116a having a 1:2 splitting ratio (e.g., a transmission and reflection splitting ratio) and a second beam splitter 116b having a 1:1 splitting ratio. In this configuration, the first beam splitter 116a can split the input beam 104 into a first sub-beam 106a and an intermediate sub-beam 106-INT having twice the intensity of the first sub-beam 106a. Then, the second beam splitter 116b can split the intermediate sub-beam 106-INT into a second sub-beam 106b and a third sub-beam 106c, wherein all sub-beams 106a to 106c have equal intensity.

[0059] Figure 1D Further depicting the reflector 132 and the lens 128, the reflector 132 is used to deflect the third sub-beam 106c, and the lens 128 is used to guide the sub-beams 106a to 106c to a common point on the DOE 108 at different incident angles, so as to generate Figure 1B A diffracted sub-beam 110 is depicted.

[0060] It is contemplated herein that the configuration of the beam splitting subsystem 102 having a plurality of cascaded beam splitters 116 can naturally provide the various sub-beams 106a-106c along different optical paths having different optical path lengths, such that the resulting diffracted sub-beams 110 can be incoherently combined to form a flat-top beam 114. For example, in Figure 1D 1 , the cascaded beam splitter 116 (and mirror 132 ) provides different optical path lengths for the sub-beams 106 a - 106 c before the DOE 108 .

[0061] It is further contemplated herein that the beam splitting subsystem 102 may incorporate any combination of polarizing or non-polarizing beam splitters 116, and may further incorporate any type of one or more polarization rotators 134, such as, but not limited to, wave plates or Pockel's cells. In this manner, the polarization state of light in the beam splitting subsystem 102 may be controlled, which may be used for any purpose, including, but not limited to, controlling the splitting ratio of any beam splitter 116 or for controlling the polarization state of any of the sub-beams 106 incident on the DOE 108. For example, a non-polarizing beam splitter 116 may split light without regard to the polarization state of the incident light, while a polarizing beam splitter 116 may transmit light polarized in one direction and reflect light polarized in another (e.g., orthogonal) direction.

[0062] As an illustration, Figure 1D A polarization rotator 134 is included before the first beam splitter 116a, which is oriented to rotate the linearly polarized input beam 104 to provide the desired 1:2 splitting ratio. In this configuration, the second beam splitter 116b can be non-polarizing or polarizing. In the case where the second beam splitter 116b is also polarizing, it can be oriented to provide the desired 1:1 splitting ratio, or placed after an additional polarization rotator 134 (not shown) to rotate the polarization of the intermediate sub-beam 106-INT to provide a 1:1 splitting ratio.

[0063] Figure 1E is a third non-limiting configuration of the beam shaping system 100 according to one or more embodiments of the present disclosure. Figure 1E The depiction is basically similar to Figure 1D , but wherein the first beam splitter 116a and the second beam splitter 116b are formed as polarization beam splitter cubes (PBSCs). Figure 1E Further depicted is a polarization rotator 134 positioned to control the polarization state of the input beam 104 (e.g., before the first beam splitter 116a), the intermediate beamlet 106-INT (e.g., before the second beam splitter 116b), and the second beamlet 106b. However, it should be understood that providing Figure 1E Rather, the beam splitting subsystem 102 may include a polarization rotator 134 at any location to control the polarization state of any light inside the beam splitting subsystem 102 and / or the polarization state of any of the sub-beams 106 incident on the DOE 108 .

[0064] Figure 1F is a fourth non-limiting configuration of the beam shaping system 100 according to one or more embodiments of the present disclosure. In particular, Figure 1F Depicting a system with multiple beam splitters 116 and without any additional lenses 128 (e.g., Figures 1C to 1E1. In this configuration, beam splitters 116a, 116b and mirror 132 are oriented to split the input beam 104 into sub-beams 106a-106c and direct these sub-beams 106a-106c to a common point on DOE 108 at different incident angles and different optical path lengths.

