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(ATM) The cause of diffraction
- To: atm@efn.org
- Subject: (ATM) The cause of diffraction
- From: Chuck Grant <grant@aretha.llnl.gov>
- Date: Mon, 9 Oct 1995 14:54:35 -0700
- Bell-Net: (510) 422-7278 (Fax 510 422-2095)
- Campus: Lawrence Livermore National Laboratory
- Department: Environmental Protection Department
- Division: Environmental Restoration Division
- In-Reply-To: <9510061644.AA04314@silas.lpl.arizona.edu>(rhill@lpl.arizona.edu)
- Location: 7000 East Ave. L-530, Livermore, California, USA 94550
- Organization: University of California
- Reply-To: chuck-grant@llnl.gov
> From: rhill@lpl.arizona.edu (Rik Hill)
>
> It was my understanding from my old optics texts that diffraction
> is caused by edges (like the aperture and spider vane edges) and
> not by obstruction. Is this not so? -Rik
>
No.
Diffraction occurs everywhere, all the time, with any wave phenomena.
It is not caused by edges or obstructions or aperatures. Simple wavefronts
modified by edges, obstructions, or aperatures just happen to diffract
in ways which produce simple patterns. But what is really going on
in all cases is an integral over the wavefront. Changing the intensity,
phase, or bounds of the wavefront (or any part of the wavefront) will
change the way the wavefront diffracts. For some simple geometries (which
are of interest to us atm'ers) this integral can be approximated by a
Fourier transform (this is the Fraunhofer approximation).
Thicker spider vanes will cause more pronounced "diffraction spikes."
Chuck