Selective reflection spectroscopy at the interface between a calcium fluoride window and Cs vapour

Abstract

A special vapour cell has been built, that allows the measurement of the atom–surface van der Waals interaction exerted by a CaF₂ window at the interface with Cs vapour. Mechanical and thermal fragility of fluoride windows make common designs of vapour cells impractical, so that we have developed an all-sapphire sealed cell with an internal CaF₂ window. Although some impurities have remained when filling up the prototype cell, leading to line broadening and a shift, the selective reflection spectrum of the Cs D₁ line (894 nm) makes apparent the weak van der Waals surface interaction. The uncertainties introduced by the effects of these impurities in the van der Waals measurement are nearly eliminated when comparing the selective reflection signal at the CaF₂ interface of interest and at a sapphire window of the same cell. The ratio of the interactions respectively exerted by a sapphire interface and a CaF₂ interface is found to be 0.55±0.25, in good agreement with the theoretical evaluation of ∼0.67.