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EM Destructive interference of two coherent beams

  1. Aug 10, 2011 #1
    Suppose you have two coherent microwave beams, one beam at 45 degrees to a reflecting wall and the other one at 90 degrees, with the two beams pointing to the same point on the wall.

    If the two beams are 180 degrees out of phase and destructively interfere at the point on the wall, will the 45 degree beam still reflect off the surface, in the same manner it will when you turn off the 90 degree beam, i.e., when there is no destructive interference?
     
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  3. Aug 10, 2011 #2

    Drakkith

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    Staff: Mentor

    I don't think that EM radiation readily interacts with each other. If not, then the phases of the two beams does not matter in this particular situation. Someone correct me if I am wrong.
     
  4. Aug 12, 2011 #3

    Claude Bile

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    Yes; because any beam must have a spatial extent, and while the centre of the beams might cancel precisely, the wings of the beams will not.

    Moral of the story: Ray optics is an approximation, and can get you in trouble in contrived scenarios such as these.

    Claude.
     
  5. Aug 12, 2011 #4
    So, is it correct to say that there will be some places of destructive interference and some of constructive interference, and that if you measured the microwave energy with a bolometer you would get the same energy while both 90 degree and 45 degree beams are on, as you would get by turning them on one beam at a time and measuring each beam's energy separately and summing?

    Also, is it correct to say that reflection of the 45 degree microwave beam off the wall requires electrons to be kicked to higher orbit and then decay, to re-emit the microwave in the "bounced " direction?

    Is it correct to say that for the various spatial bands or areas of destructive interference, this destructive interference keeps the electrons from being kicked to higher orbit, and thus, the 45 degree beam is not reflected from these "dark" areas?
     
  6. Aug 12, 2011 #5

    Drakkith

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    The reflection of radiation does not require absorption and re-emission to my knowledge. I cannot say anything on your other questions though.
     
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