Laser-induced breakdown spectros - copy (LIBS) has been investigated for potential utility as a means of detecting trace amounts of chemical explosives and residues thereof in lawenforcement, forensic analysis, and military settings. In LIBS (see figure), a laser is used to rapidly generate a microplasma of a sample, and the light emitted by the microplasma is analyzed to identify (and determine the intensities of) spectral lines of elements and compounds in the sample. In previous applications for purposes other than detection of explosives, LIBS has been shown to enable remote, rapid, multielement micro-analysis of bulk samples (solid, liquid, gas, aerosol) of compounds having concentrations in the parts-per-million range.

LIBS has several features that make it especially attractive as a means of detecting explosives:

  • Conceptually, it is simple and straightforward.
  • Little or no preparation of samples is necessary.
  • Only a very small sample is needed for production of a usable LIBS spectrum (typically, a sample mass in the approximate range of picograms to nanograms is sufficient).
  • Response time is less than 1 s.
  • LIBS sensors can be made rugged and field-portable: all components (including the laser, spectrometer, detectors, and computer) can be miniaturized.
  • LIBS offers the flexibility of operation in a point detection (proximity) mode or a stand-off mode.

In a Basic LIBS Apparatus, a laser pulse passes through a turning prism and a pierced mirror, and is focused on a sample surface to induce a microplasma. Light from the microplasma is coupled into a fiber optic, which delivers the light to a spectrometer
In the past, LIBS was used primarily to analyze one or a few elements — mostly metals — that can be identified via emission spectra lines within relatively narrow wavelength bands. More recently, the utility of LIBS for identifying compounds has been realized with the advent of high-resolution, broad-band spectrometers, which can capture the spectral lines emitted by all the elements in the laser-generated plasmas (provided that the elements are present in sufficient abundance). LIBS has already been shown to enable detection of a variety of toxic and otherwise hazardous compounds other than explosives.