Electro-optical interferometric microscopy of periodic and aperiodic ferroelectric structures

The ferroelectric domain structures of periodically poled KTiOPO4 and two-dimensional short range ordered poled LiNbO3 crystals are determined non-invasively by interferometric measurements of the electro-optically induced phase retardation. Owing to the sign reversal of the electro-optical coefficients upon domain inversion, a phase shift is observed for the inverted domains. The microscopic setup provides diffraction-limited spatial resolution allowing us to reveal the nonlinear and electro-optical modulation patterns in ferroelectric crystals in a non-destructive manner and to determine the poling period, duty cycle and short-range order as well as detect local defects in the domain structure. Conversely, knowing the ferroelectric domain structure, one can use electro-optical microscopy so as to infer the distribution of the electric field therein.