02_10_Raman - Raman Scattering Spectroscopy Materials...

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1 Raman Scattering Spectroscopy Materials characterization Industrial process control Micro-spectroscopy (to <1 μ m resolution) Remote measurements, through optical fibers (to 100 meters) Environmental monitoring Clinical diagnostics? Problems: 18-1, 18-2, 18-3, 18-6
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2 Raman scattering Advantages Observed in visible, NIR region of spectrum glass, quartz O.K. for optics and sample containers different selection rules (from IR): •H 2 O, SiO 2 are relatively weak scatterers Good for aqueous solutions; glass sample containers Microspectroscopy has better spatial resolution than IR version Easier to observe scattered light from solids than to observe reflectance Disadvantages Weak effect (efficiency 10 -7 ) Easily masked by fluorescence Requires very quiet photon detectors (dark lab) Raman scattering was discovered by Raman in 1920’s.
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3 Total Spectrum Rayleigh=elastic scattering, energy in=energy out photons are absorbed by the sample and reemitted with the same energy Raman=inelastic scattering Stokes= lower cm -1 less energy out, λ red-shift Anti-Stokes= higher cm -1 more energy out, blue shift - - + + More intense generally neglected
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4 Incident photon energy is usually less than energy of first electronic transition.
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02_10_Raman - Raman Scattering Spectroscopy Materials...

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