LAUSR

Abstract The interaction and the coupling between the plasma filaments introduce some ultrafast phenomena, which not only reveal deep physical mechanisms, but also provide clues to develop the plasma filament-based applications. In this paper, the terahertz (THz) radiation from two plasma filaments with opposite directions, which are produced by focusing two counter propagating femtosecond laser pulses with a pair of off-axis-parabolic mirrors, is measured using electro-optic sampling detection method. The experimental results show that the pre-plasma weakens the THz radiation in the cases of with and without an external biased field. The lifetime of the plasma filament is estimated using the time evolution of the THz peaks. It is found that the THz radiation keeps weaker even when one pump pulse is 300 ps before the other one, which indicates that the lifetime of the plasma filament is longer than 300 ps. In addition, the THz pulses have similar shapes at different time delays between two pump laser pulses. Its underlying physical mechanisms are discussed as well.