Wavelength Modulation Spectrum of Copper

The wavelength modulation spectrum of Cu is presented at 7°K in the range of $2.0<~\hslash \omega <~6.0$ eV. The band structure of Cu calculated by the empirical pseudopotential method is used to compute the imaginary part of the dielectric function ${\epsilon }_2\left(\omega \right)$ and the logarithmic derivative of the reflectivity, $\frac{R^{\prime }\left(\omega \right)}{R\left(\omega \right)}$. Good agreement between theory and experiment is obtained at the absorption edge and at higher energies using the one-electron approximation if dipole matrix elements are calculated from wave functions including core contributions rather than the pseudowave functions. The transitions causing the structure in $\frac{R^{\prime }\left(\omega \right)}{R\left(\omega \right)}$ are identified.