掺Yb光纤激光器阵列谱合成系统的光束传输模型及光束特性分析

建立了由掺Yb光纤激光器阵列、变换透镜、闪耀光栅和输出耦合镜组成的光束谱合成系统的光束传输模型.在考虑光栅角色散、光栅刻槽倾角误差和光栅衍射效率情况下，利用光线追迹法、衍射积分方法、光束非相干叠加原理和强度二阶矩方法，推导出高斯光束非平行倾斜入射到闪耀光栅的相位变化公式以及谱合成光束的光强分布解析表达式.分析了高斯光束非平行倾斜入射到光栅后，光栅角色散、光栅衍射效率和光栅刻槽倾角误差对掺Yb光纤激光器谱合成系统输出光束特性的影响.研究结果表明，谱合成光束具有与单根光纤激光器几乎相同的光束质量；光栅角色散对合成光束特性的影响可忽略；随着光栅刻槽倾角误差的增大，谱合成光束的光束质量明显变差；当光栅刻槽倾角误差较大时，必须考虑光栅衍射效率对合成光束特性的影响. 关键词： 掺Yb光纤激光器 非平行倾斜入射 光束谱合成 光束质量

Analysis of the beam characteristics and the propagation model of spectral combining systems for Yb-doped fiber lasers

The propagation model for the spectral combining systems including Yb-doped fiber laser arrays, transform lens, grating and output coupler has been built up. By taking into consideration the grating angle dispersion, the fabrication errors of groove angle and the diffraction efficiency of the grating, the formula for the phase change of the Gaussian beam unparallelly oblique incidence on the grating and the analytical expression for the intensity distribution of the combining beam have been derived by using the ray tracing method, the diffraction integral method, the principle of incoherent superposition of laser beams and the intensity second-order moments method. Consequently, the effects of the angle dispersion, the diffraction efficiency and the fabrication errors of groove angle of the grating on the beam characteristics of the spectral combining system have been analyzed for the case of Gaussian beam unparalleUy oblique incidence on the grating. The results show that the beam quality of the combined beam remains almost the same as that of a single fiber laser. The effect of the angle dispersion of the grating on the beam quality of combined beam can be neglected. The beam quality of combined beam degrades with the increasing of the fabrication errors of groove angle of the grating. For the case of the large fabrication errors of groove angle of the grating, the effect of the diffraction efficiency of the grating on the beam characteristics of the combined beam should be considered.