Spatially resolved second-harmonic generation in ABO(3)-type ferroelectriccrystals

ABO(3)-type ferroelectric crystals are increasingly in demand for electro-o ptical applications, like waveguide lasers, modulators or volume holographi c storage devices. The properties of most of these materials can be widely tuned by varying composition and doping. This in turn necessitates suitable methods for checking the results of such optimization attempts. Second har monic generation (SHG)-techniques can be used for nondestructive testing of crystal composition, homogeneity, doping concentration profiles and phase matching conditions. Several SHG-methods (colinear, non-colinear and micros copic techniques) can be employed to reach two- or even three-dimensional s patial resolution in the range of micron dimensions. On the background of i nversion symmetry of the host material, as for instance in incipient ferroe lectric crystals SrTiO3 or KTaO3, also the influence and distribution of in version symmetry breaking defects and defect-induced phase transitions may be detected as well as the influence of external parameters (electric held, uniaxial stress or temperature). Examples for LiNbO3 (congruent or stoichi ometric composition), for KNbO3 doped with Ta and for KTaO3 doped with Li w ill demonstrate the limits and possibilities of above techniques for specif ic systems. (C) 1999 Elsevier Science B.V. All rights reserved.