Hyperfine State-Changing Collisions of Cs(6\textit{P}$_{1/2}$) Atoms with Argon Perturbers

A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of Cs(6$P_{1/2})$ atoms that have undergone a single hyperfine state-changing collision with Ar. Argon pressure broadening rates and shifts of the Cs 6$P_{1/2}(F') \quad \to $ 8$S_{1/2}(F'')$ transitions have been determined. In the experiment, a narrowband Ti:Sapphire laser is tuned to line center of the 6$S_{1/2}(F$ = 4) $\to $ 6$P_{1/2}(F'$ = 3 or 4) transition. Then, the frequency of a narrowband cw dye laser is scanned over the 6$P_{1/2} \quad \to $ 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 }\to $ 6$P_{3/2 }$fluorescence. The experiment is conducted at room temperature, where the Cs density is low. The Ar pressure is varied from 0 -- 1.52 Torr, leading to Cs-Ar collisions that transfer population from the directly excited 6$P_{1/2}(F')$ 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 Cs(6$P_{1/2})$-Ar hyperfine state changing collisions. In addition, the one-dimensional velocity changing collision kernel for Cs(6$P_{1/2})$ atoms prepared with $v_{z }$= 0 that undergo $F'$ = 3 $\leftrightarrow \quad F'$ = 4 hyperfine state-changing collisions with argon is reported.