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Raman microscopy

Raman microscopy animated

Raman microscopy is a very specialized optical microscopy. As in any optical microscopy its spatial resolution is close to the micron.

In Raman microscopy the sample is illuminated with monochromatic light (a laser) and the light scattered by the material is analyzed by a conventional optical microscope coupled to a Raman spectrometer or a very sophisticated filter.

Most of the scattered light has the same frequency or color as the laser, but a very tiny amount experiences a frequency shift, which is characteristic of the chemical bonds or molecules present in the material. This inelastic scattering of light is called the Raman effect after C. V. Raman, who discovered it. The analysis of the scattered frequencies (Raman spectroscopy) gives information on the material chemical composition, state, aggregation, and even factors like stress, orientation, or temperature to cite some.

Raman spectroscopy became a useful technique with the introduction of lasers as a convenient monochromatic light source. It has become widely available only after the introduction of holographic or edge filters to reject the light scattered without frequency change and CCD detectors.

In Raman microscopy the Raman frequency shift is analyzed at different points in the sample. Raman microscopy can resolve parts with different chemical composition in a sample, and, together with infrared microscopy, is sometimes referred as chemical imaging. It has been applied to the study of thin films, coatings, microelectronic integrated circuits, mineral inclusions, pigments in art works, identification of narcotics and plastic explosives, biological tissues, and others.

Examples

The following figures illustrate the application of Raman microscopy to chemical imaging in materials science. The data were obtained at the Raman Microscopy Laboratory of the Materials Science Institute of Madrid (ICMM-CSIC) in collaboration with other centers.

(H,Li)NbO3 optical waveguide Polymer penetration into porous silicon

Bibliography

See, for example, G. Turrell and J. Corset, eds., Raman Microscopy. Developments and Applications (Academic Press, London, 1996).