Abstract

Two principal mechanisms for optical nonlinearity in nematic liquid crystal films, namely, orientational and thermal nonlinearities, are analyzed in the context of four-wave mixing involving two sets of laser. The incident object and reference beams that create the phase grating in the nematic via molecular reorientation or thermal heating are in the infrared. The reconstructing beam is in the visible and is incident at the Bragg angle. This produces a visible image beam. The phase-matching conditions for various wave-vector configurations (forward or conjugated geometries) are analyzed, and expressions for the resolution capability of this type of imaging setup are obtained. Experimentally, we have observed IR to visible image conversion in thin films of pure nematics or nematic doped with IR absorbing dyes. Large, observable diffractions can be generated in films of the order of 50 μm thick. The corresponding resolution elements capability was estimated to be > 10⁴. This compares favorably with previous experiments performed in high index liquids.

© 1985 Optical Society of America