Temperature-dependent van der Waals atom-surface interaction (original) (raw)
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Journal of Physics: Condensed Matter, 2009
PACS numbers : 78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity) 34.35.+a Interactions of atoms and molecules with surfaces 78.30.-j Infrared and Raman spectra 63.20.D-Phonon states and bands, normal modes, and phonon dispersion 44.40.+a Thermal radiation Abstract The temperature behaviour in the range 22°C to 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.
Laser Physics, 2007
We report on the analysis of FM selective reflection experiments on the 6S 1/2 → 8P 3/2 transition of Cs at 388 nm, and on the measurement of the surface van der Waals interaction exerted by a sapphire interface on Cs(8P 3/2). Various improvements in the systematic fitting of the experiments have permitted us to supersede the major difficulty of a severe overlap of the hyperfine components, originating, on the one hand, in a relatively small natural structure, and, on the other hand, on a large pressure broadening imposed by the high atomic density needed for the observation of selective reflection on a weak transition. The strength of the van der Waals surface interaction is evaluated to be 73 ± 10 kHz µm3. An evaluation of the pressure shift of the transition is also provided as a by-product of the measurement. Finally, we discuss the significance of an apparent disagreement between the experimental measurement of the surface interaction, and the theoretical value calculated for an electromagnetic vacuum at a null temperature. The possible influence of the thermal excitation of the surface is evoked, because the dominant contributions to the van der Waals interaction for Cs(8P 3/2) lie in the far-infrared range.
Selective reflection spectroscopy of a vapour at a calcium fluoride interface
Annales de Physique, 2007
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.
… , Molecular, Optical and …, 2003
We present a detailed experimental study of the evaluation of the van der Waals (vW) atomsurface interaction for high-lying excited states of alkali-metal atoms (Cs and Rb), notably when they couple resonantly with a surface-polariton mode of the neighbouring dielectric surface. This report extends our initial observation [Phys. Rev. Lett. 83, 5467 (1999)] of a vW repulsion between Cs(6D 3/2) and a sapphire surface. The experiment is based upon FM selective reflection spectroscopy, on a transition reaching a high-lying state from a resonance level, that has been thermally pumped by an initial one-photon step. Along with a strong vW repulsion fitted with a blue lineshift, −160 ± 25 kHz µm 3 for Cs(6D 3/2) in front of a sapphire surface (with a perpendicular c-axis), we demonstrate a weaker vW repulsion (−32±5 kHz µm 3) for Cs(6D 3/2) in front of a YAG surface, as due to a similar resonant coupling at 12 µm between a virtual atomic emission (6D 3/2-7P 1/2) and the surface polariton modes. A resonant behaviour of Rb(6D 5/2) in front of a sapphire surface exists also because of analogous decay channels in the 12 µm range. Finally, one demonstrates that fused silica, nonresonant for a virtual transition in the 12 µm range and hence weakly attracting for Cs(6D 3/2), exhibits a resonant behaviour for Cs(9S 1/2) as due to its surface polariton resonance in the 8-9 µm range. The limiting factors that affect both the accuracy of the theoretical prediction, and that of the fitting method applied to the experimental data, are discussed in the conclusion. PACS. 42.50.Xa Optical tests of quantum theory-34.50.Dy Interactions of atoms and molecules with surfaces; photon and electron emission; neutralization of ions-42.50.Ct Quantum description of interaction of light and matter; related experiments-32.70.Jz Line shapes, widths, and shifts-78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
Physical review. B, Condensed matter, 1986
An atom or a molecule approaching a surface experiences an attractive potential given by V(z)-C3/z. We have computed C3 for rare-gas atoms and simple molecules interacting with surfaces of various insulators. Our calculation utilizes (frequency-dependent} atomic polarizabilities and dynamic dielectric functions obtained from optical data. A comparison is made with C3 values deduced from multilayer adsorption data on CaF2. We show that a simple formula can be used to evaluate C3 that utilizes readily available constants. We have also computed the long-range surface-mediated interaction between two adsorbed atoms on a surface. We then present a discussion on adsorption of adatoms on hexagonal BN as compared to that on a graphite substrate. I. INTRODUCTION Considerable attention has been devoted in recent years to the problem of calculating, possibly by ab initio, reliable atom (molecule)-surface potentials. ' These efforts were motivated by the appearance of high-resolution experiments using the technique of atom beam scattering2 as well as by the interest in studying twoor quasi-twodimensional adsorbed films on substrates. An important ingredient in such calculations is the long-range behavior of the interaction, i.e. , the behavior that results when the incoming atom and the surface are well separated and no significant overlap of wave functions occurs. It has been shown that the asymptotic part of the potential is V(z)-C3/z, where C3=(1/4n) J a(iE) dE, e(iE) 1-0 ElE+1 z is the atom-surface separation, E =Pm, and C3 is a constant that depends on the dynamic atomic polarizability a and the dielectric response e of the solid. The purpose of this paper is to calculate such constants for many atom (molecule)-surface systems of interest. We have considered the interaction of H, H2, He, Ne, Ar, Kr, Xe, and C~o n the surfaces of sapphire, LiF, CaF2, and boron nitride (BN). This choice was made for the following reasons. Considerable attention has been given to the Kr-BN sys
The European Physical Journal D, 2001
A theory of van der Waals (vdW) interaction between an atom (in ground or excited state) and a birefringent dielectric surface with an arbitrary orientation of the principal optic axis (C-axis) is presented. Our theoretical approach is based on quantum-mechanical linear response theory, using generalized susceptibilities for both atom and electromagnetic field. Resonant atom-surface coupling is predicted for excited-state atoms interacting with a dispersive dielectric surface, when an atom de-excitation channel gets into resonance with a surface polariton mode. In the non-retarded regime, this resonant coupling can lead to enhanced attractive or repulsive vdW surface forces, as well as to a dissipative coupling increasing the excited-state relaxation. We show that the strongly non-scalar character of the interaction with the birefringent surface produces a C-axis-dependent symmetry-breaking of the atomic wavefunction. Changes of the C-axis orientation may also lead to a frequency shift of the surface polariton mode, allowing for tuning on or off the resonant coupling, resulting in a special type of engineering of surface forces. This is analysed here in the case of cesium 6D 3/2 level interacting with a sapphire interface, where it is shown that an adequate choice of the sapphire C-axis orientation allows one to transform vdW surface attraction into repulsion, and to interpret recent experimental observations based on selective reflection methods [H. Failache et al., Phys. Rev. Lett. 83, 5467 (1999)].
Long-range atom-surface interactions for cold atoms
Journal of Physics: Conference Series, 2005
Studies of the long-range interactions between cold atoms and surfaces are now of vital interest. The interest is partly driven by nanotechnology applications, partly by the exploding interest in the encompassing superfield of Casimir effects, and partly by the burgeoning overlap between atomic and molecular physics, condensed matter, and quantum optics. This tutorial lecture will address long-range atom-surface interactions for cold atoms, including an overview of Casimir-Polder interactions and their various manifestations. Some previous theoretical studies that are of particular relevance will be reviewed. In addition some different approaches to the problem and corresponding results, especially concerning the effects of substrate composition, geometry, and finite temperature, will be discussed. The resonant interaction between a ground state atom and an excited state atom, e.g. a Na(3s) atom and a Na(3p) atom, will not be considered here.