氧气对飞秒激光泵浦的氮气分子无腔激光效应的淬灭作用(特邀)

Quenching Effect of O2 on Cavity-free Lasing of N2 Pumped by Femtosecond Laser Pulses(Invited)

圆偏振飞秒激光泵浦氮气产生的无谐振腔激光效应在远程光学遥感方面具有非常重要的应用前景.然而,空气中氧气分子的存在显著地淬灭了该受激辐射效应.对比研究了氧气和氪、氩、氦这三种气体对于氮气分子前向和背向激射的影响,测量了纯氮气和空气中氮分子荧光的强度.结果表明,氧气和氪气这两种电离能非常接近的气体呈现出十分相似的淬灭作用;而氦气因为电离能极大,并不呈现出显著的淬灭作用.因此,可得氧气对于氮气分子激射淬灭作用的主要原因在于其引起的光丝内激光强度的下降,从而使得自由电子能量降低,导致碰撞激发效率下降.

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 O2,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 O2 and Kr,since Kr has a close ionization potential compared to O2.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 O2 on nitrogen molecules mainly stems from the fact that O2 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.