Author Affiliations
1 Shanghai Key Laboratory of All Solid-State Laser and Applied Techniques, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China2 University of Chinese Academy of Sciences, Beijing 100049, China3 Nanjing Institute of Advanced Laser Technology, Nanjing, Jiangsu 210038, China4 Nanjing Zhongke Shenguang Technology Co., Ltd., Nanjing, Jiangsu 210038, Chinashow less
Fig. 1. Output power versus year for high-brightness fiber SBC (defined as M2≤2)[33]
Fig. 2. Experimental setup for SBC of 30 kW fiber lasers[33]
Fig. 3. Experimental setup for SBC of 9.6 kW fiber laser at China Academy of Engineering Physics[39]
Fig. 4. Experimental setup for SBC of 11.27 kW fibers in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences
Fig. 5. SBC system based on MLD grating. (a) Schematic; (b) simplified model
Fig. 6. Beam deviation of incident laser array. (a) Axial translation; (b) angular deflection
Fig. 7. M2 factors of laser array under different beam deviations. (a) Axial translation σx; (b) angular deflection σθ
Fig. 8. Beam width versus propagation distance for different quartic-aberration coefficients[18]
Fig. 9. Beam quality versus focal length of transform lens[19]
Fig. 10. Thermal distortion at MLD grating surface. (a) Structural diagram of experimental measurement; (b) interferograms observed with and without laser irradiation[49]
Fig. 11. Far-field intensity distributions of combined beam and single beam under different power densities. (a) No deformation; (b) irradiation power 1 kW·cm-2; (c) irradiation power 2 kW·cm-2; (d) irradiation power 3 kW·cm-2 [22]
Fig. 12. Change on MLD grating surface after laser irradiation with average power density of 3.6 kW·cm-2. (a) Surface temperature distribution; (b) thermal deformation distribution
Fig. 13. Results of MLD gratings under different deformation heights. (a) Near-field phase modulation; (b) far-field intensity distributions
Fig. 14. Experimental setup for thermal deformation detection of MLD grating
Fig. 15. Interference fringe patterns under laser irradiation with different power densities
Fig. 16. Far-field intensity distributions under laser irradiation with different power densities. (a) 0; (b) 3.6 kW·cm-2
Fig. 17. Far-field intensity distributions of combined beam when incident lasers with different linewidths diffracted by MLD grating. (a) 0.07 nm; (b) 0.15 nm; (c) 0.19 nm; (d) 0.25 nm; (e) 0.30 nm; (f) 0.41 nm
Fig. 18. Beam quality factor M2 versus incident laser linewidth
Parameter | SiO2 | HfO2 | Fusedsilica |
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Density /(kg·m-3) | 2100 | 10300 | 2200 | Specific heat /(J·kg-1·K-1) | 722 | 146 | 670 | Heat conductivity /(W·m-1·K-1) | 7.6 | 0.647 | 1.4 | Thermal expansion /(10-6 K-1) | 0.5 | 5.8 | 0.55 | Young's modulus /GPa | 73.1 | 170 | 72 | Poisson's ratio | 0.17 | 0.27 | 0.17 |
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Table 1. Thermophysical parameters of MLD grating materials
Deformation height h /nm | 0 | 50 | 100 | 150 |
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Beam quality M2 | 1.00 | 1.48 | 2.66 | 3.82 |
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Table 2. Beam quality of combined beam for MLD gratings with different maximum deformation heights