Raman microscopy involves the illumination of a sample with monochromatic light and the analysis of the components that are inelastically scattered--that is, scattered with wavenumbers different from that of the light incident upon the sample. Under the experimental conditions used, the exciting radiation is focused to a spot with ~1-µm diameter. These conditions define the spatial resolution of the experiment. The Raman spectrum--a plot of the intensity of scattered radiation as a function of the wavenumber shift--is characteristic of the composition and the sample structure. The spectrum is sufficient, when observed with reasonable definition (typically S/N >5), to permit unambiguous identification of the sample.