The changes induced by an applied electric field in the real and imaginary parts of the dielectric constants of Au and Ag are determined, as functions of photon energy, by ellipsometer measurements combined with phase-sensitive detection. This experiment provides all the necessary data for direct calculation of the complex dielectric constant in the absence of the field, the field-induced changes, and the depth into the sample to which the dielectric constant is modulated by the field, at given photon energy from measurements taken only at that energy. Hence the Kramers-Kronig analysis and any accompanying extrapolations to experimentally inaccessible photon energies are unnecessary. Structure in the modulated dielectric constants which is masked in the normal-incidence electroreflectance spectra, such as the structure around 3 eV in Ag, is brought out much more clearly in our more direct measurements. The results are consistent with the usual interpretation of the band structure of Au and Ag, and the modulation depths are of the same order as the Thomas-Fermi screening lengths.

• Received 20 May 1968

DOI:https://doi.org/10.1103/PhysRev.174.719