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

• Published in: Optics express Vol. 29; no. 25; p. 40687
• Main Authors: Shipilo, D. E., Nikolaeva, I. A., Pushkarev, D. V., Rizaev, G. E., Mokrousova, D. V., Koribut, A. V., Grudtsyn, Ya. V., Panov, N. A., Seleznev, L. V., Liu, W., Ionin, A. A., Kosareva, O. G.
• Format: Journal Article
• Language: English
• Published: 06.12.2021
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.442534

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.