Editing Plasma diagnostics (section)

==Optical effects from free electrons==
The optical diagnostics above measure line radiation from atoms. Alternatively, the effects of free charges on electromagnetic radiation can be used as a diagnostic.

===Electron cyclotron emission===
In magnetized plasmas, electrons will gyrate around magnetic field lines and emit [[cyclotron radiation]]. The frequency of the emission is given by the [[Electron cyclotron resonance|cyclotron resonance]] condition. In a sufficiently thick and dense plasma, the intensity of the emission will follow [[Planck's law]], and only depend on the electron temperature.

===Faraday rotation===
The [[Faraday effect]] will rotate the plane of [[Polarization (waves)|polarization]] of a beam passing through a plasma with a magnetic field in the direction of the beam. This effect can be used as a diagnostic of the magnetic field, although the information is mixed with the density profile and is usually an integral value only.

===Interferometry===
If a plasma is placed in one arm of an [[Interferometry|interferometer]], the phase shift will be proportional to the plasma density integrated along the path.

===Thomson scattering===
Scattering of laser light from the electrons in a plasma is known as [[Thomson scattering]]. The electron temperature can be determined very reliably from the [[Doppler broadening]] of the laser line. The electron density can be determined from the intensity of the scattered light, but a careful absolute calibration is required. Although Thomson scattering is dominated by scattering from electrons, since the electrons interact with the ions, in some circumstances information on the ion temperature can also be extracted.