Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

J Venzke,A Becker,A Jaron-Becker

doi:10.1038/s41598-020-73196-9

Abstract

Progress in ultrafast science allows for probing quantum superposition states with ultrashort laser pulses in the new regime where several linear and nonlinear ionization pathways compete. Interferences of pathways can be observed in the photoelectron angular distribution and in the past they have been analyzed for atoms and molecules in a single quantum state via anisotropy and asymmetry parameters. Those conventional parameters, however, do not provide comprehensive tools for probing superposition states in the emerging research area of bright and ultrashort light sources, such as free-electron lasers and high-order harmonic generation. We propose a new set of generalized asymmetry parameters which are sensitive to interference effects in the photoionization and the interplay of competing pathways as the laser pulse duration is shortened and the laser intensity is increased. The relevance of the parameters is demonstrated using results of state-of-the-art numerical solutions of the time-dependent Schrödinger equation for ionization of helium atom and neon atom.

Highlights

Probing atoms and molecules in their ground or excited states with ultrashort laser pulses opens a new regime where several linear and nonlinear ionization pathways compete and interfere[20,21,22,23,24,25,26,27]
We propose a new set of generalized asymmetry parameters which are sensitive to interference effects in the photoionization of atomic systems in superposition states
The exemplary results obtained from the solutions of the time-dependent Schrödinger equation in Fig. 1 for the interaction of neon atom, prepared in the superposition of 2p−1 - and 3d2-states (d) or prepared in the same superposition but including ionization from the 2p0 and 2p1 ground states (e), with a linearly polarized laser pulse show that the photoelectron angular distributions (PADs) vary significantly as function of pulse duration and peak intensity

Summary

Introduction

Probing atoms and molecules in their ground or excited states with ultrashort laser pulses opens a new regime where several linear and nonlinear ionization pathways compete and interfere[20,21,22,23,24,25,26,27]. An atom in a superposition of two quantum states with different magnetic quantum numbers m, say the ground (g) and an excited (e) state is probed via ionization by an ultrashort linearly polarized laser pulse.

Results

Conclusion