The subject of this project is precision atomic spectroscopy and its application in laser pumped gas cell atomic clocks. The research is developed mainly in two lines: the theoretical and experimental study of the atomic resonance signals and the study of the laser sources and their frequency stabilization techniques. These two lines are strongly correlated because different aspects of the laser spectrum influence on the reference signal have been not studied in systematic manner, and constitute the heart of this project. The investigation method used in our experiments is based on the use of lasers to perform optical pumping and/or coherent population trapping, by irradiating Rb atoms contained in sealed cell with buffer gas.
A summary of the obtained results is presented in the following.
1) Rubidium gas-cell atomic frequency standards: (1a) A state of the art laser-pumped Rb clock was developed and its valorisation is now performed via a separate project funded by the ESA. This research could lead to an innovative clock for the 2° generation of GALILEO (EU-ESA satellite navigation), and reinforce the Swiss leadership in this domain; (1b) New schemes based on Coherent Population Trapping were studied. Particular attention has been devoted to the theoretical and experimental study of the influence on the CPT resonance of the laser linewidth and the buffer gas broadening. These investigations lead to define the limit in the spectral quality of the light source for CPT-based applications and could further improve the performances and/or allow miniaturisation; (1c) A new research was started on ultra-miniature (ultimately chip-scale) frequency references in collaboration with Uni NE and EPFL;
2) Tuneable and frequency stabilised laser sources: (2a) New sources were developed/studied (DFB, bragg mirrors, etc.) and the comparison between laser frequency stabilization schemes was extended to the DAVLL (Dichroic Atomic Vapor Laser Locking); (2b) A four-wavelength laser reference system for water vapour sensing near 935nm was realized, in collaboration with EPFL. It could serve as seed laser for a ground or space-borne differential absorption lidar (DIAL); (2c) A general study on the space applications of optical frequency synthesizers and combination with vapour cell frequency standards was started.