Poisson/Arago's spot in water?

nonequilibrium

Hello,

So Poisson's spot is a (peculiar) effect of light due to its wave nature (it's the bright point one would see in the middle of the shadow of a perfectly round coin).

So I was wondering, has Arago's spot been observed for water waves too? For example in a 2D equivalent, i.e. for surface gravity waves.

Andy Resnick

Interesting.... it seems that there could be, but water waves are slightly different than electromagnetic waves- the dispersion relation for example, and dissipation due to viscosity. Lamb only treats sound waves diffracted though a aperture that is smaller than the wavelength, and those results do not indicate any phenomenon similar to the spot of Arago.

Seems like a good undergraduate project, actually!

mfb

The 2D equivalent would be like an inverted single slit experiment - should be observable.