Raman spectroscopy

In Raman spectroscopy the material is illuminated with monochromatic light (with a single frequency or wavelength, usually from a laser) and the spectrum of scattered light is analyzed to find light with shifted frequencies or Raman peaks. Each Raman peak corresponds to a different vibrational mode of the material. The analysis of the scattered frequencies gives information on the material chemical composition, state, aggregation, and even factors like mechanical stress, pressure, orientation, crystallinity, or temperature to cite some.

Raman spectroscopy became more convenient with the introduction of lasers as monochromatic light sources. It became widely available after the introduction of holographic or edge filters to reject the light scattered without frequency change and CCD detectors.

The Raman effect is very weak and can be masked by other effects like luminescence. But has the advantage that it does not require special sample preparation. Also water and glass are poor Raman scatterers and Raman spectroscopy is thus convenient for biological samples and through glass containers, windows or cover slips. Also optical fibers can be used to guide the light to a separated lab.