Optical Properties of Cs for Photons of Energy 36–96 eV*

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Abstract
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 ∊1 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 4πnoα = 0.37±0.01, meff = 1.05±0.05 m, and ℏωp = 2.87±0.07 eV.