The mechanism of nitrogen fluorescence inside a femtosecond laser filament in air

The visible and near-UV fluorescence spectroscopy of air generated inside a femtosecond laser plasma filament was studied. The primary reactions, N-2(+) + N-2 double right arrow N-4(+); N-4(+) + e double right arrow N-2(C-3 Pi(u)) + N-2, populates the electronic excited state N-2(C-3 Pi(u)) of N-2. The N-2 fluorescence is not by direct electron-ion recombination of N-2(+) + e. Using a pump-probe method, the fluorescence lifetime of C-3 Pi(u) of N-2 at atmospheric pressure was determined to be about 85 ps. (C) 2009 Elsevier B.V. All rights reserved.