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

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 achiev ed, which is die highest power-coupling efficiency ever reported. It was sh own experimentally that the frequency and intensity noise level of the cohe rently-added laser are the same as those of a single injection-locked laser . In particular, no additional intensity noise was observed above the relax ation oscillation frequency of the slave laser, which is suitable for use a s the light source for a future gravitational wave detector. The frequency noise of the coherently-added laser was suppressed to 1 x 10(-4) Hz/root Hz by controlling that of the master laser, and the intensity noise was also suppressed to 1 x 10(-8) /root Hz by controlling the intensity of pump lase rs used for the slave lasers.