PhD abstract
This thesis reports a high-performance Caesium vapor cell atomic based on coherent population trapping (CPT). This clock combines a DFB diode laser (895 nm, Cs D1 line), a fibered 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 a reduction of the sensitivity of the clock frequency to laser power variations by a factor 80, in comparison with a standard Ramsey-CPT interrogation. This CPT clock 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 à 104 s.
Annex laser spectroscopy studies in Cs microfabricated cells were performed in this thesis. We shall note the preliminary demonstration of a frequency-stabilized laser 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.
Key words
atomic clock, caesium vapor cell, coherent population trapping, auto-balanced Ramsey, frequency stability, laser spectroscopy