研究目的
Investigating the formation dynamics of excited neutral nitrogen molecules inside femtosecond laser filaments in atmosphere.
研究成果
The study concludes that excited neutral nitrogen molecules inside filamentary plasma are formed mainly via electron impact excitation, with formation times varying between ～4 ps at 1 bar and ～120 ps at 30 mbar. This finding clarifies a fundamental problem and has implications for applications such as remote detection of electric fields and cavity-less air lasers.
研究不足
The study is limited to the conditions of femtosecond laser filamentation in nitrogen and air, and the interpretation relies on numerical simulations that assume specific mechanisms for the excitation of nitrogen molecules.
1：Experimental Design and Method Selection:
The study employs a laser-induced fluorescence depletion technique to measure the formation dynamics of excited neutral nitrogen molecules with femtosecond time resolution.
2：Sample Selection and Data Sources:
The experiment is conducted in a gas chamber filled with pure nitrogen or air at different pressures.
3：List of Experimental Equipment and Materials:
A commercial femtosecond laser system (Coherent Legend DUO) is used to generate pump and probe pulses. A type I BBO crystal generates second harmonic pulses for probing.
4：Experimental Procedures and Operational Workflow:
The pump and probe pulses are focused into the gas chamber, and the side fluorescence from the plasma filament is detected with a spectrometer as a function of the pump-probe time delay.
5：Data Analysis Methods:
The fluorescence signal is analyzed to monitor the formation dynamics of excited neutral nitrogen molecules, with numerical simulations based on rate equations used to interpret the results.
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