Abstract

When a coherent beam is incident on a random phase screen, such as a rotating ground glass plate, the phase fluctuations in the emerging beam tend to decrease the coherence. The coherence properties of the beams generated by such partially coherent sources have been studied extensively in recent years. In this paper, we discuss the effect of degrading the spatial coherence of the pump beam on the conversion efficiency in the second-harmonic process. We consider the situation in which a laser beam whose coherence has been degraded by a random phase screen propagates in a nonlinear medium. We restrict ourselves to the situation where the conversion efficiency is not very large so that the parametric approximation is valid. For the description of the random phase screen we consider two models: (1) a Gaussian Schell-model source¹ and (2) a model due to Berry.² Our results indicate that by an appropriate choice of parameters it should be possible to enhance the conversion efficiency of the second-harmonic beam by a factor of 2, compared to a coherent laser. We also present reciprocity relations between the coherence and intensity distributions of the pump beam in the entrance plane and the second-harmonic beam in the exit plane.

© 1986 Optical Society of America