Response of an artificial Kerr medium to moving electromagnetic gratings

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Abstract
We examine the nonlinear response of a liquid suspension of microspheres to moving electromagnetic gratings. Such gratings are associated with the overlap of pairs of nearly degenerate laser fields in coherent beam combination and four-wave-mixing applications. The Brownian suspension also serves as a useful model Kerr medium for which the response to arbitrarily strong fields is obtained. This response includes the formation of higher-order particle-density gratings oscillating at harmonics of the frequency difference between the incident fields. It is found that the first-order grating, which oscillates at the fundamental frequency, will coherently scatter the high-frequency wave into the low-frequency beam. Expressions for the particle current, power dissipation, and entropy of grating formation are obtained.