Forensic applications of raman spectroscopy

The forensic applications of Raman spectroscopy have been explored and extended using the development of novel sampling techniques and task-specific instrumentation described in this thesis. The phenomenon of Raman scattering, enhanced Raman scattering and their relevance in forensic investigations was reviewed. Particular emphasis was placed on current applications, experimental considerations relevant to in-situ Raman sampling and the deficiencies of instrumentation commercially available at the time. It was concluded that the development of novel, optimised instrumentation was essential in the application of Raman spectroscopy to portable forensic applications. The feasibility of achieving molecularly-specific and sensitive detection of TNT vapour using waveguide-enhanced, surface-enhanced resonance Raman spectroscopy was investigated using reference spectra measured using a calibrated optical system provided by a collaborator. Improvements in signal-to-noise ratio afforded by employing waveguide-enhanced sampling, higher excitation power, long integration times and an improved spectrometer design were modelled, experimentally verified, and used to predict a detection limit of 10-16g for saturated vapour-phase TNT. The theoretical performance of the optical instrument is described and verified using experimentally measured data. The feasibility of conducting specific and sensitive long-range stand-off covert observation operations against unsuspecting targets in compliance with the UK Regulation of Investigative Powers act was established using a task-optimised laboratory simulation. Using a 5mW visible excitation, short integration times (under 20s) and multiplex detection it was possible to detect and identify a tagged object from a range of up to 50m. The feasibility study yielded a robust prototype handheld system comprising a modified telephoto camera with the integrated capability of sample discrimination using Raman spectroscopy. The instrument design is described.