Single-frequency laser based on single-pass QPM frequency doubling of Tm-doped fiber MOPA

In order to obtain a 0.9 μm near-infrared continuous-wave single-frequency laser output, a 50 mm long PPLN crystal was used to perform single-pass frequency doubling of the continuous-wave 1 925.08 nm single-frequency laser output of the Tm-doped fiber MOPA, and the temperature was matched by focusing parameters and quasi-phase optimized to achieve 96.95 nm second harmonic output up to 9.07 W at a fundamental optical power of 43.4 W, with a conversion efficiency of 20.9%.The second harmonic was in single longitudinal mode with M² factors of 1.36 and 1.52 on x and y directions, respectively. The influence of focusing parameter and temperature on the conversion efficiency was experimentally investigated. The relationship between the focusing parameter and phase matching temperature acceptance was also discussed. The experimental results show that Tm-doped fiber laser quasi-phase matching one-way frequency doubling is an effective method to obtain 0.9 μm band continuous wave single frequency laser output.