UV resonance Raman spectroscopy is uniquely suitable for standoff measurements due to its high sensitivity and selectivity. When excitation wavelength falls within an electronic transition of a molecule, Raman band intensities associated with the chromophore vibrations are significantly enhanced. This resonance Raman Effect, as well as negligible fluorescence interference in the deep UV, enable the detection and investigation of enhanced species at trace concentrations at a distance. We developed a state-of-the-art, high-efficiency standoff deep UV Raman spectrometer. This spectrometer is based on a custom deep UV F/8 Cassegrain telescope with a 200 mm primary mirror. This telescope is equipped with an electric secondary focus operating from infinity to 3 m distance. The UV Raman spectrograph utilizes high-efficiency deep UV transmission grating and custom Rayleigh rejection filter. As an excitation source for Raman measurements, we utilized a recently developed 228 nm compact solid state deep UV laser. The 228 nm resonance excitation enhances the Raman intensities of vibrations of NOx groups, peptide bonds, aromatic amino acid side chains, and DNA/RNA nucleotides. We used this novel spectrometer for detection of NOx-based explosive materials at trace concentrations at a stand-off distance.
Due to its high sensitivity and selectivity, UV resonance Raman (UVRR) spectroscopy has a number of scientific and industrial applications. Deep UVRR excited within explosive absorption bands (200 – 230 nm) enables trace explosive detection at a distance due to the resonance enhancement of Raman band intensities, stronger light scattering at short wavelengths, as well as negligible florescence interference.
We are developing deep UVRR detection methodologies by investigating resonance enhancement of explosives excited in the deep UV, determining the optimal excitation wavelengths, investigating explosive UV-photochemistry, characterizing explosive UV photoproducts, and measuring UVRR spectral evolution during explosive photolysis.
We are also developing state-of-the-art UVRR instrumentation by designing and manufacturing high efficiency, high throughput standoff UVRR spectrometers, co-developing new compact solid state deep UV lasers, and designing novel deep UV optical diffracting devices.
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