ABSTRACT
In this chapter, we will describe the impact that the recent developments in atomic physics, which were described in Chapter 2, have had on the development of microwave atomic frequency standards. Some of those developments were based on earlier theoretical knowledge but started only in the 1980s because of the unavailability of appropriate technology. Developments in the field of lasers, particularly those lasers using solid-state technology, have provided new tools for addressing some of the limitations encountered in the approaches used up to that time in the development of classical atomic frequency standards. In particular, three new different approaches were studied for implementing Cs beam frequency standards. Firstly, an old idea of using laser optical pumping for state preparation was resurrected, thanks to advances in solid-state laser diodes operating at room temperature (Picqué 1974; Arditi and Picqué 1980). That approach resulted in the laboratory development of a very stable and accurate clock. Another approach was studied in the early 1980s using coherent population trapping (CPT) for both states preparation and microwave excitation (Hemmer et al. 1983). Unfortunately, that approach remained a laboratory study. Finally, a real revolution took place through the use of lasers to cool atomic ensembles in the form of molasses in the microkelvin range, resulting in a Cs standard with narrow Ramsey fringes with line width in the Hz range (Kasevich et al. 1989; Clairon et al. 1996).
