PHOTOCONDUCTIVITY STUDIES OF PHOTOREFRACTIVE POLYMERS

The photorefractive effect is observed in certain optically nonlinear polymers doped with charge-transport molecules. Since photoconduction largely controls the kinetics and the magnitude of the photorefractive effect, we have examined the photoconductivity of a representative material combination, namely, poly(bisphenol-A-diglycidyl ether 4-nitro-1,2-phenylenediamine) (bisA-NPDA) doped with the hole transport agent diethylaminobenzaldehyde diphenylhydrazone (DEH). Charge generation, with a field-dependent quantum efficiency of the order of 10(-3) to 10(-2), commences with excitation of the NPDA chromophore. Hole transport occurs by hopping among the DEH sites with a mobility, which is also field dependent, of the order of 10(-8) cm2/Vs. The range of the holes before they encounter deep traps is of the order of 10 mum. These parameters are discussed in terms of the ultimate limits that might be achieved in holographic grating speed and diffraction efficiency.