FLUCTUATIONS AND LIGHT-SCATTERING IN THIN SMECTIC FILMS

An analysis of the layer-displacement fluctuations in thin smectic-A liquid-crystal films is presented. Explicit formulas for the displacement-displacment correlation function, taking into account the surface tension and the anchoring strength, are derived. It is shown that the boundary conditions essentially affect the fluctuations not only on the surface but in the interior of the film as Well. The light scattering on the displacement-associated director fluctuations is considered. This consideration is carried out on the basis of the Green's function of the electromagnetic field for an optically anisotropic film. The calculations include multiple-reflection effects for incident and scattered light beams. It is shown that the scattered light intensity differs essentially from the intensity for the same volume in an infinite smectic medium. There is no forward scattering in the case of normal incidence and an undulation behavior of the intensity as a function of scattering angle takes place. There are maxima in the angular distribution. The magnitudes of the maxima are sensitive to the surface-tension coefficient. The possibility of measuring the surface-tension coefficient by means of an optical experiment is discussed.