Capture into Rydberg states and momentum distributions of ionized electrons

TL;DR

This paper investigates the process of electron capture into Rydberg states and the resulting momentum distributions after ionization in combined Coulomb and laser fields, using simulations and analytic models.

Contribution

It introduces a semiclassical model for electron capture into Rydberg states and analyzes how initial conditions influence capture and momentum distributions.

Findings

Electrons with moderate drift momentum and avoiding hard collisions are mainly captured.

Capture significantly affects the electron momentum distribution, creating a dip at zero momentum.

The study provides scaling relations and analytic estimates for Rydberg state population.

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.