Nonlinear propagation of Gaussian beams in binary critical liquid mixtures

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Abstract
We propose a theoretical study of the nonlinear propagation of a Gaussian laser beam in a mixture of two liquids. Retaining electrostriction (dipole radiation forces), thermal expansion, and thermodiffusion (Soret effect) as the major mechanisms in the perturbation of the medium by the field, we analyze their relative importances in the nonlinear refraction and nonlinear beam power losses. Our attention is mostly focused on the case of mixtures close to critical (consolute) points, where the nonlinearities are very large. We show that one crosses over from a situation dominated by thermal processes to a situation dominated by dipole radiation forces by diminishing the beam diameter and/or the distance to the critical point. The second case is shown to be well within the reach of realistic experiments. Finally, we discuss the potentialities of electrostriction as an alternative to sedimentation in the gravity field to study critical mixtures and the potentialities of critical mixtures as model media in nonlinear optical engineering.