[0065] Generally speaking Figures 1B to 1F , it should be understood that providing Figures 1C to 1F 106. The beam splitting subsystem 102 and the associated description are for illustrative purposes only and should not be construed as limiting. For example, the beam splitting subsystem 102 may include any number or combination of beam splitters 116 and potential additional components (e.g., lenses 128, mirrors 132, or the like) suitable for providing a plurality of temporally uncorrelated sub-beams 106. As another example, the beam splitting subsystem 102 may provide any number of sub-beams 106 and is not limited to, for example, Figures 1B to 1F As another example, DOE 108 may generate any number or arrangement of diffracted sub-beams 110 from any of sub-beams 106, and is not limited to, for example, Figures 1B to 1F As another example, the beam shaping system 100 can provide a top-hat beam 114 of any size or shape from any 1D or 2D arrangement of the diffracted beamlets 110.

[0066] Figure 3 is a flow chart illustrating steps performed in a method 300 for generating a flat-top beam 114 in accordance with one or more embodiments of the present disclosure. Applicants note that the embodiments and enabling techniques previously described herein in the context of the beam shaping system 100 should be interpreted to extend to the method 300. However, it should be further noted that the method 300 is not limited to the architecture of the beam shaping system 100.

[0067] In an embodiment, method 300 includes step 302 of splitting an input light beam 104 into three or more sub-beams 106 that propagate along optical paths having different optical path lengths using a beam splitting subsystem 102 including one or more beam splitters 116. For example, step 302 may include splitting the input light beam 104 using an additional DOE, a polarizing beam splitter 116, a non-polarizing beam splitter 116, or any suitable combination of components as the beam splitter 116. Additionally, the different optical path lengths of the sub-beams 106 may be achieved based on the arrangement of the beam splitters 116 or other components designed to provide optical paths of transparent materials having different physical distances and / or different lengths.

[0068] In an embodiment, the method 300 includes step 304 of diffracting three or more sub-beams 106 into a plurality of diffracted sub-beams 110 using the DOE 108. Step 304 may split each of the sub-beams 106 into any 1D or 2D array (e.g., pattern) of diffracted sub-beams 110. Additionally, the array of diffracted sub-beams 110 may be staggered.

[0069] In an embodiment, the method 300 includes step 306 of collecting the plurality of sub-beams 106 using one or more collection optics 112 to provide a flat top beam 114. For example, the collection optics 112 may capture the diffracted sub-beams 110 emitted from the DOE 108 and direct them along parallel optical paths to form the flat top beam 114. In an embodiment, the diffracted sub-beams 110 from one particular sub-beam 106 may partially overlap with the diffracted sub-beams 110 from another sub-beam 106 to provide a uniform intensity profile according to any selected metric, such as, but not limited to, a statistical measure of peak-to-valley deviation or variation (e.g., mean, variance, standard deviation, RMS, or the like). Additionally, the different optical paths associated with the sub-beams 106 may provide the associated diffracted sub-beams 110 to be temporally uncorrelated (e.g., incoherent) with respect to one another to mitigate interference and associated speckle effects. Therefore, the overall intensity profile of the flat-top beam 114 can be characterized by the incoherent sum of the intensities of the various diffracted sub-beams 110 .

[0070] Upon further consideration, the systems and methods disclosed herein for providing a flat-top beam 114 from staggered temporally incoherent diffracted beamlets 110 provide numerous advantages over alternative techniques.

[0071] As an illustration, Figures 4A to 4C Describes a technique for providing an effective beam with a uniform distribution based on scanning an array of temporally coherent spots over a sample. In particular, Figure 4A Depicts a cross-sectional distribution of an array 402 of temporally coherent light beams 404 in accordance with one or more embodiments of the present disclosure. In this configuration, the light beams 404 must be separated by a factor of at least 1.5 times the beam diameter to avoid interference between different light beams 404 and uniform diffraction efficiency (if generated based on diffraction). As a result, the uniformity of the array 402 is poor. Figure 4B Describes a method for scanning a Figure 4A The cross-sectional distribution of the effective total intensity (eg, summed intensity) obtained for array 402 in FIG. Figure 4C Describes one or more embodiments of the present disclosure. Figure 4B 1D cross section of the effective total intensity of line 406 shown in .

