Raman scattering refers to the scattering whose frequency changes due to the interaction between incident light and molecular motion when light passes through the medium. Also known as Raman effect. 1923 A. g. s. SME kal predicted the scattering with frequency in theory. 1928, Indian physicist C.V. Raman observed the phenomenon that the frequency of scattered light in gas and liquid changed. Raman scattering obeys the following laws: in scattered light, every original incident spectral line (frequency v0) is symmetrically accompanied by the spectral line of frequency v0 vi (I = 1, 2,3, …), the spectral line on the long wave side is called red companion line or Stokes line, and the spectral line on the short wave side is called purple companion line or anti-Stokes line; The frequency difference vi has nothing to do with the incident light frequency v0, but is determined by the nature of the scattering material. Each scattering substance has its specific frequency difference, some of which are consistent with the infrared absorption frequency of the medium. The intensity of Raman scattering is much weaker than Rayleigh scattering (see light scattering). When Raman scattering is explained by classical theory, it is considered that molecules vibrate at the natural frequency vi, and the polarizability (see polarizability) also changes periodically with vi as the frequency. Under the action of incident light with frequency v0, the coupling of v0 and vi produces three frequencies: v0, v0+vi and V 0-VI. The light with frequency v0 is Rayleigh scattering light, and the last two frequencies correspond to Raman scattering lines. The perfect explanation of Raman scattering needs quantum mechanics theory, which can not only explain the frequency difference of scattered light, but also solve the problems of intensity and polarization.

Raman scattering provides an important means to study the structure of crystals or molecules, and forms a branch of Raman spectrum in spectroscopy. Raman scattering method can be used to quickly determine the natural frequency of molecular vibration, thus determining the symmetry and internal force of molecules. Since the appearance of laser, the research on laser Raman scattering has developed rapidly, and the nonlinear effect caused by intense laser has led to a new Raman scattering phenomenon.