Revealing plasma oscillation in THz spectrum from laser plasma of molecular jet

TL;DR

This study reveals how plasma oscillations influence broadband terahertz emission from laser-induced plasma in a molecular jet, showing the effects of plasma density on THz spectral shifts and providing a simulation-based explanation.

Contribution

It demonstrates the role of plasma oscillations in broadband THz generation and explains spectral shifts through combined experimental and simulation analysis.

Findings

THz spectral shifts correlate with plasma density changes

Plasma oscillation contributes to low-density THz emission

Simulation explains broadband spectrum and spectral variations

Abstract

Contribution of plasma oscillation to the broadband terahertz emission is revealed by interacting two-color laser pulses with a supersonic jet of nitrogen molecules. Temporal and spectral shifts of THz waves are observed as the plasma density varies. The former owes to the changing refractive index of the THz waves, and the latter correlates to the varying plasma frequency. Simulation of considering photocurrents, plasma oscillation and decaying plasma density explains the broadband THz spectrum and the varying THz spectrum. Plasma oscillation only contributes to THz waves at low plasma density owing to negligible plasma absorption. At the longer medium or higher density, the combining effects of plasma oscillation and absorption results in the observed low-frequency broadband THz spectra.