Broadband terahertz radiation from two-color mid- and far-infrared laser filaments in air

Abstract

We study terahertz (THz) emission by two-color femtosecond filaments in air using pump wavelengths λ 0 from 0.8 to 10.6 μm. Comprehensive three-dimensional numerical simulations show that tens-of-centimeter long filaments created by a 10.6-μm pump pulse can produce mJ energy yields and GV/m field strengths, while the laser-to-THz conversion efficiency exceeds the percent level. Changing temperature and humidity conditions reveals a surprisingly high stability of the THz spectra against different weather conditions. We also examine the role of many-body Coulomb effects on ionization. This additional plasma source promotes longer filaments that act as efficient THz emitters, despite enhanced plasma defocusing.

Observation of extremely efficient terahertz generation from mid-infrared two-color laser filaments

“…By taking into account that nonlinear propagation plays a major role in filament-based THz sources, recently we performed theoretical investigations and numerical simulations which predict that twocolor filamentation of mid-infrared laser pulses can be a source of single cycle THz pulses with multi-millijoule energies and extremely high THz conversion efficiencies, which are more than two orders of magnitude higher than for 0.8 μm laser pulses 37,38 . These results were later confirmed numerically by Nguyen et al 39 Additionally, we showed that there is an optimal wavelength for two-color filamentation-induced THz sources: for 3.2 μm laser pulses the THz conversion efficiency reaches its maximum of about 7% 40 . Our theoretical analysis reveled that the extreme efficiency of mid-infrared two-color filamentation for THz generation is caused by a combination of many factors: strong photocurrents due to larger ponderomotive forces, longer and wider plasma channels, negligible walk-off between the fundamental and second harmonic, additional field symmetry breaking by generated high harmonics 37,38 .…”

Roadmap of Terahertz Imaging 2021

“…Regarding investigated materials, one can note that the studies were not limited to semiconductors only; a special attention gained optical rectification-based THz emission from lithium niobate [20,21] and second-order nonlinear effects for THz generation in different type of organic crystals, like DAST, DSTMS, OH1, HMQ-TMS, and BNA [22][23][24][25][26]. It is worth noting air-plasma-based THz photonics approach when a high intensity femtosecond laser can induce plasma oscillations in air [27,28], which can emit broadband THz radiation [29,30]. However, despite the fact that aforesaid systems contain beautiful physics and can serve as powerful instruments for THz spectroscopy, they are relatively bulky, and they require specific and complicated set-up arrangements.…”

Wavelength scaling of terahertz pulse energies delivered by two-color air plasmas

“…Recent studies [3][4][5][6][7] showed that increasing the pump wavelength enhances the laser-to-THz conversion efficiency which is usually limited to about 10 −4 for near-infrared (IR) pump pulses. However, there is no consensus achieved on the possible gain factors expected when pushing the FH wavelength, λ 0 , from the near-IR to the mid-IR range.…”