Diode Laser Raman Scattering Prototype for Continuous On-site Characterization of Fuels and Environmental Contaminants

We propose developing a diode laser-based full-spectrum Raman scattering instrument prototype incorporating fiberoptic coupling for rapid, continuous on-line and remote monitoring of fuels. Raman's narrow, well-defined peaks and its insensitivity to moisture contamination allow for full-spectrum detection with 0.1% sensitivity for liquids and with 30 to 60 second response times. Traditional Raman scattering performed with visible light excitation is not compatible with liquid hydrocarbon systems because of background fluorescence. Conventional gas lasers have too short of a life and are too expensive for routine commercial instrumentation. A semiconductor laser diode offers longer life than conventional lasers and can operate at near-IR wavelengths where sample fluorescence is minimized while taking advantage of the very sensitive and full-spectrum capabilities of silicon CCD array Raman spectrum detection. Fiberoptic coupling allows the safe application of Raman scattering in hazardous environments, eliminates lag time, reduces maintenance of sample handling systems while affording remote location of vibration sensitive equipment. Laboratory results have demonstrated the ability to quickly measure gasoline components and parameters including individual aromatics, such as benzene, olefine contents, unique brand formulations, octane ratings and EPA-required oxygenated additives. Phase I will compare the prototype instrument with laboratory results.