ABSTRACT
The photorefractive effect can be understood considering the following mechanisms: photoexcitation and trapping of charge carriers, transport of the photoexcited carriers through the photoinduced space charge field, and a change of the refractive indices ruled out by the electrooptic effect. In this chapter, the authors summarize the main features that characterize the photorefractive effect in oxygen-octahedra ferroelectrics and sillenites and describe the models that have been developed to explain different experimental results and the basic mechanism of the photorefractive effect. They also summarize recent results and trends in semiconductors, organic molecular crystals, newer photorefractive materials. For the experimental observation of the photorefractive effect and its mathematical description, periodic grating-like excitation phenomena are appropriate. The spatial modulation of the light intensity causes a corresponding modulation of the electron and ionized donor centers. The main sources for the charge transport in a photorefractive material are electrons and holes, but ions, ion vacancies, or other defects can also appear as charge carriers.
