Standoff detection applying laser-induced breakdown spectroscopy at the DLR laser test range

摘要

The DLR laser test range at Lampoldshausen is designed for a wide field of laser application studies under central European atmospheric conditions. Micrometeorological measurements are performed simultaneously and nearby to the laser propagation. The infrastructure is very suitable for the development of laser based standoff detection systems of biological, chemical, and explosive hazardous substances. In a first approach, laser-induced breakdown spectroscopy (LIBS) has been introduced for investigation of surface contaminants at distances up to 135 m. A basic LIBS set-up and LIBS spectra of selected samples using different excitation wavelengths from IR to UV are presented for detection at different distances. A Nd:YAG laser beam was focussed by a Cassegrain type telescope onto different samples. The light of the generated plasma plume was collected by a Newtonian telescope, analysed and detected by a broadband CCD-spectrometer system. The Nd:YAG laser yields pulse energies up to 800 mJ at a wavelength of 1064 nm and a pulse width of 8 ns. Optionally the second and third harmonics can be extracted at reduced energy. LIBS spectra produced on gold layers as thin as 5 nm deposited on silicon wafers were recorded for test of detection sensitivity and comparison of wavelengths effects. In addition, black powder as ordinary substance representing explosives was detected by LIBS technology. Spectra were recorded in single and repetitive pulsed scheme of the Nd:YAG laser at various daylight and atmospheric conditions