Spatial Distribution of Complex Refractive Index Change in Guest–Host Liquid Crystals Determined by a Phase-Sensitive Interferometric Method

Abstract

The spatial distributions of the complex photothermal refractive index change in the guest-host liquid crystals were determined by a phase-sensitive optical interferometric method using a Mach-Zehnder interferometer. The Gaussian profile of the pump laser beam reflects the spatial distribution of the laser-induced index change and the radius of the distribution was slightly larger than that of the intensity distribution of the pump beam. In addition, the radius of the distribution of the extraordinary index change is larger than that of the ordinary one. The real part of the extraordinary refractive index change was negative, while that of the ordinary one was positive. Although the absorption coefficient was negligibly small at the wavelength of the probe laser beam, the imaginary part could not be ignored. The imaginary parts of both the extraordinary and ordinary indices changes were negative. These results can be explained by the photothermal effects of the guest-host liquid crystal.