Broadening of Cyclotron Resonance Conditions in the Relativistic Interaction of an Intense Laser with Overdense Plasmas

TL;DR

This paper investigates how intense lasers interacting with overdense plasmas under strong magnetic fields can induce broadening of cyclotron resonance conditions, enabling deeper plasma penetration and efficient electron acceleration.

Contribution

It reveals that relativistic electrons cause a broadening of cyclotron resonance conditions, expanding the range of magnetic fields for effective plasma interaction.

Findings

Cyclotron resonance absorption is effective over a wider magnetic field range due to relativistic effects.

The upper limit of magnetic field for resonance scales with the square root of laser intensity.

Propagation of large-amplitude whistler waves can enhance plasma heating and particle acceleration.

Abstract

The interaction of dense plasmas with an intense laser under a strong external magnetic field has been investigated. When the cyclotron frequency for the ambient magnetic field is higher than the laser frequency, the laser's electromagnetic field is converted to the whistler mode that propagates along the field line. Because of the nature of the whistler wave, the laser light penetrates into dense plasmas with no cutoff density, and produces superthermal electrons through cyclotron resonance. It is found that the cyclotron resonance absorption occurs effectively under the broadened conditions, or a wider range of the external field, which is caused by the presence of relativistic electrons accelerated by the laser field. The upper limit of the ambient field for the resonance increases in proportion to the square root of the relativistic laser intensity. The propagation of a large-amplitude whistler wave could raise the possibility for plasma heating and particle acceleration deep inside dense plasmas.