The beam quality of diode-pumped alkali lasers (DPALs) is of major concern in the studies of these lasers. We report on experimental studies and modeling of the beam propagation factor M 2 in flowing-gas Cs DPALs with stable optical resonators and of its dependence on the resonator geometry. The measured values of M 2 are in agreement with those calculated using the optical model of multi-transverse mode operation (Auslender et al. in Opt Express 25:19767, 2017). Conditions for substantial improvement of the output laser beam quality, reducing M 2 to close to unity, are found. Changing the length of the resonator, and/or the radius of curvature of the high reflection mirror, leaving all other parameters of the laser unchanged, makes it possible to control the beam quality. Techniques for controlling M 2 in DPALs with wide-aperture beams have not been studied elsewhere and are very important for the applications of this laser. In addition to the optical model, a simple analytical method based on the model suggested by Siegman (IEEE J Quantum Electron 29:1212, 1993) is applied to the experimental results and predicts a simple scaling law for M 2 as a function of the size of the resonator fundamental mode.

中文翻译：

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通过改变谐振器参数控制 DPAL 中的光束质量

二极管泵浦碱性激光器 (DPAL) 的光束质量是这些激光器研究中的主要问题。我们报告了具有稳定光学谐振器的流动气体 Cs DPAL 中光束传播因子 M 2 的实验研究和建模及其对谐振器几何形状的依赖性。M 2 的测量值与使用多横向模式操作的光学模型计算的值一致（Auslender et al. in Opt Express 25:19767, 2017）。发现了显着改善输出激光束质量、将 M 2 降低到接近于 1 的条件。改变谐振腔的长度和/或高反射镜的曲率半径，保持激光器的所有其他参数不变，可以控制光束质量。在具有大孔径光束的 DPAL 中控制 M 2 的技术尚未在其他地方进行过研究，并且对于这种激光器的应用非常重要。除了光学模型，基于 Siegman (IEEE J Quantum Electron 29:1212, 1993) 建议的模型的简单分析方法应用于实验结果，并预测 M 2 作为尺寸的函数的简单标度律谐振器基模。