Mode-Selective Laser Propagation and Absorption in Strongly Magnetized Inhomogeneous Plasma

TL;DR

This paper analyzes how strongly magnetized inhomogeneous plasma affects laser propagation and absorption, revealing conditions for efficient energy transfer and novel wave behaviors like whistler mode propagation.

Contribution

It provides analytical models and simulations to understand mode-specific laser absorption and propagation in strongly magnetized inhomogeneous plasma, including cutoff conditions and scaling laws.

Findings

L waves reflect at cutoff density with enhanced absorption at higher magnetic fields.

R-waves' absorption decreases with magnetic field when electron cyclotron frequency is below unity.

R-waves can penetrate overdense plasma as whistler modes when cyclotron frequency exceeds unity.

Abstract

We systematically investigate the field-aligned propagation and collisional absorption of normally incident laser light in a strongly magnetized inhomogeneous plasma. Analytical expressions for electric fields in both vacuum and plasma are derived. Using analytical modelling and particle-in-cell simulations, we establish the cutoff conditions, absorption efficiencies, and scaling laws for the right-hand (R) and left-hand (L) circularly polarized waves. The dependence of collisional absorption coefficient on magnetic field strength, plasma scale length and laser intensity are quantified. In particular, L waves reflect at cutoff density, with absorption strongly enhanced as the magnetic field increases. For the R-waves, the absorption decreases with increasing magnetic field when the normalized electron cyclotron frequency is less than unity. However, when it exceeds unity, the R-waves propagate as whistler modes without a cutoff, allowing penetration into overdense plasma. This enables deep energy deposition inside overdense plasma. These results provide a framework for understanding laser-plasma energy coupling through collisional absorption in strongly magnetized inhomogeneous plasma.