Experimental investigations of the microconvective instability in optically induced gratings

A. Mezulis - E. Blums

Institute of Physics, University of Latvia, 32 Miera str., Salaspils, LV-2169

Abstract
Forced Rayleigh scattering experiments (FRS) are well known as a tool to measure diffusion D and Soret S_T coefficients . In FRS experiments the temperature grating is optically induced in a thin sample layer by focusing a periodic pattern (usually one-dimensional parallel stripes) of intense illumination. Employing ferrofluid samples, due to the Soret effect, a primary induced temperature grating creates a particle concentration grating. The steady-state of the concentration grating is examined to define S_T, whereas D may be easily calculated by knowing the half-period a of the induced grating and by measuring relaxation time τ_D of the concentration grating from its vanishing stage, after the illumination source is switched off. Figs 3, Refs 10.