Fig. 1. Limiting factors for output power increasing in fiber lasers

Fig. 2. Schematic diagram of spatial beam combining principle

Fig. 3. 50 kW laser systems^[16]. (a) Three-aperture 30 kW laser system; (b) dual-aperture 20 kW laser system

Fig. 4. Schematic diagram of principle for fiber power combiner

Fig. 5. Schematic diagram of 16 kW 32-channel CBC^[24]

Fig. 6. Experimental setup of 107-channel CBC system^[26]

Fig. 7. Schematic diagram of passive CBC with optical feedback ring cavity^[28]

Fig. 8. Schematic diagrams of SBC with parallel sub-beam. (a) Based on prism; (b) base on reflective diffraction grating

Fig. 9. Diffraction grating-based SBC system with an output power of 11.27 kW^[33]

Fig. 10. Schematic diagrams of SBC with cascaded sub-beam. (a) Based on DM; (b) based on VBG

Fig. 11. Fundamental principle of chromatic beam combining

Fig. 12. Spectral relationship between DM characteristic and combined sub-beam

Fig. 13. Schematic diagram of beam quality degradation induced by DM during beam combining process

Fig. 14. Experimental setup of three-sub-beam chromatic beam combining

Fig. 15. Maximum temperatures of DMs during beam combining process

Fig. 16. Output power and optical axis drifts of the combined laser beam during laser emission. (a) Laser power; (b) optical axis drifts

Fig. 17. Far-field spot profiles after 140 s of beam combining. (a) Combined spot of beam 1, 2, and 3; (b) combined spot of beam 1 and 2; (c) spot of beam 1

Fig. 18. Experimental setup of beam combining^[45]

Fig. 19. Spectra before and after beam combining and intensity distribution after beam combining^[45]

Fig. 20. Beam combining device and transmission curve of interference filter (IF)^[46]. (a) Four-way laser beam combining device; (b) transmission curve of IF

Fig. 21. Relationship among pump power, combined output power and combined beam quality, and combined spot profile^[46]

Fig. 22. Temporal characteristics after pulse laser SBC^[63]. (a) Single-pulse superposition; (b) laser repetition rate multiplication

Fig. 23. Simulated temperature distributions of mirrors^[57]. (a) Single beam with 500 W; (b) single beam with 10 kW

Fig. 24. Schematic diagram of beam combining optical path^[48]

Fig. 25. Spectrum of combined beam^[48]

Fig. 26. Near-field spot profiles for MOPA 1, 2, and 3 single module and beam combining at full power^[48]

Fig. 27. Three-channel beam combining device^[53]. (a) Principle of spectral mirror combining with three wavelengths; (b) physics image

Fig. 28. Experimental setup of hybrid beam combined with active phase control^{and chromatic beam combining[47]}

Fig. 29. Schematic diagram of chromatic beam combining setup^[49]

Fig. 30. Power, efficiency, and spectral transmittance of the combined laser beam^[49]. (a) Curves of power and efficiency; (b) curves of spectrum and transmittance

Fig. 31. Deformation and temperature measurement result of DM under high brightness optical load^[49]. (a) Experimental setup; (b) variation in deformation and temperature with current; (c) temperature

Fig. 32. Relationship between output beam quality and current^[51]. (a) Mx2; (b) My2

Fig. 33. Passive thermal compensation scheme^[51]

Fig. 34. Variation in BQD with output power under three measures^[51]. (a) Horizontal; (b) vertical

Fig. 35. Experimental system of filter-based SBC scheme^[52]

Fig. 36. Test results of chromatic beam combining based on wide-spectrum lasers^[52]. (a) Power and efficiency of combined beam; (b) spectrum of combined beam; (c) Mx2; (d) My2

Fig. 37. Relationship between input power and temperature of DM, and the infrared thermograms under various powers^[52]. (a) Curve of temperature and power; (b) infrared thermogram under power of 533 W; (c) infrared thermogram under power of 6366 W

Fig. 38. Experimental setup diagram of spectrum beam combining based on DM^[54]

Fig. 39. Results for combining narrow-linewidth lasers by DM^[54]. (a) Variation in combined output power and efficiency with input power; (b) spectrum at combined output power of 2355 W; (c) variation in beam quality factor with combined output power; (d) distribution of far-field spot

Fig. 40. Schematic diagram of laser chromatic beam combining setup^[55]

Fig. 41. Results for combining wide-spectrum lasers by DM^[55]. (a) Variation in combined output power and efficiency with input power; (b) output spectrum before beam combining; (c) output spectrum after beam combining; (d) beam quality after beam combining

Fig. 42. Schematic diagram of combining experiment for wide-spectrum lasers by DM based on active control technology^[59]

Fig. 43. Experimental results under open loop and closed loop conditions at highest combining power^[59]. (a) Variation in performance evaluation function with time; (b) combined beam quality

Fig. 44. Far-field spots of combined lasers^[59]

Fig. 45. Schematic diagram of chromatic beam combining setup for 2-channel laser^[44]

Fig. 46. Coating curves of DM, laser spectrum of beam combining, and spot profile^[44]. (a) Transmission curves; (b) output spectrum and spot profile

Fig. 47. Power, efficiency, and beam quality of combined beam^[44]. (a) Power and efficiency; (b) beam quality

Fig. 48. Schematic diagram of chromatic beam combining setup for 3-channel laser^[44]

Fig. 49. Coating curves, laser spectrum, and beam quality^[44]. (a) Spectra and transmission curves of 3-channel laser; (b) combined beam spectrum; (c) beam quality

Fig. 50. Schematic diagram of combining system^[60]

Fig. 51. Spot profile of combined laser and variation curves of beam quality, combined power, and efficiency^[60]. (a) Spot profile of combined laser; (b) variation curve of beam quality; (c) variation curve of combined power; (d) variation curve of combination efficiency

Fig. 52. Schematic diagram of optical damage threshold test of coatings^[60]

Fig. 53. Temperature variation on surface of coatings and observations results in microscope^[60]

Fig. 54. Principle of dichroic film-based laser beam combining and transmittance comparison^[61]. (a) Beam combining of 1060 nm and 1080 nm lasers based on dichroic film; (b) comparison of measured and designed transmittance curves of dichroic film sample

Fig. 55. Schematic diagram of overall structure^[62]. (a) Performance testing for wavelength combining device; (b) physical diagram of the beam combining device

Fig. 56. Designed structure of DM and measured spectra^[62]. (a) Designed structure of the DM; (b) measured spectra

Fig. 57. Impact of temperature rise and angular deviation^[62]. (a) Impact of temperature rise of the DM on beam quality and focus position; (b) relationship between angular deviation and beam quality