Selective Reflection Spectroscopy at the Interface between a Calcium Fluoride Window and Cs Vapour

TL;DR

This study develops a specialized vapour cell with a CaF2 window to measure atom-surface van der Waals interactions with Cs vapour, overcoming material fragility issues and providing experimental validation of theoretical interaction ratios.

Contribution

The paper introduces an all-sapphire sealed vapour cell with an internal CaF2 window for van der Waals interaction measurements at fluoride-vapour interfaces, addressing material fragility challenges.

Findings

Measured van der Waals interaction ratio of 0.55 ± 0.25 between CaF2 and sapphire interfaces.

Experimental results are in good agreement with the theoretical ratio of approximately 0.67.

Impurities affected line broadening but were mitigated by comparative measurement techniques.

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 unpractical, so that we have developed an all-sapphire sealed cell with an internal CaF2 window. Although impurities were accidentally introduced when filling-up the prototype cell, leading to a line-broadening and shift, the selective reflection spectrum on 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 interaction respectively exerted by a sapphire interface and a CaF2 interface is found to be 0.55 $\pm$ 0.25, in good agreement with the theoretical evaluation of ~0.67.