Research Teams  | Atomic spectroscopy at interfaces
Page modified Monday, September 08, 2014

Topics of interest

Atomic vapour Spectroscopy in the vicinity of an opics of interestAtomic vapour Spectroscopy in the vicinity of an interface:

  • Fundamental study of the properties of a free atom in the vicinity of an interface. Casimir-Polder interaction between an atom and a dielectric surface at non-zero temperature in the presence of surface polariton modes.
  • Sub-micron confinement of alkali atoms within the interstitial regions of an opal (quasi periodic three-dimensional structure of nanospheres), or within ultra-thin vapour cells.

Theoretical study of the interaction between an atom and an optical field with a complex spatial structure at a wavelength scale (Laguerre-Gauss beams, and nano-optics), notably the coupling with nearly forbidden atomic transitions (beyond the electric dipole approximation, and chiral properties). 

General Presentation

The group "Atomic Spectroscopy at an Interface" mostly uses sub-Doppler laser spectroscopy techniques to study the effects of confinement of atomic vapour close to a wall.

In the Cavity QED frame the atomic properties are modified due to its coupling with the fluctuating vacuum field. The presence of a reflective boundary modifies the vacuum fluctuations which gives rise to the well-known Casimir-Polder interaction between an atom and a surface. Our group uses selective reflection spectroscopy to study this fundamental phenomenon. This technique is well suited for probing atomic vapour up to a depth of l/2p, i.e. roughly 100 nm for our experiments. This distance range corresponds to an electrostatic limit (van der Waals regime) of the Casimir-Polder interaction where the atom-surface potential evolves like C3 z-3, where z is the atom-surface distance and C3 a coefficient depending on the considered atomic level |i> and the dielectric properties of the surface. Our spectroscopic approach allows the study of excited atoms for which the interaction is usually larger and, more importantly, sensitive to the presence of surface modes (surface polaritons). These modes, whose energy lies in the mid or deep infrared, can resonantly couple to the virtual transitions relevant for the considered excited state. This effect radically influences the van der Waals interaction turning it from a giant attraction to repulsion, depending on the specific atom-surface system [1].

Very recently, we have succeeded in showing a notable variation (50 %) of this interaction with the vacuum temperature [2], for a Cs(7D3/2)/sapphire system (figure 1). The thermal excitation of surface modes is the key to the observed effect [3-5], and the atom is a kind of quantum probe of the near-field emission of the heated material, which in the far-field would be nearly a realization of a blackbody emitter.

Our group has also developed spectroscopic methods to study the properties of atomic vapour confined in cells of nanometric thickness (one dimensional confinement). These nanocells, fabricated in the group of D. Sarkysian in Amenia, enabled us to measure the distance dependence of the atom-surface interaction [6] and demonstrate a Dicke type narrowing in optical frequencies [7]. We are currently exploring the spectroscopy of three-dimensionally confined vapour in the interstitial regions of an opal of nanospheres. Despite numerous defects, typical for self-organised system, the opal remains an organised structure much like a photonic crystal. The opals we use are fabricated by the Langmuir-Blodgett method in the group of S. Ravaine at CRPP-Bordeaux. We have succeeded in operating a cell of alkali-metal vapour infiltrated in an opal made of a few layers of nanospheres despite the tendency of the confined atomic vapour to generate clusters. Probing the opal with reflection spectroscopy, we observe a spectroscopic signal exhibiting a sub-Doppler component for various oblique incidences (figure 2) [8]. This narrow contribution, obtained in the linear regime of interaction, evokes a Dicke narrowing, analogous to the one currently obtained in the microwave domain (with a sub-wavelength confinement by a buffer gas), but found here in the optical domain. We are presently working to improve our understanding of both the sub-Doppler atomic signal, and the peculiar optics of the opals, deposited on a substrate (window). For this purpose, we have recently developed a one-dimensional thin layer modelling (ArXiv 1407.5777).. Moreover, in collaboration with Uruguayan partners we study atomic vapour confinement in random porous media by means of scattered light spectroscopy [9, 10].

In other works that have remained theoretical until now, we have predicted that for a non-electric dipole transition, an atom-field interaction can be detected where the electric field is locally null, as exemplified by the case of a focused Laguerre-Gauss beams, [11]. Also, we address the problems of atoms interacting with nano-objects, possibly chiral ones [12].

[1] H. Failache, S. Saltiel, M. Fichet, D. Bloch, M. Ducloy (a) Resonant van der Waals Repulsion between Excited Cs Atoms and Sapphire Surface Phys. Rev. Lett., 83, 5467--5470 (1999); (b) Resonant coupling in the van der Waals interaction between an excited alkali atom and a dielectric surface an experimental study via stepwise spectroscopy. Eur. Phys. J. D 23, 237-255 (2003).

