Two-step photoionization of barium atoms through excited P11,3 levels in optical dense approximation

The kinetics of two-step photoionization of barium atoms through excited P11,3 levels was studied by numerical simulation method in the optically dense approximation. The first laser at wavelength λ1=553.5 nm ( λ1=791 nm) pumps transition S01↔P11 ( S01↔P13 ). The second laser with λ2=266 nm ( λ2=310 nm) ionizes atoms from the level P11 ( P13 ). The third probe laser with wavelength λi=493.41 nm causes resonant fluorescence of barium ions. It is shown that the metastable D23 from the D1,2,33 triplet in barium is strongly populated through P11,3 levels. Therefore, the applying of the ionizing laser tuned to a continuum from this metastable D23 can yield a significant increase in the ionization efficiency. The laser-induced fluorescence method makes it possible to estimate the photoionization yield of barium ions with an error of up to 8%. The loading rate of the barium ion beam into the ion trap, obtained numerically, is consistent with the experimental data [Opt. Exp. 19(17), 16438 (2011)]. The deceleration of ultracold plasma recombination due to the heating of electrons in superelastic collisions for the characteristic times of a two-stage process is predicted.