Coherent interaction between the terahertz radiation emitted by filaments in air

In this article, terahertz (THz) radiation emitted by femtosecond laser pulses undergoing filamentation in air is reviewed. The origin of this radiation stems from longitudinal oscillations inside the plasma column created during filamentation. Particular attention is given to THz radiation originating from two distinct filaments, either parallel to each other or forming an angle (Vee arrangement). For these two schemes the radiation pattern and the polarization properties of the total THz radiation are calculated and verified experimentally. A method of effective spectral enhancement of THz radiation will be discussed. Finally, it will be shown that the Vee arrangement allows obtaining circularly-polarized THz radiation.