PORTABLE RAMAN SPECTROMETER FOR THE NONDESTRUCTIVE CHARACTERIZATION OF AGING SURFACES

Raman spectroscopy is a subtle, but powerful technique for the characterization of surfaces and coatings. This laser-based technique probes the vibrational states of a materiel. Inelastic scattering of the incident laser beam results in frequency shifts in the scattered spectrum which are equal to the change in energy between adjacent vibrational states. These vibration states are a function of surface temperature, stress or strain, chemical bonding, and material phase. Narrow notch Rugate filters and short wavelength, high power diode lasers are the enabling technologies for a low cost, portable Raman spectrometer. The narrow notch Rugate filter separates the bright Rayleigh backscatter and Fresnel reflection from the much weaker Raman spectrum. A compact, fiber based probe can be used to monitor surface oxidation, grain growth on critical parts due to thermal cycling, or measure surface stress and strain. In Phase I, we will trade-off probe design options, determine system requirements, design and fabricate Raman filters, construct a prototype, and demonstrate proof of concept. In Phase II, we will refine the probe design options, determine system requirements, design and fabricate Raman filters, construct of prototype, and demonstrate proof of concept. In Phase II, we will refine the probe design based on test performance, fabricate improved filters and complete the required software to make the system portable and intelligent.