The optical and dielectric constants of Cs have been obtained above the plasma frequency. The measurements were made on Cs films evaporated on a plane surface of quartz and CaF2 semicylindrical substrates, at 10-6 torr. The refractive index n is determined from the critical angle for total internal reflection at the Cs-substrate interface. The absorption coefficient k is determined from the slope of the curve at the critical angle. The real part of the complex dielectric constant ∊l differs from the value predicted by the nearly free-electron model. The effect is attributed to the existence of transitions from inner shells at higher photon energies and to interband transitions and plasmon-assisted transitions at lower energies. The derived parameters in this energy region are 4πn0α=0.37±0.01, meff=1.05±0.05 m, and ħωp=2.87±0.07 eV.
U. S. WHANG, E. T. ARAKAWA, and T. A. CALLCOTT, "Optical Properties of Cs for Photons of Energy 3.6–9.6 eV," J. Opt. Soc. Am. 61, 740-745 (1971)