[0072] like Figures 4B to 4CAs shown in FIG. 4 , the row offset of the beam 404 within the array 402 can allow the effective total intensity to be customized over certain portions of the sample via scanning. For example, Figure 4A The rows of beams 404 in FIG. 4 are displaced by 1 / 3 of the beam diameter. However, this approach has multiple limitations. For example, this approach does not provide an instantaneously uniform flat-top distribution (see, for example, Figure 4A ), but only provides a total uniformity after scanning. This can limit the applicability of this technique, especially when scanning in multiple directions is advantageous. As another example, this method can often provide non-uniform total intensity for certain areas of the sample. As an illustration, Figure 4B Region 408 in exhibits a substantially non-uniform intensity. As another example, this approach is not suitable for providing a ID flat-top beam because multiple rows of shifted beams 404 are required. As another example, the use of scanning optics may introduce undesirable complexity and / or cost.

[0073] Reference Figure 5 , Figure 5 is a simplified schematic diagram of an optical system 500 including a beam shaping system 100 that provides a top hat beam 114 according to one or more embodiments of the present disclosure. The beam shaping system 100 may be incorporated into any type of optical system 500 known in the art, such as, but not limited to, a metrology system configured to generate metrology data based on illumination using a top hat beam 114, an inspection system configured to identify and / or characterize defects on a sample based on illumination using a top hat beam 114, or a laser processing system configured to modify one or more properties of a sample using a top hat beam 114.

[0074] In an embodiment, the optical system 500 includes an illumination source 118 configured to generate an input beam 104 and a beam shaping system 100 that generates a flat top beam 114 from the input beam 104. The input beam 104, and thus the flat top beam 114, may include light of one or more selected wavelengths, including but not limited to ultraviolet (UV) radiation, visible radiation, or infrared (IR) radiation.

[0075] The illumination source 118 may include any type of illumination source known in the art to be suitable for generating the input light beam 104. In one embodiment, the illumination source 118 is a laser source. For example, the illumination source 118 may include, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, or the like. In this regard, the illumination source 118 may provide the input light beam 104 with high coherence (e.g., high spatial coherence and / or temporal coherence).

[0076] In an embodiment, the optical system 500 directs the flat top beam 114 to the sample 502 via an illumination path 504. The illumination path 504 may include one or more optical components suitable for modifying and / or adjusting the flat top beam 114 and directing the flat top beam 114 to the sample 502. In one embodiment, the illumination path 504 includes one or more illumination path lenses 506. In another embodiment, the illumination path 504 includes one or more illumination path optics 508, which may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0077] In an embodiment, optical system 500 includes objective lens 510 to focus top hat beam 114 onto sample 502. In another embodiment, sample 502 is disposed on sample stage 512 suitable for fixing sample 502 and further configured to position sample 502 relative to top hat beam 114.

[0078] In another embodiment, the optical system 500 includes one or more detectors 514 configured to capture light emitted from the sample 502 or other light (e.g., collected light 516) through a collection path 518. The collection path 518 may include one or more optical elements suitable for modifying and / or conditioning the light 516 collected from the sample 502. In one embodiment, the collection path 518 includes one or more collection path lenses 520, which may include, but need not include, the objective lens 510. In another embodiment, the collection path 518 includes one or more collection path optics 522 to shape or otherwise control the collected light 516. For example, the collection path optics 522 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translatable mirrors, scanning mirrors, or the like).

