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Optics and Spectroscopy

Investigation of Interaction of Cs Atoms with Sapphire Surface by Means of an Ultrathin Cell and the Second-Derivative Spectrometry of Vapor Absorption

Armen D. Sargsyan, T. A. Vartanyan, David G. Sarkisyan

Published May 1, 2020• 5 citations
Publisher

Abstract

Abstract The influence of interaction of Cs atoms with a dielectric surface on position and shape of the hyperfine components of the D2 line in the case of nanometer-scale distance between the atom and the surface is investigated. Using a wedged nanocell enabled investigating the dependence of shift of all hyperfine components of the D2 line corresponding to Fg = 3 → Fe = 2, 3, 4 and Fg = 4 → Fe = 3, 4, 5 transitions on distance L between the atoms and the surface of a sapphire window in the interval from 50 to 400 nm. At L smaller than 100 nm, atomic transitions experience strong broadening due to van der Waals interaction and shift to lower frequencies (the red shift). Calculation of the second derivative (SD) of the absorption spectra of vapors in a nanocell allows spectrally resolving the hyperfine components of an atomic transition down to L ~ 50 nm and determining the van der Waals interaction coefficient C3. It is demonstrated that the spectrum experiences an additional red shift with increase in the density of atoms at L < 100 nm. In contrast, a blue shift occurs with increase in the density of atoms at relatively large distances between the atoms and the surface (L ~ 400 nm). The above results are important for development of miniature submicron-size devices containing alkali metals.

DOI
10.1134/s0030400x20050112

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High resolution selective reflection spectroscopy as a probe of long-range surface interaction : measurement of the surface van der Waals attraction exerted on excited Cs atoms

Martine Chevrollier, Mich�le Fichet, Marcos Oriá +3 more

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$_{3/2}$ ($\lambda = 852$ nm) resonance line and on the 6S$_{1/2}$-7P second resonance line ($\lambda = 455$ 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 $\approx 2$ kHz $\mu$m$^3$ and $\approx 20$ kHz $\mu$m$^3$, 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.

