Electrostatic force detection with an atomic force microscope (AFM) is ideally suited for the study of the surface properties of dielectric materials. The AFM allows simultaneous detection of many physical quantities like free and trapped charge carrier density, ferroelectric domains and, of course, the topography of the sample. Usually, photorefractive materials are optically investigated: volume refractive index gratings are observed by light diffraction. In contrast, the AFM offers the

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... ility of directly observing the physical steps for the development of a photorefractive grating. Due to the high sensitivity and the unprecedented lateral resolution, the AFM provides a wealth of new possibilities for the investigation of photorefractive materials. We present results obtained with Sr 0.61 Ba 0.39 Nb 2 O 6 (SBN) crystals. The samples had as-grown as well as polished surfaces. Spatial distribution and temporal dynamics of photorefractive charge patterns are successfully resolved. Furthermore, additional charge patterns are observed that may originate from local crystal imperfections and from ferroelectric domain structures.