HIGH-RESOLUTION X-RAY CHARACTERIZATION OF PERIODICALLY DOMAIN-INVERTED NONLINEAR-OPTICAL CRYSTALS

A high-resolution triple-axis diffractometer has been used for the str uctural characterization of periodically domain-inverted nonlinear opt ical crystals of KTiOPO4 and LiNbO3. Striations have been revealed in high-strain-sensitivity multiple-crystal topographs of the domain-inve rted regions of both these samples and these are dominated by orientat ion contrast. The combination of high-resolution reciprocal-space mapp ing and topography has shown that the extended diffraction streak in t he q([)2(1) over bar0$] direction for the domain-inverted LiNbO3 origi nates from the 'minutely misonented structure' which is related to the original configuration of dislocations. The reason for the generation of the structural imperfections via the domain-inversion processing i s interpreted in terms of the converse piezoelectric effect.