Crystal Growth and Optical Properties of Beryllium-Free Nonlinear Optical Crystal K3Ba3Li2Al4B6O20F

A beryllium-free nonlinear optical (NLO) crystal K3Ba3Li2Al4B6O20F (KBLABF) with sizes up to 18 X 13 X 8 mm(3) was successfully grown by the top-seeded solution growth method using LiOH-H3BO3-BaF2 flux. The key limiting factors on the crystal morphologies and sizes were carefully analyzed. Meanwhile, by using the minimum deviation technique, the refractive index dispersion was measured and fitted well by the Selhneier equations. The results suggest that KBLABF is a negative uniaxial crystal with moderate birefringence of 0.06050-0.06834 at a wavelength range from 363 to 852.1 nm. Furthermore, the type-I phase matching range for fundamental (second harmonic) light is down to 486 (243 nm) in theory, which indicates that KBLABF crystal could achieve 532 and 266 nm light generation by direct second harmonic generation. As compared with the famous NLO crystals beta-BaB2O4 and CsLiB6O10, KBLABF crystal exhibits a smaller walk-off angle and larger acceptance angle at the wavelength of 532 nm while having a comparable short absorption edge, sufficient birefringence, and moderate NLO response. Furthermore, in contrast to highly hygroscopic CsLiB6O10, it is nonhygroscopic. These attributes make KBLABF a promising candidate for practical applications in UV light generation.