The van der Waals potential between metastable atoms and solid surfaces: Novel diffraction experiments vs. theory (original) (raw)
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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)].
Van der Waals contribution to the inelastic atom-surface scattering
Journal of Electron Spectroscopy and Related Phenomena, 2003
A calculation of the inelastic scattering rate of Xe atoms on Cu(111) is presented. We focus in the regimes of low and intermediate velocities, where the energy loss is mainly associated to the excitation electron-hole pairs in the substrate. We consider trajectories parallel to the surface and restrict ourselves to the Van der Waals contribution. The decay rate is calculated within a self-energy formulation. The effect of the response function of the substrate is studied by comparing the results obtained with two different approaches: the Specular Reflection Model and the Random Phase Approximation. In the latter, the surface is described by a finite slab and the wave functions are obtained from a one-dimensional model potential that describes the main features of the surface electronic structure while correctly retains the imagelike asymptotic behaviour. We have also studied the influence of the surface state on the calculation, finding that it represents around 50% of the total probability of electron-hole pairs excitation.
… , 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)
Atom-surface van der Waals repulsion
We explore experimentally a situation when the van der Waals long-range atom-surface interaction is turned into epulsion, as due to a resonant coupling between a virtual emission of the excited atom, and a virtual absorption of the dielectric surface in a polariton mode.
Exploring the van der Waals atom-surface attraction in the nanometric range
Europhysics Letters (EPL), 2007
Optical tests of quantum theory 34.50.Dy Interactions of atoms and molecules with surfaces; photon and electron emission; neutralization of ions 32.70.Jz Line shapes, widths, and shifts The van der Waals atom-surface attraction, scaling as C 3 z-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 6P 3/2 →6D 5/2 transition. The measured C 3 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.
Atom Symmetry Break and Metastable Level Coupling in Rare Gas Atom-Surface van der Waals Interaction
Physical Review Letters, 2001
van der Waals interactions between an atom and a planar surface exhibit a quadrupolar component in D 2 z -D 2 ͞3 (D, atomic dipole;ẑ, normal to surface). This coupling is responsible for an atom symmetry break, mixing levels of the same parity such as metastable 3 P 0 , 3 P 2 levels of rare gas atoms. The strongly exoenergic 3 P 0 -3 P 2 transition in Ar and Kr is observed by a time-of-flight technique, using as a surface the edge of a copper slit. The results confirm the predicted strong peaking of the angular distribution of inelastically scattered atoms and give a good estimate of the transition probability.
van der Waals coefficients for alkali-metal atoms in material media
Physical Review A, 2014
The damping coefficients for the alkali atoms are determined very accurately by taking into account the optical properties of the atoms and three distinct types of trapping materials such as Au (metal), Si (semi-conductor) and vitreous SiO2 (dielectric). Dynamic dipole polarizabilities are calculated precisely for the alkali atoms that reproduce the damping coefficients in the perfect conducting medium within 0.2% accuracy. Upon the consideration of the available optical data of the above wall materials, the damping coefficients are found to be substantially different than those of the ideal conductor. We also evaluated dispersion coefficients for the alkali dimers and compared them with the previously reported values. These coefficients are fitted into a ready-to-use functional form to aid the experimentalists the interaction potentials only with the knowledge of distances.