The wikipedia page on polarizers states about wire grid polarizers that :

"Electromagnetic waves that have a component of their electric fields aligned parallel to the wires will induce the movement of electrons along the length of the wires. Since the electrons are free to move in this direction, the polarizer behaves in a similar manner to the surface of a metal when reflecting light, and the wave is reflected backwards along the incident beam (minus a small amount of energy lost to Joule heating of the wire)"

Could you please explain to me why the electric current induced in the wires of a wire grid polarizer does only re emit EM radiation back to the source (reflection) instead of both ways ?


1 Answer 1


It does emit raditation in both ways, but in forward direction two waves cancel the electric field: You have to remember yourself (or learn) about relfection of EM waves on metal plates. The electrons that oscillate create an electric field at the surface that is always opposite to the incident field of the wave. From that one can be able to see that in the forward way the field of the EM wave and the field from the oscillation of electrons cancel. In backwards direction however, they create a standing wave.

The basic principle of the grid wire polarizer is now that this process only happens for a certain orientation, i.e. that of the wires.

  • $\begingroup$ That's interesting, let's try to reconcile this with malus' law: let's consider an horizontal polariser with a 45 deg polarized incident light. Malus says the transmitted power is 50%. But your explanation says that 50% passes through the grid (a), 50% is absorbed by the grid, of which 50% (=25% of incident) is reflected and 50% (=25% of incident(b)) is re-transmitted but with inverse phase. Then we'd get the 50%(a)-25%(b) =25% of total transmitted power instead of the 50% predicted by malus. $\endgroup$ Commented Mar 23, 2022 at 15:12
  • $\begingroup$ That is a good follow-up question. I can say a mirror ideally does not absorb 50% of the power, but relfects 100%. I hope some one can comment on why 100% is relfected for a mirror (neglecting Joule heating) and how to reconcile this with the picture that I gave, which is usually given. $\endgroup$
    – Martin
    Commented Mar 23, 2022 at 15:36
  • $\begingroup$ mirror is easier , it's like a wire grid but in all directions at once, therefore everything is absobed then reemitted $\endgroup$ Commented Mar 23, 2022 at 16:00
  • $\begingroup$ I'm not sure this is the correct mechanism. The wires made by one particular company are 170 nm thick, much larger than Al skin depth. I think polarizations parallel to the wires "see" a mirror, while those perpendicular "see" nothing. $\endgroup$
    – garyp
    Commented Mar 23, 2022 at 16:05
  • $\begingroup$ @garyp hard to comment on your exemple without the frequency the polarizer is intended for (and the corresponding skin depth) or the mechanical constraint on the wire or the manufacturing constraints $\endgroup$ Commented Mar 23, 2022 at 17:16

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