Paper

The fast decay of ionized nitrogen molecules in laser filamentation investigated by a picosecond streak camera

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Published 14 June 2017 © 2017 IOP Publishing Ltd
, , Citation Mingwei Lei et al 2017 J. Phys. B: At. Mol. Opt. Phys. 50 145101 DOI 10.1088/1361-6455/aa75f8

0953-4075/50/14/145101

Abstract

A column of bright filament is generated when a strong 800 nm femtosecond laser propagates in pure nitrogen gas, from which some fluorescence emission lines are observed. These emission lines can be assigned to the transitions of ${{{\rm{N}}}_{2}}^{+}\,({{\rm{B}}}^{2}{{{\rm{\Sigma }}}_{{\rm{u}}}}^{+}\to {{\rm{X}}}^{2}{{{\rm{\Sigma }}}_{{\rm{g}}}}^{+})$ and N2 (C3Πu → B3Πg). By using a picosecond streak camera, we investigated the fluorescence decay dynamics of ${{{\rm{N}}}_{2}}^{+}\,({{\rm{B}}}^{2}{{{\rm{\Sigma }}}_{{\rm{u}}}}^{+}\to {{\rm{X}}}^{2}{{{\rm{\Sigma }}}_{{\rm{g}}}}^{+}).$ It was found that the decay time is in the sub-nanosecond range when the gas pressure is several millibar, more than two orders magnitude shorter than its spontaneous emission lifetime. Through monitoring the population evolution of ${{{\rm{N}}}_{2}}^{+}\,({{\rm{B}}}^{2}{{{\rm{\Sigma }}}_{{\rm{u}}}}^{+})$ as a function of free electron density, we concluded that the fast decay originates from the collision between ${{{\rm{N}}}_{2}}^{+}\,({{\rm{B}}}^{2}{{{\rm{\Sigma }}}_{{\rm{u}}}}^{+})$ and free electrons in the plasma filament.

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10.1088/1361-6455/aa75f8