Molecular Recollision Interferometry in High Harmonic Generation

TL;DR

This paper employs extreme-ultraviolet interferometry to measure and analyze the phase of high-order harmonic generation in aligned CO2 molecules, revealing molecular-scale quantum interferences and electron wave dispersion effects.

Contribution

It introduces a novel interferometric approach to measure harmonic phase and extract electron dispersion information in molecular HHG.

Findings

Reversal in harmonic phase observed at higher orders with increased molecular alignment

Quantum interference between molecular wave function and recolliding electron confirmed

Dispersion relation of the returning electron wavepacket characterized

Abstract

We use extreme-ultraviolet interferometry to measure the phase of high-order harmonic generation from transiently aligned CO2 molecules. We unambiguously observe a reversal in phase of the high order harmonic emission for higher harmonic orders with a sufficient degree of alignment. This results from molecular-scale quantum interferences between the molecular electronic wave function and the recolliding electron as it recombines with the molecule, and is consistent with a two-center model. Furthermore, using the combined harmonic intensity and phase information, we extract accurate information on the dispersion relation of the returning electron wavepacket as a function of harmonic order. This analysis shows evidence of the effect of the molecular potential on the recolliding electron wave.