Optical properties and crystal growth of lead tetraborate

This paper reports growth and optical properties of PbB4O7, a new host for chi((2))-type nonlinear optical interactions. Large, inclusion-free single crystals (20 x 8 x 8 mm(3)) of PbB4O7 have been grown from self-flux and stoichiometric melts contained in Pt crucibles, using a resistance heated furnace. The crystal has an orthorhombic structure, with space group P2(1) nm. The optical absorption spectrum is essentially featureless from the band edge near 300 nm through the visible and near infrared regions. The principal indices of refraction have been measured with high accuracy using a modified angle of deviation technique. These crystals are optically biaxial, point symmetry mm2: their non-zero d-coefficients d(15) = d(31), d(24) = d(32) and d(33) have been measured using the Maker fringe technique. The optical properties are compared with those of other nonlinear optical crystals and related to the differences in their respective structures. (C) 1997 Elsevier Science B.V.