I. Maurin

Exploring the van der Waals atom-surface attraction in the nanometric range

The van der Waals atom-surface attraction, scaling as C3z?3 for z the atom-surface distance, is expected to be valid in the distance range 1?1000?nm, covering 8?10 orders of magnitudes in the interaction energy. A Cs vapour nanocell allows us to analyze the spectroscopic modifications induced by the atom-surface attraction on the 6P3/2 ? 6D5/2 transition. The measured C3 value is found to be independent of the thickness in the explored range 40?130?nm, and is in agreement with an elementary theoretical prediction. We also discuss the specific interest of exploring short distances and large interaction energy.

Temperature dependence of the dielectric permittivity of CaF2, BaF2 and Al2O3: application to the prediction of a temperature-dependent van der Waals surface interaction exerted onto a neighbouring Cs(8P3/2) atom

The temperature behaviour in the range 22-500 °C of the dielectric permittivity in the infrared range is investigated for CaF(2), BaF(2) and Al(2)O(3) through reflectivity measurements. The dielectric permittivity is retrieved by fitting reflectivity spectra with a model taking into account multiphonon contributions. The results extrapolated from the measurements are applied to predict a temperature-dependent atom-surface van der Waals interaction. We specifically consider as the atom of interest Cs(8P(3/2)), the most relevant virtual couplings of which fall in the range of thermal radiation and are located in the vicinity of the reststrahlen band of fluoride materials.

Optics of an opal modeled with a stratified effective index and the effect of the interface

Reflection and transmission for an artificial opal are described through a model of stratified medium based upon a 1D variation of an effective index. The model is notably applicable to a Langmuir–Blodgett-type disordered opal. Light scattering is accounted for by a phenomenological absorption. The interface region between the opal and the substrate, or the vacuum, induces a periodicity break in the photonic crystal arrangement, which exhibits prominent influence on the reflection, notably away from the Bragg reflection peak. Experimental results are compared with our model. The model is extendable to inverse opals, stacked cylinders, or irradiation by evanescent waves.

Probing an atomic gas confined in a nanocell

Since the recent realization of extremely thin vapour cells (local thickness: 20-1000 nm), we investigate the optical properties of these 1-D confined vapours. Aside from their interest for Doppler-free spectroscopy, nanocells offer a new tool to evaluate collisional shift and broadening, yielding an access to the open problem of collisions under confinement. It also allows probing of the atom-surface interaction in a range of unusual short distances. The experimental exploration of the distance dependence, normally evolving according to the z -3 van der Waals (vW) dependence (z : the atom-surface distance), is worth doing because it could be affected by imperfections of the real surface, such as roughness, adsorbed impurities or charges. A detailed lineshape analysis is now under progress, with tight constraints imposed to the fitting by the twin information brought by simultaneous reflection and transmission spectra. Another issue is a possible resonant enhancement, susceptible to induce a repulsive vW, due to the coupling between atom excitation and a surface mode.

Experimental observations of temperature effects in the near-field regime of the Casimir-Polder interaction

We investigate the temperature dependence of the Casimir–Polder interaction on the electrostatic limit. This unusual phenomenon relies on the coupling between a virtual atomic transition and a thermal excitation of surface polariton modes. We first focus on the scenario in which a Cs(8P3/2) atom is next to a CaF2 or BaF2 surface. Our theoretical predictions show a strong temperature dependence of the van der Waals coefficient at experimentally accessible conditions. A series of spectroscopic measurements performed in a specially designed Cs vapor cell containing a CaF2 tube is presented. Our results illustrate the sensitivity of atom–surface interaction experiments to the quality and chemical stability of the surface material and emphasize the need for using more durable materials, such as sapphire. Finally, we discuss selective reflection experiments with Cs(7D3/2) in an all-sapphire cell that clearly demonstrate a temperature-dependent van der Waals coefficient.

