FLUCTUATIONS AND LIGHT-SCATTERING IN THIN SMECTIC FILMS

An analysis of the layer-displacement fluctuations in thin smectic-A l iquid-crystal films is presented. Explicit formulas for the displaceme nt-displacment correlation function, taking into account the surface t ension and the anchoring strength, are derived. It is shown that the b oundary 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. T his consideration is carried out on the basis of the Green's function of the electromagnetic field for an optically anisotropic film. The ca lculations include multiple-reflection effects for incident and scatte red light beams. It is shown that the scattered light intensity differ s essentially from the intensity for the same volume in an infinite sm ectic medium. There is no forward scattering in the case of normal inc idence and an undulation behavior of the intensity as a function of sc attering angle takes place. There are maxima in the angular distributi on. The magnitudes of the maxima are sensitive to the surface-tension coefficient. The possibility of measuring the surface-tension coeffici ent by means of an optical experiment is discussed.