固体激光器中正交偏振模式间增益竞争的研究

Gain Competition Between Orthogonally Polarized Modes in Solid-State Lasers

由兰姆半经典激光理论可知,固体激光器中两个模式能否同时振荡取决于两个模式之间的耦合程度,其定义为增益竞争引起的互饱和系数与自饱和系数之比。实验中,利用两个四分之一波片搭建了双频Nd…YAG固体激光器,实现了频差从30 MHz到1.3GHz连续可调的双频激光输出,在此基础上,测量了两正交偏振模式在不同频差输出条件下的噪声功率谱密度,计算出表征两个模式间增益竞争程度的耦合系数。理论上,根据兰姆半经典理论推导出耦合系数的表达式,验证了实验中耦合系数随着频差增加而减小的变化趋势,分析了影响耦合系数的因素,为进一步优化双频固体激光器提供理论基础。

According to Lamb′s semiclassical laser theory,whether the two modes in a solid-state laser can oscillate simultaneously depends on the mode-coupling coefficient between them.The coupling coefficient is defined as the ratio of cross-saturation factors and self-saturation factors.A dual-frequency NdYAG solid-state laser is built with two quarter-wave plates,and the frequency difference from30 MHz to 1.3 GHz is obtained.On this basis,the noise power spectrum density of two orthogonally polarized modes is measured under different frequency differences,by which the coupling coefficients of gain competition between two modes are calculated.In theory,based on the Lamb′s semiclassical laser theory,the coupling coefficient expression is deduced,and the trend that the coupling coefficient decreases with the increasing of frequency difference is verified.The factors influencing the coupling coefficient are analyzed.It provides the theoretical foundation for further optimization of dual-frequency solid-state laser.