A nonlinear-optical investigation technique for the domain structuring in ferroelectric crystals is reported. Noncollinear optical frequency doubling in a quasiphase-matched scheme allows for conclusions on the $k$-space representation of the domain morphology or—putting it in other terms—on the $k$-space representation of the correlation lengths (k-space spectroscopy). As an example, the ferroelectric-to-paraelectric phase transition of the relaxor ferroelectric strontium-barium niobate (SBN) is studied. One important result is that homogeneously poled crystals of SBN do not uniquely go through the phase transition as commonly assumed. Instead, the correlation length shows a characteristic anisotropic behavior in the phase-transition region.

• Received 25 July 2006

DOI:https://doi.org/10.1103/PhysRevB.74.132104