Parameters of laser ionization of explosives for ion mobility spectrometry

Abstract

The possibility of optimizing the parameters of laser radiation for increasing the efficiency of ionization of vapors of explosives in a laser field asymmetric ion mobility spectrometer (FAIMS) was investigated. The dependences of TNT ion signal on intensity of laser radiation, pulse energy and repetition frequency of laser pulses were obtained. Optimum value of the intensity of laser radiation for ionization in air was experimentally obtained - 3•10 7 W/cm 2 . It is shown that defocusing of laser radiation and expansion of the ionization region increase the TNT signal if the radiation intensity remains at the optimum level. It is shown that repetition rate should be such that the interval between pulses is shorter than the time of diffusion of non-ionized molecules into the laser irradiation region. A scheme for a multi-pass laser beam through the ion source of a spectrometer was proposed. The scheme will effectively use laser radiation and improve the ionization efficiency of nitro aromatic molecules.