Reflectivity of Metals at High Temperatures

The reflectivity and other optical constants of metals at high temperatures are discussed on the basis of the Drude theory and the theory of electron‐phonon collision. The electron‐phonon collision frequency is dependent on the temperature through the temperature dependence of the phonon population. The temperature dependence of the collision frequency determines that of optical properties of metals. Variations of the real and the imaginary parts of the dielectric constant and of the complex refractive index with temperature are considered. General expressions for the temperature coefficients of the optical constants are given. The reflectivity is shown to decrease with increasing temperature. Numerical calculations were carried out for several metals at a few wavelengths and at temperatures from room temperature to their melting temperatures. The results are given in graphs and in a table. Curves for the reflectivity show that the absolute value of the temperature coefficient of the reflectivity is greater for a metal having a lower reflectivity at room temperature. Calculated values of the reflectivity at room temperature are in reasonable agreement with handbook data. However, the calculated reflectivity for silver at its melting point is not coincident with the reported experimental data (the only data available at present), in spite of the qualitative agreement between our results and the experiment. A brief discussion on possible explanations of the discrepancy is made.