Spatially resolved second-harmonic generation in ABO3-type ferroelectric crystals

ABO(3)-type ferroelectric crystals are increasingly in demand for electro-optical applications, like waveguide lasers, modulators or volume holographic 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 harmonic 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 microscopic techniques) can be employed to reach two- or even three-dimensional spatial resolution in the range of micron dimensions. On the background of inversion symmetry of the host material, as for instance in incipient ferroelectric crystals SrTiO3 or KTaO3, also the influence and distribution of inversion symmetry breaking defects and defect-induced phase transitions may be detected as well as the influence of external parameters (electric field, uniaxial stress or temperature). Examples for LiNbO3 (congruent or stoichiometric composition), for KNbO3 doped with Ta and for KTaO3 doped with Li will demonstrate the limits and possibilities of above techniques for specific systems. (C) 1999 Elsevier Science B.V. All rights reserved.