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arXiv:1905.05969 · Journal of Physics B Atomic Molecular and Optical Physics

Selective reflection from a potassium atomic layer with a thickness as small as λ /13

Armen D. Sargsyan, Emmanuel Klinger, Claude Leroy, Ifan G. Hughes, David G. Sarkisyan, Charles S. Adams

Published Aug 6, 2019• 11 citations
arXivHTMLPDF

Abstract

Abstract We demonstrate that a method using the derivative of the selective reflection (SR) signal from a nanocell is a convenient and robust tool for atomic laser spectroscopy, achieving a nearly Doppler-free spectral resolution. The recorded linewidth of the signal from a potassium-filled cell, whose thickness ℓ lies in the range 350–500 nm, is 18 times smaller than the Doppler linewidth (∼900 MHz full width at half maximum) of potassium atoms. We also show experimentally a sign oscillation of the reflected signal’s derivative with a periodicity of λ /2 when ℓ varies from 190 to 1200 nm confirming the theoretical prediction. We report the first measurement of the van der Waals atom-surface interaction coefficient C 3 = 1.9 ± 0.3 kHz × μ m 3 of potassium 4 S 1 / 2 → 4 P 3 / 2 transitions with the nanocell’s sapphire windows, demonstrating the usefulness and convenience of the derivative of SR technique for cell thicknesses in the range 60–120 nm.

DOI
10.1088/1361-6455/ab38fe

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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.

Journal of Contemporary Physics (Armenian Academy of Sciences)•Sep 1, 2025•0 citations
Abstract We demonstrate that a method using the derivative of the selective reflection (SR) signal from a nanocell is a convenient and robust tool for atomic laser spectroscopy, achieving a nearly Doppler-free spectral resolution. The recorded linewidth of the signal from a potassium-filled cell, whose thickness ℓ lies in the range 350–500 nm, is 18 times smaller than the Doppler linewidth (∼900 MHz full width at half maximum) of potassium atoms. We also show experimentally a sign oscillation of the reflected signal’s derivative with a periodicity of λ /2 when ℓ varies from 190 to 1200 nm confirming the theoretical prediction. We report the first measurement of the van der Waals atom-surface interaction coefficient C 3 = 1.9 ± 0.3 kHz × μ m 3 of potassium 4 S 1 / 2 → 4 P 3 / 2 transitions with the nanocell’s sapphire windows, demonstrating the usefulness and convenience of the derivative of SR technique for cell thicknesses in the range 60–120 nm.
We studied selective reflection (SR) of laser radiation from a window of a nanocell with thickness L ~ λ 1,2 /2 filled with Rb and Cs atoms, where λ 1 = 780 nm and λ 2 = 852 nm are the wavelengths resonant with the D 2 laser lines for Rb and Cs, respectively. It is demonstrated that the negative derivative of the SR signal profile for L > λ /2 changes to the positive one for L < λ /2. It is shown that the real-time formation of the SR signal profile derivative (SRD) with the spectral width 30–40 MHz and located at the atomic transition is, in particular, a convenient frequency marker of D 2 transitions in Rb and Cs. The amplitudes of SRD signals are proportional to the atomic transition probabilities. A comparison with the known saturated absorption (SA) method demonstrated a number of advantages, such as the absence of cross-over resonances in the SRD spectrum, the simplicity of realization, a low required power, etc. An SRD frequency marker also operates in the presence of the Ne buffer gas at a pressure of 6 Torr, which allowed us to determine the Ne–Rb collisional broadening, whereas the SA method is already inapplicable at buffer gas pressures above 0.1 Torr. The realization simplicity makes the SRD method a convenient tool for atomic spectroscopy. Our theoretical model well describes the SRD signal.
The features of the effect of selective reflection from rubidium vapor in a nanocell with the thickness L ≈ λ/2 and L ≈ λ/4, where λ = 795 nm is the wavelength of laser radiation resonant with the Rb D 1 line, are studied. It is shown that, because of the behavior of the nanocell as a low-Q-factor Fabry–Pérot etalon, the sign of the derivative of the selective reflection spectra changes near L ≈ λ/2 from negative at L > λ/2 to positive at L < λ/2. The simplicity of the experimental implementation, large amplitude, and sub-Doppler width (40MHz) of a detected signal at an atomic transition frequency are appropriate for applications in metrology and magnetometry. In particular, selective reflection from the nanocell is a convenient frequency marker of atomic transitions; in this case, the amplitudes of peaks are proportional to the transition probabilities. The remote optical monitoring of a magnetic field with a spatial resolution L = λ/4 ≈ 199 of nm is possible on the basis of the splitting of selective reflection peaks in a strong magnetic field (up to 3 kG). A theoretical model describes well the experimental results.
Abstract The effect of selective reflection (SR) of laser radiation from the boundary of 87 Rb D 2 -line atomic vapors and a dielectric window was studied using a nanocell (NC) with a vapor column thickness of ~300 nm. The formation of an SR with a spectral width of 25 MHz, located on atomic transitions, is demonstrated. This is a record narrowing of the 670 MHz Doppler width by a factor of 27 using single-pass geometry. The SR signal reaches several percent of the intensity of its forming radiation, and the SR amplitude’s linear dependence is maintained up to 100 mW/cm 2 , which is almost two orders of magnitude greater than the saturation intensity of optical processes when using centimeter-long cells with atomic vapors. Such a high saturation intensity value is achieved by using the nanocell.
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.
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.