NET 2-BEAM-COUPLING GAIN IN A POLYMERIC PHOTOREFRACTIVE MATERIAL

Two-beam-coupling gain coefficients exceeding the absorption coefficie nt are demonstrated for the first time to our knowledge in an organic photorefractive system. The material is based on the photoconducting p olymer poly(N-vinylcarbazole), doped with the optically nonlinear chro mophore 3-fluoro-4-N,N-diethylamino-beta-nitrostyrene and sensitized f or charge generation with 2,4,7-trinitro-9-fluorenone. The photorefrac tive performance is significantly better than that of any previously d escribed organic. Diffraction efficiencies as large as 1% in a 125-mum sample, grating growth times of the order of 100 ms, and beam-couplin g gain coefficients >10 cm-1 were observed at 647 nm (writing intensit y of 1 W cm-2, applied field of 40 V mum-1).