REFRACTIVE-INDEX ANISOTROPY AND DISPERSION IN GEHLENITE, CA2AL2SIO7, BETWEEN 308-NM 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 lambda = 632.8 nm, the ordinary and the extraordinary refractive indices n(o) and n(e) were n(o) = 1.663 +/- 0.0015 and n(e) = n(o) -0.0085 +/- 0.0002, respectively. The dispersion was fitted to a Sellmeier function n2 = 1 + Alambda2/(lambda2 - B), with A(o) = 1.712 +/- 0.004, A(e) = A(o) - (25 +/- 1) X 10(-3) , B(o) = (1.196 +/- 0.005) X 10(-2) (mum)2, and B(e) = (1.133 +/- 0.005) X 10(-2) (mum)2.