Direct observation of Space Charge Dynamics by picosecond Low Energy Electron Scattering

TL;DR

This study uses time-resolved low-energy-electron-scattering to directly observe and model the space charge dynamics caused by femtosecond laser pulses on copper, revealing Coulomb explosion behavior.

Contribution

It provides the first direct measurement and modeling of space charge evolution on femtosecond timescales using low-energy electron scattering.

Findings

Space charge causes Coulomb explosion with transients around 1 ns.

The electron cloud's initial size and number are quantified.

Experimental results agree with non-relativistic Coulomb explosion models.

Abstract

The electric field governing the dynamics of space charge produced by high intensity femtosecond laser pulses focused on a copper surface is investigated by time-resolved low-energy-electron-scattering. The pump-probe experiment has a measured temporal resolution of better than 35 ps at 55 eV probe electron energy. The probe electron acceleration due to space charge is reproduced within a 3-dimensional non-relativistic model, which determines an effective number of electrons in the space charge electron cloud and its initial diameter. Comparison of the simulations with the experiments indicates a Coulomb explosion, which is consistent with transients in the order of 1 ns, the terminal kinetic energy of the cloud and the thermoemission currents predicted by the Richardson-Dushman formula.