Enabling high-precision 3D strong-field measurements - Ionization with low-frequency fields in the tunneling regime

TL;DR

This paper introduces a novel high-precision measurement technique for strong-field ionization using low-frequency fields, revealing new electron dynamics and momentum structures at near-threshold energies.

Contribution

It presents a method combining ultrafast mid-IR light sources and a reaction microscope to achieve meV-level precision in electron energy measurements in the tunneling regime.

Findings

Observation of near-zero momentum electrons

Detection of low momentum structures below 1 eV

High-precision measurements at 1 meV energy resolution

Abstract

Ionization of an atom or molecule presents surprising richness beyond our current understanding: strong-field ionization with low-frequency fields recently revealed unexpected kinetic energy structures (1, 2). A solid grasp on electron dynamics is however pre-requisite for attosecond-resolution recollision imaging (3), orbital tomography (4), for coherent sources of keV light (5), or to produce zeptosecond-duration x-rays (6). We present a methodology that enables scrutinizing strong-field dynamics at an unprecedented level. Our method provides high-precision measurements only 1 meV above the threshold despite 5 orders higher ponderomotive energies. Such feat was realized with a specifically developed ultrafast mid-IR light source in combination with a reaction microscope. We observe electron dynamics in the tunneling regime ({\gamma} = 0.3) and show first 3D momentum distributions demonstrating surprising new observations of near-zero momentum electrons and low momentum structures, below the eV, despite quiver energies of 95 eV.