Enhanced forward THz yield from the long DC-biased femtosecond filament

We observed huge, almost two orders of magnitude, increase in the energy of the forward terahertz (THz) emission by the long femtosecond filament if transverse electrostatic field is applied along its full length. This proves summation of emission both from different parts of a single filament and from multiple filaments. The observed THz radiation has a narrow angular shape with a maximum in the direction of laser radiation and a spectrum in the range of 0.05-0.3 THz with a maximum at about 0.1 THz. Numerical simulations based on the UPPE well explain the experimental findings.