THz Frequency Modulation by Filamentary Plasma Grating

The frequency of terahertz pulse induced by dual-color laser-induced plasma filament was measured at different positions of the filament to analyze terahertz generation processes. It was experimentally observed that the most broad frequency bandwidth was attained at the tail of laser-induced plasma filament and more higher frequency components were generated under the intervention of filamentary plasma grating, which was attributed to the increased peak electron density from inelastic collisional ionization, while another infrared pulse was focused on the plasma grating to reaccelerate preformed electrons. The results demonstrated that the electron reacceleration process played an important role in determining terahertz frequency bandwidth.