Aperture obstruction influences birefringence evaluation of a Nd : YAG laser system with tandem-set rods

In this study, we derive a theoretical and experimental expression for evaluating the thermally induced birefringence (TIB) in a Nd : YAG laser system with double rods in tandem. The analytical solution determines the optimum oscillator geometry corresponding to the minimum depolarization loss while the so-called aperture obstruction is considered in the calculation model. It can be seen that the experimental results closely follow the theoretical evaluation for both the depolarized degree and the birefringent distribution of a probe beam. We also find that the traditional evaluation method, which neglects the thermally induced lens effect and aperture truncation during the optical design, leads to an obvious deviation in determining the optimum arrangement of a laser system for compensation of birefringence. The method presented in this paper is thought to be useful in analysing any high-powered oscillators or amplifiers with high pulse energy.