Seeded spectral beam combiner for high power scaling

Abstract

A spectral beam combining system receives a multi-spectral seed beam from a seed laser source and generates an output laser beam that is higher power compared to the multi-spectral seed beam. The system has a first 2f stage comprising a first grating and a first transform optic, the first 2f stage configured to direct the multi-spectral seed beam toward a Fourier plane at which multi-spectral components of the seed beam are spatially separated; amplifiers positioned at the Fourier plane, in which the amplifiers are configured to amplify the multi-spectral components, the amplifiers being spaced apart according spatial separation of the multi-spectral components at the Fourier plane; and a second 2f stage comprising a second transform optic and a second grating, the second 2f stage configured to direct amplified multi-spectral components from the Fourier plane and recombine them into the output laser beam.

Description

Docket No. 503541-70021SEEDED SPECTRAL BEAM COMBINER FOR HIGH POWER SCALING RELATED APPLICATION

[0001] This application claims priority benefit of U.S. Provisional Patent Application No. 63 / 749,548 filed January 25, 2025, which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The field of the present disclosure relates to laser devices, particularly a method for creating high power laser beams. Specifically, this disclosure uses a seeded spectral beam combiner approach.BACKGROUND INFORMATION

[0003] Power scaling of lasers beyond the 1 kilowatt level can enable or improve industrial, defense, and scientific applications. For example, welding, cutting, and machining applications can improve their processing times with higher laser power. Defense applications such as directed energy or countermeasure applications would enable faster or more distant engagement opportunities. Novel scientific applications such as laser fusion, laser propulsion, or laser power beaming all benefit from an increase in available power.

[0004] The scaling of laser power using a single amplifier aperture is limited and beam combination techniques such as spectral or coherent beam combining are actively being used and developed to scale the output power beyond that of a single aperture. Despite their recent advancement, alignment sensitivities and demanding requirements on the individual laser sources make these approaches challenging to scale.SUMMARY OF THE DISCLOSURE

[0005] Embodiments described in this disclosure mitigate the alignment sensitivities and laser source requirements and allow for scaling beyond current capabilities.

[0006] High average power scaling of lasers is limited by the ability to extract waste heat from the gain medium. The heat extraction scales better with smaller gain apertures and longer propagation lengths but higher laser power1503541\70021\FG: 104586258.1Docket No. 503541-70021requires larger apertures and shorter propagation lengths in order to avoid damage and nonlinear effects that are detrimental to a good output beam.

[0007] Ultimately each approach will encounter a limit where a single aperture configuration cannot exceed a certain amount of output power. At that point, scaling of multiple apertures by beam combining is the preferred approach. In most cases the combined beam still needs to maintain the diffraction-limited beam propagation characteristics of a single aperture, thus achieving a combined diffraction-limited beam is crucial for most applications. The output beam however, does not need to contain a monochromatic output wavelength because a limited bandwidth is compatible with most applications.

[0008] Several beam combination approaches have been demonstrated, such as polarization, spectral, or coherent combining. In this disclosure, the traditional approach to spectral beam combining is improved by employing a seeded configuration to make the system less sensitive to alignment tolerances and reduce the requirements on the laser sources that provide the power scaling. The duplication and mirroring of the optical elements intrinsically provides a configuration with ideal alignment that is required for beam combining.BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0009] Fig. 1 is a block diagram of a typical spectral beam combining system.

[0010] Fig. 2 is a block diagram of two improved spectral beam combining systems in a seeded configuration.

[0011] Fig. 3 is set of raytracing diagrams for folded spectral beam combining systems in a seeded configuration.

[0012] Fig. 4 is a block diagram of two improved spectral beam combining systems in a seeded configuration with amplifiers.

[0013] Fig. 5 is a ray tracing diagram of a seeded beam combining system with a closeup view of the amplifiers.

[0014] Fig. 6 is a ray tracing diagram of two seeded beam combining systems with different focal length configurations.

[0015] Fig. 7 is a block diagram of a seed and two successive amplifier stages.2503541\70021\FG: 104586258.1Docket No. 503541-70021

[0016] Fig. 8 is a diagram of the spectral distribution of seed sources and successive amplifiers in a spectral beam combining system.

[0017] Fig. 9 is a diagram of the temporal distribution of seed sources and successive amplifiers in a spectral beam combining system.

[0018] Fig. 10 is a block diagram of an ultrafast oscillator configured as a seed to spectral beam combiner amplifier.

