Curved Diffraction - Explaining Why Light Behaves So

[Hodranoel]

I'm doing some experiences with a laser about diffraction caused by an edge, and I have some question to ask.

Unfortunately, I've found very few literature (almost nothing) about diffraction caused by an EDGE.
Everyone explains well diffraction caused by slits; someone explains diffraction caused by wires (for example hairs).


Why the direction of this kind of diffraction is affected by the angle between the edge and the light beam? (if i point the laser beam in a direction normal to the edge, the diffraction is normal to the edge, if i point the beam nearly parallel to the edge, the diffraction, is nearly parallel to the edge).

Please... Explain me why the diffraction curves in this case!
This is not a reflection caused by the very thin smoothness of this edge, because I've also coloured the edge of pure black, and this diffraction curve still there, but the diffusion you can see at the end of this curves vanishes.

Thank you!

and sorry for my probably bad english!

 

[pallidin]

See here:

http://en.wikipedia.org/wiki/Knife-edge_effect

 

[Hodranoel]

I found an exhaustive answer in the Geometrical Theory of Diffraction (GTD)!

There is a substantial difference between edge and wedge: an edge it's i.e. a border of a polygon and the diffraction caused by it it's always a straight line.

A Wedge, it's an edge between two polygons, and the diffraction caused by it it's a cone. In the case the direction of the light incident to the wedge is normal to the edge, the cone degenerates in a disk (and it's projection on a screen plane it's ovbiusly a straight line).

Very very interesting!

If you are interested you should read this: http://www.opticsinfobase.org/view_...76052.pdf?da=1&id=76052&seq=0&mobile=no&org="

Unfortunately this theory is not very known out of the field of radiowave propagation, even if it comes from the optics field.