How do Wire-Grid Polarizers work?

[Yuqing]

I've read about wire-grid polarizers from wikipedia. The article says that waves perpendicular to the wires cannot induce electron movement and hence they pass through with minimal energy loss. On the other hand, waves parallel to the wires are reflected by the wires because electron movement is possible. What I don't understand is why the electron movement doesn't also induce a transmitted wave. The article claims that the wave is existent but simply canceled out with the original incident wave, but don't waves need to be absorbed to cause electron movement? Also, why must the wires need to have a separation less than the wavelength?

 

[Valerie Park]

The wire-grid polarizer works by exploiting the fact that materials are capable of supporting wave oscillations in two orthogonal directions. Waves oscillating in a direction perpendicular to the wires are not efficiently coupled to the electrons in the metal and hence don't induce electron movement. These waves pass through the wire-grid polarizer with minimal energy loss. On the other hand, waves oscillating in the same direction as the wires are efficiently coupled to the electrons in the metal, causing them to move. This motion of electrons induces an electric field that opposes the original incident wave, and the combination of the two waves cancels out each other. The separation between the wires should be less than the wavelength of the incident light. If the separation is larger than the wavelength, then the two orthogonal directions can no longer be considered independent and both the incident wave and the wave induced by electron movement will be able to pass through the wire-grid polarizer.

 

[astrokreng]

Wire-grid polarizers work by selectively filtering out certain polarizations of light waves. The wires in the polarizer are aligned in a specific direction, typically parallel to each other. When a light wave passes through the polarizer, the waves that are perpendicular to the wires are able to pass through with minimal energy loss because they cannot induce electron movement. However, waves that are parallel to the wires are reflected by the wires because they are able to induce electron movement.

To understand why the electron movement does not induce a transmitted wave, it is important to understand how light waves interact with matter. Light waves can be thought of as oscillating electric and magnetic fields. When these fields interact with matter, they can cause the electrons in the material to oscillate as well. In wire-grid polarizers, the electrons in the wires are able to move freely in the direction parallel to the wires, but not in the perpendicular direction. This means that when a wave parallel to the wires interacts with the electrons, they are able to move and reflect the wave, but when a wave perpendicular to the wires interacts, the electrons are not able to move and the wave is able to pass through.

As for why the wires need to have a separation less than the wavelength, this is because of a phenomenon called diffraction. When waves encounter an obstacle or a slit that is smaller than their wavelength, they diffract, or spread out, in different directions. In wire-grid polarizers, the separation between the wires is designed to be smaller than the wavelength of the light waves passing through. This causes the waves that are parallel to the wires to be reflected, while the waves that are perpendicular to the wires are able to pass through without being diffracted.

In summary, wire-grid polarizers work by selectively filtering out certain polarizations of light waves based on the orientation of the wires. The electron movement induced by the waves parallel to the wires causes them to be reflected, while the waves perpendicular to the wires are able to pass through. The wires in the polarizer must have a separation less than the wavelength of the light waves to effectively filter out the desired polarization.