Filament-induced amplified spontaneous emission in air–hydrocarbons gas mixture

Filament-induced amplified spontaneous emission, ASE, in air–hydrocarbons (~2%) gas mixture, CH4, C2H2, and C2H4, was investigated by detecting fluorescence emitted from CH fragments prepared in the electronically excited A2Δ state in the filament. The fluorescence signal recorded from the side direction of the filament was linearly proportional to the length of the filament, while the fluorescence signal emitted in the backward direction of the laser propagation increased nonlinearly with the filament length. This difference showing that the filament acted as a gain medium in which the spontaneous emission from CH was amplified (ASE). This process realized by a small amount of hydrocarbon molecular species in air can be applied to remote sensing of pollutants in air.