How Does Energy Flow Differ from Light Propagation in Anisotropic Media?

[sanjibghosh]

In case of anisotropic medium the energy is flowing in a different direction with respect to the direction of light propagation .How can it possible ? If so,then in what form the energy is flowing ?

How can I detect that energy is flowing in a different direction not the direction of light propagation?

 

[Andy Resnick]

That's a very perceptive observation. All I know on this subject I learned from Born and Wolf.

For an anisotroptic medium, the electric and magnetic material fields D and H are not colinear with E and B. Typically we relax that a little and say only D and E are not colinear (dielectric tensor). The Poynting vector is E x H and may not be colinear with the direction of a wave normal- this is what is meant by the energy is not propogated in the direction of the wave normal. The phase velocity retains the same definition and is propogated in the direction of the wave normal, while the 'ray velocity' points in the direction of the Poynting vector.

In general terms, the two surfaces (one, an ellipsoid containing the wave normals and the other, an ellipsoid containing the ray vectors) are very complicated- the wave normal surface is 6th degree, while the ray surface is 4th degree. Picturing what happens to a single plane wave is not simple.

Fortunately, anisotropic crystals are either uniaxial or biaxial. Wave propogation in uniaxial crystals is straightforward- the complex surface simplifies to an ellipsoid, and there are two eigenstates- the extraordinary and ordinary ray.

For a biaxial crystal, the propogation is much more complicated and leads to conical refraction- the energy propagates in a cone.

Does that help? It's tough to picture.

 

[astrokreng]

An optical anisotropic medium is a material that has different optical properties depending on the direction of light propagation. This means that the medium is not uniform in all directions and has different refractive indices for different directions. This can occur due to the internal structure of the medium, such as the arrangement of molecules or crystals.

In such a medium, the energy is flowing in a different direction than the direction of light propagation. This is possible because light is an electromagnetic wave and can interact with the electric and magnetic fields of the medium. If the medium is anisotropic, the electric and magnetic fields of the light wave will interact differently in different directions, resulting in a different direction of energy flow.

To detect this energy flow, one can use techniques such as polarimetry or birefringence measurements. These methods can measure the changes in polarization or refractive index of the light as it passes through the anisotropic medium, indicating the direction of energy flow.

The form in which the energy is flowing can vary depending on the type of anisotropic medium. In some cases, it may be in the form of heat, as the energy of the light wave is converted into thermal energy due to the interactions with the medium. In other cases, it may be in the form of a change in the direction or polarization of the light itself.

In conclusion, anisotropic mediums allow for energy to flow in a different direction than the light propagation due to the interactions between the light wave and the medium's internal structure. This can be detected and measured using various techniques and can take different forms depending on the specific properties of the medium.