The laser-induced birefringence in nematogens; the influence of beam spatial and temporal profiles

Abstract

Measurements of the laser-induced birefringence in the isotropic phase of nematogens close to the nematic - isotropic transition are of interest in the study of pre-transitional phenomena in liquid-crystalline systems. Hitherto, the variable spatial and temporal profile of the intensity of the laser beam as it traverses the sample has not been allowed for in the analyses and interpretation of experimental data. A theoretical analysis is presented of the output from a conventional crossed-polarizer apparatus which embraces the effect of these profile variances. Their influence on apparent data is accounted for in terms of the de Gennes pre-transitional theory for nematogens. Specific cases are discussed in which either fast or slow detection systems are used.