Radiative lifetimes and collisional deactivation cross sections of the5d6pstates of laser-ablated Ba in He gas

Abstract

We have measured radiative lifetimes and collisional deactivation cross sections of the $5d6p$ excited states of Ba atoms in He buffer gas. Barium atoms are produced by laser ablation of a solid Ba sample, whereby populating the $6s5d{}^{3}{D}_{J}$ metastable states about $0.1--1%$ of the total population. The $5d6p{}^{1,3}{P}^{o},{ }^{1,3}{D}^{o},$ and ${}^{1,3}F\ifmmode^\circ\else\textdegree\fi{}$ states, most of which are not accessible from the ground state by single-photon transition, are excited from the metastable states by a laser, and radiative lifetimes as well as collisional deactivation cross sections are determined from the decay rates of the laser-induced fluorescence. Radiative lifetimes of the $5d6p{}^{3}{P}_{J}^{o},{ }^{3}{D}_{J}^{o},$ and ${}^{3}{F}_{J}^{o}$ states do not depend on J, indicating the validity of LS coupling scheme. Collisional deactivation cross sections by He are in the range of $5--20 {\mathrm{\AA{}}}^{2}$ for the $5d6p{}^{3}{D}_{J}^{o},{ }^{1}{D}_{2}^{o},$ and ${}^{3}{F}_{3,4}^{o}$ states, whereas those for the $5d6p{}^{3}{P}_{J}^{o},{ }^{1}{P}_{1}^{o},{ }^{3}{F}_{2}^{o},$ and ${}^{1}{F}_{3}^{o}$ states are less than $1.5 {\mathrm{\AA{}}}^{2}$ in the He pressure range of 60--400 Pa. Among $5d6p$ manifolds, the ${5d}^{2}{}^{3}{P}_{2}$ state is populated by the collisional deactivation from the laser-excited $5d6p{}^{3}{D}_{1}^{o}$ state, leading to the sensitized fluorescence from ${5d}^{2}{}^{3}{P}_{2}.$ Radiative lifetime and collisional deactivation cross section of the ${5d}^{2}{}^{3}{P}_{2}$ state are also determined from the decay rates of the sensitized fluorescence.