Journal de Physique II•Apr 1, 1992•91 citations
Abstract The influence of interaction of Cs atoms with a dielectric surface on position and shape of the hyperfine components of the D2 line in the case of nanometer-scale distance between the atom and the surface is investigated. Using a wedged nanocell enabled investigating the dependence of shift of all hyperfine components of the D2 line corresponding to Fg = 3 → Fe = 2, 3, 4 and Fg = 4 → Fe = 3, 4, 5 transitions on distance L between the atoms and the surface of a sapphire window in the interval from 50 to 400 nm. At L smaller than 100 nm, atomic transitions experience strong broadening due to van der Waals interaction and shift to lower frequencies (the red shift). Calculation of the second derivative (SD) of the absorption spectra of vapors in a nanocell allows spectrally resolving the hyperfine components of an atomic transition down to L ~ 50 nm and determining the van der Waals interaction coefficient C3. It is demonstrated that the spectrum experiences an additional red shift with increase in the density of atoms at L < 100 nm. In contrast, a blue shift occurs with increase in the density of atoms at relatively large distances between the atoms and the surface (L ~ 400 nm). The above results are important for development of miniature submicron-size devices containing alkali metals.
The influence of the interaction of Cs atoms with a dielectric surface on the position and shape of the hyperfine components of the D2 line at nanometer-order distances between atoms and the surface is studied. The use of a nanocell with a wedge-shaped gap made it possible to study the dependence of the shifts of all the hyperfine components of the D2 line corresponding to the transitions Fg = 3- Fe = 2, 3, 4 and Fg = 4- Fe = 3, 4, 5, on the distance L between the atoms and the sapphire surface windows in the range of 50–400 nm. At L less than 100 nm, due to the van der Waals interaction, there is a strong broadening of atomic transitions and a shift of their frequencies to the low-frequency region of the spectrum (red shift). The calculation of the second derivative (SD) of the vapor absorption spectra in the nanocell allows one to spectrally resolve the hyperfine components of the atomic transition down to L about 50 nm and measure the coefficient of the van der Waals interaction C3. It is shown that, at L <100 nm, an additional red shift occurs with increasing atomic density, while at relatively large distances between atoms and the surface L about 400 nm, an increase in atomic density causes a blue shift of the atomic transition frequencies. The above results are important in the development of miniature submicron devices containing atomic vapor of alkali metal.
The effect of the dielectric surface on the 39K D1 line (Fg = 1, 2 → Fe = 1, 2 transitions) at nanometer distances has been experimentally studied for the first time. A nanocell that is filled with atomic potassium and has a wedge gap has been used to study the effect of atoms at distances of 50–800 nm from the technical sapphire window surface. At distances L < 100 nm from the sapphire surface, the van der Waals interaction strongly broadens atomic transitions and their frequencies are redshifted. The second derivative method applied to the absorption spectra of the nanocell has allowed the first measurement of the van der Waals interaction coefficient C3 = (1.2 ± 0.3) kHz μm3 for the 39K D1 line. It has been shown that the dipole–dipole interaction between 39K atoms results in the additional redshift at an increase in the density of atoms for the nanocell thickness L < 70 nm. The results obtained are important for the development of submicron devices containing free atoms.
Abstract The Van der Waals effect (VW) in 39K atomic vapours was experimentally studied using a nanocell made of technical sapphire. At distances of less than 100 nm from the sapphire surface, a strong broadening of atomic transitions and their frequency shifts to the low-frequency region of the spectrum occur. The method of selective reflection (SR) of laser radiation from the sapphire window-atomic vapours boundary was used as a sub-Doppler method, which made it possible to measure the VW interaction coefficient C3 for the potassium atoms. It is shown that a change in the nanocell thickness from 100 to 50 nm results in a decrease in C3, as calculated from the “red” VW shift, i.e., the so-called “retardation” of the VW effect, which was predicted in theoretical works and experimentally observed. The obtained results are important for the development of miniature submicron devices containing atomic vapours.
The van-der-Waals effect (VW) in 39K atomic vapours was experimentally studied using a nanocell made of technical sapphire. At distances of an atom from the sapphire surface of less than 100 nm, a strong broadening of atomic transitions and their frequency shifts to the low-frequency region of the spectrum occur. The method of selective reflection (SR) of laser radiation from the sapphire window-atomic vapours boundary was used as a sub-Doppler method, which made it possible to measure the VW interaction coefficient C3 for the potassium atoms. It was shown that a change in the nanocell thickness from 100 to 50 nm leads to a decrease in C3 calculated from the "red" VW shift, i.e. the so-called "retardation" of the VW effect, which was predicted in theoretical works, was experimentally registered. The obtained results are important in the development of miniature submicron devices containing atomic vapours.
The effect of the van der Waals interaction of cesium atoms with the sapphire windows of a nanocell was experimentally investigated using the selective reflection process. The distance L between the windows varied in the range of 50–2000 nm and the nanocell was filled with the vapors of cesium atoms. For the Cs atoms (the transition 6 S 1/2 → 6 P 1/2 ), the C 3 coefficient of the van der Waals interaction with the sapphire windows of the nanocell is measured. It is shown that it is possible to determine the magnetic fields with the spatial resolution of 70 nm using the selective reflection spectrum and, consequently, both the homogeneous and highly gradient magnetic fields can be measured.
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−3z^{-3}z−3 potential dependence (zzz: distance to the wall). We present detailed results of two series of experiments at a Cs vapor/dielectric window interface on the 6S1/2_{1/2}1/2​-6P3/2_{3/2}3/2​ (λ=852\lambda = 852λ=852 nm) resonance line and on the 6S1/2_{1/2}1/2​-7P second resonance line (λ=455\lambda = 455λ=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\approx 2≈2 kHz μ\muμm3^33 and ≈20\approx 20≈20 kHz μ\muμm3^33, 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.