[0079] The detector 514 may be located at any selected position within the collection path 518. In one embodiment, the optical system 500 includes a detector 514 at a field plane (e.g., a plane conjugate to the sample 502) to produce an image of the sample 502. In another embodiment, the optical system 500 includes a detector 514 at a pupil plane (e.g., a diffraction plane) to produce a pupil image. In this regard, the pupil image may correspond to the angular distribution of light from the detector 514 of the sample 502. For example, diffraction orders associated with diffraction of the flat-top beam 114 from the sample 502 may be imaged or otherwise observed in the pupil plane. In a general sense, the detector 514 may capture any combination of reflected (or transmitted), scattered, or diffracted light from the sample 502.

[0080] Optical system 500 may include any number or type of detectors 514 suitable for capturing light from sample 502, such as, but not limited to, photodiodes, charge coupled devices (CCD) or complementary metal oxide semiconductor (CMOS) devices, line sensors, or time delay integration (TDI) sensors.

[0081] In another embodiment, the optical system 500 includes a scanning subsystem to scan the sample 502 relative to the measurement field during the metrology measurement. For example, the sample stage 512 can position and orient the sample 502 within the focal volume of the objective lens 510. In another embodiment, the sample stage 512 includes one or more adjustable stages, such as but not limited to a linear translation stage, a rotation stage, or a tip / tilt stage. In another embodiment, although not shown, the scanning subsystem includes one or more beam scanning optics (e.g., a rotatable mirror, a galvanometer, or the like) to scan the flat top beam 114 relative to the sample 502.

[0082] The illumination path 504 and collection path 518 of the optical system 500 may be oriented in a wide range of configurations suitable for illuminating the sample 502 with the top hat beam 114 and collecting light emitted from the sample 502 in response to the incident top hat beam 114. For example, Figure 5 , optical system 500 may include beam splitter 524 oriented so that common objective 510 can simultaneously direct top hat beam 114 to sample 502 and collect light from sample 502. As another example, illumination path 504 and collection path 518 may contain non-overlapping optical paths.

[0083] In an embodiment, the optical system 500 includes a controller 526 including one or more processors 528 configured to execute program instructions maintained on a memory 530 or storage medium. In this regard, the one or more processors 528 of the controller 526 may perform any of the various process steps described throughout this disclosure.

[0084] The one or more processors 528 of the controller 526 may include any processor or processing component known in the art. For the purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 528 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In one embodiment, the one or more processors 528 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute a program (the program is configured to operate or operate in conjunction with the optical system 500) as described throughout this disclosure.

[0085] The memory 530 may include any storage media known in the art suitable for storing program instructions that can be executed by the associated one or more processors 528. For example, the memory 530 may include non-transitory storage media. As another example, the memory 530 may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical storage devices (e.g., disks), tapes, solid-state drives, and the like. It should also be noted that the memory 530 may be housed in a common controller housing with the one or more processors 528. In one embodiment, the memory 530 may be remotely located relative to the physical location of the one or more processors 528 and the controller 526. For example, the one or more processors 528 of the controller 526 may access a remote memory (e.g., a server) that is accessible via a network (e.g., the Internet, an intranet, and the like).

[0086] The subject matter described herein sometimes illustrates different components contained in or connected to other components. It should be understood that such depicted architectures are exemplary only, and in fact many other architectures that realize the same functionality can be implemented. In a conceptual sense, any component arrangement that realizes the same functionality is effectively "associated" so that the desired functionality is realized. Therefore, any two components combined to realize a specific functionality herein can be regarded as "associated" with each other so that the desired functionality is realized, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be regarded as "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be regarded as "coupleable" to each other to realize the desired functionality. Specific examples that can be coupled include but are not limited to physically interactive and / or physically interactive components, and / or wirelessly interactive and / or wirelessly interactive components, and / or logically interactive and / or logically interactive components.

[0087] It is believed that the present disclosure and its many attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made to the form, construction and arrangement of components without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are illustrative only, and the appended claims are intended to cover and encompass such variations. In addition, it should be understood that the invention is defined by the appended claims.

