Differentiation of Positional Isomers of Propyl Alcohols Using Filament-Induced Fluorescence

We experimentally demonstrate the recognition of positional isomers of propyl alcohol vapor through nonlinear fluorescence induced by high-intensity femtosecond laser filaments in air.By measuring characteristic fluorescence of n-propyl and isopropyl alcohol vapors produced by femtosecond filament excitation,it is found that they show identical spectra,that is,those from molecular bands of CH,C;,NH,OH and CN,while the relative intensities are different.By comparing the ratios of the CH and C;signals,the two propyl alcohol isomers are differentiated.The different signal intensities are ascribed to different ionization potentials of the two isomer molecules,leading to different production efficiencies of fluorescing fragments.