Claude Audoin

The classical caesium beam frequency standard: fifty years later

The caesium beam frequency standard using the separated oscillatory field technique proposed by Ramsey in 1950 has seen intensive development over the last fifty years. Its practical implementation as a primary time standard made possible the realization of the second with a precision better than that obtained by means of astronomical measurements and provided the basis for its redefinition in terms of atomic properties in 1967. This paper describes the basic principles underlying the operation of such atomic standards, reviews the progress made during the last fifty years since its invention, and provides an update on the state-of-the-art accuracy and frequency stability achieved today in this field.

Effect of the Atom Transit Time on the Frequency Stability of Cesium Beam Frequency Standards

The effect of the transit time of the atoms in cesium beam tubes is analyzed in the case of fast sine-wave and square-wave fre- quency modulations and in the case of square-wave phase modulation. Analytical expressions are given for the slope of the error signal and for the frequency stability. The effect of the modulation frequency and of the separation between the second interaction region and the atom detection zone is illustrated for the interaction time distributions en- countered when optical methods are implemented for the state selec- tion and the detection of the cesium atoms.