Picture of How To Make a Simple Double-Slit
This 'ible will show two simple methods to make a double-slit, that is small enough to create an interference pattern.

Interference is an effect waves show, when they interact with each other. If two (or more) waves have the same wavelength and a fixed phase relationship they are called "coherent". And if such coherent waves hit the same spot, they can support each other, annihilate each other (yes, you did read right: light + light = more light or no light) or something in between depending on their phase difference. The special thing about laser light is its huge coherence length meaning the light emitted by a laser is practically always coherent. A double-slit (or better a lattice) splits up the laser beam into two (or many) "beams". Beyond the double-slit or lattice each new "beam" spreads in every direction interfering with the other one(s). This creates a characteristical pattern of maxima and minima: the interference pattern. For further information have a look at the wikipedia articles about the double-slit experiment and interference.

Disclaimer: This instructable presupposes responsible handling of laser sources. DO NOT DIRECTLY LOOK INTO ANY LASER BEAM. Always handle laser beams with caution. I'm not responsible for any injuries (e.g. damaged or blinded eyes) due to wrong handling of your laser source.
awkko808 made it!4 months ago

Made a simpler version, but still worked. Using the aluminum foil was a great idea, thank you!

thanks.Your site is very excelent ,& usuful. be success
Johenix1 year ago
Back in the 1960's we used stacked razor blades to cut or scratch paralel slits in graphite on microscope slides to measure the wavelength of light. Two blades, two slits- three blades, three slits ect.
This is pretty cool. I made my own slits not too long ago using a very similar method. Getting the slits to be parallel and very close together was a little tricky. I eventually tried using mechanical pencil graphite as a spacer. I made the slits by cutting up against the graphite and it worked pretty well. For my next experiment I am going to use commercially available slits that are scratched into glass slides. They're cheap and well calibrated.