Photoelectron angular distribution from the high-order above-threshold ionization process in IR+XUV two-color laser fields

TL;DR

This paper investigates the angular distribution and spectral features of high-order above-threshold ionization in IR+XUV laser fields, revealing how photon absorption and electron collision dynamics shape the observed patterns.

Contribution

It introduces a detailed analysis of the dip structures and interference patterns in HATI spectra, linking them to photon absorption and collision processes in two-color laser fields.

Findings

Dip structure in the spectrum is related to XUV photon absorption during laser-assisted collision.

Angular distribution results from coherent summation over different ionization channels.

Interference patterns arise from orbit interference at specific collision times.

Abstract

High-order above-threshold ionization (HATI) spectrum in IR+XUV two-color laser fields has been investigated. We found that the quantum features corresponding to the absorption of the XUV photon is well illustrated by a peculiar dip structure in the second plateau of the HATI spectrum. By the channel analysis, we show that the angular distribution of the spectrum is attributed to the coherent summation over contributions of different channels, and the dip structure in the spectrum is directly related to the absorption of one XUV photon of the ionized electron during the laser-assisted collision (LAC) with its parent ion in the two-color laser fields. Moreover, by employing the saddle-point approximation, we obtain the classical energy orbit equation, and find that the dip structure comes from the fact that the LAC is limited at a certain direction by the momentum conservation law as the electron absorbs one XUV photon during the collision, where the probability of the HATI gets its minimum value. Finally, we find that the interference pattern in the whole spectrum is attributed to the interference of different orbits at collision moments $t_0$ and $2\pi/\omega_1-t_0$ in the LAC process.