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Recreating double slit experiment without laser

  1. Mar 1, 2014 #1

    I am trying to recreate the double slit experiment using ordinary light, i.e. sunlight or light from a light bulb or torch. I do not wish to use a laser for various reasons. I have experimented with the distance, spacing, and width of the slits, but I cannot get an interference pattern. Can someone please give me some advice, or just tell me how to do this. thanks.
  2. jcsd
  3. Mar 1, 2014 #2


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    Gold Member

    And why is that?

    You should recall, that the waves from the sources, in this case from the 2 slits, add or subtract from one another to give the pattern for interference. If the wavelength of the sources are not in phase then the pattern is not as 'distinct' as when the wavelengths are the same. Sunlight is composed of many frequencies of light. with all these frequencies interfering with one another from the 2 slits any interference pattern is washed out and all you will see is an illuminated screen.

    Try a monochromatic light as that from a laser.

    This is a brief description:
  4. Mar 1, 2014 #3
    Thanks 256bits, I understand what you are saying, but there is a specific reason which I do not want to explain for not using monochromatic light. Didn't Young conduct this experiment using sunlight? I don't care about how well defined the interference pattern is, I just want to be able to distinguish between the light passing between two slits and light passing through one. So I dont really care how well I can see the pattern, I just need to observe that it is having some effect.
  5. Mar 1, 2014 #4


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    Staff: Mentor

    http://www.physicsclassroom.com/class/light/u12l3d will start you in the right direction. You'll need a room that you can easily darken and a window that's exposed to direct sunlight.
  6. Mar 1, 2014 #5
    There's a couple of important differences if you're not using a laser.

    Firstly you'll want to use a pinhole before the slits to make your beam coherent. This is going to reduce your beam intensity, so the darker you can make your surroundings, the more coherent you can make your beam.

    Secondly, the interference pattern will look different, since the peaks and troughs are in different places for the different frequencies of light. Try this search to see what sort of thing it is that you're looking to achieve: https://www.google.co.uk/search?q=white+light+interference

    If you have access to a laser (an optical mouse or pointing device, for instance), it might help to confirm that your geometrical arrangement is correct. If you see an interference pattern with it, but not with your white light source, then you know that you have a problem with your beam or that you're looking for the wrong thing.

    Also remember a single slit does produce a diffraction pattern, so if you're not seeing these from each individual slit, then it should provide you with clues as to what's going wrong.

    It is possible to do this at home, but it's quite fiddly compared to a proper lab set up.

    If you get it working - would you post a photo?
    Last edited: Mar 1, 2014
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