激光窗口热透镜效应对光束质量的影响

 分析了高功率激光通过窗口时，引起的窗口热透镜效应及其对激光光束质量的影响。用冲量定理方法，推导了二维热传导方程的广义傅里叶级数解，然后按照平面热应力问题，运用有限元方法数值计算热变形。考虑热变形、折射率随温度变化，忽略光弹性效应，解出出光面的波前相差分布，讨论了远场光束质量。以空心环形光束为例，计算了熔融石英(SiO₂)和白宝石(Al₂O₃)两种常用窗口的温升分布、热变形、波前相差和光束质量，分析了冷却、辐照时间、光强分布的空间梯度和各种材料参数对光束质量的影响。

Influence of Laser Window's Thermal Lensing Effect on the Beam Quality

This paper concerns the thermal lensing effect that occurs as laser going through an optical window, and its influence on beam quality. By the method of impetus theorem, 2D solution of the thermal conduction equation is derived, in the form of generalized Fourier series. Then, the finite element method is applied to simulate the thermal deformation as a plane-stress problem. Combined with the thermal deformation and the shift of the refractive index with the temperature, the wavefront distortion is calculated without considering the optic-stress effect. Furthermore, the beam quality on far field is discussed. Temperature rise, thermal deformation, wavefront distortion and beam quality of fused quartz(SiO_2) window and white bijou(Al_2O_3) window irradiated by the annulus beam are simulated as examples. The influence of cooling window, the laser output duration and spatial gradient of the beam energy intensity, and material parameters on the beam quality is analyzed.