Coherence properties of a doubly resonant monolithic optical parametric oscillator

We describe a doubly resonant optical parametric oscillator (DRO) pumped with the second harmonic of a narrow-linewidth Nd: YAG laser. The linewidth of the DRO signal was less than 13 kHz, the DRO was shown to generate a phase-locked subharmonic of the pump at degeneracy, and the signal and the idler were shown to be mutually coherent with the pump and to be phase anticorrelated with each other away from degeneracy. The signal–idler heterodyne linewidth was 500 Hz, and pump phase modulation was shown to transfer to the DRO phase at degeneracy.