# Light double slit interference - at home

• DieCommie

#### DieCommie

Hello Physics Forums Gurus!

I am wondering if it would be possible to set up a double slit interference pattern for light at home?

Well, I know its possible... but I am just an uneducated student. What kind of dimensions would I need for the slits? I think I would need the light to hit the slits very parallel. How could I achieve this? My hair brained thought is that the source could be in a dark tube to absorb nonparallel light, and at the end the light would be near parallel.

This is quite possible.
But the double slit is the hard part of it, unless you can buy one.

But, to see the wave nature of light, there is no need for a double slit experiment.
Personally, when I was 15 I did the thin hair experiment, without even a laser.

I used a halogen lamp enclosed in a box with a tiny hole in it. (I stopped the experiment when it start to burn)
This source of light was put at a few meters of the hair.
The projection of this hair on a screen (or on a film in a reflex box without objective, I don't remember) was macrophotographed and magnified: I got very nice Young fringes.

Today, it is much easier to do these things.
Buy a powerful laser pointer and play with it: with tiny holes or slits made of razor blades or even nicely cut paper. Be carefule for your eyes!
When I am lazy at my desk (at home!), I often play this game: projection of interference pattern on the walls. I can easily obtain 10 cm wide patterns, easily visible. (my pointer is rather powerful because it is a the pointer of a thermometer for measuring on distant walls, I bought it to analyse the heat losses in my house).

Michel

Question:
Why is it possible to observe fringes without using a coherent light source (laser)?
And fortunately ... otherwise the wave nature of light would not have been discovered so early before lasers were available.

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Easy way: get a cheap laser pointer. Pluck one hair from your head. Point laser through at wall, and hold the hair across the laser beam.

If you know a bit about Fourier transforms, you should be able to work out why it works. For specifically the double-slit pattern, try to hold the hair bent double.