A Study on Angular Distribution of THz Radiation Driven by Two-Color Laser-induced Microplasma

TL;DR

This paper develops an analytical model to analyze how two-color laser-induced microplasma in nitrogen gas emits THz radiation in different directions, considering polarization and phase effects, and demonstrates control over the radiation pattern.

Contribution

It extends the photo-current model to three dimensions and explores the influence of polarization and phase difference on THz angular distribution.

Findings

Second harmonic significantly influences THz polarization and distribution.

Rotating the radiation pattern is possible with circular polarization by adjusting phase.

The model accurately predicts direction-dependent THz waveforms.

Abstract

We present an analytical method to study the angular distribution of THz radiation driven by two-color laser-induced microplasma in nitrogen gas. Directionally dependent temporal waveforms of the radiated THz pulse is calculated. To do so, we have extended the photo-current model to calculate three-dimensional distribution of the photo-induced current from which the far field THz radiation is computed. We have also studied the effect of optical polarization state and phase difference on the angular distribution of radiation. Our study shows that for two orthogonally-polarized colors, not only THz polarization state, but also the angular distribution of THz radiation is mostly influenced by the second optical harmonic. The possibility of rotating the angular radiation pattern around the axis of the laser propagation is illustrated for circularly-polarized laser drivers by changing the optical phase difference.