PROCESSES LIMITING THE RATE OF RESPONSE IN PHOTOREFRACTIVE COMPOSITES

The processes limiting the rate of response of highly diffractive, reo rientationally enhanced photorefractive polymer composite materials ar e identified from a series of degenerate four wave mixing and Mach-Zeh nder interferometric measurements. In the regime of low intensity citi ng beams charge generation limits the rate of holographic grating form ation, but at higher intensities charge transport or reorientation of dye molecules can restrict the rate of grating formation more strongly . A grating risetime of 540 ms is observed in a composite of high dye content with high reorientational mobility of the dye molecules. In th is case it is proposed that the charge carrier mobility of the doped p oly(N-vinylcarbazole):2,4,7-trinitro-9-fluorenone (PVK:TNF) matrix is the principal limiting factor in grating response rates. (C) 1998 Else vier Science B.V. All rights reserved.