Terahertz radiation from extended two-colour air filaments

摘要

We investigate the pulse shape and intensity of terahertz (THz) radiation generated in extended air filaments, which are produced by focusing on fld = 42 and 83 of 1-2.3 mJ two-color femtosecond laser pulses. These consist of fundamental- and second-harmonic radiation. We show the intensity modulation caused by the screening of radiation from a part of the filament. This modulation is due to interference effects in the distributed plasma THz source and dependent on the initial phase shift between harmonics. We experimentally demonstrate the evolution of a THz pulse generated in different areas along plasma channel. We also perform spectral modulation of the emitted THz radiation by emphasizing distinct frequencies.