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

HORACE: atomic clock with cooled atoms in a cell

Emmanuel Guillot, Paul-Éric Pottie, Constance Valentin, P. Petit, N. Dimarcq

Published Jan 22, 2003• 3 citations

Abstract

Our aim is to use cold atoms not for reducing instability or inaccuracy in the range of 10/sup -16/ or better, but to use them for reducing the size of atomic clocks. The key idea of HORACE is to fold in a microwave cavity every zone of the atomic resonator of a standard clock: zones of cooling and atomic preparation, zone of interrogation and zone of detection. Then the cell of HORACE has to be a microwave cavity as well as an optical cavity. Thus cooling of cesium atoms can only be obtained by isotropic cooling light generated inside it. In this paper, we first expose the main features of HORACE and two different configurations. Metrological aspects as well as the way the atoms would be efficiently cooled are then developed. A preliminary validation of HORACE is also demonstrated.

DOI: 10.1109/freq.1999.840712

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IEEE Transactions on Instrumentation and Measurement•Jan 1, 2001•4 citations

Our aim is to use cold atoms not for reducing instability or inaccuracy in the range of 10/sup -16/ or better, but to use them for reducing the size of atomic clocks. The key idea of HORACE is to fold in a microwave cavity every zone of the atomic resonator of a standard clock: zones of cooling and atomic preparation, zone of interrogation and zone of detection. Then the cell of HORACE has to be a microwave cavity as well as an optical cavity. Thus cooling of cesium atoms can only be obtained by isotropic cooling light generated inside it. In this paper, we first expose the main features of HORACE and two different configurations. Metrological aspects as well as the way the atoms would be efficiently cooled are then developed. A preliminary validation of HORACE is also demonstrated.

The HORACE device is a compact cold atom clock where about 10/sup 8/ cesium atoms are laser cooled at a few /spl mu/K, then interrogated and detected directly in a 20 cm/sup 3/ spherical microwave cavity. The optimization of the short term stability with the cooling and interrogation durations is presented, leading to an estimation of the Allan deviation of /spl sigma//sub y/(/spl tau/) -1 10/sup -13/ /spl tau/ /sup - 1/2 /on earth and /spl sigma//sub y/(/spl tau/) = 7 10/sup -14/ /spl tau//sup -frac12;/ in space. The quantum projection noise, the Dick effect and the detection laser noises are taken into account. The calculations are based on a preliminary model for the recapture of cold atoms, in reasonable agreement with measurements.

In the compact cold atoms clock HORACE caesium atoms are successively laser cooled, submitted to a Ramsey microwave interrogation scheme and then detected by linear absorption directly inside the microwave cavity. The whole physics package and optical bench have been entirely redesigned to optimize such an in-situ detection and to perform a normalization scheme. Main efforts have been concentrated on technical issues such as magnetic shielding, microwave cavity polishing and tuning, use of fast mechanical switches to realize the optical sequence.