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

We investigate a new ultrahighly sensitive nonlinear optical response in pu re nematic liquid crystals composed of rodlike molecules characterized by c onjugated acetylene groups. Under the combined application of low-intensity optical waves and dc electrical fields, a photorefractivelike grating form ation has been found in degenerate four-wave mixing experiments. Polarizati on-dependent pump-probe experiments reveal the underlying orientational eff ect of a space-charge field. The photorefractive-like origin of the grating s was proved by two beam-coupling experiments in which a refractive-index g rating 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 optic s. (C) 2001 Optical Society of America.