Optical Frequencies Metrology

Strontium optical clock

Atomic fountains using cold cesium atoms, currently defining the second from a microwave atomic transition, will soon reach their ultimate accuracy. In the near future, optical clocks based on narrow atomic transitions in the visible spectrum will certainly prove to be better frequency standards than fountains.

An optical atomic clock using strontium atoms is being developed at SYRTE. To reach high accuracy, strontium atoms are slowed down — or cooled — and trapped in a lattice of optical dipole traps. The frequency of the clock transition of strontium has been measured by probing with an ultra-stable laser and by comparison with a cesium fountain. An accuracy of 10^-14 has been achieved by measuring and canceling perturbations due to the trapping potential. Strontium optical clock are expected to soon provide a better accuracy than in the best atomic fountains. Further characterization will therefore be achieved by comparison with a second strontium clock, currently under construction.

Gauche: High vacuum enclosure where strontium atoms are trapped in an optical lattice.
Droite: Clock in operation: the blue lasers slow down the strontium atoms.