# Interference Pattern: Non-Laser Light Sources

• Quantumgravity

#### Quantumgravity

Is there any way to perform the double slit experiment and see the interference pattern without using a laser? If so, what type of light do you need?

As far as I understand it- the light need not be chromatic at all.

As far as I understand it- the light need not be chromatic at all.
What do you mean by chromatic?

As for how to do it.. collimate the light by letting it pass through a very narrow gap (say, between two razor blades). Then have it go through another such gap, or your double slit perhaps. You may need some kind of lens to appreciate the pattern. Works fine with a normal battery torch.. well.. actually it's a pain because you likely need a dark room to be able to see the small amount of light involved, and you need to block out the extra torchlight.. it's fiddly.

Sorry- I meant coherent. It may have to be reasonably monochromatic in order to see interference.

The interference will occur even if the light is not monochromatic, but of course all the patterns will overlap and mix and the overall pattern, whilst still there, will be more difficult to see.

It does have to be coherent though, which is the reason for the collimation.

As for how to do it.. collimate the light by letting it pass through a very narrow gap (say, between two razor blades). Then have it go through another such gap, or your double slit perhaps. You may need some kind of lens to appreciate the pattern. Works fine with a normal battery torch.. well.. actually it's a pain because you likely need a dark room to be able to see the small amount of light involved, and you need to block out the extra torchlight.. it's fiddly.

Right. We do it by using a semi-transparent "diffuser" screen as the final target, and looking at the back side, in the direction of the slits and the light source. If you turn out the room lights and block stray light from the source, you can easily get a dim but clearly visible interference pattern that's perhaps a centimeter wide. Our initial collimating slit is 0.1 mm wide, and we use a small high-intensity desk lamp as the light source, with a clear-glass bulb so the filament makes for a fairly small source already.

Thanks for the input.

actually any light that has been emitted by the same source is coherent, so you can get an interference pattern using sunlight and or a flashlight. however an led would be better as there would be fewer differences over the emitter surface.