Observations of internal beam production in barium titanate phase conjugators

Abstract

We have observed a variety of internal beam configurations in photorefractive BaTiO3 pumped by a cw Ar+ laser at 514.5 nm. Among these configurations was a total-internal-reflection ring resonator contained entirely within the crystal, with light circulating unidirectionally in the plane of the beam fanning. Phase-conjugate responses were in general found to depend critically on system parameters, in particular, on the separation between the pump focusing lens and the crystal. During the pulsation mode of the phase-conjugate reflection, a sudden frequency shift of 5–10 Hz was observed to occur during the pulse’s trailing edge. Certain internal beam patterns were found to be frozen into the crystal and were nearly invariant to small lateral motions of the pump beam across the crystal. Phase-conjugate returns, which would appear to the naked eye to be cw, were often found to possess nearly periodic fluctuations in amplitude and in center frequency.