[0019] Fig. 11 is a block diagram of fiber laser configured as a seed to spectral beam combiner amplifier.

[0020] Fig. 12 is a block diagram of free space laser configured as a seed to spectral beam combiner amplifier.DETAILED DESCRIPTION OF EMBODIMENTS

[0021] Spectral beam combing (SBC) is a power scaling approach primarily used with fiber laser sources. One method uses multiple narrow band dichroic beam splitters to combine multiple sources with different wavelengths along a common optical axis. This approach is complex both in setup and alignment since each source needs to be separately aligned and overlapped with the combined beam. Long-term stability and environmental sensitivity are major concerns for this implementation.

[0022] The technical progress of high damage-threshold diffraction gratings, particularly dielectric transmission designs, that can support high average power by reducing intrinsic absorption and optimizing diffraction efficiency, enables a much simpler system that is shown in Fig. 1. Multiple laser sources with different wavelengths are arranged in a linear array (101) along a launch plane (111). Each source emits a beam, preferably of diffraction-limited nature (102) towards a transform optic (103). The transform optic is typically a lens or assembly of lenses that directs the beams from the individual apertures (102) towards (104) the grating (105). The grating shown here is a transmission grating, but reflection designs can be utilized as well. The grating combines the beams from the different wavelengths into a single output beam (106) with an overall diffraction-limited beam quality, albeit made up from multiple spectral components. The transform optic (103) that is placed between the laser sources and the grating is at a distance equal to its focal length on both sides (107 and 108). At a distance of one focal length, the transform optic3503541\70021\FG: 104586258.1Docket No. 503541-70021changes the angle of the incoming rays (102) depending on the position along the linear arrangement dx (109). In a paraxial approximation this angle (110) can be expressed astheta = - dx / f.The angle of the rays incident on the grating and thus the spacing dx and the properties of the transform optic are chosen such that the angle of the diffracted light (106) is common to all wavelengths, taking into account the wavelength dependency of the incident and diffracted angles for the grating. Other designs with multiple lens elements or combinations of reflective and transmissive elements are possible that can reduce the overall footprint of the beam combiner, but the effective focal length remains the same.

[0023] The beam quality of the combined beam (106) cannot exceed the beam quality of the individual sources (102) but can be degraded by alignment errors or intrinsic parameters of the laser sources. For example, a large divergence of the input beam will limit the output beam quality, although optical designs can be implemented to minimize that impact. Another limitation is the spectral width of the individual sources. Since the transform optic imparts a specific angle for each wavelength, any spread in wavelength from a fixed position, will result in a spread in angle incident on the diffraction grating. Consequently, the diffracted beam will have a larger angle spread and thus the beam quality of the combined beam will be limited. This imposes tight requirements on the individual source in terms of spectral and spatial beam parameters. For example, fiber lasers, which are the preferred source for SBC, encounter nonlinear spectral broadening such as Stimulated Brillouin Scattering that create a spectrally broad beam that significantly reduces the beam quality of the combined beam.

[0024] It is evident, that replicating the ideal distribution of rays and wavelength in the launch plane of the spectral beam combiner is challenging to achieve with any source.

[0025] Fig. 2 depicts a setup that mirrors the spectral beam combiner along the launch (111) or Fourier plane (124) by replicating the grating (122 and 126) and the transform optic (123 and 125). The term Fourier plane refers to a plane formed by a transform optic in which angularly dispersed spectral components of a beam are spatially separated, including planes located at or 4503541\70021\FG: 104586258.1Docket No. 503541-70021near a focal distance of the transform optic. It is apparent that this arrangement replicates any seed beam (121) into the output beam (127) while at the same time providing the spectral dispersion of a traditional SBC system at the Fourier plane of the system (124). This is primarily due to the one-to- one imaging properties of the transform optics (123 and 125) in a 4f system. It is feasible to change the focal length of one or both of the transform optics introduced here (123 and 125) as long as the corresponding grating (122 and 126) and distances are changed accordingly.

