Results are presented on theoretical calculations of the signal-to-noise ratio and of the short-term stability realizable in passive rubidium frequency standards. Measurements made on systems using either the separate hyperfine filter or the integrated hyperfine filter approach are reported. It is concluded that shot noise produced by the lamp at the photodetector is responsible for the observed white frequency noise spectrum limiting the stability in the short-term region.

On the signal-to-noise ratio and short-term stability of passive rubidium frequency standards

Preliminary results on the stabilization of a 1772-MHz oscillator to a resonance Raman transition in an atomic beam of sodium are presented. Short-term stability of 5.6 x 10(-11) (tau = 100 sec) for a 15-cm Ramsey interaction-region separation has been achieved. Sources of frequency drift are briefly discussed.

Stabilization of a microwave oscillator using a resonance Raman transition in a sodium beam.

The principles of operation of atomic frequency standards are described. Details are given of their physical construction. Their characteristics as well as their availability, principal uses and impact are specified. The basic concepts involved in atomic frequency standards and the terminology commonly used in this field are summarized. The role of quartz crystal oscillators which are slaved to active and passive atomic frequency standards is emphasized. The traditional atomic frequency standards are reviewed, i.e. the hydrogen maser, the caesium beam tube and the passive rubidium cell frequency standards.

https://iopscience.iop.org/article/10.1088/0022-3735/9/9/001/pdf

Atomic frequency standards and clocks

In recognition of the October 1964 declaration of the International Committee of Weights and Measures that the physical measurement of time be based on a particular transition between two hyperfine levels in the ground state of cesium 133, a review of the characteristics of cesium beam atomic frequency standards is presented. This article discusses the general requirements for frequency and time standards, advantages offered by the atomic standard as compared to astronomical standards, various other atomic standards in brief, the operating principles of cesium standards, measures of performance, error sources in cesium standards, characteristics of several standards in current operation, comparison of cesium standards, and atomic time standards derived from atomic frequency standards.

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Cesium Beam Atomic Time and Frequency Standards

Frequency stability specification and measurement :: high frequency and microwave signals

The instability of passive atomic frequency standards caused by shot noise introduced by the atomic reference is calculated. This instability can be characterized by a figure of merit for the atomic reference, and the asymptotic functions for the rms frequency fluctuation for long and short averaging times expressed in terms of this quantity. Measurements of the rms frequency fluctuation of cesium atomic beam and rubidium vapor frequency standards are compared with theory, and the predicted performances of various existing and proposed atomic standards are tabulated. It is feasible to build atomic beam frequency standards whose stability for averaging times less than one second is limited by noise in the crystal oscillator rather than by shot noise, a criterion generally met by rubidium vapor frequency standards. For long averaging times, shot noise will always be the fundamental limiting factor in atomic frequency standard stability.

R. F. Lacey

Papers

Short-term stability of passive atomic frequency standards

Short-Term Stability of Passive Atomic Frequency Standards