片状热容激光器热效应有限元分析

 基于激光介质的非均匀内热源模型，利用有限元数值方法，模拟计算了热容模式下高功率激光二极管阵列(LDA) 重复脉冲泵浦片状激光介质的瞬态温度分布和热应力分布及其波前畸变和应力双折射。结果表明:热容模式下，当增益介质不能够被全口径泵浦时，也会出现严重的热效应，介质的表面靠近边缘处会出现大的拉应力集中，介质表面的最大轴向位移和最大拉应力随泵浦光斑尺寸缩小而增大；而当全口径泵浦时，介质表面热形变大大减弱，较小的拉应力存在于介质内部，而且泵浦光斑和介质的几何形状对热分布有很大影响。结果还表明，介质片表面变形和热光效应是产生波前畸变的主要原因，而热应力双折射产生的附加相移与激光介质的切割方向有关，它对光束产生较大的退偏作用，从而影响激光器的输出性能。理论模型得到了实验结果的验证。

Finite element analysis on thermal effect of heat capacity laser disk

Considering inhomogeneous heat generation and real heat-transfer conditions, the transient temperature and thermal ,;tress distribution in disk of heat capacity laser pumped by high power LDA are simulated and analyzed by use of finite element methods. Optical distortions and birefringence are computed subsequently. The results indicate that the magnitude of the thermal effect in heat capacity disk laser are seriously underestimated in the condition of the medium not being full-aperturedly pumped. Simulation results also indicate that for the same pump intensity, the temperature and thermal stress distribution are not only related with the medium geometry and the special distribution of pump intensity but also related with filling factor of pump area versus hard aperture of disk. When the filling factor is less than 1, the concentrated tensile stress appears near the edge of hard aperture, while the filling factor reaches up to 1, the surface exhibits less compressive stress and the center shows less tensile stress. Deformation of disk surfaces and refractive index changing with temperature are primary factors of optical distortions. Stress-birefringence is related with Miller indices of the disk surface, which results in depolarization and also affects the laser output quality. Comparisons between code predictions and experimental results are also given, which agree well with each other.