Ramanszórás

Ramanszórás, or Raman scattering, is an inelastic scattering process in which photons interact with a material and exchange energy with its vibrational or rotational modes. After interaction, the scattered photons have different energies than the incident photons. If the scattered photon loses energy, the process is called Stokes scattering; if it gains energy, it is referred to as anti-Stokes scattering. The energy difference, measured in wavenumbers (cm−1), is characteristic of the molecular vibrations and serves as a fingerprint for chemical composition.

The effect arises because molecular polarizability changes during vibrations. Raman scattering is typically weak compared with Rayleigh (elastic) scattering, and the intensity depends on the change in polarizability with the vibrational mode. Experiments usually employ a monochromatic laser as the excitation source and collect the scattered light with a spectrometer to resolve the Raman shifts. Raman spectra provide information about molecular structure, bonding, and symmetry, often complementing infrared spectroscopy.

History and extensions. Ramanszórás was discovered independently by C. V. Raman and K. S. Krishnan in 1928, earning Raman the 1930 Nobel Prize in Physics. In addition to spontaneous Raman scattering, techniques such as stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) have expanded the method into high-sensitivity imaging and microscopy.

Applications and limitations. Raman spectroscopy is widely used for chemical identification, materials characterization, pharmaceuticals, polymers, and biological tissues. It offers non-destructive analysis with minimal sample preparation and can be performed under ambient conditions. Limitations include inherently weak signals, potential fluorescence backgrounds, and sample heating or damage at high laser powers.