Periodic Behavior in Photorefractive Two Beam Coupling

It is well known that the behavior of dynamical processes described by non-linear equations may lead to period doubling bifurcations and quasi-periodic behavior. Krolikowski, et.al. (1) have predicted that for four wave mixing, in the presence of an applied external field, periodic behavior can be observed. These predictions show that the observed period is constant in time for a given set of parameters. We have completed two beam coupling experiments using a helium neon laser as a source, and barium titanate as the photorefractive material. In the absense of an applied electric field we have observed periodic behavior during these experiments.