A method for detecting ultralow quantities of explosives in air and explosive traces using a state-of-the-art picosecond
chip Nd3+:YAG laser has been elaborated. The method combines field asymmetric ion mobility spectrometry (FAIMS)
with laser ionization of air samples and laser desorption of analyzed molecules from examined surfaces. Radiation of the
fourth harmonic (λ = 266 nm, τpulse = 300 ps, Epulse = 20-150 μJ, ν = 20-300 Hz) was used. The ionization efficiencies for
trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and glyceryl trinitrate (NG) were investigated. The
dependences on frequency, pulse energy, peak intensity, and average power for TNT and RDX were determined. It was
shown that the optimal peak intensity should be no less than 2∙106 W/cm2; at lower peak intensities, the increase of the
average laser power in the interval 5–15 mW enhanced the ion signal. The results of detection of TNT, RDX, and NG
vapors under these conditions were compared with the results obtained using nanosecond laser excitation. The detected
ion signals for all explosives were shown to be two- to threefold higher in the case of picosecond excitation.
The FAIMS laser desorption regime was developed where a laser beam exiting the detector after removal of a special
plug was used. The results of TNT and RDX detection are presented.
The chip Nd3+:YAG laser has a small emitter and a consumed electric power of 25 W. The estimated detection threshold
of the prototype picosecond laser FAIMS analyzer of explosives is (1-3)∙10-15g/cm3 for TNT vapors.