Two-step photoionization of barium atoms through excited 1,3P1 levels in optical dense approximation

The kinetics of two-step photoionization of barium atoms through excited P-1,3(1) levels was studied by numerical simulation method in the optically dense approximation. The first laser at wavelength lambda(1) = 553.5 nm (lambda(1) = 791 nm) pumps transition S-1(0) ? P-1 (1 )(S-1(0 )? P-3 (1)). The second laser with lambda(2) = 266 nm (lambda(2) = 310 nm) ionizes atoms from the level P-1(1 )(P-3(1)). The third probe laser with wavelength lambda(i) = 493.41 nm causes resonant fluorescence of barium ions. It is shown that the metastable D-3(2) from the (3)D(1,2,3 )triplet in barium is strongly populated through P-1,3(1) levels. Therefore, the applying of the ionizing laser tuned to a continuum from this metastable D-3(2) 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.