Quantum efficiencies of gold and copper photocathodes in the VUV and X-ray range

Abstract

The quantum efficiency, η, of gold and copper photocathodes has been measured in the photon-energy range from 50 eV to 10 keV. The experiments were performed with monochromatized synchrotron radiation at the radiometry laboratories of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage rings BESSY I and BESSY II. Relative standard uncertainties of η lower than 0.036 were achieved using a cryogenic electrical-substitution radiometer as the primary detector standard. The samples were cleaned, stored and examined in an ultra-high-vacuum chamber. The quantum efficiency of cleaned gold and copper was found to be reproducible within 2 parts in 102 to 3 parts in 102. A simple model assumes to be proportional to the product of absorption coefficient, μ, and photon energy, hν. The relative course of the absorption coefficient was also measured with relative standard uncertainties below 0.04. As proportionality was only locally fulfilled, a more sophisticated model for quantum efficiency was developed.