the start time resulting in very short integration times relative to integrations times noted above 200 microseconds for use of mpi spectrometer 20 in ambient air the shorter integration times allow for acquiring an mpi measurement at each wavelength by exposing target 22 to many more pulses of light 32 than is generally convenient when operating mpi spectrometer 20 in ambient air the increased number of light pulses provides an improved snr for the measurements fig2 shows a graph 80 of mpi spectrum 81 and 82 for the explosives rdx and tatp respectively acquired under ambient conditions by an mpi spectrometer similar to mpi spectrometer 20 shown in fig1 the abscissa of the graph shows wavelength scaled in nanometers the ordinate shows mpi charge accumulated for each wavelength in arbitrary units the spectrometer specification was similar to that described above for the exemplary embodiment and operated with 5 ns pulses spectra 81 and 82 are useable to detect presence of rdx and tatp in quantities as small as small as a few picomoles at 95 confidence level mpi spectra for other explosives such as hmx ten and tnt drugs such as mda 3 4 methylenedioxyamphetamine and thc tetrahydrocannabinol and various polycyclic aromatic hydrocarbons pahs such as melamine anthracene and chrysene were acquired using an mpi spectrometer in accordance with an embodiment of the invention and similarly indicated detection sensitivities of a few picomoles at 95 confidence level fig3 a shows a graph 90 of an mpi spectrum 91 acquired for the psychedelic molecule mdma ecstasy the mpi spectrum exhibits a.