Progress in Laser Induced Breakdown Spectroscopy and Raman Spectroscopy for Hazardous Material Detection

In recent years, terrorist attacks utilizing explosives and public safety incidents related to chemical and biological hazards have caused a large number of casualties and property losses. Thus, it is urgent to develop techniques for these hazardous materials detection. Laser-induced breakdown spectroscopy (LIBS) is a spectroscopic analysis technique which uses the light emitted from a laser-induced plasma to determine the composition of the sample based on plasma emission intensities. Raman spectrum can reflect the molecular characteristics of the materials to be measured, and it is widely used in the substances detection and identification. As laser-based spectroscopies, LIBS and Raman spectroscopy are the only currently viable techniques that can be utilized to sense trace amounts of hazardous materials such as explosives and chemical/biological agents at standoff distances because of their intrinsic capability for minimally destructive, in-situ and standoff detection. Therefore, they have gained considerable attention recently. The recent research progresses in hazards detection based on LIBS and Raman spectroscopy are reviewed in this paper. The advantages of LIBS include strong signal intensity, real-time, and the high sensitivity of detection. However, LIBS is subject to poor reproducibility and undesirable matrix effects and hard to discrimate between organic dangerous substances and interferents with the same elements and different molecular structure. Unlike LIBS which provides information on the relative elemental content of molecules within the laser plasma, Raman scattering measures the molecular vibration frequencies and offers the information on the molecular composition of the sample and is suitable for distinguishing organic hazards from organic interferents. One drawback with Raman spectroscopy is the weakness of signal intensity, which makes it sensitive to ambient light and fluorescence. Therefore, integrating LIBS with Raman spectroscopy can provide complementary information and it has the potential to become a useful analytical tool for hazardous materials detection. We emphasize the development of fused LIBS-Raman sensor system for standoff explosive detection in this review. However, combined analysis systems with LIBS and Raman spectroscopy have their own problems such as high cost, complicate structure and data processing, and so on. Further studies on the improvement of detectability of LIBS-Raman combined system for trace hazard detection, the exploitation of strategies for reducing the spectral variability and fusing the data of LIBS and Raman spectroscopy, and the robustness under changing ambient environment conditions need to be further developed. This review compares currently used LIBS, Raman and LIBS-Raman combined techniques for hazardous materials standoff detection. Some prospects of the development of LIBS and Raman spectroscopy for hazards detection are also discussed at the end of the review.