Raman scattering or the Raman effect is the inelastic scattering of a photon. Elasticity is a branch of physics which studies the properties of elastic materials. ... The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, infrared radiation, microwaves, radio waves, and visible light are all forms of light. ...

When light is scattered from an atom or molecule, most photons are elastically scattered (Rayleigh scattering). The scattered photons have the same energy (frequency) and, therefore, wavelength, as the incident photons. However, a small fraction of scattered light (approximately 1 in 1000 photons) is scattered from excitations with optical frequencies different from, and usually lower than, the frequency of the incident photons.^[1] In a gas, Raman scattering can occur with a change in vibrational, rotational or electronic energy of a molecule (see energy level). Chemists are concerned primarily with the vibrational Raman effect. It has been suggested that this article or section be merged with Electromagnetic radiation. ... In particle physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle still characterizing a chemical element. ... In science, a molecule is a group of atoms in a definite arrangement held together by chemical bonds. ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... Rayleigh scattering causing a reddened sky at sunset Rayleigh scattering (named after Lord Rayleigh (RAY-lee)) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... The wavelength is the distance between repeating units of a wave pattern. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ...

In 1922, Indian physicist Chandrasekhara Venkata Raman published his work on the "Molecular Diffraction of Light," the first of a series of investigations with his collaborators which ultimately led to his discovery on 28 February 1928 of the radiation effect which bears his name. The Raman effect was first reported by C. V. Raman and K. S. Krishnan, and independently by Grigory Landsberg and Leonid Mandelstam in 1928. Raman received the Nobel Prize in 1930 for his work on the scattering of light. In 1998 the Raman Effect was designated an ACS National Historical Chemical Landmark in recognition of its significance as a tool for analyzing the composition of liquids, gases, and solids.^[2] Sir Chandrasekhara Venkata Raman, CBE (Tamil: சந்திரசேகர வெங்கடராமன்) (November 7, 1888 – November 21, 1970) was an Indian physicist, who was awarded the 1930 Nobel Prize in Physics for his work on the scattering of light and for the discovery of the Raman effect, which is named after him. ... February 28 is the 59th day of the year in the Gregorian calendar. ... Year 1928 (MCMXXVIII) was a leap year starting on Sunday (link will display full calendar). ... Sir Chandrasekhara Venkata Raman, CBE (Tamil: சந்திரசேகர வெங்கடராமன்) (7 November 1888 – 21 November 1970) was an Indian physicist, who was awarded the 1930 Nobel Prize in Physics for his work on the scattering of light and for the discovery of the Raman effect, which is named after him. ... Grigory Samuilovich Landsberg (Григорий Самуилович Ландсберг) (January 10, 1890 - February 2, 1957) Russian physicist. ... Leonid Isaakovich Mandelshtam (Леонид Исаакович Мандельштам, last name more often spelled as Mandelstam) (May 4, 1879 - November 27, 1944) was a Russian/Soviet physicist of Jewish background. ... Year 1928 (MCMXXVIII) was a leap year starting on Sunday (link will display full calendar). ... The Nobel Prizes (Swedish: ) are awards in Physics, Chemistry, Literature, Peace, Physiology or Medicine and Economics. ... Year 1930 (MCMXXX) was a common year starting on Wednesday (link is to a full 1930 calendar). ... The ACS National Historic Chemical Landmarks Program was launched by the American Chemical Society in 1992 and has recognized over 50 landmarks to date. ...

Raman scattering: Stokes and anti-Stokes

The interaction of light with matter in a linear regime allows the absorption or simultaneous emission of light precisely matching the difference in energy levels of the interacting electrons.

The Raman effect corresponds, in perturbation theory, to the absorption and subsequent emission of a photon via an intermediate electron state, having a virtual energy level (see also: Feynman diagram). There are three possibilities: In quantum mechanics, perturbation theory is a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one. ... In this Feynman diagram, an electron and positron annihilate and become a quark-antiquark pair. ...

• no energy exchange between the incident photons and the molecules (and hence no Raman effect)
• energy exchanges occur between the incident photons and the molecules. The energy differences are equal to the differences of the vibrational and rotational energy-levels of the molecule. In crystals only specific photons are allowed (solutions of the wave equations which do not cancel themselves) by the periodic structure, so Raman scattering can only appear at certain frequencies. For amorphous materials like glasses, more photons are allowed and thereby the discrete spectral lines become broad.

