Time-resolved and two-dimensional NIR FT-Raman spectroscopy.
The near-IR Fourier transform (NIRFT) Raman technique permits the measurement of Raman spectra without interference by fluorescence. Absorption by mols. contg. X-H bonds in the NIR range requires a 180 Deg scattering geometry. In this way, Raman spectroscopy of samples on surfaces is possible, both the detecting of small spots and the mapping of the sample distribution over larger areas. The spatial resoln. extends into the micrometer range. Mapping of the inorg. pigment distribution of an initial letter of a medieval manuscript is demonstrated. For time-resolved measurements, the step-scan technique, previously developed for IR spectroscopy, may be used in NIR FT-Raman spectroscopy as well. It allows the study of photochem. and photophys. processes, the application of modulation techniques, and the investigation of \"noisy\" samples. Photoisomerization of the dye merocyanine 540 has been obsd. with the step-scan technique upon periodic excitation with a flash lamp.
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