PARAMETRIC AMPLIFICATION AND OSCILLATION WITH WALKOFF-COMPENSATING CRYSTALS

We measure and model parametric gain and oscillation for two crystals arranged for walkoff compensation. We show how the orientation of the crystals determines the relative sign of the nonlinear mixing coeffici ent in the two crystals. This sign dramatically influences small signa l gain and oscillator performance, and we show how to determine the co rrect crystal orientation from parametric-gain measurements. The perfo rmance of two-crystal oscillators is examined with particular attentio n to beam tilts, conversion efficiency, and beam quality. We find redu ced efficiency and increased oscillation threshold when the coefficien ts have opposite signs in a two-crystal ring oscillator. Sign reversal seems to have little influence on spectral purity or far-field beam p rofiles when the oscillator is seeded. (C) 1997 Optical Society of Ame rica.