Refractive-index anisotropy and dispersion in gehlenite, Ca_2Al_2SiO_7, between 308 and 1064 nm

Refractive-index anisotropy and dispersion were measured in a tetragonal gehlenite (Ca2Al2SiO7) single crystal between 308 and 1064 nm at room temperature. Use was made of the bireflectance effect in an oriented single-crystal prism for obtaining an accurate measurement of the anisotropy. At the wavelength λ = 632.8 nm, the ordinary and the extraordinary refractive indices no and ne were no = 1.663 ± 0.0015 and ne = no − 0.0085 ± 0.0002, respectively. The dispersion was fitted to a Sellmeier function n2 = 1 + Aλ2/(λ2 − B), with Ao = 1.712 ± 0.004, Ae = Ao − (25 ± 1) × 10−3, Bo = (1.196 ± 0.005) × 10−2 (μm)2, and Be = (1.133 ± 0.005) × 10−2 (μm)2.