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