Synthesis and characterization of highly efficient photorefractive polymer composites with long phase stability

We have synthesized the chromophores 4-[(4'-nitrophenyl)azo]-1,3-bis[(3 "- or 4 "-vinylbenzyl)oxy]benzene (NPADVBB) and 4-[(4'-nitrophenyl)azo]-1,3-bis(benzyloxy)benzene (NPADB). New polymer composites based on the photoconductor poly(9-vinylcarbazole), the plasticizer 9-ethylcarbazole, NPADVBB, and the sensitizers 2,4,7-trinitro-9-fluorenone and (2,4,7-trinitro-9-fluorenylidene)malonitrile were prepared. Ellipsometric measurements and degenerate four-wave mixing experiments were performed at 633 and 830 nm. The composites showed excellent phase stability, and nearly complete diffraction was observed at 633 nm. The two-beam coupling gain was limited by the small phase shift between the interference pattern and the index grating.