Photoelectron spectroscopy of laser-dressed atomic helium

TL;DR

This paper investigates how laser fields influence photoelectron emission from excited helium atoms, revealing forbidden transitions and energy shifts through combined experimental measurements and numerical simulations.

Contribution

It provides new insights into laser-dressed atomic helium's photoelectron spectra by combining experimental XUV-IR measurements with theoretical Schrödinger equation solutions.

Findings

Identification of electric dipole-forbidden transitions.

Observation of laser intensity-dependent energy shifts.

Agreement between experimental data and numerical simulations.

Abstract

Photoelectron emission from excited states of laser-dressed atomic helium is analyzed with respect to laser intensity-dependent excitation energy shifts and angular distributions. In the two-color XUV (exteme ultra\-violet) -- IR (infrared) measurement, the XUV photon energy is scanned between \SI{20.4}{\electronvolt} and the ionization threshold at \SI{24.6}{\electronvolt}, revealing electric dipole-forbidden transitions for a temporally overlapping IR pulse ($\sim\!\SI{e12}{\watt\per \centi\meter\squared}$). The interpretation of the experimental results is supported by numerically solving the time-dependent Schr\"odinger equation in a single-active-electron approximation.