Characterization of terahertz emission from a dc-biased filament in air

Abstract

We demonstrate that the terahertz emission from a dc-biased filament can be regarded as a sum of an elliptically polarized terahertz source (generated by a filament without external electric field) and a linearly polarized terahertz source induced by the external electric field applied to the filament. The peak frequency and linewidth of the linearly polarized terahertz source are related to the average plasma density of the filament.

Generation of Elliptically Polarized Terahertz Waves from Laser-Induced Plasma with Double Helix Electrodes

“…[13][14] In all these experiments, the trajectory of released electrons, which contribute to the THz polarization state, is determined by the direction of the external field or the relative phase of two-colored optical fields. Although an imperfection of THz polarization state such as elliptical polarization from these plasma sources has been reported, [13,15] insightful physical and theoretical explanation are required for further polarization control and manipulation.…”

“…[10][11]16] This drifting current, which contributes to the far-field THz radiation, is aligned with the direction of an external DC field [12,15] or asymmetric optical field. [13][14] In our experiment with a pair of double helix electrodes, during the travel of the ionization front, which associates with the propagation of intense laser pulses, the induced net electron current is revolving along the filament due to the longitudinal variation of applied DC electrical field.…”

Intense broadband THz generation from femtosecond laser filamentation

“…For example, by applying a transverse DC bias to the plasma region, an order-ofmagnitude increase in the THz field was reported by Löffler et al [5,6] . Recently, Houard et al [7] and Chen et al [8] have applied external electric fields transversely to single-color filaments and Liu et al [9] have applied an external electric filed longitudinally to single-color filaments. 3 orders enhancement of THz amplitude with up to 10 kV/cm external electric field has been reported [7] .…”

THz radiation from an ultrashort-laser-induced fast spark dense plasma

“…Note that THz radiation with 0.1−0.3 THz has been observed in a single color laser field [9]. In addition, the radiation frequency was almost constant from laser-induced filaments in air with DC bias [10]. On the other hand, the model to explain the generation of THz radiation in air includes the plasma frequency [11].…”