Anomalous relaxation of populations in hyperfine Zeeman sublevels of Cs atoms induced by collisional modification of the Cs hyperfine interaction

Cs vapour in , Ar, Kr, Ne, He and Xe buffer gases was optically pumped with a diode laser in a magnetic field of 1.516 T. The relaxation of the population imbalance in the hyperfine Zeeman sublevels of the ground state was detected with another diode laser. A phenomenological theory is presented which explains the optical transients and the time variation of the populations in the hyperfine Zeeman sublevels. Both experimental and theoretical results showed that there were relaxation transients of populations in some hyperfine Zeeman sublevels of optically pumped Cs with `anomalous' shapes. The experimental results showed that the `anomalous' relaxation depended strongly on the buffer-gas species and the buffer-gas pressure. Theoretically, it was found that the combined electron-spin - nuclear-spin transition, which is mainly induced by collisional modification , caused the `anomalous' shapes of the transients. The collisional transfer cross section for the binary collisional interactions was estimated to be . `Anomalous' relaxations of populations in the hyperfine Zeeman sublevels are discussed. The results of the calculation are in good agreement with the experimental results.