All materials show a Kerr effect, but certain liquids display it more strongly than others.
The Kerr electro-optic effect, or DC Kerr effect, is the special case in which a slowly varying external electric field is applied by, for instance, a voltage on electrodes across the sample material.
Under this influence, the sample becomes birefringent, with different indices of refraction for light polarized parallel to or perpendicular to the applied field.
The difference in index of refraction, Δn, is given by where λ is the wavelength of the light, K is the Kerr constant, and E is the strength of the electric field.
This difference in index of refraction causes the material to act like a waveplate when light is incident on it in a direction perpendicular to the electric field.
If the material is placed between two "crossed" (perpendicular) linear polarizers, no light will be transmitted when the electric field is turned off, while nearly all of the light will be transmitted for some optimum value of the electric field.
Higher values of the Kerr constant allow complete transmission to be achieved with a smaller applied electric field.
Some polar liquids, such as nitrotoluene (C7H7NO2) and nitrobenzene (C6H5NO2) exhibit very large Kerr constants.
These are frequently used to modulate light, since the Kerr effect responds very quickly to changes in electric field.
The optical Kerr effect has also been observed to dynamically alter the mode-coupling properties in multimode fiber, a technique that has potential applications for all-optical switching mechanisms, nanophotonic systems and low-dimensional photo-sensors devices.
[6][7] The magneto-optic Kerr effect (MOKE) is the phenomenon that the light reflected from a magnetized material has a slightly rotated plane of polarization.
It is similar to the Faraday effect where the plane of polarization of the transmitted light is rotated.
For materials exhibiting a non-negligible Kerr effect, the third, χ(3) term is significant, with the even-order terms typically dropping out due to inversion symmetry of the Kerr medium.
Combining these two equations produces a complex expression for P. For the DC Kerr effect, we can neglect all except the linear terms and those in
For non-symmetric media (e.g. liquids), this induced change of susceptibility produces a change in refractive index in the direction of the electric field: where λ0 is the vacuum wavelength and K is the Kerr constant for the medium.
The refractive index change is thus proportional to the intensity of the light travelling through the medium.
The optical Kerr effect manifests itself temporally as self-phase modulation, a self-induced phase- and frequency-shift of a pulse of light as it travels through a medium.
The beam is prevented from self-focusing indefinitely by nonlinear effects such as multiphoton ionization, which become important when the intensity becomes very high.
As the intensity of the self-focused spot increases beyond a certain value, the medium is ionized by the high local optical field.
[11] This article incorporates public domain material from Federal Standard 1037C.