Characterization Of Photorefractive Materials Using Holographic And Photoconductivity Techniques

Photorefractive materials exhibit photoconductive and electro-optic properties. The first step in the optical recording process in these materials is the building up of a spatial modulation of electric charges via charge carriers excitation from localized to extended states where they diffuse and/or are drifted and then retrapped in a localized state. In this way the pattern of light onto the sample is converted into a spatial modulation of charges and its corresponding space-charge electric field produces a volume index-of-refraction modulation via electro-optic effect. The latter is the resulting volume phase hologram. The position of the photoconductive centers in the localized states in the material band gap as well as the density and properties of the donor/acceptor centers and charge carriers transport properties are therefore important parameters characterizing the materials and determining their performance as far as optical recording is concerned. For determining these parameters we use optical, holographic, conductivity and photoconductivity techniques. Photoconductivity is useful for detecting the position of the photoconductive localized states in the band gap whereas holography allows finding out the diffusion and Debye lengths, quantum efficiency for charge carriers generation and hole-electron competition. We successfully apply some of these techniques for characterizing different materials with particular emphasis on nominally undoped photorefractive Bi12TiO20 and show how different dopants affect its properties and its holographic recording performance. © 2008 American Institute of Physics.992704709Frejlich, J., (2006) Photorefractive Materials: Fundamental Concepts, Holographic Recording, and Materials Characterization, , Wiley-Interscience New YorkMontenegro, R., Inocente-Junior, N., Frejlich, J., (2006) Rev. Sci. Inst, 77, pp. 043905-43911. , 043905-6Aldrich, R., Hou, S., Harvill, M., (1971) J. Appl. Phys, 42, pp. 493-494Garcia, P.M., Cescato, L., Frejlich, J., (1989) J. Appl. Phys, 66, pp. 47-49Freschi, A.A., Garcia, P.M., Frejlich, J., (1997) Appl. Phys. Lett, 71, pp. 2427-2429Barbosa, M.C., Mosquera, L., Frejlich, J., (2001) Appl. Phys. B, 72, pp. 717-721Barbosa, M., Frejlich, J., (2003) J. Opt. A:Pure Appl. Opt, 5, pp. S416-S419Barbosa, M.C., Frejlich, J., Photorefractive materials characterization using feedback-controlled running hologram (2003) Trends in Optics and Photonics Series, 87, pp. 31-3