Czochraski growth, defect analysis and refractive index of Ba2TiGe2O8 crystal with excellent optical nonlinearities

Abstract Ba2TiGe2O8 (BTG) shows excellent second-order nonlinearity and electro-optical effects. However, it is difficult to grow a perfect BTG single crystal, and the accurate refractive indexes of this crystal are unavailable at present. In this paper, a sizeable single BTG crystal with high quality was grown by Czochraski (CZ) method. SEM and EDS analyses of crystal defect indicate that the volatilization of GeO2 and the obvious supercooling feature of BTG melt were the main inducements of inclusion defects. The accurate refractive indexes were measured by the self-collimating method. The birefringence and SHG results show that the angle phase matching of SHG at 1064 nm hardly be achieved in this crystal. Nevertheless, the effective frequency-doubled laser output may be achieved by using the technique of periodic polarization reversal for quasi phase matching. In view of the high optical transmittance and the huge nonlinear optical coefficients, BTG crystal may be a good candidate material for nonlinear optical devices and electro-optical devices.