Abstract

For the past two decades, intense lasers have supported new schemes for generating high-energy particle beams in university-scale laboratories. With the direct laser acceleration (DLA) method, the leading part of the laser pulse ionizes the target material and forms a positively charged ion plasma channel into which electrons are injected and accelerated. DLA has been realized over a wide range of laser parameters, using low-atomic-number target materials. In this presented work we reveal that at these higher laser intensities, the leading edge of the laser pulse depletes the target material of its ionization electrons prematurely. We demonstrate experimentally and numerically that for efficient DLA to prevail, a target material of sufficiently high atomic number is required to maintain the injection of ionization electrons at the peak intensity of the pulse when the DLA chan-nel is already formed.

© 2023 The Author(s)