Three-body recombination of ultracold barium plasma created by two-step photoionization of atoms through an excited 6s6p P11 level

Abstract

The kinetics of ionization and recombination of an ultracold barium plasma created in a two-step process, taking into account the transfer of resonant radiation in 3D cylindrical geometry, is studied by numerical simulation. At the first step, a pump laser excites the upper level of the resonant transition 6s2 S10↔6s6p P11 (λ1=553.5 nm). At the second step, the laser with quantum energy exceeding the ionization potential from the level 6s6p P11 (λ2=417.79 nm) ionizes the atoms. A scheme is proposed for increasing the efficiency of electron yield: at the second ionization step, the laser radiation with frequency corresponding to the continuum from the metastable D32 is used. The electron temperature from the initial value 0.1 K during the action of the pump and ionizing lasers increases by more than 200 times due to superelastic processes. As a result, the time of three-body recombination of plasma increases significantly. The results of numerical simulation indirectly confirm the fact of Killian et al. [Phys. Rev. Lett. 83(23), 4776 (1999)] that the deceleration of recombination of ultracold xenon plasma can be explained by the heating of electrons in superelastic quenching collisions.