Title : Efficiency of two-step photoionization of barium atoms through excited 3^P_1 level
Abstract:
The collisional-radiative model of two-step photoionization of barium atoms through the excited level using the pumping laser at nm and the ionizing laser at nm was constructed. The model of rate balance equations of multilevel barium atoms took into account the transfer of radiation at the atomic transition. The action of the probe laser at the wavelength nm was simulated to initiate resonance fluorescence. The problem has an integro-differential structure and it is solved by the method of numerical simulation in the optically dense approximation. The report demonstrates the results of modeling of the photoexcitation and photoionization kinetics of barium atoms and resonant fluorescence of barium ions. It is shown that the use of the method of quantitative spectral analysis in case of measuring the ionization yield of a barium ion beam for loading this beam into a optical trap can be considered justified. The prospects of increasing the efficiency of barium ionization in a two-step scheme using the excited level are related mainly to an increase in power of the ionizing laser, rather than the pumping one. The results of modeling of the ionization kinetics for the optically dense medium also indicate an increase in electron temperature by more than a factor of two from superelastic electron collisions with excited barium atoms over the typical ionization time. This fact suggests that the increase in the time of three-body recombination of the ultracold plasma observed in paper [Phys. Rev. Lett. 83 4776 (1999)] can be caused by the heating of electrons in superelastic processes. The numerically obtained rate of barium ion beam loading into an optical trap is consistent with the experimental data [Opt. Exp. 19(17), 16438 (2011)].
Audience Take Away Notes :
- The collisional-radiative model of barium photoplasma creation what describes the kinetic of two-step ionization of atoms and fluorescence of barium ion. The model takes into account the radiative transfer in the lines of atom ( , nm) and ion ( ).
- The laser-induced fluorescence method makes it possible to estimate the photoionization yield of barium ions with an error of up to 8%.
- Deceleration of the ultracold plasma recombination due to the heating of electrons from superelastic collisions for the characteristic times of a two-step process is predicted.
