Study on the Control of Thermal Birefringence in the Laser-Diode Pumped Solid-State Laser Driver

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a) An LD pumped solid state laser is expected to deliver high average laser power output with high efficiency at hight repetion rate and is a promising candidate of laser driver for an inertial fusion power plant. The key issue in the development of high power solid state laser is to reduce the thermally induced distortion of laser output. The main efforts of this study are aimed to analyze the thermal properties of LD pumped solid state laser and to develop the new techniques to compensate for the thermal effects. For these purposes, the temperature distributions in the laser system were calculated by the simulation code named STREAM,and a code to calculate the spatial distribution of thermally induced birefringence was newly developed and applied to the design of laser system.b) We performed the high-sensitivity measurements of two-dimensional (2D) thermal birefringence distribution in a laser-diode (LD) Pumped Nd : glass (HAP4) laser lasing (at 1054nm) and under no lasing conditions … More . The thermal birefringence was reduced under the lasing condition owing to the depletion of stored energy by stimulated emission. By inserting a 90 degree 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.c) A novel laser architecture of laser-diode pumped eight pass 1064-nm Nd : YAG zig-zag slab laser amplifier was developed aming to achieve high energy extraction efficiency and good bcam quality. A high energy extraction efficiency of upto 73% for the laser mode volume has been achieved in this amplififier operating at an initial small signal gain of 3.36. The excellent beam quality factor M squared of 1.2 has been obtained. The compensation of thermal birefringence in this amplifer was successfully performed using a 90 degree quartz rotator. Less