Optical detection in magnetic state-selection Cs beam tubes for transportable Cs beam clocks

Abstract

Cs beam clocks are indispensable instruments for time and frequency measurements. We adopt an optical detection method, which employs an external distributed-feedback laser diode, for counting the number of Cs atoms in a Cs beam tube using magnetic state selection. Our method converts the number of Cs atoms into that of emitted fluorescent photons, thereby largely enhancing the signal amplitude so that it can be detected by common circuits without involving additional noises. The signal-to-noise ratio in this experiment reaches 3000 in a bandwidth of 1 Hz. In comparison to the traditional detection method that adopts magnetic state-selectors, ionizers, mass spectrometers and electron multipliers, the optical detection method can simplify the structure and extend the lifetime of the Cs beam tubes. A Cs beam clock adopting this detection method demonstrates a short-term stability of 9 × 10−12 τ−1/2 and has been operating continuously for more than nine months.