Nonlocal dynamic gratings and energy transfer by optical two-beam coupling in a nematic liquid crystal owing to highly sensitive photoelectric reorientation

We investigate a new ultrahighly sensitive nonlinear optical response in pure nematic liquid crystals composed of rodlike molecules characterized by conjugated acetylene groups. Under the combined application of low-intensity optical waves and dc electrical fields, a photorefractivelike grating formation has been found in degenerate four-wave mixing experiments. Polarization-dependent pump-probe experiments reveal the underlying orientational effect of a space-charge field. The photorefractive-like origin of the gratings was proved by two beam-coupling experiments in which a refractive-index grating was phase shifted by pi /2 with respect to the interference grating. The huge optical nonlinearity found in such materials makes them promising for future applications in all-optical image processing and adaptive optics.