Backward air lasing actions induced by femtosecond laser filamentation: influence of population inversion lifetime

TL;DR

This study explores how the lifetime of population inversion in excited N2 molecules influences the generation of backward nitrogen lasers using femtosecond laser filamentation, highlighting conditions for intense backward laser production.

Contribution

It experimentally demonstrates the critical minimum population inversion lifetime (~0.8 ns) needed for backward nitrogen laser generation in air, advancing understanding of laser filamentation dynamics.

Findings

Backward nitrogen laser at 357 nm requires ~0.8 ns inversion lifetime

Population inversion duration directly affects laser intensity

Results inform remote atmospheric sensing applications

Abstract

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 lifetime of population inversion 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 ambient air, which are highly in demand for high sensitivity remote atmospheric sensing application.