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Joint Conference of the IEEE International Frequency Control Symposium and International Symposium on Applications of Ferroelectrics (IFCS-ISAF)

Towards a Raman-Ramsey Clock based on a Cold Cesium Beam

Chenfei Wu, Xueshu Yan, Jianwei Zhang, Lijun Wang

Published Jul 1, 2020• 0 citations
Publisher

Abstract

The continuous cold atomic clocks have the potential to overcome the Dick effect and to develop compact devices. In this paper, we present a process towards a Raman-Ramsey clock based on a continuous beam of cold cesium using optical separated oscillatory fields instead of a microwave cavity. The Raman-Ramsey fringes for clock transition are observed with a contrast of ~68%, and the central fringe width is ~175 Hz for the interaction-zone separation of 30 mm.

DOI
10.1109/ifcs-isaf41089.2020.9234851

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The continuous cold atomic clocks have the potential to overcome the Dick effect and to develop compact devices. In this paper, we present a process towards a Raman-Ramsey clock based on a continuous beam of cold cesium using optical separated oscillatory fields instead of a microwave cavity. The Raman-Ramsey fringes for clock transition are observed with a contrast of ~68%, and the central fringe width is ~175 Hz for the interaction-zone separation of 30 mm.
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Herein, we report the scheme of an optically pumped atomic clock based on a cold cesium atomic beam source. We propose the laser system and physical mechanism of this atomic clock, wherein the atomic beam travels in an upper parabolic trajectory, thereby eliminating the light shift effect. In the experiments, when the length of the free evolution region was 167 mm, the line width of the Ramsey fringe was 37 Hz. When the expected signal-to-noise ratio of the Ramsey fringe that can be achieved is 36,000, the expected short-term frequency stability is about 3.6 × 10–14/√τ, which is significantly higher than that of a conventional optically pumped cesium clock of similar volume.
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Compact cold-atom frequency standards, characterized by low frequency drift and high accuracy, continue to attract significant interest to address the growing demand for portable, high-performance time-keeping solutions. This paper presents and experimentally demonstrates a proof-of-principle prototype of a compact cold-atom Ramsey clock. The system is based on a multi-standing-wave field microwave cavity operating in the TE₀₁₃ mode and employs a free-falling atom scheme to simplify optical frequency control. The chosen TE₀₁₃ cavity is a cylindrical microwave resonator (CMR) fabricated from oxygen-free copper (OFC), which offers advantages in size and microwave leakage control over the conventional TE₀₁₁ cavity for this free-fall configuration. Its structure, which also serves as the vacuum chamber, is sealed with ceramic windows and coupled via rectangular waveguides. During operation, atoms interact with the first and third standing-wave fields to implement Ramsey interrogation. Experimental results show optimal pulse timing with τ1=16 ms, which aligns closely with theoretical predictions (τ1=16.1 ms). The measured central Ramsey fringe has a full width at half maximum (FWHM) of 8.9 Hz and a contrast of 89.1%, corresponding to a measured relative frequency instability of 6.4×10−13τ-1/2.
SummaryIn this paper we reported our progress toward an atomic beam clock based on a transverse cooled rubidium beam. The atomic beam is generated from an atomic oven and collimated via micro-channel arrays and a two-dimensional optical lattice. After optical pumping, the rubidium beam interacts with two spatially separated Raman beams with a π/2 − π/2 sequence. High contrast Raman-Ramsey fringes are observed by using fluorescence detection. Preliminary result shows that the estimated frequency stability of the atomic clock reaches $2.6 \times {10^{ - 11}}/\sqrt \tau $. The atomic beam clock is proposed as a part of atomic beam inertial navigation unit for field applications.