[0026] It is important to distinguish the Spectral Beam Combining (SBC) architecture described herein from Coherent Beam Combining (CBC) approaches. In CBC systems, all sub-apertures emit the same wavelength and must interfere constructively to form a single output. This requires the electric field of every beam to be locked in phase relative to one another, necessitating active control of the "piston" phase (sub-wavelength optical path differences) to ensure a coherent wavefront across the full aperture. In contrast, SBC systems utilize sub-apertures with distinct, non-overlapping wavelengths. Because these beams operate at different frequencies, they do not create a static interference pattern; rather, they combine incoherently as a summation of intensities. Consequently, SBC does not require subwavelength piston phase locking. However, the system remains strictly sensitive to spatial phase, specifically the wavefront tilt(pointing) and curvature (collimation) of each channel. To achieve a high- quality combined beam that acts as a single diffraction-limited source in the far field, the constituent beams must be spatially aligned such that their propagation vectors and spatial modes overlap perfectly after the combining element. This spatial phase alignment is critical for a high-quality output beam and the SBC system needs to ensure that the spatial phase relationships of the combined beams are matched and preserved.

[0027] A modified arrangement introduces a reflective surface (132) at the Fourier plane (131). Here the seed beam (128) is equivalent to the seed beam (121) and the output beam (133) is equivalent to the output beam (127). This arrangement double passes the initial grating (129) and the transform optic (130) for a more compact system and reduce alignment and component tolerance requirements. Beam separation between input (128) and output 5503541\70021\FG: 104586258.1Docket No. 503541-70021(133) beam can be achieved using a polarizer in combination with polarization optics that introduce a polarization change between input and output beam, such as quarter-wave plates or Faraday Rotator. Spatial beam separation between input and output beam can be accomplished using different embodiment as shown in Fig. 3.

[0028] An embodiment using the same grating (145) and transform optic (146) is shown in 141. The seed beam (148) is aligned along the optical axis of the system and the grating directs the seed beam towards the center of the transform optic (146). The reflective surface (147) reflects the beam back along the optical axis of the system towards the transform optic (146) and grating (145), double passing both components. The output beam exits along the same beam path as the seed beam (148). This arrangement would employ polarization optics to separate input and output beam after the spectral beam combiner.

[0029] Another embodiment using the same grating (145) and transform optic (146) is shown in 142. The seed beam (149) is offset from the optical axis of the system perpendicular to the dispersion plane of the grating. The transform optic (146) directs the beam towards the reflective surface (147) that is oriented perpendicular to the optical axis of the system. The beam is reflected and sent back towards the transform optic (146) and the grating (145) for a second pass. The output beam (150) is spatially separated from the seed beam (149) after exiting the grating.

[0030] Another embodiment using the same grating (145) but separate transform optics (151 and 153) is shown in 143. The seed beam (149) is offset from the optical axis of the system perpendicular to the dispersion plane of the grating. The first transform optic (151) is aligned along the optical axis of the seed beam after diffraction through the grating and directs the beam to the reflective surfaces consisting of a set of fold mirrors (152). The arrangement of fold mirrors reflects the beam back and duplicates the beam offset of the seed beam along the optical axis of the system. The beam is sent back towards the second transform optic (153) and grating (145). The output beam (150) is spatially separated from the seed beam (149) after existing the grating. In this embodiment the focal length of the transform optics (151 and 153) is the same.6503541\70021\FG: 104586258.1Docket No. 503541-70021

[0031] Another embodiment using separate gratings (145 and 156) and separate transform optics (154 and 155) is shown in 144. The seed beam (149) is offset from the optical axis of the system perpendicular to the dispersion plane of the grating. The first transform optic (154) is aligned along the optical axis of the seed beam after diffraction through the grating and directs the beam to the reflective surfaces consisting of a set of fold mirrors (152). The arrangement of fold mirrors reflects the beam back and duplicates the beam offset of the seed beam along the optical axis of the system. The beam is sent back towards the second transform optic (155) and the second grating (156) where the output beam (150) is diffracted from the grating. In this embodiment the focal lengths of the transform optics (154 and 155) are different and the gratings (145 and 150) are different as well.

[0032] The transform optics (123, 125, 130, 146, 151, 153, 154, and 155) are typically a transmission optic with spherical surface figure. Due to the large focal lengths, the spherical aberrations do not impact the beam quality.However, for compact systems, a transform optic with aspherical surface figure can be employed to mitigate the impact of spherical aberrations.Although the transform optics shown here are transmission optics, reflective optics in a mirror design with spherical or aspherical surface figures can be employed as well.

[0033] This concept is the starting point for chirped pulse amplification that is used to temporally stretch ultrafast lasers to mitigate optical damage during amplification. Notably, the optical designs that perform this stretching and compression are not in a 4f configuration, but rather adjust these distance to impart a positive or negative temporal chirp on the pulse. A balanced configuration as shown in Fig. 2 would not be beneficial for the chirped pulse amplification since it does not provide any pulse stretching or compression.

