Instabilities in a Self-Pumped Barium Titanate Phase Conjugate Mirror

Abstract

We report the observation of intrinsic instabilities in the reflectivity of a barium titanate, self-pumped phase conjugate mirror (SPPCM). In such a device, a laser beam is focused into a crystal of barium titanate, and a beam is generated within the crystal that has been shown by FEINBERG [1] to be the phase conjugate of the incident laser beam. A model has been proposed [2] to explain this effect in terms of self beam fanning: the incident laser beam breaks up into new spatial components by self focusing. These components undergo total internal reflection at the corners of the crystal and are redirected in such a way that they intercept the incident laser beam, thereby forming the counterpropagating pump waves needed to create the phase conjugate beam by the usual four-wave mixing process. Since the pump waves grow from noise by a highly nonlinear process, and interact strongly with the incident and conjugate beams, it might be expected that the output beam would show unstable or even chaotic behavior. An alternative model for self-pumped phase conjugation has been presented by LAM [3]. According to this model, the phase conjugate return is formed by a two-beam stimulated scattering process. This process would not be expected to produce a chaotic output.