Physical mechanisms encoded in photoionization yield from IR+XUV setups

Thomas Brabec,Éric Suraud,Congzhang Gao,Chris Mcdonald,Paul-Gerhard Reinhard,Phuong Mai Dinh

doi:10.1140/epjd/e2019-90507-4

Abstract

We theoretically examine how and to which extent physical processes can be retrieved from two-color pump-probe experiments of atomic and molecular gases driven by an attosecond XUV pulse train and an infrared (IR) pulse. The He atom, the N2 molecule and Na clusters are investigated with time-dependent density functional theory. Results are interpreted on the basis of a simple model system. We consider observables most commonly used in experiments: ionization yield, photo-electron spectra, and angular distributions. We find that the basic time-dependent signatures are dominated by the interplay of IR laser and continuum electrons. System information, contained in the signal, will in general require careful disentangling from the effects of photon-electron dynamics.Graphical abstract

Highlights

To analyze general effects of photonelectron dynamics from system properties, we developed a schematic model with one or two bound states, electron continuum, and photon field
We looked mainly at the ionization yield as a function of delay time and its Fourier analysis
We have shown that the universal modulation by the IR frequency strongly dominates the signals

Summary

Introduction

A significant number of two-color experiments have focused on the ionization yield of atoms [12,18,19,20] and small molecules [21,22,23,24,25], as a function of delay These experiments are driven by the goal to extract system-relevant information from the measured data. XUV (X) attosecond train) in two realistic examples (He atom, Na+9 cluster), and employ a simple (mostly analytical) model to work out dominant mechanisms in the measured ionization signal as a function of delay. A crucial parameter is td, the delay time taken here between the maxima of the XUV train and the IR pulse In such an experimental setup, a standard observable is the total ionization Y, which emerges after applying the pulse.

Two realistic examples

A simple model

Variation of systems and conditions

The N2 dimer

Excitation near plasmon resonance

Summary and conclusions