[0034] Fig. 4 illustrates the arrangement that add laser amplifiers (162) placed in the Fourier plane (164) of the system to provide amplification to the individual wavelength components of the seed beam (161). At the amplified beam (163) the spectral components of the beam are again overlapped spatially to form a single beam that replicates the properties of the seed beam (161) with increased power. The laser amplifiers considered in this implementation are large transmissive or reflective aperture designs such as 7503541\70021\FG: 104586258.1Docket No. 503541-70021laser rods, disks, or other volume configurations and exclude fiber lasers or fiber amplifiers. It is important to note that the amplifiers must limit changes to the spatial and spectral distribution of the rays, so any laser configurations that modifies the beam wavefront, such as internally guided fiber structures, are not compatible with this approach.

[0035] An alternative arrangement using the reflective surface (170) approach in the Fourier plane (169) is also shown. The amplifiers (166 and 167) are placed next to the mirror to illustrate a double-pass configuration or in an alternative arrangement, could include the mirror integrated into the amplifier as in reflective thin-disk architectures. The amplifiers (166 and 167) provide amplification to the individual wavelength components of the seed beam (165). At the amplified beam (168) the spectral components of the beam are again overlapped spatially to form a single beam that replicates the properties of the seed beam (165) with increased power.

[0036] In the embodiments introduced in Fig. 3 (141, 142, 143, and 144), the amplifiers are positioned at, or close to the Fourier plane. For example, in embodiments 141 and 142, the amplifiers can be placed just before the reflective surface (147) and used in a double pass configuration. Alternatively, the amplifiers themselves can include the reflective surface as in a thin-disk amplifier design. In embodiments 143 and 144, the amplifiers can be placed in the Fourier plane between the fold mirrors (152), before the fold mirrors, after the fold mirrors, or a combination thereof.

[0037] Adding amplifiers to this geometry necessitates the use of an external seed beam, since the seed beam defines the spatial and spectral properties of the beam in the Fourier plane that allow for recombination using the second transform optic and grating. Self lasing gain modules by themselves would not be able to match the geometry and tolerances that are required for SBC to work since there is no beam control or cavity that matches the beam to the parameters required for spectral beam combining. The seed beam (161 and 165) together with the grating and transform optic, provides the required ray distribution in the Fourier plane. The amplifiers do not modify the ray positions or angles, or the spectral components of the ray distribution and thus allow for replication of the seed beam with the same properties.8503541\70021\FG: 104586258.1Docket No. 503541-70021

[0038] The following compares the Fig. 4 approach to inserting multiple amplifier apertures into a single large beam without the use of a Spectral Beam Combining arrangement. Several differences are described and provide an advantage.

[0039] First, the seed beam can be spread out in space allowing for more apertures to amplify the beam than a direct amplification. This scales the integrated aperture available for amplification.

[0040] Second, the extended beam in the Fourier plane is separated by wavelengths with several impacts. Introducing any hard or soft apertures, which is desirable if gain modules are separate, introduces gaps in the spectrum as opposed to the spatial beam profile. This is equivalent to a row of individual emitters in a traditional SBC configuration that would perform similarly to a set of amplifiers with a hard aperture clip between them and not impact the usability of the combined beam.

[0041] Thirdly, the separation into wavelengths across multiple amplifier apertures, would allow for opportunities to introduce different gain materials. In most SBC systems, broad-band gain materials such as Yb doped gain media are used that support the range of possible wavelengths. While this remains an option for implementation, an alternative embodiment would select different doping materials, different host materials, or a combination thereof. Materials with narrow spectral emission profiles would be combined to cover the overall profile of the seed laser bandwidth.

[0042] Lastly, more complex arrangements can be employed that split and redirect the spectral components to provide more space to include complex amplifier architecture with large footprints, as long as the overall beam propagation still follows the 4f optical layout.