[2] A. Laliotis, T Passerat de Silans, I. Maurin, M. Ducloy, D. Bloch, Casimir-Polder interactions in the presence of thermally excited surface modes. Nature Comm. 5, 4364 (2014).

[3] M.-P. Gorza and M. Ducloy, Van der Waals interactions between atoms and dispersive surfaces at finite temperature, Eur. Phys. J. D. 40, 343-356 (2006). 

[4] T. Passerat de Silans, I. Maurin, P. Chaves de Souza Segundo, S. Saltiel, M.P. Gorza, M. Ducloy, D. Bloch, D. Meneses de Souza, P. Echegut, 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. J. of Phys.: Condens. Matter 21, 255902 (2007).

[5] A. Laliotis, T. Passerat de Silans, I. Maurin, M-P. Gorza, S. Saltiel, M.P. Gorza, M. Ducloy, D. Bloch, Experimental observations of temperature effects in the near field regime of the Casimir-Polder interaction. Laser Physics 24, 074009 (2014) .

[6] M. Fichet, G. Dutier, A. Yarovitsky, P. Todorov, I. Hamdi, I. Maurin, S. Saltiel, D. Sarkisyan, M.-P. Gorza, D. Bloch, M. Ducloy, Exploring the van der Waals Atom-Surface attraction in the nanometric range, Europhys. Lett., 765.

[7] G. Dutier, A. Yarovitsky, S. Saltiel, A. Papoyan, D. Sarkisyan, D. Bloch, M. Ducloy, Collapse and revival of Dicke-type coherent narrowing in a sub-micron thick vapour cell transmission spectroscopy, Europhys. Lett., 63, 35-41 (2003). 

[8] P. Ballin, E. Moufarej, I. Maurin, A. Laliotis, D. Bloch, (a) Three-dimensional confinement of vapor in nanostructures for sub-Doppler optical resolution, Appl. Phys. Lett. 102, 231115 (2013), and also (b) Sub-Doppler optical resolution by confining a vapour in a nanostructure, Proc. of SPIE 8770, 87700J (2013).

[9] S. Villalba, H. Failache, A. Laliotis, L. Lenci, S. Barreiro, A. Lezama, Rb optical resonance inside a random porous medium, Opt. Lett. 38, 193 (2013).

[10] S. Villalba, A. Laliotis, L. Lenci, D. Bloch, A. Lezama, H. Failache, Sub-Doppler resonances in the back-scattered light from random porous media infused with Rb vapor, Phys Rev A 89, 023422 (2014)

[11] V.V. Klimov, D. Bloch, M. Ducloy, J.R. Rios Leite (a) Detecting photons in the dark region of Laguerre-Gauss beam, Opt. Express 17, 9718-9723 (2009) ; (b) Mapping a focused Laguerre-Gauss beam : Detector dependence and interplay between spin and orbital angular momentum, Phys. Rev. A 85, 053834 (2012).

[12] V. V. Klimov, D. V. Guzatov, M. Ducloy, Engineering of radiation of optically active molecules with chiral nano-meta-particles, EPL, 97, 47004 (2012).

For links with the updated publications of SAI team, go to the item "publications".

Temperature dependence of the van der Waals C3 interaction coefficient for Cs(7D3/2)in the vicinity of a sapphire surface. The measurements are compared with the theoretical evaluation, which includes uncertainties on the exact resonant modes of sapphire, and on the atomic transition probabilities involved in the calculation.

Caption of figure 1:
Temperature dependence of the van der Waals C3 interaction coefficient for Cs(7D3/2)in the vicinity of a sapphire surface. The measurements are compared with the theoretical evaluation, which includes uncertainties on the exact resonant modes of sapphire, and on the atomic transition probabilities involved in the calculation.

FM spectrum in Reflection Spectroscopy (lambda = 894 nm) as observed on a Cs vapour cell, whose window is covered by a thin opal (10 layers) of 1µm diameter silica spheres. A sub-Doppler contribution is observed for a large range of incidences, whose shape varies rapidly with incidence, but which remains centred on the volume resonance marked by the saturated absorption spectrum ("SA ref") ((NB : for a "FM" spectrum, a FM -frequency modulation- is applied to the incident beam, and the signal is detected through a lock-in detection, yielding the frequency-derivative of the relevant spectrum: this relatively enhances the narrow contributions).

Caption of figure 2:
FM spectrum in Reflection Spectroscopy (lambda = 894 nm) as observed on a Cs vapour cell, whose window is covered by a thin opal (10 layers) of 1µm diameter silica spheres. A sub-Doppler contribution is observed for a large range of incidences, whose shape varies rapidly with incidence, but which remains centred on the volume resonance marked by the saturated absorption spectrum ("SA ref") ((NB : for a "FM" spectrum, a FM -frequency modulation- is applied to the incident beam, and the signal is detected through a lock-in detection, yielding the frequency-derivative of the relevant spectrum: this relatively enhances the narrow contributions).



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