Investigation on angular distribution of terahertz radiation from two noncollinear plasma filaments

Abstract Terahertz pulses, including a main pulse and a small pulse, radiated from two noncollinear femtosecond laser plasma filaments are analyzed with an iris in the terahertz beam. The experimental results exclude the possibility that the small terahertz pulses is from the misalignment of the optical system. The time delay between the two terahertz pulses is much longer than the propagation time of the laser pulses in the pre-plasma, thus this small terahertz pulse is induced by the laser field interaction with the pre-plasma, but not by the laser field-field interactions. The results show that the main terahertz pulse and the small terahertz pulse have obviously different angular distributions. Its underlying physical mechanisms are also discussed in the paper.