Nitrogen air lasing induced by multiple filaments array

Air lasing emission by launching intense ultrafast laser pulses in atmosphere has recently attracted increasing interest in the ultrafast laser science and atmospheric science fields,especially for remote sensing techniques.We demonstrated the fluorescence emissions at 337 nm,357 nm and 391 nm induced by multiple filaments using four kinds of step phase plates.Our results have indicated that the fluorescence signal has been amplified as it propagates along the filament through amplified spontaneous emission(ASE),and the fluorescence intensity is also enhanced in the backward direction via multiple filaments.Furthermore,the gain coefficient through ASE is increased with the number of filaments.