Optical properties of the germanate melilites Sr2MgGe2O7, Sr2ZnGe2O7 and Ba2ZnGe2O7



Refractive indices and their dispersion in the wavelength range from 365 nm to 2325 nm and transmission ranges of the tetragonal melilite-type germanates Sr2MgGe2O7, Sr2ZnGe2O7 and Ba2ZnGe2O7 were determined. The uniaxial positive crystals Sr2MgGe2O7 and Ba2ZnGe2O7 both offer the possibility for phase matched second harmonic generation, a detailed analysis of phase matching conditions is given. The refractive indices of Sr2ZnGe2O7 show an isoindex (isotropic) point at 467 nm. The investigation was performed on Czochralski grown large single crystals. The crystal structure of all three germanates were determined by means of X -ray diffraction. The results corroborate unmodulated melilite-type structures at room temperature. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)