In electromagnetics we are taught that mediums can be linear/nonlinear,isotropic/anisotropic,homogeneous/non-homogeneous...we also learn their definitions. Now we are told that if nothing is specified then take the medium to be linear,homogeneous and isotropic. I want to know examples of those mediums which do not follow these criteria as I have never encountered such.
Remember that electromagnetism includes light waves.
- Any semi-transparent volumetric medium can have space-varying properties (transparency, colors) and thus be heterogeneous.
- Polarisers, and indeed many of gems, are not isotropic, because of the cristal network orientations.
- Various materials show some saturation or change of property at very high intensity (because there are not supra-conductors)
Moreover there exist 2 kinds of mediums: continuous medium, and composed medium. E.g. cloud/fog/smoke are made of very numerous and small objects floating in air. But
These objects can have a non-symmetrical shape, and be consistantly oriented (e.g. ice cristal in some clouds, big non-spherical water droplet), causing anisotropy.
There density (number per cubic meter) is very likely to varies (cloud/fog/smoke have borders :-) ).
Regarding anisotropy, the common one is quartz. For quartz you commonly see ordinary/extraordinary rays refracted according to the two refractive indices of the two axes.
Silica optical fibres have a small nonlinearity. Because of symmetry, their even order nonlinearities go to zero but the third order nonlinearity exists and is used in soliton communication (where the nonlinearity counteracts the dispersion).
Nonlinear crystals are used in lasers for sum frequency generation. E.g. an Argon laser at 488 nm (blue) can be made to emit 244 nm in the UV with a properly aligned BBO crystal.
Nonlinearity is something we commonly experience in diodes, in this case the non-homogeneity of the doping creates a nonlinear response.