); [EMAIL_ADDRESS] (K.M. ); [EMAIL_ADDRESS] (S.G.)  
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, 119991 Moscow, Russia; ushakov.leksandr@physics. The interplay between different mechanisms of THz generation in the filament has been studied for more than ten years. The interference in spatial domain between the radially and linearly polarized THz emission from DC-biased filament was reported in [13; 21; 22] for an external field of about 1 kV/cm. For the electric field strength of 5 kV/cm and larger, the linearly polarized THz emission dominates. The competition between the mechanisms of THz generation in DC-biased filament was recently experimentally studied in Ref. [23]. The analysis of THz spectra measured by electro-optical sampling shows that the balance between the sources of radially and linearly polarized THz emission occurs for the electrostatic field of 300 V/cm [23]. The joint effect of the external DC bias and the second harmonic on THz yield, or, in other words, THz generation from a DC-biased two-color (\(\omega+2\omega+DC\)) filament, has been experimentally studied in Ref. [15]. In the case of an external electrostatic field orthogonal to the \(\omega\) pulse polarization, [PERSON] et al. [15] suggested that the THz emission could be the sum of two components: one generated by two-color (\(\omega+2\omega\)) laser-induced filamentation and the second induced by the DC electric field. To provide a well-controlled comparison of THz signal from \(\omega+2\omega\) and \(\omega+DC\) filaments, [PERSON] et al. [24] superimposed the THz waveforms measured for \(\omega+2\omega+DC\) filament with opposite polarities to the DC-bias, assuming that THz signals produced with and without external electrostatic field are added coherently. This method suggests that half a sum of two THz waveforms, obtained for the opposite directions of the external electrostatic field, highlights the contribution from the \(\omega+2\omega\) source. In Ref. [25] the \(\omega+2\omega+DC\) filament was shown to be a promising tool for THz generation with tunable spectrum. Besides, control of the THz spectrum width and modulation is important for the \"false\" absorption frequency identification when performing THz spectroscopy, especially when the reflection from the layered structures is considered [12]. In atmospheric air, the tunability of the THz spectrum from a DC-biased plasma channel cannot be large, because the DC field is limited by static breakdown threshold. However, this method can be improved by considering gases with variable density or even liquids. Indeed, impressive conversion from \(\omega+2\omega\) to THz radiation was found in the insulator liquids [26], which have a higher breakdown threshold, thus providing a lot more freedom for spectral shaping using DC bias. In this work, we experimentally study the THz emission from the DC-biased two-color (\(\omega+2\omega+DC\)) filament with the DC field parallel to polarization of the second harmonic and orthogonal to the fundamental light field polarization. In this case, the THz emission of both \(\omega+DC\) and \(\omega+2\omega\) sources is polarized along the DC field. Terahertz waveforms measured in the temporal domain are found to be the superposition of electromagnetic fields emitted by the air-based plasma in the presence of the second harmonic pulse and the DC bias. Numerical \((t,r)+z\) simulations based on the Unidirectional Pulse Propagation Equation (UPPE, [27]) and performed separately for \(\omega+DC\), \(\omega+2\omega\) and \(\omega+2\omega+DC\) sources in the conditions of the experiment reveal that biasing the two-color pulse with the DC field results in linear addition (superposition) of the THz waveforms. The paper is organized as follows. Section 2 describes the experimental setup capable of switching the electrostatic field on and off. In the same Section 2, the \(3D+\)time numerical approach to propagate the light field in air and to obtain the THz waveforms self-consistently from the simulations is presented.