Thermal Compensation of a Cw-Pumped Nd:YAG Laser

Thermally induced lensing and birefringence modify the transverse laser profile and may eliminate any global polarization state in systems utilizing Nd:YAG as a gain medium. This creates fundamental difficulties in obtaining a high-power, polarized output beam. Although abundant literature exists regarding thermal lensing, only one birefringence compensation scheme is prevalent in the literature. A modification of this scheme is given that eliminates residual birefringence. Experimental data verify the model's validity. A theoretical model is then presented that modifies the birefringence-compensated amplifier as a single power-dependent lens. After showing that solutions exist for a power-independent resonator consisting of a power-dependent lens between two flat mirrors, this amplifier is inserted into the resonator solution to produce, to first order, a resonator that is insensitive to thermally induced fluctuations in the rod focal length.