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Conference on Precision Electromagnetic Measurements

Characterization of a cold cesium source for PARCS: Primary Atomic Reference Clock in Space

Thomas P. Heavner, Leo W. Hollberg, S.R. Jefferts, John E. Kitching, D. M. Meekhof, H.G. Robinson, D.B. Sullivan

Published Nov 7, 2002• 1 citation
Publisher

Abstract

The PARCS (Primary Atomic Reference Clock in Space) project is a joint NIST JPL venture aimed at placing a Cs atomic clock aboard the International Space Station. This orbiting clock will achieve high accuracies in part due to the long Ramsey times afforded by the microgravity environment. The clock will allow a wide range of precision tests of fundamental physics including relativity theory. Our group at NIST is performing experimental studies of a "prototype" cold Cs source based on launching atoms from optical molasses. The results of our work will be applied to the design and construction of a robust, space qualified device. Additionally, this work is important for the development of future Cs fountains. We describe our apparatus, the present state of our experimental work, and planned improvements.

DOI
10.1109/cpem.2000.851002

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The PARCS (Primary Atomic Reference Clock in Space) project is a joint NIST JPL venture aimed at placing a Cs atomic clock aboard the International Space Station. This orbiting clock will achieve high accuracies in part due to the long Ramsey times afforded by the microgravity environment. The clock will allow a wide range of precision tests of fundamental physics including relativity theory. Our group at NIST is performing experimental studies of a "prototype" cold Cs source based on launching atoms from optical molasses. The results of our work will be applied to the design and construction of a robust, space qualified device. Additionally, this work is important for the development of future Cs fountains. We describe our apparatus, the present state of our experimental work, and planned improvements.
The Primary Atomic Reference Clock in Space (PARCS) project is a joint NIST-JPL-University of Colorado venture aimed at placing a Cs atomic clock aboard the International Space Station (ISS). This orbiting clock will achieve high accuracy, in part due to the long Ramsey times afforded by the microgravity environment, and allow for precision tests of fundamental physics including relativity theory. As part of this effort, we are evaluating the characteristics of a prototype cold Cs source based on launching atoms from an optical molasses. Experimental results, in conjunction with theoretical modeling of atom flux requirements, will be applied to the design and construction of a robust, space-qualified device. The apparatus described here will be used to develop other PARCS components such as the microwave cavity structure and detection systems, and to investigate two-dimensional cooling schemes for future Cs fountains and space clocks.
The PARCS (Primary Atomic Reference Clock in Space) project is a joint NIST-JPL-University of Colorado venture aimed at placing a cesium (Cs) atomic clock aboard the International Space Station (ISS). This orbiting clock will achieve high accuracy, in part due to the long Ramsey times afforded by the microgravity environment, and allow for precision tests of fundamental physics including relativity theory. As part of this effort, we are evaluating the characteristics of a prototype cold Cs source based on launching atoms from an optical molasses. The apparatus described will be used to develop other PARCS components such as the microwave cavity structure and detection systems, and to investigate two-dimensional cooling schemes for future Cs fountains and space clocks.
The PARCS (Primary Atomic Reference Clock in Space) project is a joint NIST-JPL-University of Colorado venture aimed at placing a cesium (CS) atomic clock aboard the International Space Station (ISS). This orbiting clock will achieve high accuracy, in part due to the long Ramsey times afforded by the microgravity environment, and allow for precision tests of fundamental physics including relativity theory. As part of this effort, we are evaluating the characteristics of a prototype cold CS source based on launching atoms from an optical molasses. The apparatus described here will be used to develop other PARCS components such as the microwave cavity structure and detection systems, and to investigate two-dimensional cooling schemes for future CS fountains and space clocks.
The primary atomic reference clock in space (PARCS) is a collaboration between the National Institute of Standards and Technology (NIST), the Jet Propulsion Laboratory (JPL) and the University of Colorado to build a laser-cooled cesium-beam atomic clock as a science payload for the International Space Station (ISS). The three primary goals of the PARCS experiment are: (1) to demonstrate laser cooling of atoms in space; (2) to use laser cooling to build the most accurate space clock; (3) to use the clock to test fundamental assumptions and predictions of relativity theory. We discuss aspects of the PARCS cesium physics package subsystem design addressing magnetic, microwave and vacuum requirements as well as operational scenarios.
The accelerated development of laser methods for manipulating the internal state and motion of atoms, and the recent primary evaluation in France of a cesium frequency standard using cold atoms in an atomic fountain configuration, allow the frontiers of time metrology, accuracy, and stability to be pushed near parts in the 1016 level, a factor of 100 over the present primary laboratory clocks. These positive results revived the development of more accurate cesium atomic clocks, and the Institute of National Measurement Standards (INMS), of the National Research Council of Canada (NRC) is undertaking a cesium-fountain project aimed at reaching these new levels of accuracy and stability. This paper reviews its present status. To appreciate the considerable impact of cold atoms in time and frequency metrology, we begin by recalling the background principles of traditional cesium frequency standards, their typical performance and main limitations. After introducing the important theoretical results essential to understanding the techniques of laser cooling and magneto-optical trapping, we focus on describing the characterization and control of our magneto-optical trap (MOT) and report the parameters that allow us to fill the trap with a few million atoms in less than a second and cool them to a temperature lower than 5 muK using optical molasses. We will describe the specifics of our cesium-fountain prototype, which operates with a 2-dimensional moving molasses. This special configuration is applicable for multipulse operation of the fountain, which can greatly relax the local oscillator requirements for time keeping. Finally, progress toward our objective of launching cooled atoms, at a rate of one ensemble per second, at speeds of 7 m/s, for a fountain with an interrogation time of about 1 s, will be analysed.PACS Nos.: 06.20, 06.30, and 32.80P
We present results on the performance of two important subsystems for NIST-F2 - the second-generation atomic fountain clock at NIST. Firstly, we demonstrate the efficient capture of cesium atoms from a low-velocity intense source (LVIS) of atoms into an optical molasses. Our typical LVIS flux was 10/sup 10/ s/sup -1/. The initial molasses fill rate was R/sub t=0/ = 3.8(5)/spl times/10/sup 9/ s/sup -1/, which is consistent with 100% atom capture given the lifetime of our vacuum system. Secondly, recent results for our launch performance in the (1,1,1) fountain geometry are presented. We were able to cool the atoms to a temperature of 1.5 /spl mu/K with our current design. Our plans for improving the laser cooling performance are also presented.