Abstract

Beam propagation in nonlinear media, photorefractive crystals in particular, is an active field of study. Most experiments are devoted to single-beam propagation. Another interesting case is the evolution of the periodical array of beams, of which the simplest possibility is a set of interference fringes produced by the two plane-wave intersection. We report experiments in a bismuth titanate oxide crystal with two beams crossing with a small angle and a strong external electric field applied. Because of a special experimental arrangement, we were able to apply fields up to about 50kV/cm, which is 4-5 times bigger than normally utilized values. The fringe form and spatial harmonics content were monitored. Both are in a good agreement with a computer simulation without fitting parameters. The self-focusing obtained after 5 mm thick crystal resulted in narrowing of bright fringes and up to 2.5 times growth in their maximal intensity. Up to 8 -10 higher diffraction orders could be seen. For external fields bigger than 40kV/cm, optical noise starts to develop. We suggest that it can be due to the mechanism of parametric oscillation with a feedback produced by the beam reflection from the rear crystal face [1]

© 2001 Optical Society of America