Abstract

We present results from measurements obtained using Raman-Nath diffraction patterns from laser-induced gratings in single crystals of barium titanate. Analyses of these patterns lead to determination of grating and material parameters. The experimental technique consists of passing a probe laser beam parallel to the planes of a grating formed via the photorefractive effect from the interference pattern of coherent laser writing beams which intersect in the crystal. The Raman-Nath diffraction pattern which is observed on a screen placed beyond the interaction region consists of multiple modes angularly separated and located symmetrically about the zero-order (undeflected) mode. The angle of deflection of a particular mode is a function of the ratio of probe beam wavelength to grating spacing in the crystal; the intensity of a particular mode is a function of refractive-index modulation depth. For a fixed angle between the input write beams, the grating spacing in the crystal is varied by rotating the crystal with respect to the input write beam angles. By observing relative intensity changes of the various modes, a best fit of the data to the squared Bessel function curves describing Raman-Nath diffraction gives a value of refractive-index modulation depth. This value in turn leads to the determination of the space charge field and charge concentration.

© 1987 Optical Society of America