From atomic fountains to ultra-stable lasers
Résumé
The SI second is currently defined through the ground-state hyperfine transition frequency of the cesium atom. We discuss the calibration of international time scales using one of the primary frequency standards at LNE-SYRTE. However, the future of time and frequency metrology lies in the optical domain. We describe our ongoing research on laser spectroscopy for ultra-stable lasers which will eventually enable the ultimate performance in optical clocks.