Spectral beam combing in solid-state lasers
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摘要: 对多种全固态激光中的光谱合成技术进行了探讨和研究，包括光纤激光、Yb:YAG板条激光和半导体激光。对于光纤激光，探讨了基于单个多层介质膜（MLD）光栅、一对MLD光栅、多个体布拉格光栅三种衍射光学元件的光谱合成技术中色散造成的光束质量退化问题，指出子束光谱线型的二阶矩全宽决定了光束质量的退化量，但所允许的光谱宽度又依赖于具体的技术选择途径。进而比较了三种光谱合成方案的优缺点。对于固体激光，实验演示了基于Yb:YAG晶体的板条激光实现光谱合成的原理可行性。通过设计一个基于MLD光栅的振荡器内的光谱合成装置，实现了7束子激光最高241 W的光谱合成输出，合成后光束质量β因子约4.1，表明大功率Yb:YAG板条激光具有通过光谱合束技术实现功率进一步提升的潜力。对于半导体激光，提出并设计了大模场外腔半导体激光+快轴光谱合成的技术。实验演示了9个1 mm宽LD芯片沿快轴方向的光谱合成，用β因子评价合成后的光束质量，在慢轴方向β≈6.3，在快轴方向β≈1.6，表明快轴光谱合成造成的光束质量退化是完全可控的。Abstract: This paper discusses the technique of the spectral beam combing (SBC) in the solid-state lasers, including the fiber laser, the Yb:YAG slab laser, and the diode laser. For the fiber lasers, we study the beam quality degeneration (BQD) in SBC due to the dispersion of three kinds of diffraction optics elements (DOE): single multi-layer dielectric (MLD) grating, a couple of MLD gratings and multiple volume Bragg gratings (VBG). We point out that, for all cases, BQD is determined by the full-width of the second-order moments instead of the full-width of half maximum in the spectrum of sub-beams. But the value of BQD depends on the DOEs. For solid-state crystal lasers, we demonstrate the feasibility of SBC in the Yb:YAG slab laser by designing an experiment for an intra-cavity SBC employing an MLD grating. The experiment results SBC of seven sub-beams and 241 W laser output, the beam quality after SBC is β≈4.1. It indicates that the output power of the Yb:YAG slab laser can be further scaled by SBC. Finally, we demonstrate a new technique to scale the output power of the laser diodes (LD), which includes the large modal external oscillation in the slow-axis and the SBC in the fast-axis simultaneously. The experiment results the SBC of nine LDs with the slow-axis width of 1 mm, the beam qualities after SBC are β≈6.3 in the slow-axis and β≈1.6 in the fast-axis. It means that beam quality after the SBC in the fast-axis is controllable.
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Key words:
- spectral beam combing /
- beam quality /
- slab laser /
- Yb:YAG /
- laser diode /
- spectral lineshape
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图 1 三种基于不同DOE元件的光纤激光光谱合成方案
Figure 1. Three schemes of spectral beam combining of fiber lasers based on different diffraction optics elements
图 2 不同刻线密度T-VBG衍射效率随波长偏离和入射角偏离的变化
Figure 2. Efficiency of T-VBG diffraction with different line densities change with wavelength deviation and incident angle deviation
图 3 不同刻线密度R-VBG衍射效率随波长偏离和入射角偏离的变化
Figure 3. Efficiency of R-VBG diffraction with different line densities changing with wavelength deviation and incident angle deviation
图 5 基于Yb:YAG板条的光谱合束实验方案
Figure 5. Experimental scheme of spectral beam combining based on Yb:YAG slab
图 7 合束功率随电源输入参数改变的曲线图
Figure 7. Curve of beam combining power changing with the input parameters of power supply
图 8 合束后输出激光的光谱测量结果
Figure 8. Spectral measurement results of output laser after beam combining
图 9 光谱合束后输出激光的近场与远场光斑分布
Figure 9. Near-field and far-field spot distribution of output laser after spectral beam combining
图 10 半导体激光阵列外腔光谱合成原理图
Figure 10. Schematic diagram of external-cavity spectral beam combining of semiconductor laser array
图 11 大模体积外腔半导体激光光谱合成原理图
Figure 11. Principle diagram of spectral beam combining of external-cavity semiconductor laser with large mode volume
图 12 外腔半导体激光的物理过程示意图
Figure 12. Schematic diagram of physical process of external-cavity semiconductor laser
图 13 大模场外腔半导体激光器的典型近场光斑和光束质量测量
Figure 13. The measurement of typical near-field spot and beam quality of large-mode external-cavity semiconductor laser
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