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Session P1b: Advances in Ground Atomic Clocks

Low-Cost Optically-Pumped Cesium Beam Clock
V. Dolgovskiy, F. Kroll, M. Haldimann, P. Berthoud, Oscilloquartz
Location: Royal Ballroom AB
Date/Time: Tuesday, Jan. 27, 4:00 p.m.

Cesium beam atomic clocks are designed to provide the best long-term frequency stability for commercial products. To obtain the necessary population imbalance between their two ground states, their thermal atomic beam is either magnetically deflected by static magnets or optically pumped with a narrow band laser. The main advantage of the optical pumping technology is better frequency stability for comparable clock lifetime. Oscilloquartz SA has designed its high-end product (OSA-3300 SHP) with a standard architecture for the cesium beam tube, namely with all necessary components embedded in a vacuum enclosure [1].
In view of reducing the overall cost and therefore the price of the product, Oscilloquartz SA has completely revisited the cesium tube architecture and manufacturing processes. The main idea is to keep only the mandatory components under vacuum (atomic beam source and microwave cavity), while placing other components under air (C-field coil, magnetic shields, heater). Moreover, the hermetically sealed enclosure also served as the microwave resonant Ramsey cavity. This smart enclosure is built by additive manufacturing as a single and seamless piece providing the hollow microwave guide.
The targeted frequency stability (Allan deviation = 1.4E-12 / sqrt(tau)) is identical to the enhanced performance of the magnetically deflected cesium beam clock (Microchip PRS-4400R-EP). This stability is easily met thanks to the highly useful atomic flux obtained with optical pumping without sacrificing on the cesium tube lifetime (10 years).
Low-cost cesium clocks with enhanced performance find increasing applications when densification and more resilient networks to GNSS outages are needed for Positioning, Navigation and Timing (PNT) applications of strategic and critical infrastructures.
[1] P. Berthoud et al. “Industrial optically pumped cesium beam clock”, Precise Time and Time Interval Meeting, January 23-26, 2023, Long Beach, CA, USA

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