Abstract

Electromagnetic alignment of the microparticles, by either a uniform electric field or polarized radiation, changes the gain spectrum for energy transfer via nondegenerate two-wave mixing in three distinct ways: (1) the low frequency peak of the gain spectrum, arising from the translational grating, is enhanced, (2) the high frequency portion of the gain, arising from the orientational grating, is enhanced, and (3) the high frequency portion of the gain spectrum is upshifted so that the orientational peak will occur at higher frequencies. The blue shift in the orientational peak arises because microparticle alignment reduces the rotational response time. The enhancement of the low frequency portion of the gain spectrum arises from the formation of an additional density grating that possesses some orientational characteristics. Enhancement of the high frequency orientational portion of the gain spectrum arises from two causes: the orientational grating is made deeper when the microparticles are aligned, and the formation of an additional orientational grating that has some translational characteristics. This feature of the suspension’s nonlinear electrodynamics reflects the appearance of new coherent scattering mechanisms resulting from the loss of symmetry in the presence of either a uniform electric field or polarized radiation.

© 1991 Optical Society of America