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oe1(光电查) - 科学论文

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  • Enhanced Coherent Emission from Ionized Nitrogen Molecules by Femtosecond Laser Pulses

    摘要： The forward emission spectra were experimentally measured for ionized nitrogen molecules by an 800-nm pump laser and a delayed seed laser. It was found that emission lines around both 428 nm and 391 nm are greatly enhanced with injecting either a 391-nm or 428-nm seed laser. The emission lines around 391 nm and 428 nm can be assigned to the rotational transitions of N2+ (B2Σu+, v'=0 → X2Σg+, v=0) and N2+ (B2Σu+, v'=0 → X2Σg+, v=1), respectively. They origin from seed-induced superfluorescence and resonant stimulated Raman scattering. The genetic algorithm was utilized to simulate the experimental observations and determine the relative population of B2Σu+(v'=0), X2Σg+(v=1) and X2Σg+(v=0). The result verifies that the vibrational population inversion is achieved between B2Σu+(v'=0) and X2Σg+(v=0) by the 800-nm pump laser. Our finding provides new insights into controlling the coherent emission of ionized nitrogen molecules, which has promising application in filamentation-based remote atmospheric sensing.

    关键词： femtosecond laser pulses,ionized nitrogen molecules,coherent emission,population inversion,superfluorescence,stimulated Raman scattering

    更新于2025-09-16 10:30:52

  • 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