Capture into rydberg states and momentum distributions of ionized electrons

Abstract

The yield of neutral excited atoms and low-energy photoelectrons generated by the electron dynamics in the combined Coulomb and laser field after tunneling is investigated. We present results of Monte-Carlo simulations built on the two-step semiclassical model, as well as analytic estimates and scaling relations for the population trapping into the Rydberg states. It is shown that mainly those electrons are captured into bound states of the neutral atom that due to their initial conditions (i) have moderate drift momentum imparted by the laser field and (ii) avoid strong interaction ("hard" collision) with the ion. In addition, it is demonstrated that the channel of capture, when accounted for in semiclassical calculations, has a pronounced effect on the momentum distribution of electrons with small positive energy. For the parameters that we investigated its presence leads to a dip at zero momentum in the longitudinal momentum distribution of the ionized electrons.

Photoelectron spectra and high Rydberg states of lithium generated by intense lasers in the over-the-barrier ionization regime

“…(2) Why do they survive the intense laser field (Q2)? These questions have been addressed in the literature in the past: one is the interference stabilization (IS) model [40,41,45], the other is the rescattering (RS) model [36,46]. In the RS model, the Rydberg states are formed by recombination of the returning electrons with the ion, at the end of the laser pulse.…”

“…In the RS model, the Rydberg states are formed by recombination of the returning electrons with the ion, at the end of the laser pulse. The RS model does not have to deal with Q2, but this model has been refuted [41,47], since a recombination would have to involve the emission of radiation which was not considered in the RS model according to [36,46]. In the IS model, Rydberg states are formed in the early part of the laser pulse (Q1); the survival of Rydberg states in the laser field (Q2) is explained (or modeled) by destructive interference of -type Raman transitions via the continuum states.…”

The plateau in above-threshold ionization: the keystone of rescattering physics

“…The dots scattered over the plot reflect the fact that in a part of this region the mapping is chaotic, in the sense of a sensitive dependence on the initial conditions (see, e.g., [174]). Other electrons from this region end up with negative energy at the end of the pulse, i.e., they remain bound [171,175]. The respective points were eliminated from figure 12 giving rise to the empty area around zero momentum.…”

“…We proceed by starting classical trajectories at the exit of the tunnel [171][172][173]. At the time t 0 when the electron becomes free, we fix its initial velocity, viz.…”

Dynamical Characteristics of Rydberg Electrons Released by a Weak Electric Field

“…Those experiments were the first to report a "zero-peak", i. e. an extremely narrow contribution of near-zero momentum electrons [18], subsequently confirmed and attributed to Rydberg electrons [19]. We use standard tunnel-ionization probabilities [11,20] and propagate electrons according to Newton equations of motion for about 10 7 trajectories with the Hamiltonian (1), i. e., in the attractive Coulomb potential, the driving laser pulse f (t) cos ωt and the extraction field F . Hence, the calculations comprise the formation of Rydberg electrons [2] as well the subsequent Stark dynamics.…”