No abstract

The spontaneous decay rates of an excited atom placed near a dielectric cylinder are investigated. A special attention is paid to the case when the cylinder radius is small in comparison with radiation wavelength (nanofiber or photonic wire). In this case, the analytical expressions of the transition rates for different orientations of dipole are derived. It is shown that the main contribution to decay rates is due to quasistatic interaction of atom dipole momentum with nanofiber and the contributions of guided modes are exponentially small. On the contrary, in the case when the radius of fiber is only slightly less than radiation wavelength, the influence of guided modes can be substantial. The results obtained are compared with the case of dielectric nanospheroid and ideally conducting wire.

No abstract

Transmission spectroscopy in an ultrathin vapor cell, which has been recently demonstrated as a new method of sub-Doppler spectroscopy in the optical domain, is revisited. We show that, because of an unavoidable Fabry-Perot effect, the observed signal-in transmission spectroscopy and selective reflection spectroscopy as well-is actually an interferometric mixture of the optical responses as provided in transmission and in reflection by a long macroscopic cell. After the derivation of a very general solution, we restrict ourselves to the case of a linear interaction with the resonant laser. We finally discuss the application to a two-level atom for which analytical expressions are given, in the large Doppler limit, for FM transmission and reflection signals.

We explore a situation where the van der Waals long-range atom-surface interaction is repulsive. This repulsion originates in a resonant coupling between a virtual emission at 12.15 mm of a Cs ‫ء‬ ͑6D 3͞2 ͒ atom and a virtual excitation of a surface polariton in sapphire. The experimental evidence is based upon the analysis of the spectroscopic response of Cs* in the near-infrared range with a technique that probes a distance range ϳ100 nm away from the sapphire surface. We also demonstrate the critical dependence of atom-surface forces on the sapphire crystal orientation. PACS numbers: 34.50.Dy, 12.20.Fv, 71.36. + c The van der Waals (vW) force between neutral polarizable systems [1,2] represents a universal interaction of paramount importance in numerous fields of physics, chemistry, and biology. Its attractive character is essential for the cohesion of many chemical or biological systems. vW attraction between atomic systems and metallic or dielectric bodies is also a fundamental property in cavity quantum electrodynamics (QED) [3], and its main characteristics have been experimentally studied by means of mechanical approaches (atomic beam deflection produced by surfaces [4,5], energy threshold in atomic mirrors [6]), or, in our group, spectroscopic approaches (spectral monitoring of surface-induced atomic level shifts [7-10]).In the nonretarded regime, the vW interaction between an atom and a surface originates in the quantum fluctuations of the atomic dipole: The fluctuating dipole polarizes the surface, and induces a dipole image instantaneously correlated with the atomic dipole. This near-field image is responsible for the attractive character of the vW interaction, which scales in 1͞z 3 (z is the atom-surface distance) [1].Is it possible to turn this near-field attraction into a repulsion? The answer is yes, if a resonant coupling between the fluctuating atomic dipole and a surface excitation can occur [11][12][13]. For a dispersive dielectric medium with a complex permittivity´͑v͒, the well-known electrostatic image coefficient S ͑´2 1͒͑͞´1 1͒ (with 0 # S # 1) has to be generalized to a complex frequency-dependent surface response [13]:whose resonances ("surface polaritons" [14]) are determined by the poles of S͑v͒.Consider an excited atom for which one of the dipoleallowed deexcitation channels (at frequency v a ) is near resonant with a surface polariton. Because of nonradiative, virtual coupling between the atom and surface (atomic decay followed by surface excitation), the surface response at frequency v a is magnified, implying a dielectric image coefficient, 2Re͓S͑v a ͔͒, possibly larger than one-the value obtained for an ideal reflector. Because of the resonant enhancement, S is complex and the image dipole is dephased as well. When this image is phase reversed, the near-field vW attraction is turned into a near-field vW repulsion, also scaling in 1͞z 3 . This is one among the rare situations of a long-range, state-selective repulsion exerted by a cavity wall on an atom, at distances spanning f...

PACS. 42.50.Gy -Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption. PACS. 32.70.Jz -Line shapes, widths, and shifts. PACS. 42.50.Md -Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency.Abstract.-In a thin cell of dilute vapour, the absorption spectrum exhibits sub-Doppler features due to the relative enhancement of the slow atom contribution, with respect to the transient nature of the interaction with moving atoms. For a two-level system in the linear regime, the narrowest response is predicted to be found for a λ/2 thickness, as an effect of the coherent character of the dipole response as early described by Romer and Dicke (Phys. Rev., 99 (1955) 532) in the microwave regime. We report here on the direct observation of this effect in the optical regime in an ultra-thin vapour cell. This effect is shown to vanish for a thickness equal to λ, and a revival is observed at 3λ/2, as expected from the predicted λ-periodicity. The experiment is performed on the D1 resonance line of Cs vapour (λ = 894 nm), in a specially designed cell, whose thickness varies locally.

No abstract

We compare the behavior of absorption and of resonance fluorescence spectra in an extremely thin Rb vapor cell as a function of the ratio of L / , with L the cell thickness ͑L ϳ 150-1800 nm͒ and the wavelength of the Rb D 2 line ͑ = 780 mn͒. The Dicke-type coherent narrowing [G. Dutier et al., Europhys. Lett. 63, 35 (2003)] is observed only in transmission measurements, in the linear regime, with its typical collapse and revival, which reaches a maximum for L = ͑2n +1͒ /2 (n integer). It is shown not to appear in fluorescence, whose behavior-amplitude, and spectral width, is more monotonic with L. Conversely, at high-intensity, the sub-Doppler saturation effects are shown to be the most visible in transmission around L = n.