Top-Seeded Solution Growth and Optical Properties of Deep-UV Birefringent Crystal Ba₂Ca(B₃O₆)₂

Single crystals of the birefringent material Ba 2 Ca(B 3 O 6 ) 2 (BCBO) with dimensions up to 40 × 28 × 10 mm 3 were successfully grown by top-seeded solution growth (TSSG) method from B 2 O 3 –NaF flux. It exhibits high transmittance in the range of 190–3000 nm with UV cutoff of 178 nm, which is much shorter than that (189 nm) of the commercial UV birefringent crystal, the high-temperature phase of BaB 2 O 4 (α-BBO). Meanwhile, BCBO crystal has large birefringence (Δ n = n o – n e = 0.2524–0.0862) in the wavelength range from 178 to 3000 nm and without phase transition from room temperature to the melting point. A prototype of Glan–Taylor polarizer made from BCBO crystal showed an optical extinction ratio of 10 4:1, which is comparable to those of commercial birefringence crystals. The experimental results demonstrate that the BCBO crystal can be a new promising birefringent crystal for UV, especially the sub-200 nm deep-UV range.