Voici les éléments 1 - 10 sur 27
- PublicationMétadonnées seulementHigh performance vapour-cell frequency standards(: Journal of Physics: Conference Series 723, 2015-10-27)
; ; ; ; ; ;We report our investigations on a compact high-performance rubidium (Rb) vapour-cell clock based on microwave-optical double-resonance (DR). These studies are done in both DR continuous-wave (CW) and Ramsey schemes using the same Physics Package (PP), with the same Rb vapour cell and a magnetron-type cavity with only 45 cm3 external volume. In the CW-DR scheme, we demonstrate a DR signal with a contrast of 26% and a linewidth of 334 Hz; in Ramsey-DR mode Ramsey signals with higher contrast up to 35% and a linewidth of 160 Hz have been demonstrated. Short-term stabilities of 1.4×10^-13 τ^-1/2 and 2.4×10^-13 τ^-1/2 are measured for CW-DR and Ramsey-DR schemes, respectively. In the Ramsey-DR operation, thanks to the separation of light and microwave interactions in time, the light-shift effect has been suppressed which allows improving the long-term clock stability as compared to CW-DR operation. Implementations in miniature atomic clocks are considered.
- PublicationAccès libreHigh performance vapour-cell frequency standardsWe report our investigations on a compact high-performance rubidium (Rb) vapour-cell clock based on microwave-optical double-resonance (DR). These studies are done in both DR continuous-wave (CW) and Ramsey schemes using the same Physics Package (PP), with the same Rb vapour cell and a magnetron-type cavity with only 45 cm3 external volume. In the CW-DR scheme, we demonstrate a DR signal with a contrast of 26% and a linewidth of 334 Hz; in Ramsey-DR mode Ramsey signals with higher contrast up to 35% and a linewidth of 160 Hz have been demonstrated. Short-term stabilities of 1.4×10-13 τ-1/2 and 2.4×10-13 τ-1/2 are measured for CW-DR and Ramsey-DR schemes, respectively. In the Ramsey-DR operation, thanks to the separation of light and microwave interactions in time, the light-shift effect has been suppressed which allows improving the long-term clock stability as compared to CW-DR operation. Implementations in miniature atomic clocks are considered.
- PublicationAccès libreA miniature frequency-stabilized VCSEL system emitting at 795nm based on LTCC modules(2013-11-8)
; ;Vecchio, Fabrizio ; ;Pétremand, Yves ;De Rooij, Nicolaas-F. ;Maeder, Thomas
- PublicationAccès libreMetrological characterization of custom-designed 894.6 nm VCSELs for miniature atomic clocks(2013-11-8)
; ;Al-Samaneh, Ahmed ;Kroemer, Eric ;Bimboes, Laura ; ; ;Wahl, Dietmar ;Boudot, Rodolphe ;Michalzik, Rainer
- PublicationMétadonnées seulementRb-stabilized laser at 1572 nm for CO2 monitoringWe have developed a compact rubidium-stabilized laser system to serve as optical frequency reference in the 1.55-m wavelength region, in particular for CO2 monitoring at 1572 nm. The light of a fiber-pigtailed distributed feedback (DFB) laser emitting at 1560 nm is frequency-doubled and locked to a sub-Doppler rubidium transition at 780 nm using a 2-cm long vapor glass cell. Part of the DFB laser light is modulated with an electro-optical modula-tor enclosed in a Fabry-Perot cavity, generating an optical frequency comb with spectral cover-age extending from 1540 nm to 1580 nm. A second slave DFB laser emitting at 1572 nm and offset-locked to one line of the frequency comb shows a relative frequency stability of 1·10-11at 1 s averaging time and <4·10-12 from 1 hour up to 3 days.
- PublicationAccès libreCharacterization of Frequency-Doubled 1.5-μm Lasers for High-Performance Rb ClocksWe report on the characterization of two fiber-coupled 1.5- μm diode lasers, frequency-doubled and stabilized to Rubidium (Rb) atomic resonances at 780 nm. Such laser systems are of interest in view of their implementation in Rb vaporcell atomic clocks, as an alternative to lasers emitting directly at 780 nm. The spectral properties and the instabilities of the frequency-doubled lasers are evaluated against a state-of-the-art compact Rb-stabilized laser system based on a distributed-feedback laser diode emitting at 780 nm. All three lasers are frequency stabilized using essentially identical Doppler-free spectroscopy schemes. The long-term optical power fluctuations at 780 nm are measured, simultaneously with the frequency instability measurements done by three beat notes established between the three lasers. One of the frequency-doubled laser systems shows at 780 nm excellent spectral properties. Its relative intensity noise <10−12 Hz−1 is one order of magnitude lower than the reference 780-nm laser, and the frequency noise <106 Hz2/Hz is limited by the laser current source. Its optical frequency instability is <4 × 10−12 at τ = 1 s, limited by the reference laser, and better than 1 × 10−11 at all timescales up to one day. We also evaluate the impact of the laser spectral properties and instabilities on the Rb atomic clock performance, in particular taking into account the light-shift effect. Optical power instabilities on long-term timescales, largely originating from the frequency-doubling stage, are identified as a limitation in view of high-performance Rb atomic clocks.
