All bombs make use of some type of explosive. These explosives will have their base in one of a select few compounds. When it comes to bomb detection, some of these compounds are easier to detect than others.
There are two general classes for explosives. Those that are nitrate based and those that are not. The non-nitro based explosives will typically be based on other highly reactive materials such as peroxides, perchlorates and azides. However, the nitro based explosives are far more commonly used and more easily accessible.
One of the bomb detection techniques that is in use is trace detection. One problem that is faced is that most explosives have extremely low vapour pressures. This places a limit on how effective trace detection using ambient vapour can be. The solid material has a far stronger signal potential than the vapour, making it easier to detect.
A study has been conducted into the use of optical techniques for detecting explosives. The technique is photodissociation followed by laser-induced fluorescence.
Nitrate based explosives have a broad optical absorption spectrum which makes the residue fluoresce under ultra violet light. The broad nature of the optical absorption spectrum of these explosives does present a problem in that there are many other materials which all fluoresce under UV light.
The study previously mentioned investigated the possibility of decreasing, or eliminating, optical clutter through the use of laser-induced fluorescence. Through the use of a photomultiplier with narrowband filters used to suppress the scattered laser light, it was found that all the explosives tested showed a multipeak structure which reached a maximum signal at a specific excitation wavelength. These signatures are similar enough that it can be implied that nitrate based explosives can be detected using this technique provided the explosives are in solid or liquid form. The vaporous format of these explosives varies substantially more and so is far more complicated to detect using standard bomb detection techniques.