C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Wed, 27 Dec 2006 17:42:12 -0300 (CLST)

This brings back memories :o)

Pauli asked why wire grid polarizers don't transmit.  It's a good question
- if you consider the incoming wave as exciting emitters in the wires then
you can calculate the final result by summing the emission.  That gives
you a reflect beam (good) and, from symmetry, a transmitted beam (bad).

If that's too brief, read the Wiki page -
http://en.wikipedia.org/wiki/Polarizer - but note that I wrote the
paragraph below:

It is interesting to consider why there is a reflected beam, but no
transmitted beam, when the symmetry of the problem suggests that the
electrons in the wires should re-radiate in all directions. In simple
terms the transmitted beam does "exist", but is in exact antiphase with
the continuing incident beam, and so "cancels out". This, in turn, seems
to contradict the idea that the incoming wave is "driving" the electrons
in the wires, and so is "used up" (leaving no continued beam to cancel out
the transmitted wave). In fact, if we assume that there is no heating,
then no energy is used to drive the electrons - a better mental image is
to think of them as "riding" on the waves that result from the
interaction.

I also found a paper from 1948 that looks like it would be relevant -
http://link.aps.org/doi/10.1103/PhysRev.73.184 - presumably it's war radar
technology.  Unfortunately it's not free, but the Google search result
was:

  Consider the resultant field in the plane of the dipoles to be a
  combination of the undisturbed incident wave and the waves reradiated
  in antiphase from the ...

Andrew