Mechanisms for optical oscillations in ferroelectric films

Under steady laser illumination, aperiodic spatio-temporal oscillations are observed in the light transmitted and reflected by parallel-sided samples of the ferroelectrics PMN (lead magnesium niobate, Pb(Mg1/3Nb2/3)O3), PLZT (lanthanum doped lead zirconium titanate, Pb(Zr1–xTix)O3:La), BNN (barium sodium niobate, Ba2NaNb5O15) and Ce:SBN (cerium doped strontium barium niobate, Ce3+:SrxBa1–xNb2O6). There are two distinct mechanisms for such oscillations, namely (1) unistable thermal focusing oscillations, which occur in BNN and Ce:SBN and (2) bistable or multistable Fabry-Perot switching oscillations, as observed in PMN and PLZT. The two types of oscillation have characteristic time scales differing by several orders of magnitude. We derive temperature profiles as a function of incident laser power, beamwidth and sample thickness, which quantitatively predict the spatio-temporal characteristics of the transmitted beam patterns.