Collapse and revival of a Dicke-type coherent narrowing in a sub-micron thick vapor cell transmission spectroscopy

¹ Laboratoire de Physique des Lasers, UMR 7538 du CNRS Université Paris 13 - 99 Av J.-B. Clément, 93430 Villetaneuse, France
² Institute for Physical Research, Armenian Academy of Sciences Ashtarak 2, 378410 Armenia

Corresponding author: bloch@lpl.univ-paris13.fr

Received: 10 March 2003
Accepted: 2 May 2003

Abstract

In a thin cell of dilute vapour, the absorption spectrum exhibits sub-Doppler features due to the relative enhancement of the slow atom contribution, with respect to the transient nature of the interaction with moving atoms. For a two-level system in the linear regime, the narrowest response is predicted to be found for a thickness, as an effect of the coherent character of the dipole response as early described by Romer and Dicke (Phys. Rev., 99 (1955) 532) in the microwave regime. We report here on the direct observation of this effect in the optical regime in an ultra-thin vapour cell. This effect is shown to vanish for a thickness equal to λ, and a revival is observed at , as expected from the predicted λ-periodicity. The experiment is performed on the D₁ resonance line of vapour (), in a specially designed cell, whose thickness varies locally.