The 9th Symposium on Frequency Standards and Metrology

(Extract from David Wineland 2016 J. Phys.: Conf. Ser. 723 012001)

Cesium beam standards started appearing where state selection and detection could now be accomplished with compact lasers rather than large magnets. New cavity designs were explored with the goal of further suppressing distributed cavity phase shifts. As inaccuracies became smaller, one now needed to include Stark shifts from blackbody radiation (-1.7 × 10^-14 at 300 K); an effect that has become increasingly important over the years for both Cs standards and the precise optical clocks of today. Walter Hardy (UBC) gave a very interesting talk proposing H-masers operated below 1 K where the temperature dependences of collision shifts due to Helium in the gas phase and liquid Helium on the glass bulb would cancel at a certain temperature. Hans Dehmelt described the initial laser cooling experiments on trapped ions by groups at Heidelberg and NIST. The cooling was important for suppressing time dilation, and the Heidelberg group showed the first pictures of individual atoms in a trap [15].

Optical frequency standards continued to advance with the use of significantly expanded laser beams and heavy molecules, to increase interaction times. These improvements exposed the difficulty of dealing with shifts due to wavefront curvature; however, some experiments were now using separated optical beams to observe Ramsey fringes, where loss of signal due to atomic/molecular beam divergence could be suppressed with multiple optical beam paths. Progress on frequency chains had been dramatic since the last Symposium with reports from IEN (E. Bava), NRC (K. M. Baird), NPL (D. J. E. Knight), Novosibirsk (V. Chebotayev) and NBS (K. Evenson). Despite the many stages required in the chains, this was a triumph of frequency metrology since it was now possible to relate optical frequencies to the frequency of Cesium in a phase coherent way.

[15]        Neuhauser W, Hohenstatt M, Toschek P E and Dehmelt H 1980 Phys. Rev. A 22 1137