Intensity and frequency noise characteristics of two coherently-added injection-locked Nd:YAG lasers

Abstract

Coherent addition of two injection-locked Nd:YAG lasers has been performed. A maximum output power of 4.4 W and addition efficiency of 0.94 was achieved, which is the highest power-coupling efficiency ever reported. It was shown experimentally that the frequency and intensity noise level of the coherently-added laser are the same as those of a single injection-locked laser. In particular, no additional intensity noise was observed above the relaxation oscillation frequency of the slave laser, which is suitable for use as the light source for a future gravitational wave detector. The frequency noise of the coherently-added laser was suppressed to ${{1 \times 10^{ - 4} } \mathord{\left/ {\vphantom {{1 \times 10^{ - 4} } {\sqrt {Hz} }}} \right. \kern-\nulldelimiterspace} {\sqrt {Hz} }}$ by controlling that of the master laser, and the intensity noise was also suppressed to ${{1 \times 10^{ - 8} } \mathord{\left/ {\vphantom {{1 \times 10^{ - 8} } {\sqrt {Hz} }}} \right. \kern-\nulldelimiterspace} {\sqrt {Hz} }}$ by controlling the intensity of pump lasers used for the slave lasers.