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

Abstract

PACS. 42.50.Gy -Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption. PACS. 32.70.Jz -Line shapes, widths, and shifts. PACS. 42.50.Md -Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency.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 λ/2 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 3λ/2, as expected from the predicted λ-periodicity. The experiment is performed on the D1 resonance line of Cs vapour (λ = 894 nm), in a specially designed cell, whose thickness varies locally.

Dicke coherent narrowing in two-photon and Raman spectroscopy of thin vapor cells

“…therein), with respect to the transient nature of the atom-light interaction. In linear optical absorption, a particular coherent narrowing has been experimentally observed for a λ/2 cell thickness [3,4], analogous to the one first mentioned by Romer and Dicke [5] in the microwave domain. The purpose of this note is to show that the main features of this coherent Dicke narrowing can be extended to two-(or multi-) photon transitions, as long as an effective two-level model can be considered, and for a normal incidence condition now referring to the sum of photon wave-vectors  i k r ∑  .…”

“…It exhibits a logarithmic singularity (in the limiting case ku >> γ 21 ), originating in the 1/v z contribution of fast atoms. Also, in spite of a mismatching brought by the Doppler detuning [3,4], all velocity groups interfere constructively up to the λ/2 thickness.…”

Laser spectroscopy of nanometric gas cells

“…One has predicted and experimentally observed (Fig. 5) that the "Doppler-free" absorption resonance reaches a maximum amplitude for L = A/2, 3M2, etc., and cancels for L = A, 2A ... [11]. This length dependence is a clear signature of the coherent character of light absorption in ultra thin gas cells.…”

Efficient technique for measuring laser frequency stability

“…Such atoms yield a nearly Doppler-free response. This key feature, together with a Dicke-type of coherent spectral narrowing occurring for a vapor thicknesses L = (2n + 1)λ/2 and a Fabry-Pérot type of behavior occurring for L = nλ/2 [15][16][17], where n is an integer, determine the significant difference of the optical spectra recorded with such nanocells from those in ordinary, cmsized cells.…”

“…The interaction of atoms with laser radiation in such cells is strongly anisotropic [14][15][16][17]. Atoms with a non-zero longitudinal (with respect to the laser beam) velocity component experience frequent quenching collisions with the cell walls (windows).…”