Hydrodynamic-PIC analysis of THz generation by two-color laser in various plasma gases

¹ Department of Physics, University of Tehran - Tehran 14399–55961, Iran
² Department of Atomic and Molecular Physics, Faculty of Physics, Alzahra University - Tehran, Iran

Received: 9 October 2025
Accepted: 18 November 2025

Abstract

In the present study, a theoretical and particle-in-cell (PIC) numerical investigation of terahertz (THz) emission driven by two-color femtosecond laser fields in gaseous plasmas is conducted. The model is formulated in cylindrical coordinates to capture the inherent radial symmetry of laser-plasma interactions. Starting from a hydrodynamic description of plasma electrons coupled with Maxwell's equations, the nonlinear photocurrent dynamics that underpin the emission process is derived. The results reveal that the asymmetry induced by the superposition of the fundamental and second-harmonic fields plays a central role in breaking inversion symmetry, thereby generating a net directional current that radiates in the THz regime. Systematic analysis demonstrates that gas composition, ionization fraction, and the intensity ratio of the two fields strongly influence both the spectral characteristics and efficiency of THz radiation.