The Combustion Diagnosis Of Butane/Air Flame Via Femtosecond Laser Filamentation

During the transmission of femtosecond laser pulses in nonlinear media,plasma filaments will be formed when the Kerr self-focusing and the plasma defocusing reach a dynamic balance.At the same time,There are many nonlinear effects in filamentation process,which has become the focus of researchers.The laser intensity is strong enough to stimulate the molecules in air during the filamentation formation process,and it will emit characteristic fluorescence when the excited state molecules jump to ground state.In recent years,it has gradually become a hot research topic in the field of science.In this paper,filament-induced fluorescence technique,a new combustion diagnostic technique based on femtosecond laser filaments have been applied to the combustion field,and it can realize simultaneous detection of various combustion intermediates.It is of great practical value for reducing the emission of atmospheric pollutants?such as CO,CN,NO,etc.?,remote sensing and improve the efficiency of energy conversion.The femtosecond filament-induced backward fluorescence in the butane/air flame is investigated in this paper.It is found that the spatial distributions of combustion intermediates?CN,CH and C₂?,nitrogen molecules and nitrogen molecular ions in the flame show great difference,which is mainly determined by the spatial distribution of gas temperature?density?,and also affected by the reactions.Furthermore,we demonstrate that filament-induced fluorescence technique can not only sense the combustion intermediates,but also detect combustible gas with trace amounts in air.