ABSTRACT
Light, made monochromatic and incident upon a sample, is scattered and transmitted at the incident frequency-a process known as Rayleigh scattering. Early in 1928 C V Raman and K S Krishnan reported [1-3] the visual discovery of a new form of secondary radiation. Sunlight, passed through a blue-violet filter, was used as the light source incident upon many different organic liquids and even vapours. A green filter was placed between the sample and the viewer. The filters were sufficiently complementary to suppress the strong Rayleigh scattering and leave at longer wavelengths a feeble new kind of scattered radiation. Impurity fluorescence was discounted, for the signal was robust under purification and it also was strongly polarized. It was suggested that the incident photons had undergone inelastic scattering with the material-much as the Compton scattering of x-rays by electrons. Almost simultaneously, G Landsberg and L Mandelstam [4] reported a new kind of secondary radiation from crystalline quartz illuminated by the lines of the mercury vapour lamp. Spectrograms revealed a feeble satellite line to the red of each of the Rayleigh scattered mercury lines. In each case the displacement came close to a characteristic vibrational frequency of quartz at ∼480 cm−1. They wondered whether their new secondary radiation might not be of the same type as that seen by Krishnan and Raman. Such inelastic scattering of photons soon came to be called (spontaneous) Raman scattering or, given its quantized energy displacements, simply (spontaneous) Raman spectroscopy [5].
