Attosecond delays of high harmonic emissions from isotopes of molecular hydrogen measured by Gouy phase XUV interferometer

TL;DR

This study precisely measures attosecond-scale phase differences in high harmonic emissions from isotopes of molecular hydrogen using a Gouy phase interferometer, revealing insights into molecular structure and electron dynamics.

Contribution

It introduces a novel interferometric technique for measuring harmonic phase differences between isotopes, advancing the understanding of molecular and nuclear effects in HHG.

Findings

Measured phase difference of about 200 mrad corresponding to 3 attoseconds.

Phase difference is nearly independent of harmonic order.

Results agree well with numerical simulations of molecular dynamics.

Abstract

High harmonic spectroscopy can access structural and dynamical information on molecular systems encoded in amplitude and phase of high harmonic generation (HHG) signals4. However, measurement of the harmonic phase is a daunting task. Here we present a precise measurement of HHG phase difference between two isotopes of molecular hydrogen using the advanced extreme-ultraviolet (XUV) Gouy phase interferometer. The measured phase difference is about 200 mrad, corresponding to 3 attoseconds (1 as = 10^-18 s) time delay which is nearly independent of harmonic order. The measurements agree very well with numerical calculations of a four-dimensional time-dependent Schroedinger equation. Numerical simulations also reveal the effects of molecular orientation and intra-molecular two-centre interference on the measured phase difference. This technique opens a new avenue for measuring the phase of harmonic emission for different atoms and molecules. Together with isomeric or isotopic comparisons it also enables the observation of subtle effects of molecular structures and nuclear motion on electron dynamics in strong laser fields.