Refractive index of infrared-transparent polycrystalline alumina

The refractive index of fully dense, infrared-transparent polycrystalline alumina (PCA) with a mean grain size of similar to 0.6 mu m is reported for the wavelength range 0.85 to 5.0 mu m over the temperature range T = 296 to 498 K. The temperature-dependent Sellmeier equation is n(2)-1 = (A+B [T-2-T-o(2)])lambda(2)/[lambda(2)-(lambda(1)+C [T-2-T-o(2)])(2)] + D lambda(2)/(lambda(2)-lambda(2)(2)) , where lambda is expressed in mu m, T-o = 295.15 K, A = 2.07156, B = 6.273 x 10(-8), lambda(1) = 0.091293, C = -1.9516 x 10(-8), D = 5.62675, lambda(2) = 18.5533, and the root-mean square deviation from measurements is 0.0002. This paper describes how to predict the refractive index of fully dense isotropic PCA with randomly oriented grains using the ordinary and extraordinary refractive indices (n(o) and n(e)) of sapphire spatially averaged over the surface of a hemisphere. The refractive index of alumina at 296 and 470 K agrees within +/- 0.0002 with the predicted values. Similarly, the ordinary and extraordinary optical constants k(o) and k(e) are used to predict the absorption coefficient of alumina. The refractive indices n(o) and n(e) of sapphire grown at Rubicon Technologies by the Kyropoulos method were measured at 295 K and agree with published Sellmeier equations for sapphire grown by other methods within +/- 0.0002. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.