Abstract

Anisotropic, artificial Kerr media develop large nonlinear susceptibilities under the influence of strong optical fields because of the formation of translational and reorientational gratings. When the interaction energy between the particles’ induced dipole moments and the applied field is less than the thermal energy of the host fluid, the medium is adequately described by a third- order susceptibility. However, when the interaction energy surpasses kT, higher-order terms are necessary to correctly describe this situation. We investigate this latter regime in several colloidal dispersions of titanium dioxide, whose diameters range from 100 to 300 μm. The particles possess a large intrinsic birefringence, resulting in a large reorientational nonlinearity. In addition, their average index is greatly mismatched with the host, water, so that the translational nonlinearity is also quite large. The technique we employ to investigate these samples is nondegenerate two-beam coupling with cw Ar⁺ and Nd:YAG lasers. The most striking feature we see is the direction of energy transfer reverses in the regime where the higher-order effects become important.

© 1992 Optical Society of America