Raman Spectroscopy is a non-destructive technique that is used for the identification and quantification of chemical composition. The technique was named after physicist C. V. Raman, Nobel Prize winner in 1930 for contributions to spectroscopy.
A Raman spectrometer radiates a monochromatic light source (a laser beam) into a sample, collecting the scattered light. The majority of scattered rays are in the same frequency as the incoming laser beam, a phenomenon known as elastic or Rayleigh scattering. A very small proportion of the scattered light shifts its energy level and thus frequency, due to the interaction of the electromagnetic waves of the laser beam and vibrational movements of the molecules in the sample. This is called Raman or inelastic scattering.
After plotting this Raman scattering versus frequency, the resulting Raman spectrum is used to calculate a so-called 'fingerprint', which is unique for a given compound. The user can then learn the chemical composition and features of the sample by searching the fingerprint against a database or library of known components. Raman spectra reveal vibrational modes of the sample's chemical components and are therefore an ideal spectroscopic tool for chemical identification.
Combined with an optical microscope, Raman spectroscopy is more sensitive, less affected by unwanted background interactions, and offers the spatial resolution required for chemical mapping.
In a Raman microscope, scattered laser light from the sample is analysed, resulting in a Raman spectra which is unique to every molecule and reveals a variety of chemical and physical information about the sample with a high spatial resolution, in the order of nanometres.
Advantages of Raman Spectroscopy / Microscopy:
Non-contact / in-situ sampling
Minimum sample preparation
Applicable to liquid, film, bulk, powder and crystalline sample