[0043] An embodiment using two amplifiers is shown in Fig. 5 as a raytracing diagram. In this example, a seed beam (181) is comprised of four wavelengths (182, 183, 184, and 185). In the seed beam (181) all wavelengths are overlapped. After the grating and transform optic, the wavelengths are spatially separated in the Fourier plane. Two of the wavelengths (182 and 183) overlap with the aperture of the first amplifier (186), while the other two wavelengths (184 and 185) overlap with the aperture of the second amplifier (187). The set of wavelengths is amplified by 9503541\70021\FG: 104586258.1Docket No. 503541-70021the different amplifiers as long as the gain bandwidth of the amplifier overlaps with the wavelengths. In this example, amplifier 186 provides gain for the wavelengths 182 and 183, while amplifier 187 provides gain for the wavelengths 184 and 185. After amplification the spectral components of the beam are combined again into a single output beam (188).

[0044] It is important to note that the output beams are not coherently combined, hence the alignment tolerances are not fractions of a wavelength but rather just geometric tolerances. Any small differences on the scale of wavelength differences between the amplifiers will be negligible.

[0045] In addition to the symmetric arrangement in Fig. 2, alternative arrangements that are not symmetric and have different focal lengths for the first 2f stage and the second 2f stage are considered as illustrated in Fig. 3 and Fig. 5. The term 2f refers to an optical arrangement in which a lens having a focal length f is positioned between an object plane and an image plane, where each plane is spaced at a distance from the lens, resulting in a total optical path length of 2f between the planes.

[0046] Fig. 6 shows the ray tracing diagram for a symmetric and an asymmetric embodiment. A symmetric arrangement with focal lengths of the first 2f stage equal to the focal lengths of the second 2f stage is shown in 215. The seed beam (201) is diffracted off the first grating (202) and directed towards the transform optic (203) with focal length f1 that spatially separates the spectral components in the Fourier plane (204). A symmetric arrangement of second transform optic (205) with focal length f1 and grating (206) combines the beam into the output beam 207. This arrangement has the same beam size for the seed beam on grating 202 and the output beam on grating 206. An asymmetric arrangement with focal lengths of the first 2f stage different than the focal lengths of the second 2f stage is shown in 216. The seed beam (208) is diffracted off the first grating (209) and directed towards the transform optic (210) with focal length f1 that spatially separates the spectral components in the Fourier plane (211). A second transform optic (212) with a different focal length f2 and grating (213) combines the beam into the output beam 214. This arrangement has a different beam size for the seed beam on grating 209 and the output beam on grating 213. This arrangement is useful since the output beam has more power than the seed beam and an 10503541\70021\FG: 104586258.1Docket No. 503541-70021increase in beam size is needed to accommodate the limited damage threshold of the second grating (213).

[0047] The diffraction gratings in an SBC system are typically dielectric transmission gratings that can operate at high average power and sustain a high damage threshold. The embodiments shown in Fig. 2, Fig. 3, and Fig. 6 allow for a combination of different gratings. For example, the input grating can have a lower damage threshold and lower power handling ability since it only transmits the lower power seed beam, so less expensive designs, optics with smaller apertures, or gratings used in reflection can be utilized.Specifically, reflection gratings with metal overcoat designs are more cost effective and even though their efficiency and power handling is not on par with the dielectric transmission gratings, they can still support the low power seed beam. Other embodiments, particularly the asymmetric designs shown in Fig. 3 and Fig. 6 use a different grating groove density in combination with a different focal length on the seed beam side of the SBC system to reduce the beam size of the seed beam and the system footprint.

[0048] This concept can be expanded to multiple amplifier stages as illustrated in Fig. 7. A seed source (221) provides a low power beam (224) with a broad spectrum to match the bandwidth of the amplifiers (222 and 223). This seed can be a traditional SBC system or other broadband laser source as illustrated in Figs. 10, 11, and 12. Pulsed seed lasers, particularly intrinsically broadband mode-locked sources are feasible as long as they are stretched long enough to avoid nonlinear effects. The seed beam (224) is amplified in the first stage (222) and exits the first SBC amplifier (225). The size of the beam is adjusted using a set of telescope optics (228 and 229) to increase the beam size (226) and match the combined aperture of the second set of amplifiers (223). Amplification further increases the beam power and combines it back into an amplified beam (227).

[0049] A spectral representation of different embodiments using different seed sources is shown in Fig. 8. Here the spectral power or bandwidth is shown against the wavelength (241). For a traditional SBC system, a set of narrow band sources have specific wavelengths (242, 243, 244, 245, and 246) that are combined after the diffraction grating. This is typically implemented using individual fiber lasers, operating at different wavelengths. The gain bandwidth 11503541\70021\FG: 104586258.1Docket No. 503541-70021of the laser material for these source supports lasing across the full wavelength range (249). The arrangement in Fig. 5 is represented by 247 and 248 where the wavelengths of the seed (242 and 243 as well as 245 and 246) fall within the spectral amplifier bandwidth (247 and 248 respectively) if they are made of different gain materials. If the same gain material was used, the spectral amplifier bandwidth would support lasing across all seed wavelengths (249). This figure is also useful to illustrate different seed architectures.

