Net two-beam-coupling gain in a polymeric photorefractive material

Two-beam-coupling gain coefficients exceeding the absorption coefficient are demonstrated for the first time to our knowledge in an organic photorefractive system. The material is based on the photoconducting polymer poly(N-vinylcarbazole), doped with the optically nonlinear chromophore 3-fluoro-4-N, N-diethylamino-β-nitrostyrene and sensitized for charge generation with 2, 4, 7-trinitro-9-fluorenone. The photorefractive performance is significantly better than that of any previously described organic. Diffraction efficiencies as large as 1% in a 125-μm sample, grating growth times of the order of 100 ms, and beam-coupling gain coefficients >10 cm⁻¹ were observed at 647 nm (writing intensity of 1 W cm⁻², applied field of 40 V μm⁻¹).