In physics, Thomson scattering is the scattering of electromagnetic radiation by a charged particle. The electric and magnetic components of the incident wave accelerate the particle. As it accelerates, it in turn emits radiation and thus, the wave is scattered. Thomson scattering is an important phenomenon in plasma physics and was first explained by the physicist J.J. Thomson. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... The article on electrical energy is located elsewhere. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ... Acceleration is the time rate of change of velocity, and at any point on a v_t graph, it is given by the gradient of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ... A Plasma lamp In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. ... Sir Joseph John Thomson, OM , FRS (December 18, 1756 – August 30, 1940) often known as J. J. Thomson, was an English physicist, the discoverer of the electron. ...

As long as the motion of the particle is non-relativistic (i.e. its speed is much less than the speed of light), the main cause of the acceleration of the particle will be due to the electric field component of the incident wave. The particle will move in the direction of the oscillating electric field, resulting in electromagnetic dipole radiation. The moving particle radiates most strongly in a direction perpendicular to its motion and that radiation will be polarized along the direction of its motion. Therefore, depending on where an observer is located, the light scattered from a small volume element may appear to be more or less polarized. Albert Einsteins theory of relativity is a set of two theories in physics: special relativity and general relativity. ... The Earths magnetic field, which is approximately a dipole. ... This article treats polarization in electrodynamics. ...

The electric fields of the incoming and observed beam can be divided up into those components lying in the plane of observation (formed by the incoming and observed beams) and those components perpendicular to that plane. Those components lying in the plane are referred to as "radial" and those perpendicular to the plane are "tangential", since this is how they appear to the observer. Image File history File links No higher resolution available. ...

The diagram on the right is in the plane of observation. It shows the radial component of the incident electric field causing a component of motion of the charged particles at the scattering point which also lies in the plane of observation. It can be seen that the amplitude of the wave observed will be proportional to the cosine of χ, the angle between the incident and observed beam. The intensity, which is the square of the amplitude, will then be diminished by a factor of cos²(χ). It can be seen that the tangential components (perpendicular to the plane of the diagram) will not be affected in this way.

The scattering is best described by an emission coefficient which is defined as ε where ε dt dV dΩ dλ is the energy scattered by a volume element dV in time dt into solid angle dΩ between wavelengths λ and λ+dλ. From the point of view of an observer, there are two emission coefficients, ε_r corresponding to radially polarized light and ε_t corresponding to tangentially polarized light. For unpolarized incident light, these are given by: Emission coefficient is a coefficient in the power output per unit time of an electromagnetic source, a calculated value in physics. ...

where n is the density of charged particles at the scattering point, I is incident flux (e.g. energy/time/area/wavelength) and σ is the Thomson differential cross section for the charged particles (area/solid angle), which is In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles. ... A solid angle is the three dimensional analog of the ordinary angle. ...

where the first expression is in cgs units, the second in SI units; q is the charge per particle, m the mass per particle, and ε₀ a constant, the permittivity of free space. This article or section is in need of attention from an expert on the subject. ... Look up si, Si, SI in Wiktionary, the free dictionary. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium and is determined by the ability of a material to polarize in response to an applied electric field, and thereby to cancel, partially, the field inside the material. ...

Note that this is the square of the classical radius of a point particle of mass m and charge q. For example, for an electron, the differential cross section is: The classical electron radius, also known as the Compton radius or the Thomson scattering length is based on a classical (i. ... For other uses, see Electron (disambiguation). ...

The total energy radiated is found by integrating the sum of the emission coefficients over all directions:

where σ_T is the total cross section:

which for an electron has a value of 6.652...× 10⁻²⁵ cm².

Examples of Thomson scattering

The cosmic microwave background is thought to be linearly polarized as a result of Thomson scattering. Probes such as WMAP and the future Planck mission attempt to measure this polarization. WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... WMAP image, unrelated to Planck The Planck Surveyor is the third Medium-Sized Mission (M3) of ESAs Horizon 2000 Scientific Programme. ...

The solar K-corona is the result of the Thomson scattering of solar radiation from solar coronal electrons. NASA's STEREO mission will generate three-dimensional images of the electron density around the sun by measuring this K-corona from two separate satellites. This article is about the spacecraft and the mission. ...

In tokamaks and other experimental fusion devices, the electron temperatures and densities in the plasma can be measured with high accuracy by detecting the effect of Thomson scattering of a high-intensity laser beam. A split image of the largest tokamak in the world, the JET, showing hot plasma in the right image during a shot. ... Internal view of the JET tokamak superimposed with an image of a plasma taken with a visible spectrum video camera. ... For other uses, see Plasma. ... Plasma diagnostics are experimental techniques used to measure properties of a plasma such as temperature and density. ... For other uses, see Laser (disambiguation). ...

External links

• Lecture notes on Thomson scattering
• Thomson scattering notes

References

• Billings, Donald E., ``A Guide to the Solar Corona, Academic Press, New York 1966.