Beam-quality studies of nanosecond singly resonant optical parametric oscillators

A numerical model for a singly resonant, nondegenerate optical parametric oscillator, which includes diffraction and idler absorption, has been developed. This model requires just one equation for the resonated signal field to be numerically integrated, while the pump and idler fields are reconstructed from their analytic solutions and the dynamics of the signal field. Typical results from our simulations are, for example, output intensities and threshold fluencies, which can be compared with those obtained from experiments. The spatial beam quality of output beams produced by our model is evaluated via the M/sup 2/ factor. We present results from the simulation which are consistent with experimental evidence, particularly in reference to the impact of idler absorption.