The optical properties of hot-pressed pyrolytic graphite were studied in the wavelength region from 1100 to 3000 Å. The real ($n$) and imaginary ($k$) parts of the complex index of refraction were obtained from reflectance measured at 20° and 70° incidence. The complex dielectric constant and the energy-loss function were determined from these values of $n$ and $k$. The energy-loss function, $\mathrm{Im}\left(\frac{1}{\epsilon }\right)$, was found to exhibit a maximum at a wavelength of 1800 Å corresponding to an energy of 6.9 eV. This peak corresponds to the 7.5-eV loss in electron energy-loss experiments, where it has been attributed to the excitation of the conduction-electron plasma.

• Received 19 August 1964

DOI:https://doi.org/10.1103/PhysRev.137.A639