Dispersion of the Refractive Index near the Fundamental Absorption Edge in PbS

A peak in the wavelength dependence of the index of refraction resulting from the increase in the extinction coefficient at the absorption edge has been observed in PbS. The results were obtained by analysis of the reflection spectra of n-type single crystal film and bulk samples. At 300^∘{}K the refractive index at the peak is approximately 7% larger than the square root of the optical dielectric constant. The peak moves with the absorption edge with decreasing temperature. The optical dielectric constant at room temperature was found to be 16.8.