Backward nitrogen lasing actions induced by femtosecond laser filamentation: Influence of duration of gain

We experimentally investigate generation of backward 357 nm N₂ laser in a gas mixture of N₂/Ar using 800 nm femtosecond laser pulses, and examine the involved gain dynamics based on pump-probe measurements. Our findings show that a minimum duration of gain in the excited N₂ molecules is required for generating intense backward nitrogen lasers, which is ∼0.8 ns under our experimental conditions. The results shed new light on the mechanism for generating intense backward lasers from nitrogen molecules, which are highly in demand for high sensitivity remote atmospheric sensing application.