Abstract

The dynamic behavior of grating formation in photovoltaic media is different from that in nonphotovoltaic media. For example, grating formation depends on the initial conditions as well as the boundary conditions. This fact causes a problem when we attempt to find an exposure procedure for the recording of multiple holograms. In this paper, we solve the Kukhtarev equations, taking into account various possible boundary conditions that describe the growth of holograms in photovoltaic media. We then provide theoretical plots, using published values of parameters for LiNbO₃, that describe the transient behavior of holograms. The experimental results, which show different dynamic behaviors during grating formation for different boundary conditions, are then compared with the theoretical calculations. Both the experimental results and theoretical simulation show the typical behavior of grating formation that does not occur in nonphotovoltaic media, i.e., when the writing starts from an open-circuited crystal without a nonuniform charge distribution, the diffraction efficiency increases to a maximum and then decreases to its steady state. This occurs because the change in the charge distribution owing to the photovoltaic current occurs on a time scale similar to the photorefractive time constant. The results of this paper also suggest that one simple solution to the recording of multiple holograms might be to short circuit the crystal.

© 1990 Optical Society of America