Re: Why called diffraction?

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

John Denker wrote:

> Suppose I have two pointlike scatterers.
> Delta function potentials.  Born approximation
> and all that.
>
> To my taste, I would like to call the result
> a diffraction pattern.  The fact that two is
> a finite number does not discourage me at all.

I accept your taste in this matter because I do think there is a
large portion of taste involved in the decision.  Nevertheless, my
taste would certainly be just the opposite.  It seems to me that what
you are describing is essentially a classic Michelson
"interferometer" pattern and, as such, it is a poster child for
interference phenomena.

> I don't think the numerousness of the lines in
> the grating that is the key idea.  I think the
> _spacing_ between the lines is what makes it a
> diffraction grating.  Eight or ten lines is enough
> to do a pretty good job (although not maximally
> convenient to set up).

Interesting.  Because, again, I would have said just the opposite:
To me, classic "diffraction" is what you get when the spacing between
sources is zero as in integrating over an infinite number of
infinitesimal continuous sources within an aperture or over a half
plane.