Raman Spectroscopy is a widely used and versatile form of analysis used throughout biology, chemistry and solid-state physics (1) (2) (3). Like all spectroscopic techniques it observes how light interacts with a sample in order to understand its properties. This can then be used to, for example, identify an unknown sample, monitor how stress affects a crystal structure or look for impurities. Raman Spectroscopy is not the analysis of light absorbed, emitted, or elastically scattered from a sample, but rather the inelastically scattered light.
When an object elastically scatters, it retains its original energy. Elastic scattering between light and matter is called Rayleigh scattering. It accounts for most scattering events seen between a light source and any given material. However, as discovered by C.V. Raman in 1928 (4), light can undergo inelastic scattering with matter. In this case the photon of light involved has a different energy before and after the scattering event. Having either lost (known as a Stokes shift) or gained (an anti-Stokes shift) energy from the matter it interacted with. This change of energy can be measured as a change in the wavelength (colour) of the light (Figure 1)