Emission Spectra of Water Aerosols Induced by Filamentation of Femtosecond Laser Pulses in Air

The characteristics of emission spectra induced by femtosecond laser filaments in air and water aerosol were studied. Spectra were accumulated 100 ns after 0 ns time delay relative to laser pulse. Second positive (2+) $${{N}_{2}}\left( {C{{{\kern 1pt} }^{3}}\Pi _{u}^{{}} - B{{{\kern 1pt} }^{3}}\Pi _{g}^{{}}} \right)$$ and first negative (1–) $$N_{2}^{ + }\left( {B{{{\kern 1pt} }^{2}}\Sigma _{u}^{ + } - X{{{\kern 1pt} }^{2}}\Sigma _{g}^{ + }} \right)$$ nitrogen systems were observed. Growth of continuum intensity and noise was observed at transition from filamentation in air to that of in water aerosol. Intensity of 1– system line decreased more strongly in comparison with 2+ system lines for filamentation in water aerosol what explained by quenching collisions of emitters by water molecules. Translational and vibrational temperatures were measured, 329 and 3470 K (filamentation in air), 356 and 3546 K (filamentation in water aerosol).