Probing electronic wavefunctions by all-optical attosecond interferometry

TL;DR

This paper introduces an all-optical interferometry technique using phase-locked attosecond pulses to directly measure electron wavefunction phases, revealing scattering and multi-electron effects in quantum systems.

Contribution

It presents a novel optical method for retrieving electron spectral phase information via attosecond interferometry, enabling direct phase measurements in quantum systems.

Findings

Measured phase shifts in helium and neon over large energy ranges.

Resolved dipole phase around the Cooper minimum in argon.

Detected phase signatures of multi-electron effects.

Abstract

Photoelectron spectroscopy is a powerful method that provides insight into the quantum mechanical properties of a wide range of systems. The ionized electron wavefunction carries information on the structure of the bound orbital, the ionic potential as well as the photo-ionization dynamics itself. While photoelectron spectroscopy resolves the absolute amplitude of the wavefunction, retrieving the spectral phase information has been a long-standing challenge. Here, we transfer the electron phase retrieval problem into an optical one by measuring the time-reversed process of photo-ionization -- photo-recombination -- in attosecond pulse generation. We demonstrate all-optical interferometry of two independent phase-locked attosecond light sources. This measurement enables us to directly determine the phase shift associated with electron scattering in simple quantum systems such as helium and neon, over a large energy range. In addition, the strong-field nature of attosecond pulse generation resolves the dipole phase around the Cooper minimum in argon through a single scattering angle, along with phase signatures of multi-electron effects. Our study bears the prospect of probing complex orbital phases in molecular systems as well as electron correlations through resonances subject to strong laser fields.