ABSTRACT
In the laser-induced breakdown spectroscopy (LIBS) technique, a powerful laser pulse is projected at a target to induce a set of optical signals characteristic of the target composition.1,2 As laser light alone is used to induce the signals, the technique has many advantages for the detection of explosives and can be deployed in a variety of concepts of operations (ConOps). In principle, LIBS can be used to detect bulk explosives, explosive residues on surfaces, and explosives in the vapor form. LIBS can also be used to identify materials related to explosives deployment such
7.1 Introduction .................................................................................................. 145 7.1.1 LIBS for Explosives Detection ......................................................... 145 7.1.2 Advantages of LIBS for Explosives Detection ................................. 146 7.1.3 Limitations of LIBS for Explosives Detection ................................. 147
7.2 Background ................................................................................................... 148 7.2.1 LIBS Technique ................................................................................ 148 7.2.2 LIBS Signatures from Explosives ..................................................... 150 7.2.3 Methods of Deploying LIBS Detection ............................................ 152
7.3 Review of LIBS Detection of Explosives ..................................................... 155 7.3.1 In Situ, Close-Up Detection .............................................................. 155 7.3.2 Land-Mine Detection........................................................................ 157 7.3.3 Residue Detection ............................................................................. 158 7.3.4 Standoff Detection ............................................................................ 160
7.4 LIBS Combined with Raman Spectroscopy ................................................. 161 7.5 Summary ...................................................................................................... 164 References .............................................................................................................. 164
as land-mine housing materials. The easiest target to identify is the bulk explosive, although the probability of having access to bulk materials is likely to be low. The ability to detect residues on surfaces opens new detection capabilities, as measurements can be carried out at some distance from the target and, by using repetitive laser pulses, large areas can be surveyed. In addition, LIBS can identify small residue masses (down to nanogram quantities) because of its point sampling capability. One example is the detection of residues on car surfaces (e.g., trunk lids, door handles) deposited by hand contamination during deployment of hidden improvised explosive devices (IEDs) in the vehicle. The use of LIBS to interrogate other surfaces such as shipping containers for explosive residues is also a possibility. It should be noted that in the application of LIBS for explosives detection, the main interest is in determining the presence of an explosive (within constraints of the detection limits) rather than quantication of amounts present. The recognition by a LIBS analysis of the presence of explosive residues would most likely serve as a trigger for further measurements, the use of other instrumentation for verication, or both.
