Balance of emission from THz sources in DC-biased and unbiased filaments in air

Abstract

At the frequencies from 0.1 to 1 THz, we measured the angular distributions of terahertz (THz) emission from DC-biased femtosecond filament. The external electric field (DC bias) was increased from 0 to 3.3 kV/cm and provided continuous transition from forward conical emission, corresponding to the unbiased single-color filament, to on-axis emission, corresponding to the DC-biased one. We decomposed the measured far-field THz distributions into the quadrupole and dipole contributions, the latter being increased with increasing biasing field. The superposition of quadrupole and dipole local sources was integrated numerically over the plasma channel length and fit to the experimentally obtained angular distributions. The transition from the conical to the on-axis emission occured at the external field of (3.2 ± 0.8) kV/cm in the range of frequencies studied.

Plasma-based terahertz wave photonics in gas and liquid phases

“…Such a PC can control the polarization and phase of each optical beam individually for coherent control of the THz emission [11] . THz wave emission from biased gas plasma or plasma filaments in ambient air can be classified to the case of single-wavelength laser excitation [20,22,25,46,66,69–79] . The use of single-color few-cycle laser pulses to ionize gases for intense THz wave emission can be classified into both cases [80] , since, very similar to the asymmetric optical fields synthesized from two-color optical fields, a few-cycle laser field itself can produce asymmetric fields by properly controlling the carrier–envelope phase without the involvement of the SH laser field.…”