The fast decay of ionized nitrogen molecules in laser filamentation investigated by a picosecond streak camera

Abstract

A column of bright filament is generated when a strong 800 nm femtosecond laser propagates in pure nitrogen gas, from which some fluorescence emission lines are observed. These emission lines can be assigned to the transitions of and N2 (C3Πu → B3Πg). By using a picosecond streak camera, we investigated the fluorescence decay dynamics of It was found that the decay time is in the sub-nanosecond range when the gas pressure is several millibar, more than two orders magnitude shorter than its spontaneous emission lifetime. Through monitoring the population evolution of as a function of free electron density, we concluded that the fast decay originates from the collision between and free electrons in the plasma filament.