François Tricot will defend his thesis on 27th of March 2018 at 1:30 pm on the subject “Analysis and reduction of the frequency instability noise sources in a compact CPT clock”, realized in SYRTE under the direction of Stéphane Guérandel.
The defense will take place in the amphitheater of the Institut d’Astrophysique de Paris (IAP), in front of the jury: Agnès Maître, Frédéric Du Burck, Vincent Giordano, Virgile Hermann and Jean-Marc Lesage.
Abstract: This thesis work has been granted by a CIFRE-Défense contract to study the frequency stabilities of an atomic clock based on coherent population trapping. The objective is to demonstrate a frequency stability in the range of 10-13τ-1/2 up to 10 000 s. A caesium vapour cell is used with a high-contrast excitation scheme using cross linear polarisations and a Ramsey interrogation. The short-term frequency stability is presented with the reduction of the phase and the laser power noise, both limiting clock performance at 1 s integration time. The optimisation of the microwave chain with a new local oscillator, and the implementation of a very low noise power lock loop have improved the frequency stability down to 2,3×10-13 at 1 s integration time. The fluctuations analysis of the operating parameters (laser intensity, magnetic field, temperature, etc.) and the measurement of the clock frequency show that the medium-term frequency instability is mostly limited by laser power and magnetic field fluctuations at the level of 2×10-14 at 2 000 s integration time. These analyses also show that laser power fluctuations, despite servo loop control, are related to polarisation fluctuations through temperature fluctuations inside the experiment isolation box. Finally, the studies of a dual-frequency and dual-polarisation laser for a compact CPT clock are presented, paving the way to industrialisation by reducing the optical bench.
Key words: atomic clock, vapour cell, coherent population trapping, Ramsey fringes, Dick effect, intensity noise, frequency stability.