Amplified spontaneous C3Πu–B3Πg emission and rotational and vibrational state distributions in C3Πu state of N2 in femtosecond laser induced filament in air

• Published in: Chemical physics letters 2013-08, Vol.581, p.21-25
• Main Authors: Owada, Shigeki, Azarm, Ali, Hosseini, Sima, Iwasaki, Atsushi, Chin, See Leang, Yamanouchi, Kaoru
• Format: Article
• Language: English
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2013.07.011

[Display omitted] •The length of the femtosecond laser induced filament is defined experimentally.•The fluorescence intensity from the filament is interpreted by a numerical model.•The filament acts as a gain medium for the amplification of spontaneous emission.•The vibrational and rotational temperatures are derived from the emission spectra.•The laser intensity clamping in the filament is confirmed by the spectral analysis. A femtosecond laser-induced filament in air was investigated by detecting the C3Πu–B3Πg (0,0) fluorescence of N2. The intensity of the backward fluorescence increased exponentially as a function of the filament length, showing the amplification of the spontaneous emission. The vibrational and rotational temperatures of N2 in the C state determined by spectroscopic analyses were found to take respectively almost the same values of 2800(200) and 450(100)K in the wide laser intensity range between 0.5 and 6mJ/pulse, which can be regarded as evidence of the clamping of the laser field intensity in the filament.