Formation Of CO,NO And HCN By Atmospheric Chemical Reaction Induced By Femtosecond Laser Filament And Spectral Measurement

When the ultrashort laser pulse is focused in the air,the Kerr self-focusing effect and the plasma defocus effect work together to form a plasma channel called the“filament”.Atmospheric filaments can induce atmospheric chemical reactions.At present,the mechanism and process of atmospheric chemical reactions induced by ultra-short laser filaments are not clear.In this paper,a femtosecond laser with a wavelength of 800 nm,35 fs and a repetition rate of 1 k Hz is used to generate filament and induce atmospheric chemical reactions under different atmospheric conditions.The air is rich in nitrogen,oxygen and carbon dioxide,and femtosecond filament dissociate these molecules to create complex reactions between new molecules and ions.The concentrations and evolution of CO,NO and HCN generated by laser-induced atmospheric chemical reactions were measured by using mid-infrared direct absorption spectroscopy and wavelength-modulated absorption spectroscopy.Among them,CO and HCN produced by atmospheric chemical reaction induced by filament were observed for the first time.Under low atmospheric pressure,CO,NO and HCN are affected by rotational excitation effect of ultra-short pulse laser and show enhanced absorption spectra.In the atmospheric environment,after sufficient reaction time,the concentrations of CO,NO and HCN accumulate to 80 ppm,120 ppm and 1.6 ppm,respectively.It is found that CO mainly comes from CO₂ in the atmosphere,and the OH free radical produced by water vapor in the atmosphere under the action of filament can inhibit the accumulation of CO concentration.The reaction of oxygen atoms with HCN under the action of filaments inhibits the accumulation of HCN concentration.In this paper,the mechanism and efficiency of carbon conversion to other products in atmospheric chemical reaction induced by ultra-short pulsed laser filament were studied,the influence of other atmospheric components on the conversion of C element was obtained,and the formation characteristics of harmful gases such as HCN and NO were explored.This study provides a mechanism reference for using atmospheric chemical reaction to delay the greenhouse effect,efficiently utilize the atmosphere and maintain environmental benefits.