Abstract

During the last decade, much attention has been paid to nonlinear optics in liquid suspensions of dielectric, spherically shaped microparticles.¹ Such media exhibit very large values of nonresonant third-order susceptibility (χ⁽³⁾ ~ 101^(-7) esu) through radiation-induced diffusive rear-rangement of the particle number density. We report on phase conjugation by degenerate four-wave mixing in liquid suspensions of ellipsoidal polymer microparticles. In these materials, both electrostrictive forces and orienting torques act on the particles, because of the anisotropy of particle polarizability. Thus, in addition to translational gratings, orientational gratings are created, with the particles aligned along preferred directions.² From the macroscopic point of view, this results in a completely tensorial nature of the χ⁽³⁾, whereas isotropic particle suspensions show only scalar nonlinearities. We have demonstrated this characteristic by carrying out four-wave mixing measurements with various combinations of the incoming beam polarizations. The predicted polarization states of the outcoming conjugated beam have been observed and the relative conjugation efficiencies reasonably agree with theory.²

© 1989 Optical Society of America