Quenching Effect Of O-2 On Cavity-Free Lasing Of N-2 Pumped By Femtosecond Laser Pulses < Invited >

Nitrogen gas pumped by circularly polarized femtosecond laser pulses gives rise to bidirectional lasing emission, which holds unique potential for remote optical sensing application. However, the presence of oxygen molecules strongly suppresses this lasing effect. The influence of O-2, Kr, Ar and He on the lasing effect of nitrogen molecules was compared, and the fluorescence of nitrogen molecules in pure nitrogen and ambient air was examined. It is observed that the lasing presents a similar quenching effect with the partial pressure of O-2 and Kr, since Kr has a close ionization potential compared to O-2. In contrast, for He which has a much higher ionization potential, there is no significant quenching effect. Therefore it is suggested that the quenching effect of O-2, on nitrogen molecules mainly steins from the fact that O-2 leads to a reduction of the clamped laser intensity inside the plasma filaments, which results in a decrease of the kinetic energy of the free electrons and an inefficient collision excitation.