Role of photoconductivity in molecularly doped photorefractive polymer

The photorefractive effect is a reversible mechanism of holographic grating formation in electro-optic materials, that has potential applications in integrated optics, optical data storage, optical computing, and several other areas. This effect was recently observed in photorefractive polymers doped with charge transport agents. The grating formation is initialized by the photoconductive response which includes charge generation, mobility, and trapping, occurring in successive order. Finally, the grating is formed as a result of modulation of the refractive index by the resulting space charge field, via the electro-optic (Pockels) effect. We present the results of photoconductive measurements as a function of temperature, applied electric field, and illuminated intensity. The investigation is focused on the nonlinear optical polymer bisphenol A 4-4-nitroaminostilbene mixed with 30 weight % of the hole transport agent diethylamino-benzaldehyde diphenyl hydrazone. We observed that the photoconductivity of the photorefractive polymer has the form exp[ aE ^1/2 + bE ^1/2/T ² - c/T ²] in agreement with the diorder theory of the well- known hopping model developed for charge-transport in molecularly doped polymers. We also observed that the apparent hopping distribution bandwidth increases with increased intensity, consistent with an increasing density of states.