trying to select a suitable material for the pinhole aperture of a pinhole camera. The pinhole minimum size is limited by diffraction. Is there a change in the quality/quantity of diffraction if the edge around which light diffracts is an electrical conductor or not ? (for ex in old polarizing filters the wires would interact with the electric field of the EM wave)

If the material in which you make the pinhole is uniform on the sub-wavelength scale, and if the material completely absorbs (or reflects) the light that misses the pinhole, the performance of the pinhole will only depend on the shape and size of the pinhole.

  • if so then wire polarizers woulnt work, would they ? – Manu de Hanoi Apr 29 at 14:50
  • A pinhole in a wire polarizer would not work the same as a pinhole in, say, aluminum foil. I haven't tried making a pinhole in a wire polarizer, but my first guess is that it would act like an ordinary pinhole for the polarization component normally blocked by the wire polarizer, and would have almost no effect for the other polarization component. – S. McGrew Apr 29 at 15:06
  • I meant that if the material wasnt affecting the waves that pass near a conductor then wire polarizers wouldnt work (pinholes unrelated) – Manu de Hanoi Apr 29 at 15:19
  • I don't understand the question. You could ask this as a new question, and fill in the details, leaving out the pinhole part of the question. – S. McGrew Apr 29 at 15:42
  • do you agree that a wire polarizer changes the quality of the light (polarization)? Do you agree it does so because the wires in the polariser are conductors ? If so you'd agree that the light passing through the polarizer is affected by the proximity of the conductor. Therefore light is affected by the proximity of a conductor, therefore the pinhole material matters.....That's my reasonning – Manu de Hanoi Apr 30 at 17:09

OK, now I see what you are asking. You are imagining that some of the light hits the wires and some goes between the wires, and that the polarization filtering occurs only between the wires. That's not the way it works.

Each photon is effectively much wider than the distance between the wires, so every photon that hits the wire grid polarizer "sees" the wires. However, only the photons whose E vector is aligned with the wires can induce current in the wires and be absorbed. For all practical purposes, photons whose E vector is perpendicular to the wires just go through as if the wires were not there. Essentially none of the photons whose E vector is parallel to the wires can get through, even though there seems to be space between the wires.

When a pinhole filter is used, it is typically at the focus of a lens, so a light beam is as small as it can be when it encounters the pinhole. Due to the geometry of the light beam and the lens, the beam waist is usually in the range from 5 to 40 microns in diameter, and the size of the pinhole is chosen to be slightly bigger than the beam waist. The only portions of the beam that hit the material outside the pinhole are portions due to light that has been scattered upstream by, e.g., dirt on the optics. The pinhole removes the scattered light, leaving a "clean" beam. So, light that gets through the pinhole basically never touches the material that the pinhole has been punched into.

As a result, if you make a pinhole in a wire grid polarizer and use the pinhole the way a pinhole is usually used, then most of the light, regardless of polarization, will go through the pinhole. Scattered light, though, will hit the material of the wire grid polarizer. The portion of the scattered light that has its E vector parallel to the wires in the grid will be absorbed. The portion that has its E vector perpendicular to the wires will pass right through the wire grid polarizer.

In effect, a pinhole in a wire grid polarizer will act like an ordinary pinhole for light whose E vector is parallel to the wires, and will act like a sheet of glass for light whose E vector is perpendicular to the wires.

  • thanks for your answers: -I do not intend to make a pinhole in the polarizer, I just use the polarizer as an example of how I believe a conductor material can affect the nature of light passing near (and the basis for my pinhole material selection question) -"Each photon is effectively much wider than the distance between the wires" I believe photons have no width, but they have a wavelength. – Manu de Hanoi May 3 at 2:52
  • -"Essentially none of the photons whose E vector is parallel to the wires can get through, even though there seems to be space between the wires" There is always space between the wires, otherwise no light would pass through. If there is space and yet only one polarization passes through, that means that the conductor of the wires acts at a distance on the light between the wires (assuming light having a position, which isnt quite so at that scale I know). If the conductor acts at a distance between wires, then a conductor pinhole edge should act too on the light passing near the edge – Manu de Hanoi May 3 at 2:53
  • You are right that light does not have a "position" at that scale. The wavefunction of a photon in a beam focused on a pinhole is much larger than the spacing between wires in a wire grid polarizer. IF a photon's wavefunction overlaps the edge of a pinhole, of course it will be influenced by the edge material. But if there is no overlap, there will be no influence. – S. McGrew May 3 at 4:51

Your Answer

 

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.