Daniel J. Clark, Jaroslaw Zacharski, Thomas McClelland, Frequency Electronics, Inc.

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Abstract:

In this presentation, we report on the development and maturation effort of a compact pulsed optically pumped rubidium atomic frequency standard (POPRAFS) at Frequency Electronics, Inc. (FEI) since 2017. By replacing the conventional rubidium clock’s light source (lamp) with a laser, and pulsing the light in a Ramsey scheme, long-term clock stability is expected to be largely enhanced by reducing the light shift/AC Stark shift. In fact, initial testing yielded a reduction in the light shift effect by a factor of 260 when operated in pulsed mode compared to continuous operation. Targeted clock performance characteristics include Allan deviation less than 1 × 10-11 ?? ?1/2 and a flicker floor of 3 × 10-14. Greater stability with reduced size, weight, and power (SOSA-aligned, less than 1 kg, less than 10 W) offers a novel resource as a portable and manufacturable frequency standard. This presentation will discuss FEI’s progress towards developing a next-generation atomic clock by presenting current clock performance as well as potential changes for further improvement. Along with clock performance, environmental sensitivities will be presented once tested and included in the overall evaluation of the clock. Although the clock has been demonstrated successfully in benchtop experiments, there are significant engineering challenges involved in designing a robust, stable, miniaturized pulsed laser light source. Namely, sufficient optical power must be supplied to the clock physics package to optically pump the rubidium, the laser must have low relative intensity noise (RIN), the laser must be frequency-locked to a robust reference, there must be adequate isolation between pulses, and the thermal sensitivity of the laser must be minimal. Additionally, reliability issues associated with the integration of the laser and associated control electronics will be addressed. We believe that the robust and ruggedized design of FEI’s POPRAFS will be capable of performing in a challenging military environment and may also have potential use for space applications. As all of the clock’s components, other than the light source, rely on FEI’s legacy technology as well as mature, well-studied, and fully-developed rubidium clock technology, we have confidence in our low-risk approach towards the rapid development of a new compact frequency standard.