Identifying Mechanism of Energy-Resolved Attoclock

TL;DR

This paper investigates how nonadiabatic effects influence the energy-dependent attoclock offset angle in above-threshold ionization, revealing the interplay between laser ellipticity, Coulomb effects, and electron dynamics.

Contribution

It provides a detailed analytical and numerical model that isolates nonadiabatic and Coulomb effects, clarifying the mechanism behind energy-resolved attoclock angles.

Findings

Nonadiabatic effects cause angle shifts from 0° to 90° across energy rings.

Coulomb effects soften the nonadiabatic influence, leading to smooth angle increase.

The model decouples complex effects, offering clear mechanistic insights.

Abstract

We study above-threshold ionization (ATI) of atoms in strong elliptical laser fields numerically and analytically. Recent benchmark experiments for H showed that the attoclock offset angle related to each ATI ring increases remarkably with energy and this characteristic phenomenon can be attributed to the laser-induced nonadiabatic initial velocity and position of the electron at the tunnel exit [PRL127, 273201 (2021)]. However, the specific mechanism of how the nonadiabatic effects influence this angle remains unclear. Here, by using a strong-field model that analytically and quantitatively decouples complex nonadiabatic effects and Coulomb effects, the detailed mechanism can be clearly identified. We show that due to nonadiabatic effects, the angles associated with lower (higher) energy rings are dominated by the main (minor) axis of the laser ellipse, jumping from $0^o$ to $90^o$. These field-related rigid effects are softened by Coulomb-induced exit velocity closely related to system symmetry, resulting in a significant but smooth increase in angle with energy.