A Kennard-Stepanov relation study on redistributional laser cooling in dense gaseous ensembles

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.