Incongruent Melting La_xY_ySc_4-x-y(BO₃)₄: LYSB Nonlinear Optical Crystal Grown by the Czochralski Method

Abstract

Nonlinear optical (NLO) crystals with incongruent melting of La _xY _ySc _z(BO₃)₄ ( x + y + z = 4) (LYSB)-type were grown for the first time, to the best of our knowledge, by the Czochralski method. A special thermal assembly was used and the melt composition, growth direction, and the pulling and rotation rates have been optimized. Good optical quality LYSB crystal with a diameter of about 13 mm and a length of 25 mm has been grown from the La_0.765Y_0.485Sc_2.75(BO₃)₄ starting melt composition, along the c-axis direction, using a slow rotation rate of 8-10 rpm and a high pulling rate of 2 mm/h. The grown crystal has an acentric huntite-type structure (space group R32, Z = 3) with cell dimensions a = 9.8098(4) Å and c = 7.9802(3) Å, and its chemical composition was determined to be La_0.78Y_0.32Sc_2.90(BO₃)₄. The optical transmission and the refractive indices were determined, and the second harmonic generation (SHG) and sum frequency generation (SFG, ω + 2ω) properties were reported. The laser damage threshold was also determined to be ∼2.0 GW/cm² at 1064 nm (6 ns pulses). The main nonlinear properties of Czochralski-grown LYSB crystal were found to be similar to those of flux-grown LYSB, and comparable to YAl₃(BO₃)₄ (YAB) nonlinear properties. The big advantage of Czochralski-grown LYSB crystals is that they can be grown with large size and high quality, making them promising candidates for various NLO applications, including frequency conversion of high-average power radiation sources.