[0050] The seed source needs to provide enough bandwidth to support the dispersion of the SBC system. Broadband gain materials are typically employed that support lasing across a large wavelength range (249), although a combination of gain materials with a narrower bandwidth is also possible (247 and 248). Different laser architectures can be used for the seed lasers, such as fiber lasers, solid-state lasers, gas laser, or even other SBC systems, as long as they provide a seed beam with a broad spectral bandwidth. Fig. 9 illustrates the temporal power of different seed lasers (261). The temporal profile can include ultrashort pulses from mode-locked lasers (264), pulses from Q-Switched lasers, gain switched lasers, or modulated continuous-wave lasers (263), or continuous wave beams (262). Combinations of the different architectures and pulse formats can be employed as seed lasers.

[0051] One embodiment using a mode-locked free space laser as the seed source is shown in Fig. 10. The mode-locked laser (281) generates ultra-short pulses (264) with a broad spectrum (249). The beam is propagated to the SBC amplifier (282). A beam shaping stage (283) matches the beam profile to the aperture of the SBC system. Other elements could include a pulse stretcher to mitigate nonlinear effects, pulse pickers, or pre-amplifier stages.

[0052] Another embodiment using a fiber laser as the seed source is shown in Fig. 11. The fiber laser (301) generates a spectrally broadband beam using a broadband seed or an internal broadening mechanism. The pulse format can vary from continuous wave to ultra-short pulses. The beam is matched to the SBC system (302) using beam shaping optics (303).

[0053] Another embodiment using a bulk solid-state laser as the seed source is shown in Fig. 12. The seed laser (321) generates a spectrally broadband beam with a pulse format that can vary from continuous wave to short pulses.12503541\70021\FG: 104586258.1Docket No. 503541-70021The beam is matched to the SBC system (322) using beam shaping optics (323).13503541\70021\FG: 104586258.1

Claims

Docket No. 503541-70021CLAIMSWhat is claimed is:

1. A spectral beam combining system configured to receive a multi-spectral seed beam from a seed laser source and generate an output laser beam that is higher power compared to the multi-spectral seed beam, the spectral beam combining system comprising:a first 2f stage comprising a first grating and a first transform optic having a first focal length, the first 2f stage configured to direct the multi- spectral seed beam toward a Fourier plane at which multi-spectral components of the seed beam are spatially separated;amplifiers positioned at the Fourier plane, in which the amplifiers are configured to amplify the multi-spectral components, the amplifiers being spaced apart according to spatial separation of the multi-spectral components at the Fourier plane; anda second 2f stage comprising a second grating and a second transform optic having a second focal length, the second 2f stage configured to direct amplified multi-spectral components from the Fourier plane and recombine them into the output laser beam.

2. The spectral beam combining system of claim 1 , in which the first focal length of the first transform optic is equal to the second focal length of the second transform optic.

3. The spectral beam combining system of claim 1 , in which the first focal length of the first transform optic is different from the second focal length of the second transform optic.

4. The spectral beam combining system of claim 1, further comprising a reflective surface in the first 2f stage, in the second 2f stage, or at the Fourier plane.

5. The spectral beam combining system of claim 4, in which the seed beam is aligned along an optical axis of the system, the reflective surface reflects the14503541\70021\FG: 104586258.1Docket No. 503541-70021seed beam along the optical axis, and in which the first focal length of the first transform optic is equal to the second focal length of the second transform optic.

6. The spectral beam combining system of claim 4, in which the seed beam is offset from an optical axis, the reflective surface reflects the seed beam along the optical axis of the system, the amplified multi-spectral components are offset from the optical axis, and in which the first focal length of the first transform optic is equal to the second focal length of the second transform optic.

7. The spectral beam combining system of claim 4, in which the seed beam is offset from an optical axis, in which the reflective surface comprises a first reflective surface and a second reflective surface configured to reflect the multi-spectral components twice, the amplified multi-spectral components are offset from the optical axis, and in which the first focal length of the first transform optic is equal to the second focal length of the second transform optic.

