Disentangling the Sub-Cycle Electron Momentum Spectrum in Strong-Field Ionization

TL;DR

This paper introduces a technique to extract sub-cycle electron interference features from multi-cycle strong-field ionization spectra, revealing detailed structures that enhance understanding of attosecond electron dynamics.

Contribution

A simple time-filtering method is proposed to isolate sub-cycle interference patterns in multi-cycle spectra, overcoming limitations of previous experimental approaches.

Findings

Revealed new modulations in holographic interference structures.

Successfully isolated sub-cycle features from multi-cycle spectra.

Provided a new benchmark for theoretical calculations.

Abstract

Quantum calculations of tunneling in strong-field ionization (SFI) predict intricate momentum distributions due to sub-laser-cycle attosecond electron dynamics. These are obscured in most experiments by the dominance of inter-cycle interference patterns which are the hallmark of above-threshold ionization (ATI). Highly controlled 1- to 2-cycle laser pulses produce less inter-cycle interference but cannot accurately recreate the sub-cycle features produced by uniform cycle calculations due to the effect of the carrier envelope of the pulse. We present a simple and effective technique to recover these sub-cycle features in experimental multi-cycle spectra. We time-filter the momentum distribution to highlight features originating from the interference of electron trajectory pairs with ionization times less than one field cycle apart. This method removes the ATI patterns and reveals sub-cycle interference structures in unprecedented detail. We can resolve new modulations in holographic structures that have not been previously noted in earlier experiments and which provide a new reference for comparing to calculations.