In Situ Measurements of Light Diffusion in an Optically Dense Atomic Ensemble.

This study introduces a novel method to investigate in situ light transport within optically thick ensembles of cold atoms, exploiting the internal structure of alkaline-earth metals. A method for creating an optical excitation at the center of a large atomic cloud is demonstrated, and we observe its propagation through multiple scattering events. In conditions where the cloud size is significantly larger than the transport mean free path, a diffusive regime is identified.

Non-Gaussian Correlations in the Steady State of Driven-Dissipative Clouds of Two-Level Atoms.

We report experimental measurements of the second-order coherence function g^{(2)}(τ) of the light emitted by a laser-driven dense ensemble of ^{87}Rb atoms. We observe a clear departure from the Siegert relation valid for Gaussian chaotic light. Measuring intensity and first-order coherence, we conclude that the violation is not due to the emergence of a coherent field.

Laser frequency stabilization by modulation transfer spectroscopy and balanced detection of molecular iodine for laser cooling of Yb.

We report laser frequency stabilization by the combination of modulation transfer spectroscopy and balanced detection of a relatively weak hyperfine transition of the R(158)25-0 line of molecular iodine (I), which is used as a new frequency reference for laser trapping and cooling of Yb on the S - P transition. The atomic cloud is characterized by time-of-flight measurements, and an on-resonance optical depth of up to 47 is obtained. We show laser noise reduction and characterize the short-term laser frequency instability by the Allan deviation of the laser fractional frequency.

From superradiance to subradiance: exploring the many-body Dicke ladder.

We report a time-resolved study of collective emission in dense ensembles of two-level atoms. We compare, on the same sample, the buildup of superradiance and subradiance from the ensemble when driven by a strong laser. This allows us to measure the dynamics of the population of superradiant and subradiant states as a function of time.

Collective Shift in Resonant Light Scattering by a One-Dimensional Atomic Chain.

We experimentally study resonant light scattering by a one-dimensional randomly filled chain of cold two-level atoms. By a local measurement of the light scattered along the chain, we observe constructive interferences in light-induced dipole-dipole interactions between the atoms. They lead to a shift of the collective resonance despite the average interatomic distance being larger than the wavelength of the light.