• molecule absorbs energy: Stokes scattering. The resulting photon of lower energy generates a Stokes line on the red side of the incident spectrum.
• molecule loses energy: anti-Stokes scattering. Incident photons are shifted to the blue side of the spectrum, thus generating an anti-Stokes line.

The different possibilities of visual light scattering: Rayleigh scattering (no Raman effect), Stokes scattering (molecule absorbs energy) and anti-Stokes scattering (molecule loses energy)

These differences in energy are measured by subtracting the energy of the mono-energetic laser light from the energy of the scattered photons. The absolute value, however, doesn't depend on the process (Stokes or anti-Stokes scattering), because only the energy of the different vibrational levels is of importance. Therefore, the Raman spectrum is symmetric relative to the Rayleigh band. In addition, the intensities of the Raman bands are only dependent on the number of molecules occupying the different vibrational states, when the process began. The Boltzmann distribution teaches us that more molecules occupy the lower energy levels in most cases: In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... Stokes line is named after Sir George Gabriel Stokes. ... Image File history File links Download high resolution version (887x435, 10 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high resolution version (887x435, 10 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Rayleigh scattering causing a reddened sky at sunset Rayleigh scattering (named after Lord Rayleigh (RAY-lee)) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ... In physics, the Boltzmann distribution predicts the distribution function for the fractional number of particles Ni / N occupying a set of states i which each has energy Ei: where is the Boltzmann constant, T is temperature (assumed to be a sharply well-defined quantity), is the degeneracy, or number of...

Thus the Stokes spectrum is more intense than the anti-Stokes spectrum. The word degeneracy has more than one meaning: In general, degeneracy means reverting to an earlier, simpler, state In mathematics, a limiting case in which a class of object changes its nature so as to belong to another, usually simpler, class. ... The term orbital has several meanings: In physics and chemistry it is used to describe an atomic electron configuration, see also molecular orbital and atomic orbital. ... The word degeneracy has more than one meaning: In general, degeneracy means reverting to an earlier, simpler, state In mathematics, a limiting case in which a class of object changes its nature so as to belong to another, usually simpler, class. ... The term orbital has several meanings: In physics and chemistry it is used to describe an atomic electron configuration, see also molecular orbital and atomic orbital. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero—the lowest possible temperature where nothing could be colder and no heat energy remains in a substance—is defined as zero kelvin (0 K). ...

Distinction with fluorescence

The Raman effect differs from the process of fluorescence. For the latter, the incident light is completely absorbed and the system is transferred to an excited state from which it can go to various lower states only after a certain resonance lifetime. The result of both processes is essentially the same: A photon with the frequency different from that of the incident photon is produced and the molecule is brought to a higher or lower energy level. But the major difference is that the Raman effect can take place for any frequency of the incident light. In contrast to the fluorescence effect, the Raman effect is therefore not a resonant effect. Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... It has been suggested that this article or section be merged with quantum state. ... This article is about resonance in physics. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... This article is about resonance in physics. ...

Selection rules

The distortion of a molecule in an electric field, and therefore the vibrational Raman cross section, is determined by its polarizability. In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles. ... Polarizability is the relative tendency of the electron cloud of an atom to be distorted from its normal shape by the presence of a nearby ion or dipole--that is, by an external electric field. ...

A Raman transition from one state to another, and therefore a Raman shift, can occur only when the polarizability changes during the process under consideration (that is, during the vibration or rotation). The key quantity is the derivative of the polarizability with respect to the normal mode excited during the transition. Various normal modes in a 1D-lattice. ...

Stimulated Raman scattering and Raman amplification

Raman amplification can be obtained by using Stimulated Raman Scattering (SRS), which actually is a combination between a Raman process with stimulated emission. It is interesting for application in telecommunication fibers to amplify inside the standard material with low noise for the amplification process. However, the process requires significant power and thus imposes more stringent limits on the material. The amplification band can be up to 100 nm broad, depending on the availability of allowed photon states. Raman amplification (pronounced /rʌmɑn/) is based on the Stimulated Raman Scattering (SRS) phenomenon, when a lower frequency signal photon induces the inelastic scattering of a higher-frequency pump photon in an optical medium in the nonlinear regime. ...

