Why is diffraction a wave phenomenon?

1 Answer
Jul 21, 2015

Basically diffraction is the "invasion" of the space behind an obstacle by light shining on an aperture.


Light seems to be able to pass an aperture and propagate even into the space that is covered bi the walls of the aperture:
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If you consider light as a shower of particle-like entities (photons) there is no classical reason why one of these "bends" its trajectory to pass into the shadow region behind the obstacle!
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If, instead, you consider light as a wave you can consider Huygens construction of secondary waves where each point on a front of your wave (say a crest) becomes a source of secondary spherical waves whose envelope forms the next crest!!!
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In the simple (but powerful) visual arrangement of Huygens Principle each point on a wavefront is source of spherical secondary spherical waves that will build the next wavefront...so a point near the edge of the aperture will generate a spherical wave that invades the area behind the obstacle!!!
The good thing about light is that when you need is a wave otherwise is particles...in general is a...Wavicle! :-)
Hope it helps!