Influence of laser linewidth on external-cavity frequency doubling efficiency of a 1.56μm master oscillator fiber power amplifier

By using an external-cavity frequency-doubling master oscillator fiber power amplifier (MOPA), a 700 mW continuous-wave single-frequency laser source at 780 nm is produced. It is shown that the frequency doubling efficiency is improved when the seed diode laser is optically locked to a resonant frequency of a confocal Fabry--Perot (F-P) cavity. This phenomenon can be attributed to the narrowing of the 1.56 μm laser linewidth and explained by our presented theoretical model. The experimental results are found to be in good agreement with the theoretical predictions.