Direct observation of orientation limit in a fast photorefractive polymer composite

We report on a photorefractive polymer with a 4-ms-response time in transie nt four-wave mixing experiments at 0.5 W/cm(2) writing irradiance, 95 V/mu m applied electric field, and a grating period of 3.1 mu m. Complementary t ransient ellipsometry, however, reveals orientational birefringence respons e which leads the four-wave mixing response all the way to its saturation, despite complex dynamics in these processes. Orientation does not limit the dynamic formation of photorefractive gratings in this polymer, which sugge sts that even faster photorefractive responses are possible for polymer com posites with improved charge generation and transport properties. (C) 1999 American Institute of Physics. [S0003-6951(99)00116-3].