Quantum correlation and absorption spectroscopy in an optical parametric oscillator in the presence of pump noise.

We present a linearized quantum analysis of the optical parametric oscillator that includes the effects of pump noise. We show that excess pump noise reduces the intensity correlation between the signal and idler at low frequencies, which explains the low-frequency spectrum of current experimental observations. Its dependence on the cavity loss mismatch permits the possibility of ultrasensitive intracavity absorption spectroscopy, even in the absence of nonclassical correlation observation.