Raman spectrum generation

For high intensity CW (continuous wave) lasers, SRS can be used to produce broad bandwidth spectra. This process can also be seen as a special case of four wave mixing, where the frequencies of the two incident photons are equal and the emitted spectra are found in two bands separated from the incident light by the phonon energies. The initial Raman spectrum is built up with spontaneous emission and is amplified later on. At high pumping levels in long fibers, higher order Raman spectra can be generated by using the Raman spectrum as a new starting point, thereby building a chain of new spectra with decreasing amplitude. The disadvantage of intrinsic noise due to the initial spontaneous process can be overcome by seeding a spectrum at the beginning, or even using a feedback loop like in a resonator to stabilize the process. Since this technology easily fits into the fast evolving fiber optic laser field and there is demand for transversal coherent high intensity light sources (i.e. broadband telecommunication, imaging applications), Raman amplification and spectrum generation might be widely used in the near future. Four Wave Mixing is an intermodulation distortion in optical systems, similar to the third order intercept in electrical systems. ...

Applications

Raman spectroscopy employs the Raman effect for materials analysis. The frequency of light scattered from a molecule may be changed based on the structural characteristics of the molecular bonds. A monochromatic light source (laser) is required for illumination, and a spectrogram of the scattered light then shows the deviations caused by state changes in the molecule. This article or section does not adequately cite its references or sources. ...

Raman spectroscopy is also used in combustion diagnostics. Being a completely non-intrusive technique, it permits the detection of the major species and temperature distribution inside combustors and in flames without any perturbation of the (mainly fluid dynamic and reactive) processes examined.

Stimulated Raman transitions are also widely used for manipulating a trapped ion's energy levels, and thus basis qubit states, in ion trap quantum computing. To meet Wikipedias quality standards and make it more accessible, this article needs a better explanation of technical details or more context regarding applications or importance to make it more accessible to a general audience, or at least to technical readers outside this specialty. ... Ions, or charged atomic particles, can be confined and suspended in free space using electromagnetic fields. ...

See also

• scattering
• Brillouin scattering
• Raman spectroscopy
• nonlinear optics
• fiber amplifier
• List of surface analysis methods
• Raman laser
• SERS

In particle physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles. ... Brillouin scattering occurs when light in a medium (such as water or a crystal) interacts with density variations and changes its path. ... This article or section does not adequately cite its references or sources. ... Nonlinear optics is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization P responds nonlinearly to the electric field E of the light. ... In telecommunication, an optical amplifier is a device that amplifies an optical signal directly, without the need to convert it to an electrical signal, or amplify it electrically, and reconvert it to an optical signal. ... List of surface analysis methods LIBS - Laser induced breakdown spectroscopy EBSD - Electron backscatter diffraction XRF - X-ray fluorescence analysis LOES - Laser optical emission spectroscopy LS - Light (Raman) scattering IRS - Infra Red spectroscopy SEIRA -Surface enhanced infrared absorption spectroscopy FTIR - Fourier transform infrared absorption spectroscopy; e. ... The Raman laser is a byproduct of the Raman Effect, discovered in 1928 by Nobel laureate Chandrasekhara Venkata Raman. ... SERS can mean:- Selective En bloc Redevelopment Scheme, a housing strategy in Singapore. ...

References

1. ^ Harris and Bertolucci (1989). Symmetry and Spectroscopy. Dover Publications. 
2. ^ [1]

• "A new radiation", Indian J. Phys., 2 (1928) 387 - http://www.uky.edu/~holler/raman.html
• Herzberg, Spectra of Diatomic Molecules, Litton Educational Publishing, 1950, ISBN 0-442-03385-0, pp. 61ff and 66ff

Gerhard Herzberg (December 25, 1904 – March 3, 1999) was a pioneering theoretical chemist. ...

External links

• Explanation from Hyperphysics in Astronomy section of gsu.edu
• Applications of Raman scattering
• Raman Spectroscopy - Tutorial