Raman scattering
Raman scattering or the Raman effect (icon) is the inelastic scattering
Inelastic scattering
In particle physics and chemistry, inelastic scattering is a fundamental scattering process in which the kinetic energy of an incident particle is not conserved . In an inelastic scattering process, some of the energy of the incident particle is lost or gained...

 of a photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

. It was discovered by Sir Chandrasekhara Venkata Raman and Kariamanickam Srinivasa Krishnan
Kariamanickam Srinivasa Krishnan
Padma Bhushan Sir Kariamanickam Srinivasa Krishnan, FRS, was an Indian physicist. He was a co-discover of Raman scattering, for which his mentor C. V. Raman was awarded the 1930 Nobel Prize in Physics.-Early life:...

 in liquids, and by Grigory Landsberg
Grigory Landsberg
Grigory Samuilovich Landsberg was a Soviet physicist.Grigory S. Landsberg is a co-discoverer of inelastic combinatorial scattering of light used now in Raman spectroscopy. His major scientific contributions were in the fields of optics and spectroscopy....

 and Leonid Mandelstam in crystals.

When photons are scattered
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...

 from an atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...

 or molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

, most photons are elastically scattered
Elastic scattering
In scattering theory and in particular in particle physics, elastic scattering is one of the specific forms of scattering. In this process, the kinetic energy of the incident particles is conserved, only their direction of propagation is modified .-Electron elastic scattering:When an alpha particle...

 (Rayleigh scattering
Rayleigh scattering
Rayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. It can occur when light travels through...

), such that the scattered photons have the same kinetic energy (frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

) and wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 as the incident photons.