FOCUSING AND DEFOCUSING REGIMES IN THE MULTISTABLE OPTICAL-RESPONSE OF SINGLE-CRYSTAL LEAD MAGNESIUM NIOBATE

Experimental observation of the static and dynamic response of monocry stalline lead magnesium niobate, Pb(Mg1/3Nb2/3)O-3 (PMN), at moderate power c. w. laser irradiation shows five distinct regimes depending on the beamwidth and wavefront curvature of the incident Gaussian laser beam. In one of these regimes, the system exhibits multistability and transient aperiodic regenerative oscillations similar to those observe d previously in ceramic PMN. In the other four regimes, thermal focuss ing and/or defocussing combine with nonlinear Fabry-Perot resonances t o produce qualitatively different responses. The thermal relaxation ti me is calculated theoretically as 1 - 500 s, about 10(3) longer than e arlier estimates and in agreement with experiment. Damage thresholds a re also discussed.