Growth and Characterization of Nonlinear Optical Borate Crystals: CBO, SBO and BBO

Abstract

Laser sources in UV and deep UV regions are scarce. There is high demand of efficient, compact solid state laser sources in these regions for various applications. Borate materials are being considered having potential to fulfill this demand. Owing to their noncentrosymmetric structures, high nlo coefficients, high laser damage thresholds and transparency till deep UV range make them suitable candidates to generate UV laser through second and higher harmonic generations. In this work, borate materials belonging to three different anionic groups were studied and single crystals were grown for characterization. Cesium triborate and strontium tetraborate were grown with Czochralski technique and top seeded solution growth was implemented to grow single crystals of β-barium borate. XRD measurements were carried out on grown crystals to confirm single phase. Samples were cut from these crystals and transmission spectra was recorded. Refractive indices in different crystallographic directions were obtained for different wavelengths. Sellmeier coefficients and birefringence were calculated from this data. Thermo optic coefficients of refractive index were also determined for these crystals. Temperature dependence of refractive index for strontium tetraborate was determined for the first time and unlike most of the borate materials it possessed positive thermo optic coefficient of refractive index. Conoscopic pattern of β-barium borate confirmed its negative uniaxiality