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Re: Why called diffraction?



Can anybody find a problem with this:
diffraction is defined to be:
interference of scattered waves
(sometimes excluding the trivial case
of the "zeroth-order" diffracted beam).

I guess I don't see how this would apply very easily to the case of,
say, "single slit diffraction," "edge diffraction," or "circular
aperture diffraction." Nothing that I would want very much to call
"scattering" goes on in those cases and they seem to me to be pretty
much the poster children for the phenomena called "diffraction."

Of course, all "diffraction" and "interference" phenomena (as well as
"reflection" and "refraction" phenomena for that matter) can be
considered to be the result of "Interference" (with a capital I). If
we are going to make what seems to me to be a somewhat artificial
distinction that best, if far from perfectly, maps onto standard
usage, I would say that "interference" is what happens when you
combine waves from a finite number of sources and diffraction is what
happens when you combine waves from an "infinite" number of sources.

Then, perhaps we may be forgiven for considering gratings and
crystals to produce "diffraction" effects if only because the number
of waves being combined, while finite, is certainly "very large."

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm