Above-threshold ionization at laser intensity greater than $10^{20}$ W/cm$^{2}$

TL;DR

This paper reports the first experimental observation of above-threshold ionization electrons from neon K-shell at laser intensities above 10^{20} W/cm^{2}, revealing high-energy electrons and scattering behaviors.

Contribution

It provides the first experimental measurement of ATI electrons at ultra-high laser intensities exceeding 10^{20} W/cm^{2}, including energy thresholds and angular distributions.

Findings

Threshold intensity for energetic ATI electrons is around 2×10^{20} W/cm^{2}.

Maximum electron energy exceeds 10 MeV.

L-shell electrons are scattered further forward than expected.

Abstract

We present the first experimental observation of above-threshold ionization (ATI) electrons produced by ionization of the neon K-shell in a laser field where intensity exceeds 10$^{20}$ W/cm$^{2}$. An array of plastic scintillating calorimeter detectors was used to measure the high-energy electrons at four angles in the laser forward direction. Coarse energy resolution was obtained using aluminum filters of several thicknesses to block lower-energy electrons. A threshold intensity around $2 \times 10^{20}$ W/cm$^{2}$ is observed for production of energetic ATI electrons in the laser forward direction, with maximum electron energy exceeding 10 MeV. L-shell electrons with energies < 1.4 MeV are scattered further forward along the laser direction than expected. We present comparisons of the measured total electron energies to the predictions of a Monte Carlo models employing the ADK-PPT ionization model and the Augst barrier suppression ionization model.