Directionality of THz emission from photoinduced gas plasmas

TL;DR

This paper investigates the directionality of terahertz (THz) emission from laser-induced gas plasmas, revealing differences in spectral bandwidth and generation mechanisms for forward and backward emissions through modeling and simulations.

Contribution

It introduces a semi-analytical model and simulations to explain the directional THz emission characteristics from gas plasmas, highlighting interference effects and ionization front dynamics.

Findings

Backward THz emission has a narrower spectral bandwidth.

Forward THz emission is generated at the ionization front.

Forward emission is less affected by plasma opacity.

Abstract

Forward and backward THz emission by ionizing two-color laser pulses in gas is investigated by means of a simple semi-analytical model based on Jefimenko's equation and rigorous Maxwell simulations in one and two dimensions. We find the emission in backward direction having a much smaller spectral bandwidth than in forward direction and explain this by interference effects. Forward THz radiation is generated predominantly at the ionization front and thus almost not affected by the opacity of the plasma, in excellent agreement with results obtained from a unidirectional pulse propagation model.