A 2D nanosphere array for atomic spectroscopy

We are interested in the spectroscopic behaviour of a gas confined in a micrometric or even nanometric volume. Such a situation could be encountered by the filling-up of a porous medium, such as a photonic crystal, with an atomic gas. Here, we discuss the first step of this program, with the generation and characterization of a self-organized 2D film of nanospheres of silica. We show that an optical characterization by laser light diffraction permits to extract some information on the array structure and represents an interesting complement to electron microscopy.

Selective reflection spectroscopy of a vapour at a calcium fluoride interface

Fluoride materials exhibit surface resonances located in the thermal infrared. This makes them interesting to search for a fundamental temperature dependence of the atom-surface interaction, originating in the near-field thermal emissivity of the surface. Preliminary selective reflection experiments performed on a special Cs vapour cell that includes a CaF 2 interface show a temperature dependence, yet to be analyzed.

Resonant infiltration of an opal: Reflection line shape and contribution from in-depth regions

We analyze the resonant variation of the optical reflection on an infiltrated artificial opal made of transparent nanospheres. The resonant infiltration is considered as a perturbation in the frame of a previously described one-dimensional model based upon a stratified effective index. We show that for a thin slice of resonant medium, the resonant response oscillates with the position of this slice. We derive that for adequate conditions of incidence angle, this spatially oscillating behavior matches the geometrical periodicity of the opal and hence the related density of resonant infiltration. Close to these matching conditions, the resonant response of the global infiltration varies sharply in amplitude and shape with the incidence angle and polarization. The corresponding resonant reflection originates from a rather deep infiltration, up to several wavelengths or layers of spheres. Finally, we discuss the relationship between the present predictions and our previous observations on an opal infiltrated with a resonant vapor.

Atom probing of thermally populated surface polaritons

Thermal emission has been the historic paradigm to understand quantization of energy, for light and matter. However, the universal far field blackbody radiation is not sufficient to account for the near field effects of the thermal emission [1]. When matter is heated up, surface polaritons at its boundary become thermally excited, and intense electromagnetic fields evanescently decay away from the surface. For a given material, with a well-defined shape, the population of these surface modes obeys a thermodynamic distribution, according to the local density of states in vacuum near the interface. In addition, rising up the temperature is susceptible to induce phenomenological changes of the surface mode resonances, such as broadening or shift.

Temperature dependence of the atom-surface interaction in thermal equilibrium

Summary form only given. Experimental studies of the atom-surface or surface-surface interactions provide a physical insight on the interaction of quantum bodies with the fluctuating vacuum. They can be of great practical interest in the ever expanding field of nanotechnologies. In particular the dependence of the Casimir and Casimir-Polder interaction on the thermal fluctuations is a fundamental effect that could in the future provide a useful knob for tuning these interactions. Temperature effects are usually very small and have so far been observed on a BEC placed 6-10 μm away from a fused-silica substrate due to an out of thermal equilibrium enhancement. Here we report on spectroscopic selective reflection measurements of the interaction between a Cs (7D3/2) atom and a sapphire surface. A virtual coupling between a surface resonance of sapphire at 12.1 μm and the Cs 7D3/2Æ5F5/2 transition at 10.8 μm almost eliminates the resonant contribution for this dipole transition. Reaching the temperatures required to observe an effect is extremely challenging. For this reason our experiment is performed in an all-sapphire vapour cell with super polished windows with an annealing post-treatment. The interaction is probed up to unusually high temperatures reaching more than 1000 K. Experimental measurements show C3 coefficient as a function of temperature compared to a full QED calculation. Each point is deduced by fitting reflection spectra to a theoretical model and is averaged for different vapour densities and different spots on the window. Statistical and systematic uncertainties have been reduced compared to our previous experiments performed on a different all-sapphire cell with windows of uncertain surface quality. The chemical stability of sapphire under these extreme conditions seems to be a key factor for this experimental achievement. Previous measurements between Cs (8P3/2) and a CaF2 surface in a specially designed cell were unsuccessful due to chemical deterioration of the surface. This experiment is the first to provide a sensitive measurement of temperature effects on the atom-surface interaction in thermal equilibrium and highlights the QED nature of van der Waals regime.