jgourlay
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Sizes of slits for Double Slit experiment?
The spectroscopy section of a prior topic got me reading.
If I want to demonstrate the double slit experiment with a typical laser pointer, what size roughly should the slits be and how far apart?
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Nick F
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I tried it once, using Al foil stuck onto a microscope slide. Then use a razor blade and a steel ruler to make the slits. Try to get them as close
together as possible, but it might take a few tries because even with a very sharp knife it is easy to rip the foil instead of cutting it. Also, use
as thin a layer of glue as possible to stick the foil onto the glass, this makes it easier to keep the slits narrow.
When I did it I was using it to measure the wavelength of the light, just out of curiosity to see how accurate I could get it, and it worked pretty
well. Unfortunately I didn't have a way to measure the slit separation very accurately.
You can also use two small holes (press into the foil with a needle) instead of the slits.
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Mr. Wizard
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Try taping or clamping together a stack of razor blades. If you only have the ones with the metal edge on the back, like they use for paint scraping,
you will have to pry or cut off the back. Ideally you can stack double edge blades together to get a tool that will have a known distance between the
lines. The double edge blades are sometimes harder to find. If you don't have a micrometer to measure the thickness of a single blade, stack as many
of then together as you can, press them firmly together , and measure the height of the stack. Then count the blades and divide the height by that
number to get the thickness of the blade and the distance between the lines.
Instead of foil, which is very good, try a layer of soot from a candle, or even a black marking pen, or black ink. These may not work as well, but it
won't cost anything to try them. You also might try the artist's gold leaf, which is very thin, and less likely to tear.
[Edited on by Mr. Wizard]
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12AX7
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Is gold leaf opaque enough? I mean, I can even see through CDs... how many atoms of aluminum do they put in CDs? I suppose it'd be as opaque as a
thin layer of soot anyway..
Stacked razor blades make a reasonable optical black, I don't see what relevance this has with diffraction though.
The slits should be on the micrometer range for best results. Visible light is 0.3-0.7 um. Slit size controls spread of the resulting beam, as I
recall. Of course, smaller slits don't let through as much light either. Spacing doesn't need to be as tight.
Tim
[Edited on 7-20-2008 by 12AX7]
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Mr. Wizard
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| Quote: | Originally posted by 12AX7
Stacked razor blades make a reasonable optical black, I don't see what relevance this has with diffraction though.
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You use blades stuck together to cut or mark a pair of slits in foil, aluminum 'gold leaf ' or soot. You only use the stack to figure out the
thickness of the blades,thus the separation of the slits, in lieu of a micrometer. \!/\!/ This ASCII diagram would represent the two blades, with
the dots of the exclamation points being the thickness of the blade apart. Sorry I didn't make it clear.
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12AX7
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Oh, for cutting it, that would certainly work well.
Tim
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