Thermal-birefringence-induced depolarization in a 450 W Ho:YAG MOPA system

We demonstrated an efficient, high-power Ho:YAG master-oscillator power amplifier (MOPA) system and investigated its thermal-birefringence-induced depolarization. The maximum output power was 450 W with a depolarized power of 32.1 W and depolarization of 0.071 via three power amplifiers. To our knowledge, this is the highest average power generated from a Ho:YAG MOPA system. In theory, a simplified model was built to calculate the depolarization in the amplifier, and the theoretical results agreed with the actual value well. Moreover, the overall optical-to-optical efficiency of the MOPA system was near 60%, and the beam quality M-2 factors of s-polarized laser were measured to be similar to 1.8 at 400 W. In pulse operation, the per pulse energy was similar to 11 mJ at the pulse repetition frequency of 40 kHz with the corresponding peak power of 220 kW. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement