Revisiting optical spectroscopy in a thin vapor cell: mixing of reflection and transmission as a Fabry–Perot microcavity effect

Abstract

Transmission spectroscopy in an ultrathin vapor cell, which has been recently demonstrated as a new method of sub-Doppler spectroscopy in the optical domain, is revisited. We show that, because of an unavoidable Fabry–Perot effect, the observed signal—in transmission spectroscopy and selective reflection spectroscopy as well—is actually an interferometric mixture of the optical responses as provided in transmission and in reflection by a long macroscopic cell. After the derivation of a very general solution, we restrict ourselves to the case of a linear interaction with the resonant laser. We finally discuss the application to a two-level atom for which analytical expressions are given, in the large Doppler limit, for FM transmission and reflection signals.