Electric-field-induced change of the alkali-metal vapor density in paraffin-coated cells

Alkali-metal vapor cells with antirelaxation coating (especially paraffin-coated cells) have been a central tool in optical pumping and atomic spectroscopy experiments for 50 years. We have discovered a dramatic change of the alkali-metal vapor density in a paraffin-coated cell upon application of an electric field to the cell. A systematic experimental characterization of the phenomenon is carried out for electric fields ranging in strength from 0--8 kV/cm for paraffin-coated cells containing rubidium and cells containing cesium. The typical response of the vapor density to a rapid (duration 100 ms) change in electric field of sufficient magnitude includes (a) a rapid (duration of 100 ms) and significant increase in alkali-metal vapor density followed by (b) a less rapid (duration of ~1 s) and significant decrease in vapor density (below the equilibrium vapor density), and then (c) a slow (duration of ~100 s) recovery of the vapor density to its equilibrium value. Measurements conducted after the alkali-metal vapor density has returned to its equilibrium value indicate minimal change (at the level of 10%) in the relaxation rate of atomic polarization. Experiments suggest that the phenomenon is related to an electric-field-induced modification of the paraffin coating.