Thermal birefringence effect on the performance of a laser-diode pumped solid-state laser

We report the high-sensitivity measurements of two-dimensional (2D) thermal birefringence distribution in a laser-diode (LD) pumped Nd:glass (HAP4) laser under lasing (at 1054 nm) and under no lasing conditions. The thermal birefringence was reduced under the lasing condition owing to the depletion of stored energy by stimulated emission. By inserting a 90° quartz rotator between two identical LD pumped Nd:glass rods, almost perfect birefringence compensation was achieved. The power loss due to thermal birefringence was evaluated quantitatively using the Jones matrix method. A considerable reduction of power loss, from over 12% before compensation to less than 0.4% after compensation, was observed. The output performance of this laser was in fairly good agreement with the estimation after taking into account the power loss due to thermal birefringence.