Photorefractivity in doped nonlinear organic polymers (Invited Paper)

Abstract

This paper describes the properties of a new class of materials exhibiting the photorefractive effect, doped nonlinear organic polymers. Photorefraction (at 647.1 nm) was established by a combination of hologram erasability, correlation with photoconductivity and electro-optic response, and enhancement by external fields in numerous samples (178 to 533 μm thick) of two nonlinear epoxy materials doped with hole transport agents based on p- diethylaminobenzaldehyde-diphenyl hydrazone (DEH). Diffraction efficiencies up to 0.1% were observed at bias fields near 100 kV/cm. A useful property of these materials is that poling of the nonlinear chromophores is partially reversible, permitting partial control of the grating readout independent of the space-charge field formed. The polarization anisotropy of grating readout is consistent with the photorefractive mechanism. Two-beam coupling measurements of both absorption and index gratings show (1) the absorption gratings are approximately 10 times smaller than the index gratings, and (2) the phase shift of the index grating is near 90°, which cannot occur via photochromism, heating, or any other process except photorefractivity.