Optical properties of nonlinear potassium lithium niobate crystals

Crack-free potassium lithium niobate (KLN) single crystals of different compositions have been grown by the resistance-heating Czochralski technique. The crystal structure was studied using synchrotron radiation X-ray powder diffraction, and the crystal compositions were determined by X-ray fluorescent spectroscopy. Homogeneous and crack-free samples of about 6 × 6 × 7 mm³ were used to study the lattice vibration spectra by Raman and infrared reflection spectroscopy. The results show a strong influence of Li ions in the C sites of the KLN crystal on the characteristic Raman and infrared reflectivity spectra of the Nb-O octahedral ions. In particular, the symmetric bend vibrational mode, v₅, is split into three Raman peaks; the antisymmetric bend vibrational mode, v₄, in the infrared spectrum is split into three peaks as well. The antisymmetric stretch vibrational mode, v₃, is broadened greatly and slightly split. The crystals obtained have good quality and improved second harmonic generation properties.