Grégoire COGET "Cs Coherent Population Trapping Atomic Clock with Ramsey Auto-Balanced Polling Protocol""

Thesis work of Grégoire COGET : "Cs Coherent Population Trapping Atomic Clock with Ramsey Auto-Balanced Polling Protocoley"

Abstract : This thesis reports a high-performance Cs vapor cell atomic based on coherent population trapping (CPT). This clock combines a DFB diode laser (895 nm, Cs D1 line), a fibred electro-optical modulator, an acousto-optical modulator, a Michelson system, FPGA-based low noise electronics and a N2-Ar buffer gas filled Cs vapor cell. The clock is based on an optimized CPT pumping scheme, named push-pull optical pumping (PPOP), allowing the detection of high-contrast  CPT resonances.

The clock uses a novel pulsed interrogation protocol named Auto-Balanced Ramsey (ABR). This method is based on the extraction of two error signals derived from two successive Ramsey sequences with different dark periods.    The ABR-CPT protocol, improved further with symmetrization (SABR-CPT), allows a drastic reduction of light-shifts effects, yielding in particular to reduce the sensitivity of the clock frequency to laser power variations by a factor 80, in comparison with a standard Ramsey-CPT interrogation. This clock CPT demonstrates a fractional frequency stability of 2 10-13 τ -1/2, reaching the record level (for this kind of clock) of 2.5 10-15 at 104 s.

Annex laser spectroscopy studies in Cs microfabricated cells were performed in this thesis. We shall note the preliminary demonstration of a laser frequency-stabilized using dual-frequency sub-Doppler spectroscopy in a Cs microcell, exhibiting a fractional frequency stability better than 2 10-12 at 1 s. These performances are 10 times better than those of microwave CPT-based chip-scale atomic clocks.

Thesis Jury :

- M. GARRIDO ALZAR Carlos, Charge de recherche CNRS, HDR, SYRTE
- Mme. KNOOP Martina, Directrice de Recherche CNRS, Université Aix-Marseille
- M. NEZ François, Directeur de recherche CNRS, Laboratoire Kastler Brossel
- M. ESNAULT Francois-Xavier, Ingénieur CNES
- M. BOUDOT Rodolphe, Charge de recherche CNRS, HDR, FEMTO-ST, UBFC
 -M. GIORDANO Vincent, Directeur de recherche CNRS, FEMTO-ST, UBFC

Location : Amphithéâtre Gagnepain, FEMTO-ST, 15B Avenue des Montboucons - Besançon