Schlüsselwörter
(Deutsch)
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Primärfrequenznormal, Zeit und Frequenz
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Schlüsselwörter
(Englisch)
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Primary frequency standard, time and frequency
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Kurzbeschreibung
(Deutsch)
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In früheren Projekten wurden zwei Primärfrequenznormale (FOCS-1 und FOCS-2) entwickelt und aufgebaut, welche auf einem kontinuierlichen, laser-gekühlten Strahl von Cäsium-Atomen basieren. Diese Normale sind jetzt am METAS für ihren Einsatz bereit. Die Instrumente sollen zur Realisierung der SI-Einheit Sekunde beitragen. Das Hauptziel des vorliegenden Projekts ist die metrologische Evaluation der Normale und die Integration ihrer Resultate in die Internationale Atomzeitskala TAI. Parallel dazu sollen an einem separaten Instrument Möglichkeiten zur Verbesserung des atomaren Flusses im kontinuierlichen Cs-Strahl untersucht werden.
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Kurzbeschreibung
(Englisch)
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In two preceding projects two atomic fountains – both based on a continuous beam of laser cooled cesium atoms – have been designed and assembled. They are now installed and ready for exploitation as primary frequency standard at METAS. The main purpose of these instruments is to contribute to the international effort for the realisation of the SI-second. The current project aims at evaluating metrologically the two fountains and at integrating their results into the Temps Atomique International TAI. In parallel, on a separate atomic fountain, ways to increase the atomic flux of the continuous beam will be studied.
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Projektziele
(Deutsch)
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Hauptziel ist die vollständige metrologische Evaluation der beiden Primärfrequenznormale FOCS1 und FOCS2, damit diese routinemässig zur Realisierung der Sekunde beitragen können.
Zusätzlich werden in einem separaten System Möglichkeiten zur Verbesserung des atomaren Flusses untersucht. Die Resultate dieser Studien werden nach Möglichkeiten in FOCS-1 und FOCS-2 integriert.
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Projektziele
(Englisch)
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Overall goal of the project is to bring a continuous fountain to an operational status in which it can contribute on a regular basis to the realisation of the definition of the second. A prerequisite and thus a milestone in this project is the metrological evaluation of FOCS-1 and FOCS-2. A secondary goal of the project is to investigate possible routes to increase the atomic flux on a separate, dedicated experiment (FOCS-x). Results of these studies are eventually to be integrated in FOCS-1 and FOCS-2.
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Abstract
(Englisch)
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The purpose of the project was the metrological evaluation of the primary frequency standard FOCS in order to be able to make a significant contribution to the international atomic time scale TAI and thus to the primary realisation of the SI unit second. FOCS (Fontaine Optique Continue Suisse) is the only continuous caesium fountain atomic clock, whereas all other primary frequency standards worldwide are based on a pulsed atomic beam. It is, therefore, of major interest to contribute to the metrological diversity and to have an independent approach which allows validating any systematic effect encountered so far using the pulsed approach. The continuous approach has the advantage to be able to significantly improve the frequency stability by using a high atomic flux without degrading the accuracy by collisions between the atoms.
The major hardware related steps in this project were the installation of an almost frictionless electrostatic motor used for the light trap and the modelling and refinement of the micro wave cavity. The frequency stability achieved so far by the continuous caesium fountain is 6•10-14 tau -1/2, which is almost three times better than the limit stability of a pulsed fountain using the same oscillator. The systematic evaluation and correction of all biases actually leads to an uncertainty of 1.5 parts in 1015, whereas one systematic frequency shift, probably due to a phase gradient in the microwave cavity, still needs to be evaluated and modelled. So far the relative difference between the frequency of FOCS and the universal coordinated time UTC amounts to -4•10-15, still subject to improvement after the final evaluation measurements.
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Umsetzung und Anwendungen
(Englisch)
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After the final evaluation measurements, time and frequency comparisons are carried out against other primary frequency standards worldwide. Based on these results and a publication showing the complete evaluation of all uncertainty sources, FOCS shall contribute to the small group of primary frequency standards worldwide which calibrate the international atomic time scale TAI. FOCS provides further the possibility to participate in other projects of fundamental research, such as ACES (Atomic Clock Ensemble in Space). Precise time and frequency is of primary importance for navigation, telecommunication, astronomy and basic science.
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Publikationen / Ergebnisse
(Englisch)
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- A. Joyet, G. Di Domenico, G. K. Gulati, P. Thomann, A. Stefanov, Status of the continuous fountain clocks at METAS-LTF, Proceedings of the 7th Symposium: Frequency Standards and Metrology, p. 353-357 (2009).
- G. Di Domenico, L. Devenoges, C. Dumas, and P. Thomann, “Combined quantum-state preparation and laser cooling of a continuous beam of cold atoms,” Phys. Rev. A, vol. 82, no. 5, p. 053417 (2010).
- L. Devenoges, G. D. Domenico, A. Stefanov, A. Joyet, and P. Thomann, “Improvement of the Frequency Stability Below the Dick Limit With a Continuous Atomic Fountain Clock ” accepted for publication in IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.
- G. Di Domenico, L. Devenoges, A. Joyet, A. Stefanov and P. Thomann, “Uncertainty evaluation of the continuous cesium fountain frequency standard FOCS-2,” Proc. of the joint conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum, San Francisco (2011).
- G. Di Domenico, L. Devenoges, A. Stefanov, A. Joyet, and P. Thomann, “ Fourier analysis of Ramsey fringes observed in a continuous atomic fountain for in situ magnetometry ” Eur. Phys. J. Appl. Phys. 56, 11001 (2011).
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