History

 

The phenomenon of inelastic scattering of the light that interacts with a material was postulated by Smekal in 1923 and observed experimentally the first time by Raman and Krishnan in 1928. In the original experiment, light of the sun was focused through a telescope directly on the sample, while a second optical device was used to collect the scattered radiation. The spectral selection for demonstrating the presence of a portion of frequency spectrum different from that incident one was made via optical filters, while the recording of spectra was done on photographic plates. The very low intensity of the Raman scattered light with respect to the elastical fraction has limited for many years the spread of this technique. Only the availability of LASER sources, as well as of dispersive apparatus and efficient detectors have allowed the real development of this technique. Since the late '80s, as a result of technical progress, review on scientific journals about possible applications of Raman spectroscopy (RS) different from a pure field physics studies began to appear A review specifically dedicated to the investigation on paint pigments appeared already in 1992 and this was followed by many others. However, only recently, thanks to technological developments in the field of optical filters (notch filters, interference filters) and especially of multichannel detectors, this technique could be used as a tool to spread, on a much broader scientific community, even as a field application. From this point of view, it has been essential, in recent years, the development of instrumentation for micro-Raman spectroscopy, which allowed to perform laboratory or in situ investigations.

The application of Raman spectroscopy to archeology and cultural heritage is relatively recent (not more than ten years), but it has already occupied a prominent place in the scientific community. His interest is due to the intrinsic characteristics resulting from a optical characterization with excitation at low energy. Furthermore, unlike the more common characterization techniques, such as Mossbauer spectroscopy, Raman spectroscopy is absolutely not destructive and does not require any treatment of the samples; Moreover, thanks to recent technological developments, it is also directly applicable in-situ using small but highly efficient tools.