Corona electric field triggered N₂ ⁺ lasing from a femtosecond laser filament in air

The emission of N₂ ⁺ lasing at 391 nm from 800 nm femtosecond laser filament in air at 1 atm presents significant challenges due to the quenching effect induced by oxygen molecules. We introduce a simple technique for the 391 nm N₂ ⁺ lasing emission induced by a corona electric field-assisted femtosecond filament in air. This technique greatly addresses the challenge of exciting a 391 nm lasing from 800 nm femtosecond laser filament in air at 1 atm. The laser filament assisted with corona electric filed breaks the symmetry of air and generates the effective second harmonic as a seeding pulse of 391 nm lasing, leading to stimulated amplification forward lasing action. The forward 391 nm lasing radiation is found to be significantly enhanced. This work is of great significance not only in solving the quenching problem of 391 nm lasing in air but also in understanding the generation mechanism of air lasing.