Speaker: Vitaly G. Palchikov
Topic: The role of precision optical frequency measurements in the redefinition of the time-second unit in the International System of SI Units
Abstract: Given that in the last decade the accuracy of modern optical frequency standards, based on the use of precision spectroscopy of neutral atoms and their single ions, has exceeded the accuracy of the best cesium standards (fountains) by at least 2 levels, in 2016 the International Consultative Committee for Time and Frequency developed a “Roadmap” for the transition to a new definition of the second in the International System of Units (SI). At the 27th General Conference on Weights and Measures (November 2022), this roadmap was approved in its final version (Resolution E), and the date for the transition of the global community to the new unit of time in the SI system – the second in 2030 was determined. This work provides a detailed analysis of all 5 points of the “Roadmap” for the transition to the new definition of the second, as well as discusses the events conducted by the All-Russian Scientific Research Institute for Physical-Engineering and Radiotechnical Metrology (VNIIFTRI) on the new definition of the second.

Speaker: Vyacheslav N. Baryshev
Topic: Rubidium frequency standard with pulse optical pumping and pulse excitation of microwave resonances according to the Ramsey scheme
Abstract: The instability of the frequency of rubidium frequency standards (RFS) is largely due to its strong dependence on the instability of the intensity and frequency of optical radiation caused by the Stark effect (dynamic Stark effect), which is a common drawback of continuously lamp and even laser-optically pumped microwave frequency standards. However, as early as the 1960s, was proposed an idea that would significantly reduce the light shift and consequently the instability of frequency standards in gas cells with optical pumping. This idea involved separating three operational phases of the RFS in time: optical pumping, pulsed microwave interrogation using the Ramsey scheme, and optical detection. This minimized the mutual influence of various signals, and the microwave clock transition occurred when there was no light radiation in the cell, leading to a significant suppression of the light shift. Modern technological advancements, including the use of diode lasers and digital electronics, have allowed for the highly effective implementation of this original idea. The report presents the results of frequency measurements and analysis of short-term frequency instability obtained from a laboratory prototype of the RFS based on the implemented method of pulsed optical pumping (POP) at VNIIFTRI. Assessments of the major contributions to the overall instability of the RFS with POP are also conducted.