Filament characterization via resonance absorption of terahertz wave

Abstract

In this work, we characterize the transmission properties of the focusing-laser-induced filament by using terahertz (THz) time domain spectroscopy. Significant resonance absorption of the THz wave is identified, which is attributed to the dynamic screening of the ionized electrons. The polarization and intensity of the filament-generated pulse have been varied to study their influences on the resonance absorption. Our results suggest that the electron density of the filament can be determined by fitting the phase shifts and absorption properties around the absorption. This method provides not only an alternative to the plasma diagnostics with plasma frequency at the THz range, but also a supplement to the existing generation theory of THz waves from plasma.

Absorption of terahertz wave by interaction between crossed air-plasmas

“…In particular, compared to the previous work, we observed many very different phenomena, by adjusting the time delay of the THz wave modulator, we can see not only the resonant absorption of THz waves by the filament, but also the * gaomx@nudt.edu.cn; yindonghuang@nudt.edu.cn; enhancement of THz waves due to the presence of the filament. By varying the time delay between the two air-plasmas, the THz waves are absorbed by the plasma resonance, which is consistent with our previous fi ndings [10,11]. Although different groups report the various results on the central frequency [10,12], for THz waves radiated by single-color laser generated plasma, both the absorption and radiation are related to the plasma frequency.…”

“…By varying the time delay between the two air-plasmas, the THz waves are absorbed by the plasma resonance, which is consistent with our previous fi ndings [10,11]. Although different groups report the various results on the central frequency [10,12], for THz waves radiated by single-color laser generated plasma, both the absorption and radiation are related to the plasma frequency. However, the terahertz waves produced by a two-color laser field are not exactly the same as those produced by a one-color laser field, so we observe a completely different phenomenon.…”

Terahertz near-field microscopy based on an air-plasma dynamic aperture

“…1a . Because an air-plasma has high electron density 31 , it can produce strong absorption and reflection effects in the THz frequency range. Therefore, an air-plasma can be regarded as being analogous to a metallic needle for a THz beam.…”

Why do terahertz waves generated from long two-color filament always peak at around 1 THz?

“…While, interestingly, as the two-color filament becomes longer (stronger input laser intensity), the radiated THz frequency will peak at around 1 THz, and this can be found not only from the studies using the electro-optic sampling, 12,13 but also from using the fluorescence, 14 the air-biased-coherent-detection, 15,16 and the Michelson interferometer methods. 17 For the single-color laser induced filament, it exhibits a Lorentzian-like line shape of the emission 18 and absorption 19 at the THz frequency band. Many explanations have been proposed in interpreting the underlying mechanism, for instance, the plasma oscillation, 20 resonant absorption, 19 refractive index variation of the boundary 21 and collision frequency within the plasma.…”

“…17 For the single-color laser induced filament, it exhibits a Lorentzian-like line shape of the emission 18 and absorption 19 at the THz frequency band. Many explanations have been proposed in interpreting the underlying mechanism, for instance, the plasma oscillation, 20 resonant absorption, 19 refractive index variation of the boundary 21 and collision frequency within the plasma. 18 Unfortunately, it is difficult to directly determine the underlying mechanism by simply changing the incident laser energy, because the values of plasma frequency, resonant absorption and plasma collision frequency all increase as the laser energy.…”