1,720,967 research outputs found
Raman-Ramsey resonances in atomic vapor cells: Rabi pulling and optical-density effects
Full text linkRaman-Ramsey interference has proved a very effective technique to implement compact and high performing vapor cell frequency standards. In this paper, we theoretically characterize Raman-Ramsey resonances in an optically thick atomic vapor. Specifically, some parameters of interest for frequency standards applications, like contrast and linewidth of the central Raman-Ramsey fringe, are evaluated at different temperatures for Cs-133 and Rb-87 vapor cells with buffer gas. Density narrowing and broadening effects are described and explained in terms of a three-level theory where laser field propagation through the atomic medium is taken into account. Also, we investigate light shift both in low and high atomic density regimes. Light shift, which potentially degrades the medium-to long-term stability of Raman-Ramsey clocks, is composed of two contributions. The first is a pulling effect exerted by the wide Rabi profile enclosing the interference pattern on the central Raman-Ramsey fringe. The second light-shift term is strictly related to the detection time. Calculations derived from our model well describe already existing experimental results and new behaviors are predicted
Subcollisional linewidth observation in the coherent-population-trapping Rb maser
Full text linkWe report the observation of the 87Rb ground-state hyperfine transition with a subcollisional linewidth performed in a cell with buffer gas. The transition is observed as a coherent-population-trapping maser-emission profile excited by means of a Λ interaction scheme in the high-atomic-density regime. A theoretical explanation of the phenomenon is given in good agreement with the observed linewidth behavior
Propagation and density effects in the coherent-population-trapping maser
No full textThe coherent microwave emission from an optically thick atomic ensemble in a cavity under coherent population trapping is analyzed. Transient and continuous operations are theoretically examined within the frame of a closed three-level system in the Dicke regime. The effects related to the atomic density and to the propagation in the active medium are examined with particular reference to the subnatural linewidth, the low group velocity and the shifts of the maser emission profile from the unperturbed atomic transition. The case of alkali-metal atoms submitted to a Λ excitation scheme is addressed in view of applications in the atomic frequency standard field. Experimental observations in agreement with the theoretical predictions are reported for the case of rubidium in a buffer gas. Apparent superluminal propagation is also reported and briefly discussed
Loaded microwave cavity for compact vapor-cell clocks
Full text linkVapor-cell devices based on microwave interrogation provide a stable frequency reference with a compact and robust setup. Further miniaturization must focus on optimizing the physics package, containing the microwave cavity and atomic reservoir. In this paper, we present a compact cavity-cell assembly based on a dielectric-loaded cylindrical resonator. The loaded cavity resonating at 6.83 GHz has an external volume of only 35 cm3 and accommodates a vapor cell with 0.9 cm3 inner volume. The proposed design aims at strongly reducing the core of the atomic clock, maintaining at the same time high-performing short-term stability (sigmay(tau)≤5*10-13 tau-1/2 standard Allan deviation). The proposed structure is characterized in terms of microwave field uniformity and atom-field coupling with the aid of finite-elements calculations. The thermal sensitivity is also analyzed and experimentally characterized. We present preliminary spectroscopy results by integrating the compact cavity within a rubidium clock setup based on the pulsed optically pumping technique. The obtained clock signals are compatible with the targeted performances. The loaded-cavity approach is thus a viable design option for miniaturized microwave clocks
Intensity detection noise in pulsed vapor cell frequency standards
Full text linkLaser intensity noise is currently recognized as one of the main factors limiting the short-term stability of vapor-cell clocks. In this paper, we propose a signal theory approach to estimate the contribution of the laser intensity fluctuations to the short-term stability of vapor-cell clocks working in pulsed regime. Specifically, given a laser intensity noise spectrum, an analytical expression is derived to evaluate its impact onto the clock Allan deviation. The theory has been tested for two intensity noise spectra of interest in clock applications: white frequency noise and flicker noise. The predicted results turn out in good agreement with experiments performed with a prototype of pulsed optically pumped (POP) Rb cell clock and can be extended to other compact clocks
Kr-based buffer gas for Rb vapor-cell clocks
Full text linkOptically pumped Rb vapor cell clocks are by far the most used devices for timekeeping in all ground and space applications. The compactness and the robustness of this technology make Rb clocks extremely well fit to a large number of applications including GNSS, telecommunication and network synchronization. Many efforts are devoted to improve the stability of Rb clocks and reduce their environmental sensitivity. In this paper, we investigate the use of a novel mixture of buffer gas based on Kr and N2, capable of reducing by more than one order of magnitude the barometric and temperature sensitivities of the clock, with possible improvement of their long-term stability
Laser intensity noise transfer for pulsed vapor-cell clocks with optical detection
No full textWe propose a signal-theory approach to estimate the contribution from laser intensity noise to the short-term stability of compact atomic clocks based on optical detection. We remove the approximation of white intensity noise, which is usually found in literature, and propose a method for a more faithful estimate, given an arbitrary noise spectrum at the input. This is of fundamental importance, since laser intensity noise is currently one of the main limiting factors of vapor-cell clocks
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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