Selective reflection spectroscopy at an interface with a low-density resonant vapor, especially when combined with a frequency modulation technique, is a high-resolution Doppler-free tool for probing atoms interacting with a surface. We analyze different types of relevant surface interaction, emphasizing the spectral consequences of a van der Waals surface attraction associated to a
z−3 potential dependence (
z: distance to the wall). We present detailed results of two series of experiments at a Cs vapor/dielectric window interface on the 6S
1/2-6P
3/2 (
λ=852 nm) resonance line and on the 6S
1/2-7P second resonance line (
λ=455 nm and 459 nm). Lineshape analysis at various pressures consistently shows that a van der Waals-type surface attraction has to be considered to interpret strong lineshape distortions and resonance shift. The attractive strengths are found to be equal respectively to
≈2 kHz
μm
3 and
≈20 kHz
μm
3, independently of the considered hyperfine component, within the experimental accuracy. It yields also typical parameters of pressure broadening and shift, which are shown to originate in collisional processes, at densities where the medium is opaque. Theoretical expectations for the VW strength are discussed on the basis of the results of atomic theory. The predicted values are smaller, by a typical factor of 2, than those deduced from the experiments. The validity of the theory, when applied to a dielectric interface, is discussed and seems questionable when the frequency of virtual atomic transitions involved in the van der Waals attraction potential lies in the dielectric window absorption range.
This reports on the surface attraction exerted onto Cs(8P), as measured through the selective reflection spectroscopy (SR) technique via a one- photon excitation at 388 nm from the ground state. In a series of experiments on the Cs (6S/sub 1/2/-8P/sub 3/2/) transition in front of a sapphire surface, the accuracy in the van der Waals evaluation, and with an improved fitting method, should be on the order of 10%. Further developments, expected to be reported too, concern the fine structure component Cs (6S/sub 1/2/-8P/sub 3/2/) , along with a study of SR spectroscopy at various interfaces.
Frequency-modulated selective-reflection spectroscopy of the 6S-7P Cs resonance line yields Doppler-free anomalous line shapes that we demonstrate to be fully dominated by the long-range atom-surface interaction potential. The spatial inhomogeneous broadening of the observed line shapes, as well as its dependence on the pressure, the nature of the dielectric window, and the light incidence angle, is fully interpreted with a z(-3) van der Waals attraction model. These experiments clearly prove the feasibility of a spectral analysis of atom-surface interactions.
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.