2ND-HARMONIC IMAGING OF FERROELECTRIC DOMAIN-WALLS

Domain walls in periodically poled ferroelectric KTiOPO4 and LiNbO3 cr ystals are observed by making use of second-harmonic (SH) generation e nhancement in the transition regions between neighboring domains. SH i mages of domain walls obtained with various samples for different pola rization configurations are presented. The SH generation enhancement i s found especially pronounced for the polarization of the SH radiation being perpendicular to the domain walls. The origin and selection rul es for the contrast in SH images of domain walls are discussed. The re sults obtained suggest that the domain walls produce a deteriorating e ffect on SH generation by quasiphase matching. (C) 1998 American Insti tute of Physics. [S0003-6951(98)02039-7].