Abstract

We have carried out a linearized quantum analysis of the steady-state operation of an optical parametric oscillator (OPO) without cavity detunings; our analysis emphasizes the effects of pump quantum noise and pump excess noise. We show that pump excess noise reduces the observable signal/idler intensity correlation at low frequencies only in the presence of a cavity-loss mismatch between these subharmonic waves. This effect is so strong that the combination of pump excess noise and cavity-loss mismatch explains the rapid low-frequency noise increase well above the shot-noise level that has been seen in recent signal/idler correlation measurements. Moreover, the critical dependence of intensity correlation on cavity-loss mismatch opens a new possibility for ultrasensitive intracavity absorption spectroscopy. Specifically, sinusoidal amplitude modulation of the OPO pump beam with lock-in amplification of the signal/idler photocurrent affords a sensitive probe of subharmonic cavity-loss mismatch. Although this robust measurement capability exploits the strong intracavity correlation between the signal and idler waves, it does not require that nonclassical correlation be externally observable, nor is it limited to near-threshold OPO operation.

© 1990 Optical Society of America