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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Cold atoms and cesium fountains at NRC

J.-S. Boulanger, Marie-Claude Gagné, R.J. Douglas

Published Dec 24, 2002• 4 citations
Publisher

Abstract

We present a progress report on laser-cooled cesium atoms at NRC, work which was started a few years ago in order to realize a cesium fountain frequency standard. We selected an acceleration with two-dimensional moving molasses, which can increase both the force and the interaction time by a factor of /spl radic/2 over the more common 1-D molasses scheme. This configuration also allows for trapping and cooling of atoms while previously launched atoms are still moving in the clock section of the system. We report measurements on the number of atoms, temperature, friction coefficient and spring constant of our magneto-optical trap and 1-D molasses for various conditions.

DOI
10.1109/freq.1996.560299

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Marie-Claude Gagné, J.-S. Boulanger, R J W Douglas

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

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Cesium atomic fountain clock is the quantum frequency standard with very high accuracy. Research on laser cooling and trapping of cesium atom at Peking University began in 1993. A cesium atomic fountain frequency standard is being developed. A magneto-optical trap with some 108 trapped atoms and an optical molasses with the cold atoms of the temperature of 10/spl mu/K have been achieved previously. The device has been carefully designed and is under construction. It is composed of two main parts: vacuum system and laser system. The article describes the apparatus and presents a brief introduction to some considerations on the atomic clock.

Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)•Nov 27, 2002•0 citations
We present a progress report on laser-cooled cesium atoms at NRC, work which was started a few years ago in order to realize a cesium fountain frequency standard. We selected an acceleration with two-dimensional moving molasses, which can increase both the force and the interaction time by a factor of /spl radic/2 over the more common 1-D molasses scheme. This configuration also allows for trapping and cooling of atoms while previously launched atoms are still moving in the clock section of the system. We report measurements on the number of atoms, temperature, friction coefficient and spring constant of our magneto-optical trap and 1-D molasses for various conditions.
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
By the moving molasses technique we have extracted laser-cooled cesium atoms in a continuous way directly from an optical molasses. The mean launching velocity is precisely tunable from 1 to 12 m/s. The atomic beam has a flux of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{8} \mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}/\mathrm{s}$ at 7 m/s and a longitudinal temperature of $70 \ensuremath{\mu}\mathrm{K},$ which represents the highest flux and lowest velocity spread obtained so far in a continuous beam of cold atoms. These features makes it well suited for atomic fountains. The atomic flux can be slightly increased in a two-dimensional magneto-optical trap operation (+40(+40%).(+40 A simple model accounts for the observed dependence of the flux with the magnetic-field gradient.
To achieve a primary frequency standard based on a continuous fountain of laser cooled cesium atoms, we report on the production of a bright, slow and cold continuous atomic beam. Atoms are cooled from a thermal vapor in a 45/spl deg/ laser geometry and launched directly from the optical molasses by the moving molasses technique. The effects of the source fluorescence on the continuous beam (average velocity, temperature and flux) have been observed, and ways to optimize simultaneously the atomic capture and the continuous beam are presented. Flux measurements rise to 2/spl times/10/sup 8/ at/s from a 2D magneto-optical trap at 7 m/s. The initial velocity is easily tunable from 1 to 10 m/s. If the longitudinal temperature is about 70 /spl mu/K, additional transverse cooling even reduces the transverse temperature in one dimension below 30 /spl mu/K. By extrapolating the obtained atomic flux to the continuous fountain under construction, we expect a short-term stability of 7/spl times/10/sup -14//spl tau//sup -1/2/. Other applications of continuous beams of cold atoms are suggested.
We present the current state of things with the development of the Russian cesium fountain. Design of the physical parts, the laser system, and the optical system is briefly outlined. The preliminary results of the operation and detection with a magnetic-optical trap (MOT) and molasses regimes are described. We have made detailed temperature measurements on laser-cooled cesium atoms, exploring a wide range of laser intensity and detuning. The lowest measured temperature of about 20 /spl mu/K for MOT and 2.2 /spl mu/K for molasses are reached.
Cesium atomic fountain clock is the quantum frequency standard with very high accuracy. Research on laser cooling and trapping of cesium atom at Peking University began in 1993. A cesium atomic fountain frequency standard is being developed. A magneto-optical trap with some 108 trapped atoms and an optical molasses with the cold atoms of the temperature of 10/spl mu/K have been achieved previously. The device has been carefully designed and is under construction. It is composed of two main parts: vacuum system and laser system. The article describes the apparatus and presents a brief introduction to some considerations on the atomic clock.