Nonlinear enhanced-absorption resonances in compact alkali-vapor cells for applications in quantum metrology
Denis V. Brazhnikov, S M Ignatovich, I. S. Mesenzova, А. М. Михайлов, Mikhail N Skvortsov, Andrei Goncharov, Vasily M. Entin, I. I. Ryabtsev, Rodolphe Boudot, Elena T. Taskova, Emilia A. Alipieva, C. Andreeva, S. Gateva
Abstract We review three laser spectroscopy schemes developed recently for observation of high-contrast enhanced-absorption nonlinear resonances in small alkali-vapor cells. In our experiments, optical transitions within the cesium D1 line are involved and a probe beam transmission is analyzed. The first spectroscopy method is based on the configuration with two-frequency counter propagating beams, which are linearly polarized in orthogonal directions. This configuration provides observation of high-contrast natural-linewidth resonances superimposed on broad Doppler profiles when the laser frequency is scanned. These resonances have good prospects for developing a miniature optical frequency reference. The second scheme involves two-frequency counter propagating beams with equal circular polarizations and provides observation of subnatural-linewidth resonances when the Raman frequency detuning is scanned. We use these resonances for stabilizing the microwave frequency of a local oscillator (≈ 4.6 GHz). Frequency stability of around 6 × l0-12 is achieved at 1-s averaging using a 5-mm length cell. This result makes the technique attractive for developing a miniature frequency standard in thr microwave range. The third configuration exploits single-frequency counter-propagating beams with linear orthogonal polarizations. The ultrahigh-contrast subnatural-linewidth resonances can be observed when the longitudinal magnetic field is scanned around zero. The possible application is discussed of these resonances in vector atomic magnetometry.
Abstract We review three laser spectroscopy schemes developed recently for observation of high-contrast enhanced-absorption nonlinear resonances in small alkali-vapor cells. In our experiments, optical transitions within the cesium D1 line are involved and a probe beam transmission is analyzed. The first spectroscopy method is based on the configuration with two-frequency counter propagating beams, which are linearly polarized in orthogonal directions. This configuration provides observation of high-contrast natural-linewidth resonances superimposed on broad Doppler profiles when the laser frequency is scanned. These resonances have good prospects for developing a miniature optical frequency reference. The second scheme involves two-frequency counter propagating beams with equal circular polarizations and provides observation of subnatural-linewidth resonances when the Raman frequency detuning is scanned. We use these resonances for stabilizing the microwave frequency of a local oscillator (≈ 4.6 GHz). Frequency stability of around 6 × l0-12 is achieved at 1-s averaging using a 5-mm length cell. This result makes the technique attractive for developing a miniature frequency standard in thr microwave range. The third configuration exploits single-frequency counter-propagating beams with linear orthogonal polarizations. The ultrahigh-contrast subnatural-linewidth resonances can be observed when the longitudinal magnetic field is scanned around zero. The possible application is discussed of these resonances in vector atomic magnetometry.
A new configuration for observation of magneto-optical subnatural-linewidth resonances of electromagnetically induced absorption (EIA) in alkali vapor has been verified experimentally. The configuration includes using two counter-propagating pump and probe light waves with mutually orthogonal linear polarizations, exciting an open optical transition of an alkali atom in the presence of a buffer gas. The main advantage of the novel observation scheme consists in the possibility of obtaining simultaneously high-contrast and quite narrow nonlinear signals. Here a 2.5-cm long rubidium-87 vapor cell filled with Ar buffer gas is used, and the excited optical transition is the Fg=2 → Fe=1 of the D1 line. The signals registered reach a contrast of 57.7% with a FWHM of 7.2 mG. The contrast with respect to a wide Doppler pedestal well exceeds 100%. To our knowledge, to date this is the best result for EIA resonances in terms of contrast-to-width ratio. In general, the results demonstrate that the new magneto-optical scheme has very good prospects for various applications in quantum metrology, nonlinear optics and photonics.
Abstract Electromagnetically induced absorption (EIA) of cesium atoms exposed to counter-propagating light waves with orthogonal linear polarizations is studied. Probe beam transmission through a buffer gas-filled vapor cell is monitored as a function of a static magnetic field applied parallel to the wave vectors. The light waves are tuned to a single dipole transition F g → F e in the D 1 line ( λ = 894.6 nm). The proposed magneto-optical configuration helps overcome a long-standing problem in obtaining high-contrast EIA resonances in conjunction with narrow linewidths. Our experiments demonstrate EIA contrast with respect to a broad Doppler absorption background ( C D ) as high as 1630%. Thus, a high value of C D means that background absorption is almost absent, and the vapor cell transmission profile represents only a single narrow resonance. This result is unique for EIA as well as for electromagnetically induced transparency (EIT) effects, because usually in a resonant medium, narrow EIT or EIA resonances are accompanied by natural-linewidth or other broad spectral features, even in the case of cold atoms. The resonance contrast with respect to the light transmission background ( C back ) is also high enough, reaching 75% in the experiments. The full width at half maximum of the narrowest observed EIA is approximately 0.77 mG (0.7 × 0.77 = 540 Hz in the frequency domain). The considered simple scheme has good prospects for the development of various quantum magneto-optical devices such as optical switches and atomic magnetometers.
