Ellipsometric determination of the electric-field-induced birefringence ofphotorefractive dyes in a liquid carbazole derivative

We have used ellipsometric measurements on solutions of 2-dihexylamino-7-di cyanomethylidene-3,4,4a,5,6-phentahydronaphthalene and related polyenes in liquid 9-(2'-ethylhexyl)carbazole to measure the electric-field-induced bir efringence at wavelengths of 690 nm and 830 nm. This electric-field-induced birefringence is related to the product of dipole moment squared and the p olarizability anisotropy, mu(2)Delta alpha, and to a large extent determine s the dye's photorefractive figure-of-merit (FOM). We show that mu(2)Delta alpha increases with the conjugation length and report one of the highest m u(2)Delta alpha values observed so far. (C) 1999 Elsevier Science B.V. All rights reserved.