# Small hole question

Is it possible to drill holes that only one color passes through it?
I could imagine that if you drill a hole for any color, also colors having shorter wavelength would pass it. What would happen if you added a circular obstacle in the middle to filter out unwanted colors?

It doesn’t work that way.
But don’t feel bad. Light passage through apertures smaller than the wavelength of light is even stranger than the theories about it predicted.:

http://m.iopscience.iop.org/0034-4885/72/6/064401?v_showaffiliations=yes

Lotsa articles on this. Here’s a link to one:

This has the interesting observation that

So making small holes in the hope of restricting certain wavelengths of light bigger than the holes doesn’t work.

physical structure does produce colors in structural coloration. not what the OP was talking about but extremely fascinating and spectacular.

You would get rainbow patterns in concentric circles around the straight-line direction, and a white spot directly along the straight-line direction. It’d basically be the two-slit diffraction pattern, rotated.

I don’t understand this reply. If you have a single small hole larger than the wavelength of light, you’d get an Airy Diffraction Pattern, as first derived by George Biddell Airy (although others came close). But the recent work on sub-wavelength apertures give odd and different results. But in neither case would I call the result “the two-slit diffraction pattern, rotated.”

Well, the aperture is a narrow annulus, right? That’s the same thing as a pair of slits, rotated about a point in between them. So I would expect that the diffraction pattern produced would be a rotation of the two-slit diffraction pattern.

But this is your area of expertise, so if I’m wrong on this point, I’ll take your word for it.

It looks tempting, but it doesn’t give the right answer. Even when your annulus is much larger than the wavelength of light, you have to properly add up all the contributions from the different parts of the wavefront using the Huygens-Fresnel principle, and that’s very different from simply calculating it for two points in a plane and then rotating it*. There are lots of places where a circular aperture is treated. the ones working out an annulus are fewer in number, but you can find them.
But when the size of the annulus is smaller than the wavelength of light, all Hell breaks loose. The OP’s suggestion seems reasonable, especially in light of what happens with Faraday cages, but it turns out that even people who had done careful theoretical calculations didn’t correctly predict the experimental results. See the cites in my first response upthread,

*I wrote an artuicle about Aiory himself pointing out how blindlyy applying Thomas Young’s formulation to a raindrop resulted in an invcorrect result, because it didn’t properly include all parts of the wavefront. Young himself didn’t make this mistake, but it would be easy to do.

i work with wave guide’s. the light spectrum is in. um. I work in mm. I’m guessing they split it through a prism. but I can’t tell you the wavelength per color. or even it has one individually. ill read later for more info.

How about coherent light - does bluish fit through smaller hole than reddish?