Sub-Doppler spectroscopy of Rydberg atoms via velocity selection memory in a hot vapor cell

We study resonance redistribution mechanisms inside a hot vapor cell. This is achieved by pumping cesium atoms on the 6S_1/2→6P_1/2 resonance and subsequently probing the velocity distribution of the 6P_1/2 population by a linear absorption experiment on the 6P_1/2→16S_1/2 or 6P_1/2→15D_3/2 transitions at 514 nm and 512 nm, respectively. We demonstrate that despite the existence of thermalization processes, traces of the initial velocity selection, imposed by the pump, survive in both hyperfine levels of the intermediate (6P_1/2) state. This observation allows us to perform sub-Doppler resolution vapor cell spectroscopy on Rydberg states using a simple pump-probe setup. At high cesium densities, redistribution mechanisms dominate, and the velocity selection vanishes. However, spectral analysis provides the collisional shifts and broadenings of the probed Rydberg states.