|
This proposal addresses a major issue in forensic science, namely the lack of nondestructive inspection techniques for the routine detection and identification of illicit drugs, including those cases where they are concealed in some way. Although x-ray scanners, canine detection, and external swiping with a trace detection system are currently in use, the former approach is invasive and unable to identify the type of drug, while the latter two are ineffective in the absence of detectable traces outside the enclosure containing the drugs. This proposal identifies the use of THz radiation in place of x-rays as a means for drug detection based on hyperspectral imaging. There is, however, at the present time a lack for this purpose of compact, portable, and practical sources of widelytunable THz radiation capable of routine operation in other than laboratory-type environments. This feasibility proposal aims to construct a prototype version of such a source based on novel parametric generators specifically designed for the THz region, and to carry out an initial assessment of the source for drug detection/identification in real life situations, the latter with the collaboration of the Forensic Alliance. THz waves lie in that part of the electromagnetic spectrum located between the lower frequency microwaves on the one hand and the higher frequency infrared waves on the other (frequencies lie between 1 and 10 THz). Up until recently this has proven to be a difficult range of the electromagnetic spectrum to access, often being referred to as the''terahertz gap . However, THz wave technologies have been identified in the recent Foresight Exercise as an area of particular opportunity, and of crucial importance to a number of applications, including, as here, the detection of concealed drugs. THz wave generation is now an area of intensive, international research effort. The value of THz waves in the present context is twofold. Firstly, they are able to penetrate a large range of materials such as paper, wood, plastic, fabrics, ceramics, bone, and tissue (both human and animal), and in a non-invasive way unlike the case with x-rays. Secondly, they are capable of discriminating between different heavy organic molecules (such as drugs) through frequency-dependent changes in their absorption by these molecules that differ from one type of molecule to another. This combination makes it possible both to associate a spectral fingerprint with a particular drug so enabling it to be identified, but importantly to do so even when that drug is concealed within a container made of materials of the type described above. Although a number of alternative approaches to the generation of THz waves are currently been explored, including the use of quantum cascade lasers and photoconductive switching using ultrashort pulse lasers, the approach proposed here based on parametric generation is unique in being able to deliver from a single source narrow-linewidth THz radiation that can be tuned to target particular spectral features, important in the context of spectral fingerprinting, and where the source operates at room temperature (unlike quantum cascade lasers that require to be cooled to cryogenic temperatures). So far sources based on parametric generation have been bulky and not easily transportable, hence making their in-field usage difficult. Based on over 15 years of experience in developing parametric generators for the ultraviolet, visible and infrared spectral ranges, the investigators at the University of St Andrews have come up with novel ideas, now patented, for building a compact, efficient and readily-transportable parametric generator of THz radiation. Following the construction of a prototype version of such a source a programme of assessment will be undertaken in collaboration with the Forensic Alliance to identify effective protocols for the in-field detection of illicit and concealed drugs.
|