体布拉格光栅形变对高斯光束质量平方因子的影响

Deformation of volume Bragg gratings affecting M^2-factor of Gaussian beams

考虑热效应导致的体光栅表面形变引起体光栅背景折射率和周期的变化,进而引起体光栅介质介电常数的改变,对体光栅中传输的激光束特性的影响进行了研究。采用有限差分和稀疏矩阵的方法,对激光在有变形的体布拉格光栅中传输的波动方程进行数值迭代求解,并对激光束通过有形变的反射式体布拉格光栅后的功率反射比、光束束腰宽度、远场发散角和质量平方因子的变化进行了定量分析。结果表明,随着体光栅表面形变的增大,体光栅的功率反射比明显减小,输出光束的束宽、远场发散角和质量平方因子明显增大。

Considering the changes of the background refractive index and the period of the volume Bragg grating（VBG） induced by surface thermal distortion,which further lead to the change of the dielectric constant of the VBG,the propagation properties of Gaussian laser beams propagating in the VBG have been studied. The scalar wave equation for Gaussian beam propagation in the VBG with deformation has been solved numerically and iteratively by finite-different and sparse matrix methods. The changes of the power reflection coefficient,beam waist width,far-field divergence angle and M2-factor of laser beams through the VBG with deformation have been analyzed quantitatively. The result shows that the power reflection coefficient decreases obviously with the increasing of the grating deformation,while the beam waist width,the far-field divergence angle and the M2-factor increase significantly.