Everything about Faraday Effect totally explained
In
physics, the
Faraday effect or
Faraday rotation is a
magneto-optical phenomenon, or an interaction between
light and a
magnetic field in a dielectric material. The rotation of the plane of
polarization is proportional to the intensity of the component of the magnetic field in the direction of the beam of light.
The Faraday effect, discovered by
Michael Faraday in 1845, was the first experimental evidence that light and electromagnetism are related. The theoretical basis for that relation, now called
electromagnetic radiation, was further developed by
James Clerk Maxwell in the 1860s and 1870s. This effect occurs in most optically
transparent dielectric materials (including liquids) when they're subject to strong
magnetic fields.
The Faraday effect is a result of
ferromagnetic resonance when the
permittivity of a material is represented by a
tensor. This resonance causes waves to be decomposed into two circularly polarized rays which propagate at different speeds, a property known as
circular birefringence. The rays can be considered to re-combine upon emergence from the medium, however owing to the difference in propagation speed they do so with a net
phase offset, resulting in a rotation of the angle of linear polarization.
There are a few applications of Faraday rotation in measuring instruments. For instance, the Faraday effect has been used to measure optical rotatory power, for amplitude modulation of light, and for remote sensing of magnetic fields. The Faraday effect is used in
spintronics research to study the polarization of electron spins in semiconductors.
The relation between the angle of rotation of the polarization and the magnetic field in a diamagnetic material is:
» is in radians per square meter (rad/m²).)
Faraday rotation is an important tool in
astronomy for the measurement of magnetic fields, which can be estimated from rotation measures given a knowledge of the electron number
prodensity. In the case of
radio pulsars, the
dispersion caused by these electrons results in a time delay between pulses received at different wavelengths, which can be measured in terms of the electron column density, or
dispersion measure. A measurement of both the dispersion measure and the rotation measure therefore yields the weighted mean of the magnetic field along the line of sight. The same information can be obtained from objects other than pulsars, if the dispersion measure can be estimated based on reasonable guesses about the propagation path length and typical electron densities.
Radio waves passing through the Earth's
ionosphere are also subject to Faraday rotation; as the above equation indicates, the effect is proportional to the square of the wavelength. At 435 MHz (UHF), one should expect in the order of 1.5 complete rotations of the wavefront as it transits the ionosphere, whereas at 1.2 GHz less than a quarter of one rotation is likely.
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