Saturated absorption and electromagnetically induced transparency of residual rubidium in dense cesium vapor

In the sealed-off cesium vapor cell studied in this work, a residual rubidium fraction of approximately $\sim$1% was observed. We investigate the optical response of these trace Rb atoms in a sealed 1~cm long Cs-filled vapor cell. Despite the low concentration, laser excitation at 795~nm allows the observation of saturated absorption and electromagnetically induced transparency (EIT) resonances. The surrounding Cs vapor effectively acts as a buffer medium, reducing the Rb atomic velocity and increasing the interaction time with the laser field, which improves the EIT signal. The experiments are performed in an all-sapphire cell that can be heated up to 500${}^{\circ }$C without window blackening, unlike conventional glass cells. From the measured spectra, Cs–Rb collisional cross sections are estimated. These results show that residual atomic species in high-temperature vapor cells can be exploited for spectroscopic and nonlinear-optical studies.