Okay, let's begin with the story!

Who doesn't like physics, especially if they are beautiful, like in Young's Double Slit Experiment?
And who doesn't love to reproduce it at home?

Well, certainly not me! So here's what I did:
I took a piece of paper and made two small and narrow slits in it, really close together. I don't think this is possible with scissors, anyway I used a knife.
It took me some tries, it is not that easy and you have to make them as narrow and close as possible!
Also, some sources recommend painting the paper black to prevent the light from shining through. I tried it, I didn't see much of a difference. Maybe my paper is thick enough.

Anyway, I took the paper with the slits, folded it with a 90 crease and made it stand on a table. (I just lay my mousepad on it, literally the next thing I found.) Then I taped the button of a laser pointer in a fixed pressed position, so I could let go of it and keep it shining. (Warning, laser pointers may be dangerous!)
I aligned laser pointer and paper in such a way, that the laser pointer was shining right through the slits and onto a wall. The slits were about 1/4 to 1/5 mm apart and about as thick. The paper was about 5 cm from the laser pointer and the wall about 1.5 m behind that.

It required a bit of tweaking but in the end I got this! (I made the photo with my phone and in the dark, so excuse the quality. Feel free to call my phone profanities after this, you have my permission.)


The laser shining through the paper (Note the colored spots and other slits, I indeed tried many times!)


And from the back:
This is awesome! I remember reading about this a while ago, and its a cool experiment. I've never thought about how you could recreate it though. Great job!
Thanks, it was indeed a cool feeling to see that pattern myself and know how it worked. And it was kind of fun to try to cut the slits that narrow and close together, knife excercises! Smile
I don't think the slit separation should really matter, provided you can hit both with one coherent light source. Might be that with enough distance in which to diverge (imperfect focus giving you a laser dot of nonzero size) you'd lose the interference effects, but I suppose if anything the most relevant number is the apparent radial size of the target area.

Continuing to think about it though, if I assume your red laser has about a 600nm wavelength, if divergence like I speculate about were a meaningful factor if would imply the distance from the source across the target could affect visual results while varying by less than a micrometer, which is clearly not the case. Considering the analogy of waves in water, of course that thought is nonsense.


Anyway, I've also done this experiment. It's kind of neat.
btw, you don't have to make any assumptions about the wavelength, grab a diffraction grating with a known slits-per-millimeter, and measure it for yourself: https://www.amazon.com/s/ref=nb_sb_noss/175-1651601-1404824?url=search-alias%3Daps&field-keywords=diffraction%20grating

The angle of separation is a pretty simple function of the wavelength.
elfprince13 wrote:
btw, you don't have to make any assumptions about the wavelength, grab a diffraction grating with a known slits-per-millimeter, and measure it for yourself: https://www.amazon.com/s/ref=nb_sb_noss/175-1651601-1404824?url=search-alias%3Daps&field-keywords=diffraction%20grating

The angle of separation is a pretty simple function of the wavelength.

Wouldn't that be doable with some sort of diffraction with homemade materials? Like use a prizm of glass with known angles, or something like that?
Nik wrote:
elfprince13 wrote:
btw, you don't have to make any assumptions about the wavelength, grab a diffraction grating with a known slits-per-millimeter, and measure it for yourself: https://www.amazon.com/s/ref=nb_sb_noss/175-1651601-1404824?url=search-alias%3Daps&field-keywords=diffraction%20grating

The angle of separation is a pretty simple function of the wavelength.

Wouldn't that be doable with some sort of diffraction with homemade materials? Like use a prizm of glass with known angles, or something like that?
In theory yes, but you might need unusually good characterization of the prism's optical characteristics (the refractive index) in addition to carefully-controlled geometry.

But in general, I'd imagine so:
The slits also give you the advantage of being able to check your setup using symmetry.
  
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