Observation of Ion-wave Satellites to Laser Harmonics in Intense Picosecond Laser-Solid Interaction

TL;DR

This paper reports the first observation of ion-wave satellites to laser harmonics in intense laser-solid interactions, revealing how strong optical fields modify plasma wave dynamics and Debye shielding.

Contribution

It provides experimental evidence of ion-wave satellites and explains their frequency shifts through a novel understanding of Debye shielding reduction under intense laser fields.

Findings

Observation of red- and blue-shifted harmonic satellites

Frequency shifts less than expected for ion-plasma waves

Reduction of Debye shielding in intense laser fields

Abstract

Detailed spectra of harmonics produced from ultra-intense, sub-picosecond, high-contrast laser pulses incident on solid targets have shown the first observation of regular red- and blue-shifted satellites. Their frequency shift is slightly less than the frequency of a nominal, pure ion-plasma wave associated with electron critical density, where an ion-acoustic wave would be expected. We explain this as the result of a substantial reduction of Debye shielding as the intense optical fields compete to drive electrons in large-amplitude oscillations. This general effect leads to a larger, dynamical and anisotropic Debye length, which should have a broad impact on plasma physics in this regime.