Waltz of the atoms Collective behaviors in a Sr stream

Accurate and stable frequency standards are crucial for technologies such as navigation, geodesy, and advance sensing, while also enabling the search for new physics. Recent research has proposed a shift from dual-standard systems, combining atomic ensembles for long-term stability with optical cavities for short-term precision, towards fully atom-based "single-standard" architectures. This thesis explores a novel approach to realize a continuous superradiant laser using a thermal beam of strontium (Sr) atoms, a promising candidate for a fully atom-based frequency standard.
A continuous superradiant laser relies on the interaction between a cavity mode and an atomic ensemble to achieve continuous emission. Unlike traditional lasers, the cavity acts as a dissipative element, while the atomic medium stores the coherence that defines the emitted frequency.
This thesis combines theoretical and experimental innovations toward realizing such a laser. First, it introduces a refined theoretical framework for atom-cavity interactions, accounting for experimental design elements such as geometrical tilts. Next, it describes the experimental setup, focusing on the development of an efficient pumping and collimation scheme to create a velocity-selected thermal atomic beam. Two versions of the setup are explored: one using a cavity with a linewidth much broader than the atomic gain medium, and the other using a cavity with comparable linewidth. Both show collective strong coupling between the atomic ensemble and the cavity mode, with continuous optical amplification. Crucially, the achieved amplification level suggests that we are close to surpassing the superradiant lasing threshold.