Orientation dependence of the picosecond nonlinear optical signals in KTa1-xNbxO3 crystals.

Abstract

The mixed-crystal system of KTa1-xNbxO3 (KTN) has been the subject of. numerous laser studies due to its promise as a nonlinear optical material. However, the optical properties of KTN crystals change with composition due to different structural phases. As the niobium concentration x increases from 0 (KTaO3) to 1 (KNbO3) the perovskite-structure of KTN undergoes a phase transition from a cubic paraelectric phase to the tetragonal and orthorhombic ferroelectric phases.1-6 Experimental data on these structural changes support a model where the Ta,Nb ions are displaced from central positions in the octahedron of oxygen ions to one of eight equivalent positions along the cube diagonals. The different structural phases are a consequence of the preferential occupation of a certain set of sites by the Ta,Nb ions.1-6