This vibrational spectroscopy
method uses a monochromatic
(single frequency) laser
beam to illuminate the sample. The detection consists of scanning just below (or above) the frequency of the laser to detect smaller peaks. These are due to photons
that have either lost or gained energy from interaction with a molecular vibration of the sample. This change in energy is equal to the energy of the particular vibration.
To be active in Raman spectroscopy a vibration must cause a change in the polarizability of the molecule.
Raman spectroscopy was proposed and developed by Sir Chandrasekhra Venkata Raman (C.V.Raman) who received the 1930 Nobel Prize for Physics for this work.