A method for detecting ultra-low quantities of explosives with use a picosecond laser FAIMS analyzer

摘要

A method for detecting ultralow quantities of explosives in air with use a state-of-the-art picosecond chip Nd~(3+):YAG laser has been developed. The method combines field asymmetric ion mobility spectrometry (FAIMS) with laser ionization of examined air samples. Radiation of λ= 266nm, τ_(pulse)= 300ps, E_(pulse)= 30-150μJ, v = 20-300Hz was used. Processes in the ion source for the use both picosecond and nanosecond ionization modes were analyzed. Parameters of the laser ion source have been specially optimized. The dependences on frequency, pulse energy, peak intensity, and average power for trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) were obtained. It was shown that the optimal peak intensity should be no less 3·10~6 W/cm~2. The detected ion signals for all explosives were shown to be threefold higher for picosecond excitation in comparison with use a nanosecond laser of the same average power. The estimated detection threshold of the prototype equals 1·10~(-15) g/cm~3. The results are promising for the development of a highly sensitive, portable laser explosive detector.