Plasma mechanisms of pulsed terahertz radiation generation

Abstract

We present the results on generating terahertz radiation in the plasma of an optical discharge arising in the atmosphere during the focusing of femtosecond laser radiation. Different generation schemes related to focusing of the optical radiation by spherical and axicon lenses, with a constant electric field imposed on the laser spark region, as well as with the use of bichromatic laser radiation, are studied. Directivity patterns and polarization distributions of the terahertz radiation are analyzed in detail for different generation techniques. Comparison with the experimental results obtained by other research groups is given. Possible nonlinear mechanisms of the terahertz radiation generation are discussed.

Terahertz radiation from air plasma, generated by linearly polarized femtosecond pulses with short focal length lens

“…This effect depends on geometric parameters of plasma column (plasma wave length to column diameter ratio). For the chosen parameters results show good agreement with experimental data [4].…”

“…In the common scheme of generation using short focal length (80-400mm) parabolic lens, short laser pulse (50fs, 2.5 mJ) with linear polarization a radiation pattern with pronounced transverse orientation depending on optic polarization was obtained (see pic. a) [4]. This effect could not be explained in terms of ponderomotive force like in [5] due to it's cylindrical symmetry character.…”

Superposition of 2ω and Electrostatic Field Induced Terahertz Waveforms in DC-Biased Two-Color Filament

“…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.…”

Breaking of the Axial Symmetry of Terahertz Radiation from Single-Color Filament Plasma

“…These experimental studies were carried out with significantly different detectors: a narrowband heterodyne detector sensitive to a frequency of about 0.1 THz [4] and a bolometer operating in the frequency range from 0.1 to 3 THz [5]. The terahertz radiation pattern obtained in [6,7] is completely different and has two maxima located in the vertical axis for the horizontal polarization of a pump laser pulse. The authors of many works considered the spectrum of terahertz radiation [8] and its angular distribution [4] separately.…”