- PublicationMétadonnées seulementAging studies on micro-fabricated alkali buffer-gas cells for miniature atomic clocks(2015-4-22)
; ;We report an aging study on micro-fabricated alkali vapor cells using neon as a buffer gas. An experimental atomic clock setup is used to measure the cell's intrinsic frequency, by recording the clock frequency shift at different light intensities and extrapolating to zero intensity. We find a drift of the cell's intrinsic frequency of (−5.2 ± 0.6) × 10−11/day and quantify deterministic variations in sources of clock frequency shifts due to the major physical effects to identify the most probable cause of the drift. The measured drift is one order of magnitude stronger than the total frequency variations expected from clock parameter variations and corresponds to a slow reduction of buffer gas pressure inside the cell, which is compatible with the hypothesis of loss of Ne gas from the cell due to its permeation through the cell windows. A negative drift on the intrinsic cell frequency is reproducible for another cell of the same type. Based on the Ne permeation model and the measured cell frequency drift, we determine the permeation constant of Ne through borosilicate glass as (5.7 ± 0.7) × 10−22 m2 s−1 Pa−1 at 81 °C. We propose this method based on frequency metrology in an alkali vapor cell atomic clock setup based on coherent population trapping for measuring permeation constants of inert gases. The authors gratefully acknowledge fruitful discussions with M. Pellaton (Université de Neuchâtel) and S. Karlen (CSEM SA, Neuchâtel, Switzerland) on buffer gas permeation, Y. Pétremand (CSEM) for providing the vapor cells, and D. Varidel (Université de Neuchâtel) for support with the H-maser reference. This work was funded by the Swiss National Science Foundation (FNS) and co-financed by the Swiss Commission for Technology and Innovation (CTI)
- PublicationAccès libreRb vapor-cell clock demonstration with a frequency-doubled telecom laserWe employ a recently developed laser system, based on a low-noise telecom laser emitting around 1.56 μm, to evaluate its impact on the performance of an Rb vapor-cell clock in a continuous-wave double-resonance scheme. The achieved short-term clock instability below 2.5·10−13·τ−1∕2 demonstrates, for the first time, the suitability of a frequency-doubled telecom laser for this specific application. We measure and study quantitatively the impact of laser amplitude and frequency noises and of the ac Stark shift, which limit the clock frequency stability on short timescales. We also report on the detailed noise budgets and demonstrate experimentally that, under certain conditions, the short-term stability of the clock operated with the low-noise telecom laser is improved by a factor of three compared to clock operation using the direct 780-nm laser.
- PublicationAccès libreImpact of microwave-field inhomogeneity in an alkali vapour cell using Ramsey double-resonance spectroscopyWe numerically and experimentally evaluate the impact of the inhomogeneity of the microwave field in the cavity used to perform double-resonance (DR) Ramsey spectroscopy in a buffer gas alkali vapour cell. The Ramsey spectrum is numerically simulated using a simple theoretical model and taking into account the field distribution in a magnetron-type microwave resonator. An experimental evaluation is performed using a DR pulsed optically pumped (POP) atomic clock. It is shown that the sensitivity to the micro-wave power of the DR POP clock can be reproduced from the combination of two inhomogeneities across the vapour cell: microwave field inhomogeneity and atomic ground-state resonance frequency inhomogeneity. Finally, we present the existence of an optimum operation point for which the microwave power sensitivity of our DR POP clock is reduced by two orders of magnitude. It leads into a long-term frequency stability of 1 × 10-14.
- PublicationAccès libreInterferometric measurements beyond the coherence length of the laser source
;Salvadé, Yves ;Przygodda, Frank ;Rohner, Marcel ;Polster, Albert ;Meyer, Yves ;Monnerat, Serge ;Gloriod, Olivier ;Llera, Miguel ;Matthey, Renaud ; ;Interferometric measurements beyond the coherence length of the laser are investigated theoretically and experimentally in this paper. Thanks to a high-bandwidth detection, high-speed digitizers and a fast digital signal processing, we have demonstrated that the limit of the coherence length can be overcome. Theoretically, the maximal measurable displacement is infinite provided that the sampling rate is sufficiently short to prevent any phase unwrapping error. We could verify experimentally this concept using a miniature interferometer prototype, based on a frequency stabilized vertical cavity surface emitting laser. Displacement measurements at optical path differences up to 36 m could be realized with a relative stability better than 0.1 ppm, although the coherence length estimated from the linewidth and frequency noise measurements do not exceed 6.6 m.
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