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.
We report on experiments investigating laser cooling of atomic gases by collisional redistribution of radiation, a technique applicable to dense mixtures of alkali metals with noble gases. Thermal deflection spectroscopy is one of the methods used to measure the temperature change of the laser-cooled gas. In this work we describe experiments focusing on a different technique for precise determination of the local temperature achieved by the cooling within the gas cell. We investigate the Kennard-Stepanov relation, a thermodynamic, Boltzmann-type scaling between the absorption and emission spectral profiles of an absorber, which applies in many liquid state dye solutions as well as in semiconductor systems. To this end, absorption and emission spectra of rubidium atoms and dimers in dense argon buffer gas environment have been recorded. We demonstrate experimentally that the Kennard-Stepanov relation between absorption and emission spectra is well fulfilled for the collisionally broadened atomic and molecular transitions of the system, which allows for the extraction of the thermodynamic temperature.
We study laser cooling of atomic gases by collisional redistribution of fluorescence. In a high pressure buffer gas regime, frequent collisions perturb the energy levels of the alkali atoms; which enables the absorption of a far red detuned irradiated laser beam. Subsequent spontaneous decay occurs close to the unperturbed resonance frequency, leading to a cooling of the dense gas mixture by redistribution of fluorescence. Thermal defection spectroscopy indicates large relative temperature changes down to and even below room temperature starting from an initial cell temperature near 700K. We are currently performing a detailed analysis of the temperature distribution in the cell. As we expect this cooling technique to work also for molecular-noble gas mixtures, we also present initial spectroscopic experiments on alkali-dimers in a dense buffer gas surrounding.