The detection of narrow and high-amplitude optical resonances in atomic cells is of crucial importance for the development of compact and high-stability lasers or vapor-cell optical references. In this work, using monochromatic light and appropriate polarization settings for the counterpropagating pump and probe beams, we demonstrate the detection of enhanced-absorption sub-Doppler resonances on the D1 line of the Rb atom. We report a theoretical model showing that the Zeeman coherence induced between magnetic sublevels---especially in the $F\ensuremath{\rightarrow}{F}^{\ensuremath{'}}=F\ensuremath{-}1$ systems, with F and ${F}^{\ensuremath{'}}$ being the hyperfine quantum numbers of the ground and excited states, respectively---plays a key role in the observed enhanced-absorption process. The theoretically predicted behavior matches the experimental observations well. The impact of light polarization, laser intensity, magnetic field, and cell temperature on the Doppler-free resonance features is experimentally investigated. For application, two identical diode lasers are frequency-stabilized onto enhanced-absorption sub-Doppler resonances. The fractional frequency stability of the laser beatnote is measured to be $1.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ at 1s and $8.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ at 104s. These results demonstrate the potential of this scheme for the implementation of a compact or even chip-scale optical frequency reference, which might find applications in instrumentation, navigation, and metrology.
Level-crossing (LC) resonances in alkali-metal vapors are widely used for atomic magnetometry. One of the most simple and robust techniques involves a single circularly polarized light wave, while a transverse magnetic field (Bx⊥k) is scanned around zero to observe the subnatural-linewidth resonance of electromagnetically induced transparency (EIT) in the light wave transmission. This technique allows miniaturization of the magnetic field sensor to a great extent, maintaining high sensitivity of measurements. To obtain a high quality factor of the LC resonance and, therefore, high performance of the sensor, either a high temperature (>120 °C) or an extended volume of the vapor cell (V≫1 cm3) is usually required. Here, we propose a slight modification to the commonly used configuration, which can provide high-quality LC resonances in small (≪1 cm3) vapor cells at a relatively low temperature of 60 °C or less. The modification consists in adding the second (pump) counterpropagating light wave with opposite circular polarization (σ+σ− configuration). In our experiments, the waves excite the D1-line ground-state level Fg=4 in cesium atoms in the presence of a buffer gas (Ne, 130 Torr). In the proposed scheme, a subnatural-linewidth electromagnetically induced absorption (EIA) resonance is observed. We compare parameters of the EIA resonance with those obtained in the single-wave scheme to show benefits of using the proposed σ+σ− configuration. The results have good prospects for developing a low-power miniaturized atomic magnetometer with a wide operating range.
Abstract Locking laser frequencies to Doppler-free spectra produced by the interaction of light with alkali atoms in a vapor cell is a promising approach for realizing compact atomic optical frequency reference. In this work, we employ counter-propagating monochromatic laser beams with a polarization angle of 45° to interact with 87 Rb atoms in a 3 mm cubic vapor cell, inducing coherent resonance. By detecting the laser polarization rotation, we obtain a Doppler free spectral line, which is used as a reference for laser frequency locking, thus realizing an optical reference. We build two nominally identical systems and measure their beatnote, yielding a fractional frequency stability of 5.3×10 -13 at 1 s. This study demonstrates that the proposed scheme is a competitive approach for realizing high performance compact atomic optical reference.
Sub-Doppler spectroscopy in alkali-metal vapor cells using two counterpropagating dual-frequency laser beams allows the detection of high-contrast sign-reversed natural-linewidth sub-Doppler resonances. Previously, a qualitative theory based on a simplified \ensuremath{\Lambda}-scheme model has been reported to explain underlying physics of this phenomenon. In this paper, an extended theoretical model of dual-frequency sub-Doppler spectroscopy (DFSDS) for the Cs D1 line is reported. Taking into account the real atomic energy structure, main relaxation processes, and various nonlinear effects, this model describes quantitatively the respective contributions of involved physical processes and predicts main properties (height and linewidth) of the sub-Doppler resonances. Experimental tests are performed with a Cs vapor microfabricated cell and results are found to be in correct agreement with theoretical predictions. Spatial oscillations of the sub-Doppler resonance amplitude with translation of the reflection mirror are highlighted. A beat note between two laser systems, including one stabilized with DFSDS on a Cs vapor microcell, yields a fractional frequency stability of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.16em}{0ex}}{\ensuremath{\tau}}^{\ensuremath{-}1/2}$ until 10-s averaging time. These results demonstrate that DFSDS could be an interesting approach for the development of a high-performance microcell-based optical frequency reference, with applications in various compact quantum devices.