Abstract

By establishing a theoretical model for terahertz (THz) generation from a laser-induced air plasma filament and the subsequent propagation process, we study the physical mechanisms of THz wave radiation regulation in the multi-color femtosecond laser field. It is proved that the total THz radiation in the far field is affected by three factors: the ionized electron density, transient current distribution along the laser filament, and coherent superposition between THz waves generated by each point along the filament. The results show that the wavelength, relative phase, energy ratio, pulse width, laser frequency ratio, and frequency combination of the multi-color laser are all correlated to their radiated THz energy with different changing laws. The proper regulation of a three-color filament can realize a 4 orders of magnitude increase in the generated THz pulse energy as compared with the conventional THz generation by a two-color filament. These results provide the theoretical basis for the enhancement of THz radiation energy, and they are of great significance for clarifying the physical process of laser filament.

© 2020 Optical Society of America

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