Diode Laser Raman Scattering Prototype Gas Phase Environmental Monitoring

We proposed developing a diode-laser-based, full spectrum Raman scattering instrument incorporating a multipass, external cavity enhancement cell for full spectrum, gas phase analysis of environmental pollutants. Narrow, well-defined Raman peaks and insensitivity to moisture contamination allow for full-spectrum with detection on the order of 1 percent sensitivity with 1 to 2 minute integrations. Conventional Raman instrumentation is too expensive and not sensitive enough for industrial applications. For excitation of Raman scattering Arion lasers have too short of a life and are too expensive for continuous use. Semiconductor laser diodes offer longer life than conventional lasers and now have sufficient power for rapidly obtaining Raman signals. Traditionally environmental instrumentation requires hot stack gases to be cooled prior to being measure. Cooling stack gas results in condensation and loss of water soluble species. Phase II focused on a laser power build-up of cavity design that would be stable, simple to reproduce, and cost effective. We assembled a bench prototype power build-up cavity with solid-state laser diode pumping that incorporated an efficient spectrograph (patent pending), application specific software, user interface, and calibration procedures. Although the prototype was not stable for on-line testing in industrial environmental monitoring applications, the bench prototype was extensively tested in the laboratory.