The Raman-spectroscopy is a contact-free analysis method for the characterisation of materials.
The substance to be analysed absorbs monochromatic light, e.g. a laser. The light scattered by the material contains the irradiated wavelength (Rayleigh scattering) as well as photons of other wavelengths, the so called inelastic or Raman scattering. The shift in energy results from the excitement of the vibrations in the molecules or from crystal vibrations (phonons).
By depicting the intensity of the inelastically scattered light as a function of the shift in energy relative to the laser light absorbed - indicated as wave numbers (cm-1) – you get the Raman spectrum.
Like the infrared spectroscopy, the Raman-spectroscopy is a vibrational spectroscopic method of analysis. The Raman spectra can for example be used for the definite identification of chemical substances.