The measurement of time (Französisch)

The history of chronometry is traced from the Egyptian sundial and Roman candle-clock to the atomic frequency standards of the 1970s and '80s. The work of the Laboratoire Primaire due Temps et des Frequences is summarised with reference to optical pumping of Cs atoms, and measurement of He-Ne and CO₂ laser frequencies to within one part in 10¹¹ or 10¹². Complexity of heterodyne devices for frequencies higher than a few GHz is highlighted. The time-dissemination service of the Laboratoire is also described with its master clock and four slaves working with a well-defined TV frame pulse and clock signals received via the Transpac switched network from eight other laboratories; French Atomic Time is recalculated once a month. International time comparisons use LORAN and GPS satellite radionavigation signals. Reference is made also to hydrogen maser and rubidium standards for such purposes as colour TV subcarrier frequency control, aircraft or missile guidance, and space probe tracking.