Tawy Goronwy, Wang Jian, Damzen Michael J
Opt Express. 2019 Nov 25;27(24):35865-35883. doi: 10.1364/OE.27.035865.
It is essential to understand the pump-induced lensing and aberration effects in solid-state lasers, such as Alexandrite, since these set limits on laser power scaling whilst maintaining high spatial TEM beam quality. In this work, we present direct wavefront measurements of pump-induced lensing and spherical aberration using a Shack-Hartmann wavefront sensor, for the first time, in a diode-pumped Alexandrite laser, and under both non-lasing and lasing conditions. The lens dioptric power is found to be weakly sub-linear with respect to the absorbed pump power, and under lasing, the lensing power is observed to decrease to 60 % of its non-lasing value. The results are inconsistent with a thermal lens model but a fuller theoretical formulation is made of a combined thermal and population lens model giving good quantitative agreement to the observed pump power dependence of the induced-lensing under non-lasing conditions and the reduced lensing under lasing conditions. The deduced value for the difference in excited to ground state polarizability is consistent with prior measurement estimates for other chromium-doped gain media. The finding of this paper provide new insight into pump-induced lensing in Alexandrite and also provides a basis for a fast saturable population lens mechanism to account for self-Q-switching observed recently in Alexandrite laser systems.
了解诸如紫翠宝石等固态激光器中泵浦诱导的透镜效应和像差效应至关重要，因为这些效应在保持高空间TEM光束质量的同时，对激光功率缩放设置了限制。在这项工作中，我们首次在二极管泵浦的紫翠宝石激光器中，在非激光和激光条件下，使用夏克-哈特曼波前传感器对泵浦诱导的透镜效应和球差进行了直接波前测量。发现透镜焦度相对于吸收的泵浦功率呈弱次线性关系，并且在激光状态下，观察到透镜功率降至其非激光状态值的60%。结果与热透镜模型不一致，但一个更完整的理论公式由热透镜和粒子数透镜组合模型给出，该模型在非激光条件下对观察到的泵浦功率依赖的诱导透镜效应以及激光条件下降低的透镜效应给出了良好的定量一致性。推导出的激发态与基态极化率差异值与其他掺铬增益介质的先前测量估计值一致。本文的发现为紫翠宝石中泵浦诱导的透镜效应提供了新的见解，也为一种快速可饱和粒子数透镜机制提供了基础，以解释最近在紫翠宝石激光系统中观察到的自调Q现象。
