Optical phase locking in the microradian domain: potential applications to NASA spaceborne optical measurements.

We have constructed and demonstrated a high-performance optical phase-locked loop between two cw Nd:YAG lasers. The feedback system is relatively simple, employing only the laser's internal piezoelectric transducer and an external acousto-optic modulator. A residual phase noise of the order of 1microrad between two optical fields is achieved in the locked condition, as is verified by time- and frequency-domain analyses by the two-oscillator approach that is conventionally used in rf measurement. Potential applications to NASA space-based optical measurements are discussed.