Thomas Young's Double Slit Experiment

[Cmertin]

I have to recreate Thomas Young's Double slit experiment and take pictures of the interference patters for a research paper. My teacher has a powerful red laser at school that I can use, though i know that the interference pattern changes with the changing frequencies. I was wondering if a 5 mw laser pointer would be powerful enough for this experiment. If it is not powerful enough, what would be the best to get. There is a 100mw laser pointer on ebay that I could buy, though it is $60 and I don't want to spend that much if I don't have to.

Any help will be appreciated
Thanks,
Cmertin

 

[mgb_phys]

You can easily see fringes with even a low power 1mW red laser pointer.
You really DO NOT want to play with 100mW laser from ebay.

To see the fringes more clearly just do it in a darker room.
If you are taking pictures of the fringes by projecting them onto film there is no limit to how low power you can use. If you are planing to photograph them indirectly with a digital camera it might be trickier

 

[Cmertin]

Thanks.

I plan on doing this in a dark room, and projecting the fringes on a whiteboard and then taking a picture of them and then including them in the lab. We've done this lab before and were able to get pretty clear pictures with our camera phones, so I don't see why an actual camera wouldn't be able to get a clear picture.

 

[mgb_phys]

If you can see a projected image on a screen (ie whiteboard) you should be able to photograph it with a digital camera.

A lot of textbooks describe experiments with film, such as having a light source that only emits a few photons/second and using an hour long exposure on film to show there are still fringes - which wouldn't work with a digital camera.
You can also have problems if the digital camera can't focus or the optical effect you are trying to see is removed by the camera's software because it isn't somethign the designers expected in a normal family photo.

 

[Cmertin]

Oh, ok, thanks for all your help. =p

 

[Chek]

Here's a video of someone using a cheap laser pointer to get the double slit effect. He used pencil lead to block the photons. It would be easy to use similar materials to make a more permanent double slit screen.