Effect of Plasma Modulation on Terahertz Waves Emitted by Gas Filamentation

This paper adopts a method combining theoretical calculation and numerical simulation, and revisits the basic physical mechanism of terahertz generation by the interaction between femtosecond laser and plasma based on the photocurrent model via utilizing the time-domain finite-difference (FDTD) algorithm. We first explained the synchronization of terahertz emission and plasma step ionization under three-dimensional condition, and confirmed that the terahertz emission will be modulated during the plasma excitation process. Subsequently, by analyzing the effect of plasma modulation on the terahertz emission under near-field and far-field conditions, it was found that the two-color field mainly plays a role in exciting the plasma and generating photocurrent radiation, while the plasma plays the role in modulating photocurrent radiation and generates terahertz emission, confirming the important influence of plasma modulation on terahertz generation in three-dimensional conditions.