固体激光器中的热致双折射效应严重地限制了基模输出功率的提高,为了获得大功率高质量的激光输出,需要对热致双折射效应进行补偿。在理论上对双棒在腔内串接补偿热致双折射效应的条件进行了改进,通过设计合理的腔结构和腔内元器件,应用4f成像系统空间滤波器并考虑石英旋光器的厚度,使得腔内光束的退偏率降至2.5%以下。使用矩阵光学的方法简化了对含有这样一个复杂光学系统的谐振腔稳定性和腔内光束半径等特性的分析。通过在腔内加入一个正透镜来扩大基模体积,实验中在双氪灯连续抽运Nd∶YAG激光器中得到了61 W线性偏振的激光基模输出,表明在大基模体积谐振腔的设计中,双折射效应的补偿十分必要。

The thermal-induced birefringence is a key factor limiting the output power of a laser system in fundamental mode. Birefringence compensation is mandatory for high power lasers with good beam quality. The principle of birefringence compensation by use of two Nd∶YAG rods is investigated. Considering the thickness of a quartz polarization rotator, a revised model is presented by use of proper cavity structure and components with a 4f imaging spatial filter for birefringence compensation. The depolarization ratio less than 2.5% is achieved experimentally. By means of matrix optics, a cavity containing a two-rod system is equivalent to a thin lens, which allows one to analyze the system properties such as stability of the resonator and beam radius in the cavity. A positive lens is inserted into the cavity to enlarge the fundamental mode volume, 61W linearly polarized output is obtained in a lamp continuous wave (CW)-pumped Nd∶YAG laser. It is shown that the birefringence compensation is essential for a dynamic stable resonator with a lage fundamental mode volume.