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 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 report the observation and characterization of a high-contrast dual-frequency Doppler-free ground-state crossover resonance in the D1 line of 87Rb.The crossover appears at a two-photon detuning exceeding the natural linewidth of the excited state and is formed by the optical pumping effect. Unlike the previously proposed resonance at zero two-photon detuning, which we show becomes sensitive to magnetic-field fluctuations due to residual ellipticity of the optical fields-resulting in frequency shifts and profile asymmetry-the crossover resonance is largely immune to this effect. Our theoretical analysis attributes the observed sensitivity to the dispersive contribution of ground-state coherences to absorption. Stability measurements under magnetic-field fluctuations demonstrate that using the crossover resonance provides more than an order-of-magnitude improvement, making it a promising reference for frequency stabilization in compact, field-deployable optical standards.
We report the observation and characterization of a high-contrast dual-frequency Doppler-free ground-state crossover resonance in the D1 line of 87Rb. The crossover appears at the two-photon detuning δ exceeding the natural linewidth of the excited state and is formed by the hyperfine optical pumping. We show that the previously proposed resonance at zero two-photon detuning is sensitive to magnetic-field fluctuations due to residual ellipticity of the optical fields that produces the profile asymmetry and frequency shifts, while the crossover resonance is largely immune to this effect. Our theoretical analysis attributes the observed sensitivity to the dispersive contribution of ground-state coherences to absorption. Stability measurements under magnetic-field fluctuations demonstrate that using the crossover resonance at large δ provides more than an order-of-magnitude improvement, making it a promising reference for frequency stabilization in compact, field-deployable optical standards.
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.
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.