Photonics Dictionary

Raman scattering

Raman scattering, also known as the Raman effect or Raman spectroscopy, is a phenomenon in which light undergoes inelastic scattering when interacting with matter, such as molecules, crystals, or nanoparticles. Named after Indian physicist Sir C. V. Raman, who discovered it in 1928, Raman scattering provides valuable information about the vibrational and rotational modes of molecules and materials.

Principle: When a photon interacts with a molecule, most of the scattered light retains the same energy (elastic scattering, Rayleigh scattering). However, a small fraction of photons interacts with the molecule in such a way that the energy of the scattered photon differs from that of the incident photon. This difference in energy corresponds to the energy of a molecular vibration or rotation.
Stokes and anti-Stokes shifts: In Raman scattering, the scattered photons can have energies lower (Stokes shift) or higher (anti-Stokes shift) than the incident photon energy, corresponding to vibrational transitions where energy is either gained or lost by the molecule.
Raman spectroscopy: The technique involves analyzing the scattered light to determine the frequencies of these energy shifts. By measuring the intensities and frequencies of the Raman scattered light, detailed information about the molecular structure, chemical bonds, and crystalline properties of the material can be obtained.
Raman spectroscopy is widely used in various fields, including:

Chemistry: Characterizing molecular structures and identifying chemical compositions.

Materials science: Analyzing crystallinity, defects, and composition in materials like semiconductors and polymers.

Biology and medicine: Studying biological molecules, cells, tissues, and pharmaceuticals.

Forensics and art conservation: Analyzing pigments, dyes, and cultural heritage materials.

Environmental monitoring: Detecting pollutants and contaminants in water and air.

Raman scattering is a powerful analytical technique due to its non-destructive nature, high sensitivity, and ability to provide detailed molecular information. It has become an indispensable tool in research, industry, and various scientific disciplines for investigating the properties and behavior of matter at the molecular and atomic levels.
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