A theoretical and experimental study of fluctuations of the optical parametric oscillator

Twin beams generated by OPOs show quantum noise reduction. For type I crystals they reduce in the degenerate case to a single mode, which below threshold exhibits some degree of squeezing. In the nondegenerate case squeezing occurs in the spectrum of their intensity difference. After a theoretical analysis of their spectral properties in both non- and degenerate cases, measured intensity noise correlation and single beam spectra are discussed for pump powers up to 14 times the threshold value.