Diffraction of Laser Light

In this short video, from the National STEM Learning Centre and Network and the Institute of Physics, Michael de Podesta explains how a laser can be used to show the diffraction and interference of light. Using a laser pen in the classroom, the wave nature of light is demonstrated as a thin wire is used to generate an easily-seen interference pattern.

Two versions of the video are presented. One is suitable for teachers and fully explains the demonstration and how the interference pattern is produced. The second is aimed at students and could be used in place of the demonstration.

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Lovely diffraction demo! It is really nice with a wire, because as you say in the video, students are expecting to see a dark band in the middle! With a pin hole through foil, for example, they would expect to see a bright spot in the centre! I loved it and I think it is a great way to challenge misconceptions and convince students that there really is something quite amazing going on beyond the wire!
Great work!


Thank you for the awesome demo. This is a really useful resource with the notes and especially with the 2 different movie files. I like the fact that the equipment is simple and that makes the demonstration even more effective.
Please continue making more movies.


I love this video - the pace and language is perfect for my Year 13 students, and the ability to show the effect so clearly without having to be in the lab with the right equipment is extremely useful.


Great resource! I cant get enough of it!


I have just discovered this web-site today! I am loving it so far! The physics videos are a great asset to have in the classroom! Seeing is believing!! I'll be back!


Great video of a magnificent demonstration - thanks for that! My only quibble is that it's not altogether true that we only very rarely see any phenomenon that really exposes the wave nature of light! Iridescence, supernumerary rainbows, coronas in the clouds around the sun and moon - all of these are inexplicable if you don't know that light acts as a wave, and none of them are unusual things to notice... although the role of wave phenomena in producing them is easy to miss!

I've expounded on this a bit in a post here, if anyone's interested: http://oolong.co.uk/lightwaves


I am  student... and i really loved the video... very helpfull :)


The only problem is that it doesn't explain why the pattern of bright and dark spots continues so far on either side. For example, the waves passing to the left of the wire will diffract round to the right, and interfere with waves passing to the right. So far, so good. But the waves missing the wire on its right will only go to where the blob of light was before the wire was introduced, so according to this explanation interference should only happen within the area of the original blob, and then have a line of diffracted light going further out on each side.

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