Photorefractivity in new organic polymeric materials

Two experimental studies of new photorefractive polymer materials are described. First, an examination of the fabrication, stability, and photorefractive behavior of a recently-reported high-efficiency polymeric composite 33%PVK:50%DMNPAA:16%ECZ:1%TNF (K. Merrholz et at., Nature 371, 497) shows that this material is metastable, crystallizing on time scales from hours to days depending upon preparation. The grating phase shift also varies considerably from sample to sample. In the second part of this paper, first measurements and analysis of the properties of a new photorefractive polymer composite which contains a liquid nonlinear optical chromophore are presented. This new composite, which is immune to crystallization even at high chromophore loading levels, shows a useful diffraction efficiency of several percent at high fields, but the index of refraction grating is shown to consist of two components; a smaller photorefractive index grating and a grating which is not photorefractive in origin as shown by grating translation measurements.