Demonstration of an optical mixing technique to drive Kinetic Electrostatic Electron Nonlinear waves in laser produced plasmas

TL;DR

This paper demonstrates an optical mixing technique using shifted laser beams to drive and detect KEEN waves in laser-produced plasmas, revealing nonlinear wave phenomena beyond traditional plasma theory.

Contribution

It introduces a novel method of using Raman-shifted laser beams to experimentally generate and observe KEEN waves in plasma, confirming theoretical predictions.

Findings

Successful generation of KEEN waves in plasma

Detection of KEEN waves via Thomson scattering

Validation of nonlinear wave phenomena beyond linear theory

Abstract

A nitrogen gas Raman cell system has been constructed to shift a 70 J 527 nm laser beam to 600 nm with 20 J of energy. The 600 nm probe and a 200J, 527 nm pump beam were optically mixed in a laser produced (gas jet) plasma. The beating of the two laser beams formed a ponderomotive force that can drive Kinetic Electrostatic Electron Nonlinear (KEEN) waves discovered in Vlasov-Poisson simulations by Afeyan et al [1,2]. KEEN waves were detected in these experiments where traditional plasma theory would declare there to be a spectral gap (ie no linear waves possible). The detection was done using Thomson scattering with probe wavelengths of both 351 nm and 263.5 nm.