Polarization self-modulation effect in photoconductive electrooptic crystals

Inhomogeneous illumination of any photoconductive crystal results in the formation of the space-charge field, which is a replica of the intensity distribution. If the crystal also possesses the electrooptic effect, the polarization state of the intensity pattern becomes spatially modulated since the pattern propagates in the self-induced non-uniform electric field. The polarization self-modulation has essentially three-dimensional character. After propagation the crystal of proper thickness, the polarization state of the transmitted light wave can vary from linear through circular to linear orthogonal in spite of the initial polarization being strictly uniform. This modulation can be readily visualized by installation of a polarization analyzer after the crystal. The polarization self-modulation is very important for correct description of nonlinear interaction of light waves in photorefractive crystals. Moreover, it has an important practical application for design of adaptive sensors of speckle-pattern displacements and adaptive interferometers capable to measure transient displacement of rough surfaces with sensitivity approaching to the classical homodyne interferometer.