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6 GHz electromagnetic wave guiding along a femtosecond laser plasma filament
摘要： To study the electromagnetic (EM) wave guiding performance of the plasma filament generated by the intense femtosecond (fs) laser pulse, a 3D physical model of the wave-plasma interaction is built and discussed with the commercial simulation software XFDTD. Then, an experiment is conducted to verify the EM wave guiding performance of the fs laser plasma filament. Our investigation illustrates that the 6 GHz EM wave can propagate along the fs plasma filament, making the EM field enhance out of the rectangular waveguide and attenuate in the rectangular waveguide. Besides, the filament can cause 4.74 dB enhancement of the wave energy relative to freely propagating the signal. Furthermore, the experimental result indicates that the guiding performance of the plasma filament on the TE polarization wave is better than that on the TM one, which is consistent with the theoretical result. For TE polarization wave, the plasma filament can reduce the microwave signal in the waveguide, which is lesser than that of the Cu wire in the experiment. The research results confirm that the fs laser plasma filament can guide the EM wave with a better performance relative to freely propagating the signal.
关键词： waveguide,guiding,plasma filament,femtosecond laser,EM wave
更新于2025-09-12 10:27:22
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Experimental and analytical evaluation of the acoustic radiation of femtosecond laser plasma filament sound sources in air
摘要： Plasma ?laments in air induced by femtosecond laser pulses lead to the generation of strong shock waves. This letter presents a systematic study, both experimental and theoretical, of the acoustic radiation by femtosecond laser-generated ?laments. A theoretical model is developed based on the experimental results and is used to evaluate the directivity of the ?lament’s acoustic radiation within and beyond the audible frequency range. It is shown that the acoustic directivity of plasma ?laments can be derived from the model of a weighted acoustic line source, consisting of elementary point sources with N-shaped excitation.
关键词： acoustic radiation,plasma filament,femtosecond laser,directivity,shock waves
更新于2025-09-12 10:27:22
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Formation Dynamics of Excited Neutral Nitrogen Molecules inside Femtosecond Laser Filaments
摘要： Nitrogen molecules are promoted to excited neutral states during femtosecond laser pulse filamentary propagation in atmosphere, leading to a characteristic UV fluorescence. Using a laser-induced fluorescence depletion technique, we measure the formation dynamics of these excited neutral nitrogen molecules with femtosecond time resolution. We find that the excited neutral molecules are formed in an unexpected ultrafast timescale of ～4 ps at 1 bar and ～120 ps at 30 mbar pressure. From this observation we deduce that the excitation of neutral N2 occurs via multiple collisions with hot free electrons. Numerical simulations based on rate equations reproduce well this ultrafast formation time and its dependence on gas pressure, and thus support this interpretation.
关键词： electron impact excitation,femtosecond laser,plasma filament,UV fluorescence,nitrogen molecules
更新于2025-09-12 10:27:22