Claims

1. A system comprising: a beam splitting apparatus comprising one or more beam splitters configured to split an input beam into three or more sub-beams that propagate along optical paths having different optical path lengths; a diffractive optical element (DOE) configured to diffract the three or more sub-beams into a plurality of diffracted sub-beams; and One or more optical elements configured to collect the plurality of diffracted sub-beams to provide a flat-top beam.

2. The system of claim 1, wherein the intensity of the flat-top beam is spatially uniform within a selected tolerance.

3. The system of claim 1 , wherein the input beam is temporally coherent, wherein the diffracted sub-beams associated with the three or more sub-beams are mutually incoherent based on the different optical path lengths, and wherein an intensity of the flat-top beam is associated with an incoherent summation of the intensities of the multiple diffracted sub-beams.

4. The system of claim 1, wherein the plurality of diffracted sub-beams partially overlap in the flat-top beam.

5. The system of claim 1, wherein the one or more beam splitters include an additional DOE configured to split the input beam into the three or more sub-beams.

6. The system of claim 5, wherein the beam splitting device further comprises one or more lenses to direct the three or more sub-beams from the additional DOE to the DOE.

7. The system of claim 1, wherein the beam splitting device further comprises: One or more optical retarders for providing the different optical path lengths of the three or more sub-beams.

8. The system of claim 7, wherein at least one of the optical retarders comprises: At least one of an optical fiber or a transparent optical element having a selected length.

9. The system of claim 1, wherein the one or more beam splitters comprise: Two or more beam splitters.

10. The system of claim 1, wherein at least one of the one or more beam splitters comprises: Polarizing beam splitter.

11. The system of claim 1, further comprising: One or more polarization rotators configured to adjust the polarization of at least one of the input beam or any of the three or more sub-beams.

12. The system of claim 1, wherein at least one of the two or more beam splitters comprises: Non-polarizing beam splitter.

13. A system comprising: a laser source configured to generate an input light beam; a beam splitting apparatus comprising one or more beam splitters configured to split the input beam into three or more sub-beams that propagate along optical paths having different optical path lengths; a diffractive optical element (DOE) configured to diffract the three or more sub-beams into a plurality of diffracted sub-beams; and One or more optical elements configured to collect the plurality of diffracted sub-beams to provide a flat-top beam.

14. The system of claim 13, wherein the diffracted sub-beams associated with the three or more sub-beams are mutually incoherent based on the different optical path lengths, and wherein an intensity of the flat-top beam is associated with an incoherent summation of intensities of the plurality of diffracted sub-beams.

15. A method comprising: using a beam splitting device including one or more beam splitters to split an input beam into three or more sub-beams, the sub-beams propagating along optical paths having different optical path lengths; diffracting the three or more sub-beams into a plurality of diffracted sub-beams using a diffractive optical element (DOE); and The plurality of diffracted sub-beams are collected using one or more optical elements to provide a flat-top beam.

16. The method of claim 15, wherein the intensity of the flat-top beam is spatially uniform within a selected tolerance.

17. The method of claim 15, wherein the input beam is temporally coherent, wherein the diffracted sub-beams associated with the three or more sub-beams are mutually incoherent based on the different optical path lengths, and wherein an intensity of the flat-top beam is associated with an incoherent summation of the intensities of the multiple diffracted sub-beams.

18. The method of claim 15, wherein splitting the input light beam into the three or more sub-beams using the one or more beam splitters comprises: An additional DOE is used to split the input beam into the three or more sub-beams.

19. The method of claim 15, wherein the one or more beam splitters in the beam splitting device include at least two beam splitters, wherein using the one or more beam splitters to split the input beam into the three or more sub-beams comprises: The input beam is split into three or more sub-beams using at least two beam splitters.

20. The method of claim 15, further comprising: At least one of the three or more sub-beams is delayed using one or more optical retarders to provide the different optical path lengths of the three or more sub-beams.

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