Coherence Properties of Light from Optical Parametric Oscillators
ABSTRACT :
Nonclassical light beams generated by degenerate and non-degenerate optical parametric oscillators (OPO) have played an important role in studies of nonclassical properties of light such as those reflected in squeezing, quantum entanglement, and other nonclassical features of photon statistics. Fluctuation properties of these nonclassical light beams have been studied by using several different coherent state representations of the field density matrix. This talk will discuss the use of positive-P representation of the density matrix to map nonlinear quantum dynamics of an OPO onto c-number stochastic equations. By using the insights gained from these equations, exact analytical expressions for the positive-P functions both for the degenerate and nondegenerate OPOs can be obtained. From these functions simple expressions for various experimentally measurable quantities such as the mean and variance of the light intensity, quadrature squeezing, and photon number distributions can be derived. These expressions are valid below, near and above threshold of oscillation. How these properties are transformed as the oscillator makes a transition from below to above threshold will be discussed and the results for the OPOs will be compared and contrasted with those for the single-mode and two-mode lasers.