TIME-RESOLVED AND 2-DIMENSIONAL NIR FT-RAMAN SPECTROSCOPY

The near-infrared Fourier transform (NIR FT) Raman technique permits t he measurement of Raman spectra without interference by fluorescence. Absorption by molecules containing X-H bonds in the NIR range requires a 180-degrees scattering geometry. In this way, Raman spectroscopy of samples on surfaces is possible, both the detecting of small spots an d the mapping of the sample distribution over larger areas. The spatia l resolution extends into the micrometer range. Mapping of the inorgan ic pigment distribution of an initial letter of a mediaeval manuscript is demonstrated. For time-resolved measurements, the step-scan techni que, previously developed for infrared spectroscopy, may be used in NI R FT-Raman spectroscopy as well. It allows the study of photochemical and photophysical processes, the application of modulation techniques, and the investigation of ''noisy'' samples. Photo-isomerization of th e dye merocyanine 540 has been observed with the step-scan technique u pon periodic excitation with a flash lamp.