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In photonics, anapoles first appeared in 2015 as zeros in the Mie-coefficient of a particular
physics
Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...
, an anapole () is a system of currents
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (hy ...
that does not radiate into the far field. The term "anapole" first appeared in the work of Zel'dovich, in which he thanks A. S. Kompaneets, who first proposed the name.
An anapole is a system of currents that transforms under all transformations of the symmetry group O(3) as a certain multipole
A multipole expansion is a mathematical series representing a function that depends on angles—usually the two angles used in the spherical coordinate system (the polar and azimuthal angles) for three-dimensional Euclidean space, \R^3. Multipol ...
(or the corresponding vector spherical harmonic), but does not radiate to the far field.
Photonics
In photonics, anapoles first appeared in 2015 as zeros in the Mie-coefficient of a particular multipole
A multipole expansion is a mathematical series representing a function that depends on angles—usually the two angles used in the spherical coordinate system (the polar and azimuthal angles) for three-dimensional Euclidean space, \R^3. Multipol ...
in the scattering spectrum. They can also be explained as destructive interference of a "cartesian multipole" and a " toroidal multipole". The anapole state is not an eigenmode The mode of electromagnetic systems describes the field pattern of the propagating waves.
Some of the classifications of electromagnetic modes include;
* Modes in waveguides and transmission lines. These modes are analogous to the normal modes of ...
. Total scattering cross-section is not zero in the anapole state, due to the contribution of other multipoles.
The terms "anapole" and toroidal moment were once used synonymously,Popov, A. I., D. I. Plokhov, and A. K. Zvezdin. "Anapole moment and spin-electric interactions in rare-earth nanoclusters." Europhysics Letters 87.6 (2009): 67004. but this is no longer common.
See also
* Toroidal momentReferences
{{Reflist Electric current Electromagnetic radiation Photonics