Terahertz wave guiding by femtosecond laser filament in air

In this paper, superluminal propagation of terahertz (THz) pulse has been observed by investigating the THz waveform emitted from different length of filaments. Further numerical simulation has implied that a THz waveguide-like photonic structure may be formed in air, leading to the superluminal propagation of the THz pulse. The underlying physical mechanisms and the control techniques of this type THz generation method might be revisited based on our findings. It might also potentially open a new approach for long-distance propagation of THz wave in air.