Optical nonlinearities in the supercooled phase of nematic liquid crystal drops

Raman scattering with different incident powers and varying chopping freque ncies of the input laser is used to study the microscopic origin of the thi rd-order nonlinear optical susceptibility (chi(3)) of a nematic liquid crys tal drop. Thermal self-focusing arises in the nematic state if intrinsic re sidual absorption is present. Conversely, self-focusing associated with mol ecular reorientations comes in view at low input powers and produces stimul ated Raman scattering if the drop is supercooled below the melting point. T he latter effect is related to the substantial increase in the time scale f or molecular reorientations in the supercooled nematic. The possibility of using chi(3) and Raman scattering for the study of the dynamics of supercoo led organic Liquids is suggested. (C) 1999 Elsevier Science B.V. All rights reserved.