Abstract

Material parameters, including refractive index modulation depth, space charge field, and trap charge density, in photorefractive barium titanate are determined using a novel laser-induced grating spectroscopic probe technique. In this method, shown in Fig. 1, coherent laser beams (grating writing beams) intersect inside the crystal and induce (write) a refractive index grating via the photorefractive effect. A laser probe beam is applied to the crystal parallel to the grating planes (i.e. at normal incidence to the plane of the grating writing beams, in a Raman-Nath type configuration) and is diffracted into higher order modes (|m|≥1) located symetrically at angles ±θ_Dm about the undiffracted (m=0) mode. The crystal is in air and is supported by an optical flat attached to a rotating platform (not shown in Fig. 1) which allows us to rotate the crystal about the z-axis, thus varying the intersection angle of the grating writing beams in the crystal (for fixed writing beams in air), thereby varying the grating spacing, Λ_g, in the crystal. Additionally, the platform provides for tilt adjustment of the x-y plane in order to precisely align the induced phase grating planes and the probe beam to obtain symmetry in the intensities of the positive and negative modes (orders) of diffraction.

© 1988 Optical Society of America