Dual-frequency sub-Doppler spectroscopy: Extended theoretical model and microcell-based experiments

Abstract

Doppler-free spectroscopy using two counter-propagating dual-frequency laser beams in alkali vapor cells has been demonstrated recently, providing the detection of high-contrast sign-reversed natural-linewidth sub-Doppler resonances. However, to date, only a qualitative theory based on a simplified Λ-scheme model has been reported to explain underlying physics of this phenomenon. In this work, we develop a general and extended theoretical model of dual-frequency sub-Doppler spectroscopy (DF SDS) for Cs D 1 line. The latter considers the real atomic energy structure, main relaxation processes and various nonlinear effects including optical pumping, optical transition saturation, Zeeman and hyperfine coherent population trapping (CPT) states. This model allows to describe quantitatively the respective contributions of involved physical processes and consequently to estimate main properties (height and linewidth) of detected sub-Doppler resonances. Experimental results performed with a Cs vapor micro-fabricated cell are reported and explained by theoretical predictions. Spatial oscillations of the sub-Doppler resonance amplitude with translation of the reflection mirror are highlighted. Reported results show that DF SDS could be a promising approach for the development of a fully-miniaturized and high-performance optical frequency reference, with applications in various compact quantum devices.

Short-term stability of Cs microcell-stabilized lasers using dual-frequency sub-Doppler spectroscopy

“…1(c), which is surrounded by a mu-metal magnetic shield. After the cell, the light impinges a quarter-wave plate (QWP) and is reflected back by a mirror positioned to enhance the constructive contribution of hyperfine Zeeman effects and increase the sub-Doppler resonance contrast [42]. The reflected light beam is then directed using a cube right before the cell to a photodiode for the detection of the spectroscopic signal and the generation of a derivative error signal using a lock-in amplifier (Stanford Research SR-860).…”

“…In [37], the frequency stabilization of a DBR laser onto a Rb microcell, using some light routing through an integrated silicon nitride waveguide and grating system to the cell, was demonstrated at the level of 10 with a microresonator comb for direct-comb spectroscopy [38] or an ultra-compact Fabry-Perot cavity [39]. In [40,41], the detection of high-contrast sign-reversed naturallinewidth sub-Doppler resonances, explained in a detailed quantitative model [42], was reported using a dual-frequency sub-Doppler spectroscopy (DFSDS) technique. However, no detailed resonance spectroscopy and short-term stability budget were performed.…”

Electromagnetically induced absorption scheme for vapor-cell atomic clock

“…The current short-term stability performances of the EIA-clock remain encouraging since they compare favorably with those of a N-resonance atomic clock based on a 7.5-cm long vapor cell [31] or other CPT-based clock prototypes [18,60,61]. For further progress, the laser FM noise contribution to the short-term stability budget could be reduced by stabilizing the laser using sub-Doppler spectroscopy techniques [56,62]. In addition, we suppose that the EIA clock should benefit from the use of Ramsey-based interrogation protocols, both for reduction of the photon shot noise contribution since higher laser powers might be used and mitigation of light shift issues [28,29,[63][64][65].…”

“…This situation leads to the observation of a dark resonance. At the opposite, if |NC 1 and |NC 2 are orthogonal, the probe beam may experience strong absorption [55,56]. In a long enough cell, regions with strong probe-field absorption (bright regions) alternate then with regions of low probe-field absorption (dark regions).…”

Exploring Dual-Frequency Sub-Doppler Spectroscopy for a Cs Microcell-Based Optical Frequency Reference

“…This technique has been employed to improve the frequency stability of Cs vapor cell atomic clocks [14], [15]. More recently, an extended theoretical model of DF SDS has been developed [16], highlighting the interest to apply this spectroscopy technique to short-length cells since optimized contrast of the sub-Doppler resonance can be obtained with proper adjustment of the retroreflection mirror. In the present work, we propose to investigate the potential of DF SDS in a Cs microfabricated vapor cell for laser frequency stabilization application.…”