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Journal of Physics B Atomic Molecular and Optical Physics

Doppler-free selective reflection spectroscopy of the 6 s 2 S 1 / 2 → 7 p 2 P 3 / 2 transition of Caesium using an optical nanocell

Armen D. Sargsyan, Rodolphe Momier, David G. Sarkisyan

Published Sep 23, 2025• 3 citations
Publisher

Abstract

Abstract Selective reflection (SR) spectroscopy of the 6 s 2 S 1 / 2 → 7 p 2 P 3 / 2 electric dipole transition of Caesium ( λ = 456 nm) is performed for the first time using a nanometric-thin cell (L = 50–1500 nm, T = 200 ∘ C). We successfully form narrow resonances corresponding to the F g = 3 , 4 → F e = 2 , 3 , 4 , 5 hyperfine transitions. All transitions are well spectrally resolved, and the geometry of the cell allows us to obtain a strong 30 times narrowing of the Doppler width with a single beam pass. For lower thicknesses ( L < 400 nm), we observe a red shift of the SR lines, which we attribute to atom-surface interactions, and provide estimates of the C 3 interaction coefficient. The oscillator strengths of the 6 s 2 S 1 / 2 → 7 p 2 P 3 / 2 hyperfine transitions are about two orders of magnitude smaller than that of the Cs D 2 line at 852 nm. Our experimental measurements are in good agreement with theoretical calculations. We emphasize the advantage of nanocell spectroscopy compared to the well-known saturated absorption method and present possible applications.

DOI
10.1088/1361-6455/ae0a98

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Journal of Experimental and Theoretical Physics•Oct 1, 2021•2 citations
Abstract Selective reflection (SR) spectroscopy of the 6 s 2 S 1 / 2 → 7 p 2 P 3 / 2 electric dipole transition of Caesium ( λ = 456 nm) is performed for the first time using a nanometric-thin cell (L = 50–1500 nm, T = 200 ∘ C). We successfully form narrow resonances corresponding to the F g = 3 , 4 → F e = 2 , 3 , 4 , 5 hyperfine transitions. All transitions are well spectrally resolved, and the geometry of the cell allows us to obtain a strong 30 times narrowing of the Doppler width with a single beam pass. For lower thicknesses ( L < 400 nm), we observe a red shift of the SR lines, which we attribute to atom-surface interactions, and provide estimates of the C 3 interaction coefficient. The oscillator strengths of the 6 s 2 S 1 / 2 → 7 p 2 P 3 / 2 hyperfine transitions are about two orders of magnitude smaller than that of the Cs D 2 line at 852 nm. Our experimental measurements are in good agreement with theoretical calculations. We emphasize the advantage of nanocell spectroscopy compared to the well-known saturated absorption method and present possible applications.
The features of Doppler-free resonances detected by probing the 133 Cs atom 6S 1/2 → 7P 3/2 transition at 456 nm in a nanometric-thick vapor layer are investigated. The matrix element of this transition is about 11 times smaller than that of the Cs D 2 line (852 nm). When the vapor layer thickness is ℓ = λ /2 ≃ 230 nm, we observe Dicke narrowing of the lines, accompanied by a red frequency shift of the atomic transitions, which is attributed to atom–surface interactions. Realizing optical pumping with ℓ ≃ 460 nm in a single-pass configuration, we observe Doppler-free resonances with a linewidth of <20 MHz, located at the atomic transition frequencies, with a correspondence of the amplitudes to the transition intensities. These narrow resonances are of interest for high-resolution spectroscopy and instrumentation and could serve as a frequency reference.
Doppler-free spectroscopy of the Cs 6S1/2−7P3/26\text{S}_{1/2}-7\text{P}_{3/2}6S1/2​−7P3/2​ atomic transition at 456 nm in a nanometric-thick vapor layer
The features of Doppler-free resonances detected by probing the 133^{133}133Cs atom 6S1/2−7P3/26S_{1/2}-7P_{3/2}6S1/2​−7P3/2​ transition at 456 nm in a nanometric-thick vapor layer are investigated. The matrix element of this transition is about 11 times smaller than that of the Cs D2_22​ line (852 nm). When the vapor layer thickness is ℓ=λ/2≃230\ell = λ/2 \simeq 230ℓ=λ/2≃230 nm, we observe Dicke narrowing of the lines, accompanied by a red frequency shift of the atomic transitions, which is attributed to atom-surface interactions. Realizing optical pumping with ℓ≃460\ell\simeq 460ℓ≃460 nm in a single-pass configuration, we observe Doppler-free resonances with a linewidth <20<20<20 MHz, located at the atomic transitions frequencies with a correspondence of the amplitudes to the transition intensities. These narrow resonances are of interest for high-resolution spectroscopy and instrumentation, and could serve as a frequency reference.
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.
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.
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.
Abstract The sub-Doppler absorption and fluorescence spectra at the frequencies of D1- and D2-line transitions in Cs atomic vapor, enclosed in a nanocell (NC) with a thickness L ~ 400 nm, have been investigated experimentally at a near-room temperature. It is shown that a decrease in the NC temperature to 35°C causes narrowing of the absorption lines to values smaller than the Doppler width by a factor of 6, due to which the strong spectral broadening induced by laser field can be measured. The high intensity threshold for optical pumping (which limits the fluorescence intensity in centimeter-length cells) made it possible to record fluorescence spectra (using laser power of several milliwatts) at a temperature of 20°C; thus, a frequency marker of transitions in the range of D1,2 lines can be developed based on a room-temperature NC. A comparison with a widely used marker based on saturated absorption is performed.