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Bulletin of the Russian Academy of Sciences Physics

Influence of Intensity Ratio of Resonant Spectral Components on Q-Factor of Dual-Frequency Doppler-Free Resonance in 87Rb Atoms

Kirill M. Sabakar, Eugene A. Tsygankov, Dmitry S. Chuchelov, Maria I. Vaskovskaya, Sergei A. Zibrov, Vitali V. Vassiliev, Vladimir L Velichansky

Published May 1, 2026• 0 citations
Publisher

Abstract

Abstract Doppler-free resonance of the 87Rb D1 line induced by bichromatic counter-propagating waves with different intensity ratios of the two resonant spectral components is investigated. It is shown that the maximal amplitude is achieved at unequal intensities for the low-frequency eigen and crossover resonances, and at equal intensities for the high-frequency eigen resonance. Measurements of the Q-factor (the contrast-to-width ratio) demonstrate that for all studied resonances, its maximal value is attained at an intensity ratio different from 1. For the low-frequency eigen resonance, the maximal Q-factor enhances by a factor of six at an intensity ratio of 5 as compared to the case of equal intensities.

DOI
10.1134/s1062873826700814

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Abstract Doppler-free resonance of the 87Rb D1 line induced by bichromatic counter-propagating waves with different intensity ratios of the two resonant spectral components is investigated. It is shown that the maximal amplitude is achieved at unequal intensities for the low-frequency eigen and crossover resonances, and at equal intensities for the high-frequency eigen resonance. Measurements of the Q-factor (the contrast-to-width ratio) demonstrate that for all studied resonances, its maximal value is attained at an intensity ratio different from 1. For the low-frequency eigen resonance, the maximal Q-factor enhances by a factor of six at an intensity ratio of 5 as compared to the case of equal intensities.
We investigate Doppler-free absorption lines induced by counter-propagating polychromatic optical fields in the D1 line of 87Rb atoms. Cases of orthogonal and parallel polarizations are considered. The resonance associated with Fe = 1 demonstrates unusual behaviour with two-photon detuning: the amplitude grows while the width becomes smaller. The crossover resonance involving transitions to both sublevels Fe = 1, 2 of the excited state is more pronounced at parallel polarizations than at orthogonal and has smaller width compared to the lines corresponding to atomic transitions. A qualitative explanation of experimentally observed features is given.
We investigate the dual-frequency Doppler-free resonance in the D1 line of alkali-metal atoms for any accessible value of the nuclear spin I. The consideration is performed using the symmetries of the dipole operator and the basis, where the quantization axis is directed along the polarization of the one of optical waves. We show that there is the absence of the optical pumping in the scheme with parallel polarizations for the center of the crossover, resulting in its smallest width. Secondly, the growth in the absorption for the center of the peak with Fe=I-1/2 and the decrease of its width with the two-photon detuning in the case of~orthogonal polarizations is explained. Particular attention is paid to the special case of I=3/2, where this effect is the most pronounced. The experiment with 87Rb, 85Rb, and 133Cs atoms is in agreement with the analysis.
Abstract Destruction of the laser-induced coherence in the ground state of alkali atoms manifests itself as an ultra-narrow resonance in the atomic spectrum. Depending on the geometry of irradiation and observation, the coherent spectroscopy studies CPT (coherent population trapping), EIT (electromagnetically-induced transparency) or EIA (electromagnetically-induced absorption). In the present work, we investigated EIA on the D1 87Rb line by applying a counter-propagating dual-beam scheme. The main advantage of this scheme is the high resonance contrast – an important parameter for many applications. In our previous work performed in a paraffin-coated cell we observed that, unlike the resonance in buffer gas cell detected in the same experimental scheme, the EIA signal has a complex form, because it is formed by two atomic sub-ensembles in the vapor cell with different relaxation rates determined by the laser excitation conditions. We focused on the narrow component, since it has a higher amplitude-width ratio, making it preferable for applications. We investigate the influence of the atomic vapor density and the pump laser intensity on the resonance parameters in order to optimize the amplitude ratio of the wide and narrow components and achieve the highest amplitude-width ratio value for the narrow component of the EIA resonance.
We demonstrate a bichromatic Doppler-free spectroscopy of an 87 R b D 1 line by using a dual-frequency, counterpropagating laser field with orthogonal linear polarizations. A reversed Doppler-free resonance dip is observed in the dual-frequency scheme, and a significant improvement of frequency discrimination curve is acquired due to the coherent population trapping (CPT) effect. The influence of the static magnetic field and laser intensity on the spectroscopy is studied in both single- and dual-frequency schemes. After locking the laser frequency to the 87 R b D 1 line in the dual-frequency stabilization scheme, the beat note fractional frequency stability is at the level of 7 × 10 − 12 at 1 s integration time. This technique can be used in various applications, such as CPT atomic clocks, laser spectroscopy, quantum optics, and laser-cooling experiments.
Abstract The influence of the spectral linewidth of single-frequency lasers on the parameters of the electromagnetically induced absorption resonances in rubidium vapour is examined. We use two counter-propagating pump and probe beams to prepare high-contrast magneto-optical resonances in a Hanle-configuration on Rb atoms contained in a paraffin-coated optical cell. Due to the spectral linewidth of the excitation laser, various groups of atoms are involved in creating the coherent resonance, which changes its parameters. The experimental results show the potential of the system to improve the signal-to-noise ratio for more sensitive measurement of weak magnetic fields.
The method of Doppler - free comb - spectroscopy for dipole transitions was proposed. The calculations for susceptibility spectrum for moving two-level atoms driving by strong counter propagating combs have been done. The used theoretical method based on the Fourier expansion of the components of density matrix on two rows on kv (v-velocity of group of atoms, k-projection of wave vector) and Ω (frequency between comb components). For testing of validity of this method the direct numerical integration was done. The narrow peaks with homogeneous width arise on the background of Doppler counter. The contrast of these peaks is large for largest amplitudes of comb-components. Power broadening is increasing with increase of field amplitudes. The spectral range of absorption spectrum is determined by the spectral range of comb generator and all homogeneous lines arise simultaneously.