Thesis on the subject of lasercooling and trapping of neutral mercury for the purpose of making a lattice clock.

Due to the recent success, in terms of accuracy and precision, of a number of strontium optical lattice optical frequency standards, and the classification of the 5s² ¹S₀ to 5s5p ³P₀ transition in neutral strontium as a secondary definition of the SI unit of the second, many new strontium lattice clocks are under development. The strontium optical lattice clock (Sr OLC) at the National Physical Laboratory (NPL) is one such project. This thesis describes the design and build of the NPL Sr OLC, discussing the considerations behind the design. Details of the first cooling stage are given, which includes the characterisation of a novel permanent-magnet Zeeman slower by measurements of the longitudinal velocity distributions and loading of the MOT at 461 nm. Development of a narrow linewidth laser system at 689 nm is described, which is used for initial spectroscopy of the second-stage cooling transition. In particular, this work describes progress towards two independent ultra-narrow linewidth clock lasers. The new generation of strontium lattice clock experiments have focused on characterising the systematic frequency shifts and reducing their associated fractional frequency uncertainties, as well as reducing the fractional frequency instability of the measurement. One focus of the Sr OLC at NPL is to help characterise the frequency shift of the clock transition due to black-body radiation (BBR), which is currently the largest contributor to the uncertainty budget of the measured clock frequency. Our approach, discussed here, is to make a direct, differential measurement of the shift with the atoms housed alternately in environments of differing temperatures. Better characterisation and control of the BBR frequency shift of the strontium clock transition is crucial for the future of the Sr OLC as a leading frequency standard.

Cette thèse est consacrée aux progrès récents des horloges à réseau optique au strontium du LNE-SYRTE, Observatoire de Paris. L'incertitude systématique et la stabilité des horloges optiques sont 2 ordres de grandeur meilleures que les horloges atomiques micro-ondes au cesium qui réalisent la seconde SI, bénéficiant maintenent a des applications en physique fondamentale, astronomie et géosciences. Dans un futur proche, une redéfinition de la seconde SI est attendue, quand les horloges optiques se seront révélées aussi fiables et reproductibles que les horloges a micro-ondes. La thèse présente trois étapes décisives dans cette direction. Nous présentons un fonctionnemment operation quasi-continu de nos horloges Sr pendant plusieurs semaines. Des comparaisons de fréquences locales et à distance avec diverses références de fréquence micro-ondes et optiques montrent que les horloges optiques sont reproductibles par des laboratoires independants. Nous avons démontré un premier réseau tout optique entre des horloges optiques à l'échelle continentale. Les horloges au Sr ont été utilisées pour préparer 5 rapports de calibration du Temps Atomique International (TAI) qui ont été validés par le BIPM comme première contribution au TAI par des horloges optiques. Certains de ces résultats ont été utilisés pour borner l'amplitude d'une possible violation de l'invariance de Lorentz analysant les comparaisons d'horloges distantes. Enfin, nous avons effectué une caractérisation complète des déplacements de fréquence associés aux sources laser à semiconducteur utilisées pour le piégeage des atomes dans l'optique d'applications pour des horloges transportables et spatiales. / This thesis describes the latest progresses regarding the Sr optical lattice clocks at LNE-SYRTE, Observatoire de Paris. Nowadays, the systematic uncertainty and stability of optical clocks are 2 orders of magnitude better than cesium microwave fountains currently realizing the SI second, with applications in fundamental physics, astronomy and geoscience. In the near future, a re-definition of the SI second is expected, once optical clocks are proven to be as reliable and reproducible as their microwave counterparts. The thesis presents three decisive steps in this direction. First, we demonstrate nearly continuous Sr clocks over several weeks. Second, local and remote frequency comparisons against various microwave and optical frequency standards show that OLCs are reproducible over time, and by independent laboratories. We notably demonstrated the first all-optical agreement between optical clocks at continental scale. Third, the Sr clocks were used to calibrate the Temps Atomique International (TAI). The five calibration reports, which we produced, were validated by the BIPM, as the first contribution to TAI with optical clocks. In addition, some of these results were used to improve bounds on a putative violation of the Lorentz invariance by testing the stability of the frequency ratio between remote clocks. Finally, we conducted a full characterization of the frequency shifts associated with semi-conductor laser sources for the trapping light, including optical measurements and frequency shifts measurements, with applications for transportable and space clocks.