Analysis of Gaussian-beam degenerate optical parametric amplifiers for the generation of quadrature-squeezed states

This paper investigates the generation of quadrature-squeezed states of light using a degenerate optical parametric amplifier (DOPA) that is pumped by a focused Gaussian beam. The formulation that is presented facilitates the calculation of squeezing for an arbitrary local oscillator beam. This formulation also establishes a formal equivalence between the classical parametric gain and the measured level of squeezing. The maximum squeezing that can be achieved using a Gaussian-beam local oscillator is determined to be limited to 13.4 dB, as a consequence of gain-induced diffraction. The phase lag of the maximally squeezed quadrature is shown to be significantly different from the plane-wave theoretic value of π/2, unless the focusing is very weak. The use of a second DOPA for generating a local oscillator beam that is matched to the squeezed field is also investigated. In this case, squeezing is limited only by the available pump power.