INTERACTION ATOME-SURFACE : INTERACTION DE VAN DER WAALS ENTRE UN ATOME EXCITÉ ET UNE SURFACE DIÉLECTRIQUE THERMIQUEMENT ÉMISSIVE: OSCILLATIONS DE BLOCH POUR UN ATOME ADSORBÉ

In this thesis we have studied different aspects of the interaction between an atom and a dielectric surface. We have experimentally searched situations where the long range van der Waals interaction changes with the vacuum temperature as governed by its surrounding environnement. Such a situation occurs when the thermal surface emission resonantly couples in the near field to an atomic absorption. Our research deals with the interaction between a Cs(8P) atom and a CaF2 surface, and was performed through selective reflection spectroscopy. Until now, experimental values for C3 coefficient of the van der Waals interaction are in contradiction with the theoretical predictions. We have nevertheless refined our theoretical predictions by introducing in the calculations the temperature evolution of the dielectric constant, as obtained from new temperature dependent measurements of the surface reflectivity for CaF2, BaF2 and sapphire. We have also observed, in an auxiliary saturated absorption experiment, new lines around the 6S1/2→8P transitions, that we have attributed to dimers specifically formed by our lasers beams. Such lines appear for unusually low vapour densities. At a shorter distance range of atom-surface interaction, where the interaction potential combines van der Waals attraction and repulsion in the immediate vicinity of the surface, we have analysed the possibility of observing Bloch oscillations, on the basis of calculations for a He atom adsorbed on a LiF surface and submitted to an external force.Dans cette thèse nous avons étudié différents aspects de l'interaction entre un atome et une surface diélectrique. Nous avons notamment recherché expérimentalement des situations où l'interaction de van der Waals à longue portée varie avec la population thermique de photons du vide, telle qu'imposée par un équilibre avec l'environnement. Une variation avec la température est prévue lorsqu'il y a un couplage virtuel résonnant en champ proche entre l'émission thermique de la surface (dans l'IR) et une absorption atomique. Notre recherche a porté sur l'interaction entre Cs(8P) et une surface de CaF2 en utilisant la spectroscopie de réflexion sélective. Jusqu'à présent, les valeurs expérimentales du coefficient C3 de l'interaction de van der Waals sont en contradiction avec les prédictions théoriques. Nous avons pourtant raffiné les prédictions théoriques en introduisant dans les calculs la dépendance en température de la constante diélectrique, à partir de nouvelles mesures de la réflectance sur des surfaces de saphir, CaF2 et BaF2 effectués à différentes températures. Nous avons, en outre, observé, sur une expérience auxiliaire d'absorption saturée, des raies inédites autour de la transition 6S1/2→8P, que nous avons attribuées à des dimères spécifiquement formés par nos faisceaux lasers. Ces raies apparaissent pour des densités de vapeur inhabituellement faibles. A un régime de plus faible distance de l'interaction atome-surface, où le potentiel combine attraction van der Waals et répulsion au voisinage immédiat de la surface, nous avons analysé la possibilité d'observer des oscillations de Bloch, en considérant le cas d'un atome d'Helium adsorbé sur une surface de LiF et soumis à une force externe

Laser-induced atomic adsorption: a mechanism for nanofilm formation

We demonstrate and interpret a technique of laser-induced formation of thin metallic films using alkali atoms on the window of a dense-vapour cell. We show that this intriguing photo-stimulated process originates from the adsorption of Cs atoms via the neutralisation of Cs$^+$ ions by substrate electrons. The Cs$^+$ ions are produced via two-photon absorption by excited Cs atoms very close to the surface, which enables the transfer of the laser spatial intensity profile to the film thickness. An initial decrease of the surface work function is required to guarantee Cs$^+$ neutralisation and results in a threshold in the vapour density. This understanding of the film growth mechanism may facilitate the development of new techniques of laser-controlled lithography, starting from thermal vapours.Comment: 5 pages, 4 figures. EPL, accepted for publicatio

EXTRA SUB-DOPPLER LINES IN THE VICINITY OF THE THIRD RESONANCE 6S-8P OF ATOMIC Cs ATTRIBUTED TO OPTICALLY INDUCED Cs DIMERS

International audienceWe report on the observation of extra sub-Doppler lines in a saturated absorption experiment when exploring the vicinity of the 6S1/2 8P3/2 transition of Cs ( = 388 nm). These extra lines are observed only under a relatively strong irradiation of both the pump and the probe beams. Extra narrow lines are also observed in co-propagating nonlinear spectroscopy, and around the lines of the V-type three-level system 8P3/2 - 6S1/2 - 8P1/2 (1 = 388 nm, 2 = 389 nm). We attribute theses extra-lines to a probing of high-lying molecular caesium, produced as a result of the optical excitation of Cs atoms, as the low Cs atom density ( 1012cm-3) is unable to populate significantly the dimer states in the condition of thermal equilibrium

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 in 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 where a Cs(8P3/2) atom is next to a CaF2 or a 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 vapour 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 of using more durable materials, such as sapphire. We finally discuss selective reflection experiments on Cs(7D3/2) in an all-sapphire cell that clearly demonstrate a temperature dependent van der Waals coefficient.Comment: accepted for publication in Laser Physic

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 CaF2 interface show a temperature dependence, yet to be analyzedComment: selected to appear in Annales de Physique- COLOQ 1