Formation Dynamics of Excited Neutral Nitrogen Molecules inside Femtosecond Laser Filaments

Rostyslav Danylo 1 Xiang Zhang 1 Zhengquan Fan 1 Dongjie Zhou 1 Qi Lü 1 Bin Zhou 1 Qingqing Liang 1 Songlin Zhuang 1 Aurélien Houard 2 André Mysyrowicz 3 Eduardo Oliva 4, 5 Yi Liu 1, 3
1 Shanghai Key Lab of Modern Optical System
2 ILM - Interaction Laser-Matière
LOA - Laboratoire d'optique appliquée
3 LOA - Laboratoire d'optique appliquée
4 IIFN - Univ Politecn Madrid, ETS Ingenieros Ind, Inst Fusin Nucl, C Jose Gutierrez Abascal 2, E-28006 Madrid, Spain
5 Departamento de Ingenieria Energetica,
Abstract : 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 N 2 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.
Keywords : laser filamentation nonlinear optics ultrafast optics
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Rostyslav Danylo, Xiang Zhang, Zhengquan Fan, Dongjie Zhou, Qi Lü, et al.. Formation Dynamics of Excited Neutral Nitrogen Molecules inside Femtosecond Laser Filaments. Physical Review Letters, American Physical Society, 2019, 123, pp.243203. ⟨10.1103/PhysRevLett.123.243203⟩. ⟨hal-02414411⟩

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