Abstract

High-precision temperature dependent reflectance (dR/dT) spectra of typical high-reflectance mirror coatings have been measured from 320 nm to 3.8 μm. It is over this wavelength region that the interplay of Drude free electron behavior and the absorption peaks caused by electron interband transitions lead to complicated reflectance spectra. In this region an inversion of the sign and increase in the magnitude of dR/dT is observed. The standard Drude model is applicable through the infrared down to ~1 μm and predicts an increase in reflectance with a decrease in temperature at the rate of 1–4 × 10^-5/°C. The shorter wavelength visible light reflectance spectra is dominated by interband transition and shows the opposite relationship of a decrease in reflectance as temperature is decreased on the order of 8 × 10^-5 to 3 × 10^-4/°C. The complex dielectric constants ε₁ and ε₂ as a function of temperature are determined via a Kramers-Kronig phase reconstruction, and a physical model of the system using a Drude term and a single oscillator is discussed.

© 1991 Optical Society of America