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Velocity preserving transfer between highly excited atomic states: Black Body Radiation and Collisions

We study the excitation redistribution from cesium $7\mathrm{P}_{1/2}$ or $7\mathrm{P}_{3/2}$ to neighboring energy levels by Black Body Radiation (BBR) and inter atomic collisions using pump-probe spectroscopy inside a vapor cell. At low vapor densities we measure redistribution of the initial, velocity-selected, atomic excitation by BBR. This preserves the selected atomic velocities allowing us to perform high resolution spectroscopy of the $\mathrm{6D\rightarrow 7F}$ transitions. This transfer mechanism could also be used to perform sub-Doppler spectroscopy of the cesium highly-excited $\mathrm{nG}$ levels. At high densities we observe interatomic collisions redistributing the excitation within the cesium $\mathrm{7P}$ fine and hyperfine structure. We show that $\mathrm{7P}$ redistribution involves state-changing collisions that preserve the initial selection of atomic velocities. These redistribution mechanisms can be of importance for experiments probing high lying excited states in dense alkali vapor.