高功率激光谱合成系统中热效应的分析

Analysis of Thermal Effect in High Power Laser Spectrum Beam Combining System

建立了基于体布拉格光栅实现高功率光纤激光器谱合成的物理模型,考虑强激光照射在体布拉格光栅上,部分能量被体布拉格光栅所吸收,光能在体光栅内部转化为热能,从而导致光栅发生形变。用有限元方法仿真了不同功率高功率激光导致的体布拉格光栅的温度场和应变场的分布,在此基础上将体光栅进行分片处理后,采用有限差分Crank-Nicholson和稀疏矩阵方法,通过反复迭代求解波动方程,数值计算了5束光纤激光经不同形变的体布拉格光栅谱合成后合成光束的光强分布和光束质量M2因子。研究结果表明,高功率激光引起的体布拉格光栅表面的热形变不仅会导致合成光束的光强降低并发生畸变,而且还会使光束质量M2因子变得越来越大,光束质量变差。

The physical model for the spectral combining system of high power fiber laser beams by the volume Bragg grating(VBG)glass was built.When the strong laser irradiation on the VBG,some energy was absorbed by VBG.The light energy was converted into heat energy in grating,which leads to the surface distortion of the VBG.In this paper,the distributions of the temperature and the strain fields of the VBG irradiated by different high-power Gaussian have been analyzed by finite element method.On this basis,after the bulk grating is divided into slices,the finite difference Crank-Nicholson and sparse matrix method are used to solve the wave equation through iterative iteration,and the five beam of fiber laser with different deformation body Prague gratings are calculated.The beam quality and intensity distribution of several fiber laser beams passing through the SBC system have been analyzed numerically by using the finite–different and sparse matrix methods,and the VBG dealt with by slice and the numerical iteration solution of the scalar wave equation in the VBG.The results show that the surface thermal distortion of the VBG due to highpower lasers not only lead to the reduction and distortion of the intensity distribution,but also cause the M^2 becomesbigger and bigger,and beam quality of the combined beam becomes worse.