Laser-induced optical pumping measurements of cross sections for fine- andhyperfine-structure transitions in sodium induced by collisions with helium and argon atoms

Optical pumping of the ground states of sodium can radically alter the shap e of the laser-induced fluorescence excitation spectrum, complicating measu rements of temperature, pressure, etc.. which are based on these spectra. M odeling of the fluorescence using rate equations for the eight hyperfine st ates of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to det ermine, from the shape of experimental spectra, cross sections for Delta F transitions of the P-3/2, state induced by collisions with helium and argon atoms, for a range of values assumed for the P-1/2, Delta F cross sections . The hyperfine cross sections measured using this method, which to our kno wledge is novel, are compared with cross sections for transitions involving polarized magnetic substates m(F) measured previously using polarization s ensitive absorption. Also, fine-structure transition (Delta J) cross sectio ns were measured in the pumped vapor, giving agreement with previous measur ements made in the absence of pumping. [S1050-2917(99)04605-3].