Refractive index of infrared-transparent polycrystalline alumina

Abstract

Abstract. The refractive index of fully dense, infrared-transparent polycrystalline alumina (PCA) with a mean grain size of ∼0.6 μm is reported for the wavelength range 0.85 to 5.0 μm over the temperature range T ¼ 296 to 498 K. The temperature-dependent Sellmeier equation is.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 AE0.0002 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 AE0.0002.

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“…As discussed in our previous work, transparent alumina is an ideal material for ballistic protection applications where visible or infrared wavelength transmission is required . However, to achieve these favorable properties, alumina must be sintered to high densities (>99.99%TD) to eliminate light scattering due to porosity .…”

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“…Transparent alumina is a candidate for protection applications, such as nose cones, radomes, and ballistic blast shields . Alumina can reach optical transparency at high relative densities .…”

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