Philippe Ballin

Three-dimensional confinement of vapor in nanostructures for sub-Doppler optical resolution

We confine a Cs thermal vapor in the interstitial regions of a glass opal. We perform linear reflection spectroscopy on a cell whose window is covered with a thin film (10 or 20 layers) of ∼1000 nm (or 400 nm) diameter glass spheres and observe sub-Doppler structures in the optical spectrum for a large range of oblique incidences. This original feature associated with the inner (3-dimensional) confinement of the vapor in the interstitial regions of the opal evokes a Dicke narrowing. We finally consider possible micron-size references for optical frequency clocks based on weak, hard to saturate, molecular lines.

First observation of the temperature dependence of the van der Waals Casimir-Polder interaction in the condition of thermal equilibrium

The Casimir-Polder (C-P) interaction between an atom and a surface, described as early as 1948, but observed much later on, is now a topic of broad interest, as connected to fundamental problems of quantum fluctuations, with the atomic energy levels renormalized by the wall-dependent vacuum fluctuations. Dependence of the C-P interaction with the equilibrium temperature is predicted, but had not been observed until now. However, more pronounced effects were predicted in an out-of-equilibrium situation, and were remarkably observed on a Rb BEC, at 6–10 µm from the wall, with the vacuum temperature (∼ 300K) strongly differing from the surface temperature (∼ 1000 K) [1].

Vapour confined in an opal of nanospheres: Observation of sub-Doppler optical resonances reminiscent of the Dicke narrowing

Atomic vapours provide convenient frequency references, made precise when insensitive to the Doppler-broadening, and there is a growing technological need to fabricate compact atomic clocks [1]. Various technological reasons, including chemical and adsorption processes, may limit the confinement of a vapour, but an intrinsic limit lies in the mesoscopic nature of a confined gas, when the walls confine the atomic motion.