Terahertz emission from a single-color ultraviolet filament

Terahertz (THz) emission from a single-color ultraviolet (UV) (248 nm) filament in air is studied experimentally and compared to that of an infrared (IR) (744 nm) filament for similar pulse durations, focusing conditions, and excess of pulse power over the critical power for self-focusing. An angular distribution of the THz emission for both UV and IR filaments is conical with the close cone angle. In contrast, the THz radiation energy and spectrum differ significantly. The energy of THz emission from the UV filament is 1–2 orders of magnitude lower than the THz yield from the IR filament. The THz spectrum of the UV filament is shifted to the low-frequency range and is narrower compared to the spectrum of THz emission from the IR filament. We explain qualitatively the difference in THz yields and spectra by lower intensity and plasma density in the UV filament.