Hyperfine state-changing collisions ofCs(6P1∕2)atoms with argon perturbers

Abstract

A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of $\mathrm{Cs}(6{P}_{1∕2})$ atoms that have undergone a single hyperfine state-changing collision with Ar. In addition, argon pressure broadening rates and shifts of the cesium $6{P}_{1∕2}({F}^{\ensuremath{'}})\ensuremath{\rightarrow}8{S}_{1∕2}({F}^{\ensuremath{''}})$ transitions have been determined. In the experiment, a single mode, cw Ti:sapphire laser is tuned to line center of the $6{S}_{1∕2}(F=4)\ensuremath{\rightarrow}6{P}_{1∕2}$(${F}^{\ensuremath{'}}=3$ or 4) transition. Then, the frequency of a single mode cw dye laser is scanned over the $6{P}_{1∕2}\ensuremath{\rightarrow}8{S}_{1∕2}$ manifold to probe the populations of the $6{P}_{1∕2}$ hyperfine levels. Absorption of probe laser photons is monitored by detecting $8{S}_{1∕2}\ensuremath{\rightarrow}6{P}_{3∕2}$ fluorescence. The experiment is conducted at room temperature, where the Cs density is low $(n\ensuremath{\sim}3.4\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$, and thus the probability of a $\mathrm{Cs}\text{\ensuremath{-}}\mathrm{Cs}$ collision is negligible during the $\mathrm{Cs}(6{P}_{1∕2})$ radiative lifetime. The Ar pressure is varied from 0 to $1.52\phantom{\rule{0.3em}{0ex}}\mathrm{Torr}$, and $\mathrm{Cs}\text{\ensuremath{-}}\mathrm{Ar}$ collisions cause population to be transferred from the directly excited $6{P}_{1∕2}({F}^{\ensuremath{'}})$ level to the other $6{P}_{1∕2}$ hyperfine level. The data are analyzed using a density matrix formalism to yield the rate coefficients for $\mathrm{Cs}(6{P}_{1∕2})\text{\ensuremath{-}}\mathrm{Ar}$ hyperfine state-changing collisions. In addition, the one-dimensional velocity changing collision kernel for $\mathrm{Cs}(6{P}_{1∕2})$ atoms prepared with ${v}_{z}=0$ that undergo ${F}^{\ensuremath{'}}=3\ensuremath{\leftrightarrow}{F}^{\ensuremath{'}}=4$ hyperfine state-changing collisions with argon is reported.