Collisionless Absorption of Intense Laser Beams by Anharmonic Resonance

TL;DR

This paper identifies anharmonic resonance as the primary physical mechanism behind collisionless laser energy absorption in overdense plasmas, advancing understanding of laser-plasma interactions.

Contribution

It demonstrates that anharmonic resonance in plasma or electron potentials is the key process for collisionless absorption, providing a new physical insight.

Findings

Anharmonic resonance causes phase shifts enabling energy transfer.

Resonance explains collisionless absorption in overdense plasmas.

A new wave breaking scenario is proposed.

Abstract

Two decades after the invention of chirped pulse amplification the physical mechanism of collisionless absorption of intense laser radiation in overdense matter is still not sufficiently well understood. We show that anharmonic resonance in the self-generated plasma potential of the single plasma layers (cold plasma model) or of the individual electrons (warm plasma), respectively, constitutes the leading physical mechanism of collisionless absorption in an overdense plasma. Analogously to collisions, resonance provides for the finite phase shift of the free electron current relative to the driving laser field which is compulsory for energy transfer from the laser beam to any medium. An efficient new scenario of wave breaking is also indicated.