Spectroscopy and thermalization of dense atomic gases in redistributional laser cooling

Laser cooling via collisional redistribution of fluorescence utilizes dense mixtures of alkali metals with noble buffer gases. Typical pressure values of the buffer gas are of the order of a few hundred bar, ensuring a frequent number of collisions between the two atomic species. The energy levels of the alkali atoms are thus perturbed so that excitation using far red-detuned laser light becomes feasible. Energy is then extracted via spontaneous emission occuring close to the unperturbed atomic resonances. Optimization of the cooling effect strongly depends on excitation conditions, namely the choice of detuning of the cooling beam, which in turn is dependent on the used pressure. We here report on spectroscopy measurements of atomic rubidium under high pressure buffer gas conditions. While thermal deflection spectroscopy has been previously used to measure the temperature change of the laser-cooled gas, an alternative approach for temperature measurements utilizing the Kennard-Stepanov relation is also investigated. We here exhibit that the collisionally thermalized atomic resonances well follow this thermodynamic scaling, allowing for temperature extraction of the dense gas mixture.