Numerical study of Langmuir wave coalescence in laser-plasma interaction

TL;DR

This paper uses particle-in-cell simulations to analyze how laser interactions with plasma can produce Langmuir wave coalescence and electromagnetic emissions, shedding light on laboratory and space plasma phenomena.

Contribution

First numerical analysis of laser-induced Langmuir wave coalescence in plasma using particle-in-cell simulations, detailing wave spectra and parameter effects.

Findings

Electromagnetic emission occurs at twice the plasma frequency.

Laser intensity influences the angular distribution and polarization of emissions.

Simulation results match experimental observations of plasma emissions.

Abstract

Type-III-burst radio signals can be mimicked in the laboratory via laser-plasma interaction. Instead of an electron beam generating Langmuir waves (LW) in the interplanetary medium, the LWs are created by a laser interacting with a millimeter-sized plasma through the stimulated Raman instability. In both cases, the LWs feed the Langmuir decay instability which scatters them in several directions. The resulting LWs may couple to form electromagnetic emission at twice the plasma frequency, which has been detected in the interplanetary medium, and recently in a laboratory laser experiment [Marqu\`es et al. Phys. Rev. Lett. 124, 135001 (2020)]. This article presents the first numerical analysis of this laser configuration using particle-in-cell simulations, providing details on the wave spectra that are too difficult to measure in experiments. The role of some parameters is addressed, with a focus on laser intensity, in order to illustrate the behavior of the electromagnetic emission's angular distribution and polarization.