8. The spectral beam combining system of claim 4, in which the seed beam is offset from an optical axis, in which the reflective surface comprises a first reflective surface and a second reflective surface configured to reflect the multi-spectral components twice, the amplified multi-spectral components are offset from the optical axis, and in which the first focal length of the first transform optic differs from the second focal length of the second transform optic.

9. The spectral beam combining system of claim 1 , in which the first transform optic comprises a spherical lens configured to optimize the spatial alignment of beams.

10. The spectral beam combining system of claim 1 , in which the first transform optic comprises an aspherical lens configured to optimize the spatial alignment of beams.15503541\70021\FG: 104586258.1Docket No. 503541-7002111. The spectral beam combining system of claim 1 , in which the first grating is a reflection grating.

12. The spectral beam combining system of claim 1 , in which the first grating is a dielectric transmission grating.

13. The spectral beam combining system of claim 1, in which the second grating is a reflection grating.

14. The spectral beam combining system of claim 1, in which the second grating is a dielectric transmission grating.

15. The spectral beam combining system of claim 1, further comprising the seed laser source configured to emit in a mode-locked, pulsed, or continuous wave format.

16. The spectral beam combining system of claim 1, in which the amplifiers are configured to independently amplify each spectral component while preserving spatial phase relationships.

17. The spectral beam combining system of claim 1, in which the second transform optic and the second grating are arranged to spatially overlap the amplified multi-spectral components to form the output laser beam.

18. The spectral beam combining system of claim 1, in which the amplifiers positioned at the Fourier plane include gain media selected to provide wavelength-specific amplification corresponding to the spectral components of the multi-spectral seed beam.

19. The spectral beam combining system of claim 1 , in which the first and second stages are arranged in a compact optical configuration, with the Fourier plane defined at an intermediate focal point location between the stages.16503541\70021\FG: 104586258.1Docket No. 503541-7002120. The spectral beam combining system of claim 1 , in which the system is configured to accept a pulsed or continuous wave input from the multi-spectral seed laser source and maintain compatibility with both temporal formats.

21. A method for laser beam generation, comprising:receiving a multi-spectral seed beam;directing the seed beam through a first 2f stage comprising a first grating and a first transform optic, in which the first 2f stage spatially separates spectral components of the seed beam at a Fourier plane;amplifying the spectral components at the Fourier plane using amplifiers configured to amplify the spectral components while preserving spatial phase relationships;directing the amplified spectral components through a second 2f stage comprising a second transform optic and a second grating; and recombining the amplified spectral components into an output laser beam that is higher power compared to the multi-spectral seed beam.

22. The method of claim 21 , in which a focal length of the first transform optic of the first 2f stage is equal to a focal length of the second transform optic of the second 2f stage.

23. The method of claim 21 , in which a focal length of the first transform optic of the first 2f stage differs from a focal length of the second transform optic of the second 2f stage.

24. The method of claim 21 , further comprising reflecting the multi-spectral components using a reflective surface positioned in the first 2f stage, in the second 2f stage, or at the Fourier plane.

25. The method of claim 24, in which the multi-spectral seed beam is aligned along an optical axis of the system, and in which the reflective surface reflects the multi-spectral components along the optical axis.17503541\70021\FG: 104586258.1Docket No. 503541-7002126. The method of claim 24, in which the multi-spectral seed beam is offset from an optical axis of the system, and in which reflecting the multi-spectral components causes the amplified multi-spectral components to be offset from the optical axis.

27. The method of claim 24, in which reflecting the multi-spectral components comprises reflecting the multi-spectral components twice using a first reflective surface and a second reflective surface to fold an optical path between the first 2f stage and the second 2f stage.

28. The method of claim 27, v a focal length of the first transform optic of the first 2f stage is equal to a focal length of the second transform optic of the second 2f stage.

29. The method of claim 27, in which a focal length of the first transform optic of the first 2f stage differs from a focal length of the second transform optic of the second 2f stage.

30. The method of claim 21 , in which amplifying the spectral components comprises amplifying different wavelength subsets of the spectral components using different gain media positioned at the Fourier plane.

31. The method of claim 21 , in which amplifying the spectral components is performed without substantially altering angular distributions of the spectral components at the Fourier plane.

32. The method of claim 21 , in which recombining the amplified spectral components produces an output laser beam having diffraction-limited beam quality.18503541\70021\FG: 104586258.1

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