Conservation of angular momentum

[rays]

If the incident radiation is linearly polarized can the scattered radiation be circularly or elliptically polarized? If the scatter is a lossless dielectric the scattered radiation is not elliptically polarized. How about if the scatter is conducting? if the scattered radiation is elliptically polarized, does it violate the conservation of angular momentum?

Many thanks!

 

[mfb]

Scattering where?
In general, the material can get (or lose) angular momentum. In addition, angular momentum in some specific frame can come from the position of the photon itself (together with the velocity), its intrinsic angular momentum is just one component.

 

[rays]

mfb,

Thank you for the quick reply!

In classical eletromagnetic theory, if the incident EM wave is linearly polarized (no angular momentum) and it is scattered by a fixed spherical perfect conductor, then can the scattered EM wave be elliptically polarized?

rays

 

[mfb]

I would expect this in the general case (at least for some scattering angles), but I don't know.

 

[PJC01]

I can confirm that the principle of conservation of angular momentum states that the total angular momentum of a system remains constant unless acted upon by an external torque. This means that any changes in the angular momentum of a system must be balanced by changes in another part of the system.

In regards to the question of whether the scattered radiation can be circularly or elliptically polarized if the incident radiation is linearly polarized, the answer is yes, it is possible. This is because the polarization of light is determined by the orientation of the electric field vector. When linearly polarized light is scattered, the orientation of the electric field vector can change, resulting in circular or elliptical polarization.

However, when the scatter is a lossless dielectric, the scattered radiation will not be elliptically polarized. This is because a lossless dielectric does not absorb or dissipate energy, so the scattered radiation will maintain its original polarization.

On the other hand, if the scatter is conducting, the scattered radiation can be elliptically polarized. This is because a conducting material can absorb and dissipate energy, causing a change in the orientation of the electric field vector and resulting in elliptical polarization.

But does this violate the conservation of angular momentum? The answer is no. The total angular momentum of the system will remain constant, as the changes in the polarization of the scattered radiation are balanced by changes in the material's mechanical momentum due to the absorption and dissipation of energy.

In summary, the conservation of angular momentum remains valid in the case of scattered radiation, regardless of the polarization state, as long as there is no external torque acting on the system.