Population inversion in fluorescing fragments of super-excited molecules inside an air filament
摘要
An original idea is reviewed.When a molecule is pumped into a super-excited state,one of its decay channels is neutral dissociation.One or more of the neutral fragments will fluoresce.Hence,if a lower state of such fluorescing fragments was populated through other channels but with a lower probability,population inversion of the fluorescing fragments would be naturally realized.This idea seems to be validated,so far,by comparing published work on three hydrocarbon molecules,CH4,C2H2,C2H4,and water vapor,H2O.After super-excitation in a femtosecond laser filament in air mixed with these molecules,the fluorescence from the CH or OH fragments exhibits population inversion,i.e.,amplified spontaneous emission was observed in the backscattering direction of the filament.