Raman

Raman primarily refers to the Raman effect, a phenomenon named after Indian physicist Chandrasekhara Venkata Raman. In science, Raman often denotes Raman spectroscopy, a family of techniques that probe vibrational, rotational, and other low-frequency modes in matter. The term is also used as a surname and appears in various biographical and historical contexts.

The Raman effect is inelastic scattering of photons by molecules or crystals. When light interacts with a sample, most photons are elastically scattered (Rayleigh scattering). A small fraction exchanges energy with molecular vibrational modes, emerging with shifted wavelengths. The resulting lines, called Stokes and anti-Stokes bands, appear at positions determined by the vibrational energies of the material and are typically reported as Raman shifts in wavenumbers (cm−1). The effect was described by C. V. Raman in 1928, and he shared the 1930 Nobel Prize in Physics for this discovery.

Raman spectroscopy relies on monochromatic light to excite the sample. The intensity and positions of Raman lines reveal molecular structure, chemical composition, and interactions. Because many materials exhibit weak Raman signals, enhancements from surface effects or nanostructures are often used.

Variants and related methods include surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS), and coherent anti-Stokes Raman spectroscopy (CARS). Raman imaging and micro-Raman spectroscopy allow spatially resolved measurements on small volumes or microscopic samples.

Applications span chemistry, materials science, pharmacology, geology, and biology. Raman techniques are valued for being non-destructive and requiring minimal sample preparation, though fluorescence and sample fluorescence can complicate analysis.