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This video is one by Veritasium on Poisson's Spot.

https://youtu.be/y9c8oZ49pFc

In the later half of the video where he does the experiment by using a laser, why does the laser beam have to pass through a diverging lens. Is it mandatory for it to pass through a diverging lens and why?

Also, if it is mandatory to use a diverging lens, are there any common household items that can be used instead of a specialized diverging lens? For the demonstration, would a circular coin also work or does the object have to be a sphere?

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I have done this demonstration successfully several times with a low power laser (a laser pointer) and a five cent coin taped to a thin wooden coffee stir stick.

The diverging lens is needed to spread the laser beam enough so that the width of the beam is wider than the diameter of the coin.

Coins with reeded edges, as opposed to smooth, don't seem to work.

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