The Naked Scientists

The Naked Scientists Forum

Author Topic: How can light intefere across diffenet planes?  (Read 2258 times)

Offline sciconoclast

  • Sr. Member
  • ****
  • Posts: 149
    • View Profile
How can light intefere across diffenet planes?
« on: 10/09/2010 00:02:52 »
This is an extremely simple observation.

If laser light is directed onto a triangular center post with an apex angle of 15 degrees an "X" like interference pattern will appear.  The upper legs of the "X" will mostlikely have broad bands and spacing, the lower legs will have finer bands and spacing ( the upper pattern varies with the distance from the laser and the lower pattern varies with the position of the laser light on the post, or in other words the width of the post at that point ).   At the center of the "X" there will be a composite pattern of distended bands where the lower legs are in close proximity.

There is a lot going on here but in this post I would like to consentrate on the lower most portion of the "X".   When one side of the triangular post is shielded from the laser the lower portion of the diffraction pattern is changed into a single distended band.   This shows availability of paths to both edges is necessary to create the interference in the lower portion of this interference pattern.

In quantum theory an interference pattern can only occur when multiple probable paths converge at the target screen and in classical wave theory it can only occur when there is crest to crest overlap at the screen.   So if the outer portions of the lower legs of the "X" pattern reach the screen in different areas and the edge from which they are diffracted is known, how can there be an interference pattern.

I am attaching a sketch but this is such a simple experiment anyone can view it for themselves.



 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8125
  • Thanked: 53 times
    • View Profile
How can light intefere across diffenet planes?
« Reply #1 on: 10/09/2010 00:47:47 »
... availability of paths to both edges is necessary to create the interference

Diffraction at one sharp edge is sufficient to create an interference pattern ...

Quote
Diffraction from a Knife Edge



http://www.sciencephoto.com/images/imagePopUpDetails.html?pop=1&id=652050110
« Last Edit: 10/09/2010 00:52:02 by RD »
 

Offline sciconoclast

  • Sr. Member
  • ****
  • Posts: 149
    • View Profile
How can light intefere across diffenet planes?
« Reply #2 on: 10/09/2010 17:02:50 »
Thanks for the interest.

    Yes I am aware of knife or single edge patterns and I have performed a lot of experiments utilizing them.   If the two interference patterns were each separate knife edge patterns corresponding to each of the separate edges then blocking one edge should not alter the other knife edge pattern.

     The pattern that remains after one edge is blocked is not a Knife edge pattern.   It is instead the pattern from laser light passing through a single slit at an extremely acute angle.   The edges of the slit are the remaining post edge and the laser aperture edge opposing it; and, the plane of the slit is along a line between those two edges.

     The slight curvature of the bands is a dead giveaway. This type of pattern is discussed in more detail along with a wave interference pattern diagram in an earlier post of mine on 25/05/2010 titled "Is This Interference Pattern Anomalous" which has been moved to the New Theories section. 

     Measurements of the asymmetric pattern that is produced match the predictions for such a pattern for the distance from the laser to the post.   The two patterns in the lower half when both edges are exposed match the mathematical predictions for a normal, vertically parallel edged post fringe interference pattern if the average width of the post at the center of the laser beam is used.

     The observation that the upper portion of the pattern remains in the acute incident angle single slit spacing regardless of the number of edges exposed, while in the lower portion the post interference pattern supersedes suggest, this phenomena probably has something to do with the upper paths diverging while the lower paths are initially converging even thought it is in separate planes. 
     
 

Offline sciconoclast

  • Sr. Member
  • ****
  • Posts: 149
    • View Profile
How can light intefere across diffenet planes?
« Reply #3 on: 11/09/2010 18:21:28 »
Let me try again!

That last reply of mine was a little long and maybe off point. Here is a shorter response, more to the point.

The entire quote from my post is "This shows that availability of paths to both edges is necessary to create the interference in the lower portion of this interference pattern".

I was not referring to interference patterns in general as the out of context portion implies but a specific pattern in this experiment.

                                           I hope this helps.
 

Offline sciconoclast

  • Sr. Member
  • ****
  • Posts: 149
    • View Profile
How can light intefere across diffenet planes?
« Reply #4 on: 25/09/2010 19:38:09 »
Back Again.

      Evidently no one else is seeing what I think I am seeing here, so I have modified the experiments to possibly make what is happening clearer.   I have placed a single slit in front of the triangular post.   This of course adds double slit bands on a horizontal line to the pattern but light now hitting the post edges with a more divergent angle of incidence opens the pattern up.

     The compound pattern in the center is now gone.   The patterns diffracting downwards start out as an elongated band, then change to finely space bands, which eventually cross unaltered, and then continue on.   However, when one of the edges is covered the remaining pattern diffracting down from the opposite edge changes to a single elongated band or streak.

     It is obvious that even with both edges exposed the photon paths from their respective edges is known and that some of them never even cross another path.   Yet the pattern is obviously a double edge pattern.   This seems to be a direct contradiction to quantum theory.

Sketch of altered experiment:



In order to achieve proper exposure of the lower portion of the pattern I removed all but the center portion of the screen.  This allows the center to be photographed without being blinded by the rest of the pattern which passes on by.

Photo with both edges:



Photo with one edge:


    I hope this clarifies the observations.
« Last Edit: 25/09/2010 19:44:18 by sciconoclast »
 

The Naked Scientists Forum

How can light intefere across diffenet planes?
« Reply #4 on: 25/09/2010 19:38:09 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length