Emergence of a higher energy structure in strong field ionization with inhomogeneous electric fields

TL;DR

This paper shows that small spatial inhomogeneities in laser fields can produce a higher energy peak in electron spectra during strong field ionization, enabling potential attosecond electron pulse sources.

Contribution

It introduces the concept of a higher energy structure (HES) caused by inhomogeneous fields, demonstrated through combined quantum and classical simulations.

Findings

HES appears above the classical cut-off energy.

HES is highly sensitive to the carrier envelope phase.

HES can be used to generate attosecond electron pulses.

Abstract

Studies of strong field ionization have historically relied on the strong field approximation, which neglects all spatial dependence in the forces experienced by the electron after ionization. More recently, the small spatial inhomogeneity introduced by the long-range Coulomb potential has been linked to a number of important features in the photoelectron spectrum, such as Coulomb asymmetry, Coulomb focusing, and the low energy structure (LES). Here, we demonstrate by combined quantum and classical simulations that a small time-varying spatial dependence in the laser electric field creates a prominent higher energy peak at energies above the "classical cut-off" for direct electrons. This higher energy structure (HES) originates from direct electrons ionized near the peak of a single half-cycle of the laser pulse. The HES is separated from all other ionization events (providing sub-cycle resolution) and is highly sensitive to the carrier envelope phase (CEP). The large accumulation of electrons with tuneable energy suggests a promising method for creating a localized source of electron pulses of attosecond duration using tabletop laser technology.