Photorefractive properties of new polymer composites incorporating poly[ethynediyl-arylene-ethynediyl-silylene]s

Abstract

The photorefractive properties of low glass transition temperature, T_g, composites based on oligomeric poly[ethynediyl-arylene-ethynediyl-silylene]s as optical chromophores, poly(9-vinylcarbazole) as photoconductor, N-ethylcarbazole and phenyltrimethoxysilane as plasticizer, and fullerenes as charge generators have been investigated. The nonlinear optical effects, including four-wave mixing and two-beam coupling were studied at 633 nm. The photorefractive origin of the refractive index changes was confirmed by the achievement of a two-beam gain as high as 67 cm⁻¹ under an externally applied electric field (E₀ = 16 V µm⁻¹). Refractive index gratings affording two-beam gains up to 51 cm⁻¹ can also be written under zero-field conditions. A possible explanation for this unique property of the materials is that chromophore orientation asymmetry can be induced by the longitudinal intensity gradient.