Detection of Chemicals in Mixed, Two-Dimensional Raman Spectra

NRL has developed the SWOrRD system for measuring two-dimensional Raman Spectra. The device consists of tunable 2d ultraviolet laser that illuminates the sample at various wavelengths and collects a single Raman spectrum at each laser wavelength. The single spectra are combined to form a two-dimensional spectrum (laser wavelength by scattered wavenumber). In this paper we introduce a novel method for the detection of known agents within measured 2d spectra. Our method is based on 'linear mixed pixel' techniques from hyperspectral imagery; in particular, we generalize the Adaptive Subspace Detector (ASD) to a from suitable for the SWOrRD system. Our detector uses the individual laser tune to define a set of points within wavenumber space; the set of points corresponding to a 2d spectra defines a particular subspace that contains each material. These subspaces are then used with ASD to identify targets. Supported in part by Defense Threat Reduction Agency.