Abstract

The unique multispectral transparency properties of diamond, combined with its chemical inertness, hardness, and mechanical strength, enable a variety of optical applications requiring infrared transparency in aggressive environments. Knowledge of the optical properties of diamond at elevated temperatures enables the use of Fizeau interferometry as an in situ, non-contact probe of temperature, for homoepitaxial diamond growth studies, for example, and may be useful for other applications as well. The temperature dependence of the index of refraction of type IIa natural diamond was determined by Fizeau interferometry using a HeNe laser. Subtracting the contribution of thermal expansion to the optical path length, the logarithmic temperature derivative of the refractive index, 1/n dn/dT, is found to rise from 4 × 10^-6 at room temperature to 2.0 × 10^-5 at 1200°C at a wavelength of 633 nm.