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

Progress toward a Raman-Ramsey Clock Based on a Transverse Cooled Rubidium Beam

Pei-Qiang Yan, Weichen Jia, Yanying Feng

Published May 15, 2023• 0 citations
Publisher

Abstract

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.

DOI
10.1109/eftf/ifcs57587.2023.10272081

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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 2.6×10−11/τ2.6 \times {10^{ - 11}}/\sqrt \tau 2.6×10−11/τ​. The atomic beam clock is proposed as a part of atomic beam inertial navigation unit for field applications.
We reported on the progress toward an atomic clock based on a continuous cold 87Rb atomic beam. The atomic beam source is generated directly from a 2D+Magneto-Optical Trapping (MOT) with the flux of about 3×109atoms/s and mean longitudinal velocity of 10 m/s. The beam had a free evolution time of 9 ms over the separated distance of 90 mm, producing a 54-Hz-wide Raman-Ramsey fringe. The Signal-to-Noise ratio (SNR) of Raman-Ramsey fringes is effectively increased by modulation and demodulation methods, which offer a promising approach to improving the frequency stability of the atomic clock.
The phenomenon of all-optical Ramsey interference using pulsed coherent population trapping (CPT) beams provides a new avenue for developing frequency standards using atomic vapor. In this study, we show that frequency narrowed Ramsey fringes can be produced in rubidium vapor without the effect of power broadening. We observed fringes of width as narrow as 1 kHz using a buffer-gas filled rubidium cell. A compact injection-locked laser (ILL) system was used to generate CPT beams. Studies also show that ac Stark effect on Ramsey fringes can be reduced, and higher frequency stability can be achieved in a clock application. The results are encouraging to propose an architecture for development of a pulsed CPT Ramsey clock. In this paper, we also provide related discussions on clock frequency stability, and our plans for future experiments.
Highly stable atomic frequency standards are of increasing importance for a variety of space applications, ranging from communication to navigation and time transfer to tests of fundamental science. The requirements for an atomic clock vary significantly depending on the application, and for many space systems, compactness and robust design are at a premium, and stability dominates over absolute accuracy. We report on progress with our design for a compact laser-cooled Cs- beam atomic clock suitable for satellite applications such as GPS. The basic design features a continuous, cold atomic beam extracted from a magneto-optic trap (MOT). This cold atomic beam is then to be used in a laser-pumped Ramsey clock, with the clock signal derived from either a microwave C-field or, alternatively, by Raman resonance between the Ramsey fields. In order to reduce light shifts from the MOT light and improve signal-to-noise, the atomic beam will be optically deflected and transversely cooled upon extraction from the MOT. We estimate that the shot-noise-limited stability achievable with this physics package can be 2 to 3 orders of magnitude better than current Cs-beam clocks used in satellite applications. We present our experimental progress towards a working frequency standard, including characterization of our six-beam magneto-optic cold atom trap and production and characterization of a cold atomic beam.
Precision studies of stimulated-resonance Raman interactions in a sodium atomic beam were performed with emphasis on Ramsey’s separated-field excitation. Ramsey fringes were obtained for a field separation of up to 30 cm, and the data were consistent with theoretical predictions. Possible applications of this Raman interaction to clock development also were studied by stabilizing a microwave oscillator to a Raman–Ramsey fringe. The resulting oscillator stability of 1.5 × 10−11 for a 1000-sec averaging time compares favorably with commercial cesium clocks when differences in atom transit time and transition frequency are taken into consideration. Finally, potential sources of long-term frequency error, which are important for clock applications, were also partially investigated.