Three-dimensional ferroelectric domain visualization by Čerenkov-type second harmonic generation

We show that focusing a laser light onto the boundary between antiparallel ferroelectric domains leads to the non-collinear generation of two second harmonic (SH) beams. The beams are emitted in a plane normal? to the domain boundaries at the angles that satisfy the Čerenkov-type phase matching condition. Moreover, these beam disappear when the laser light is focused on a homogenous part of a single domain. We utilize this effect for 3-dimensional visualization of fine details of the ferroelectric domain pattern with a submicron accuracy.