DESIGN AND SYNTHESIS OF AN ULTRAVIOLET-TRANSPARENT NONLINEAR-OPTICAL CRYSTAL SR2BE2B2O7

POWERFUL, tunable ultraviolet laser sources, required for many spectro scopic applications, rely on the frequency-doubling of lasers in the v isible range. Such second-harmonic generation (SHG) depends on the dev elopment of nonlinear optical (NLO) materials with high SHG coefficien ts, a wide transparent region in the ultraviolet, and moderate birefri ngence. Few such materials are available; those most widely used at pr esent are the inorganic crystals beta-BaB2O4 (BBO)(1) and LiB3O5 (LBO) (2). These crystals are effective for SHG only down to wavelengths of 205 nm (ref. 3), because of a limited ultraviolet-transparent range in the former case and birefringence problems in the latter. We have dev eloped previously(4) a new inorganic NLO crystal, KBe2BO3F2 (KBBF); wh ich avoids both of these problems to a large degree. But it is hard to grow large crystals of KBBF because of weak binding between its layer ed structural units. We have now developed an improved material by rat ional design: Sr2Be2B2O7 (SBBO), which shares (and in fact slightly im proves on) all of the favourable NLO properties of KBBF and is easy to grow as large (so far up to 7 x 7 x 3 mm) crystals of high optical qu ality. The large SHG coefficients and wide range of ultraviolet transp arency make this material a promising candidate for frequency doubling into the ultraviolet.