EM Destructive interference of two coherent beams

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Discussion Overview

The discussion revolves around the destructive interference of two coherent microwave beams reflecting off a wall, exploring the implications of phase differences on reflection and energy measurements. It touches on concepts from electromagnetic theory and ray optics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the phases of the two beams matter, suggesting that electromagnetic radiation does not readily interact with each other.
  • Another participant argues that while the center of the beams may cancel due to destructive interference, the spatial extent of the beams means that there will still be regions where the beams do not cancel completely.
  • A participant proposes that there will be areas of both destructive and constructive interference, suggesting that measuring microwave energy with a bolometer would yield the same results whether both beams are on or if they are measured separately.
  • There is a question raised about the mechanism of reflection, specifically whether it involves electrons being excited to higher orbits and then re-emitting radiation, and how this relates to areas of destructive interference.
  • Another participant states that reflection does not necessarily require absorption and re-emission, indicating uncertainty about the mechanism described in the previous point.

Areas of Agreement / Disagreement

Participants express differing views on the interaction of the beams and the mechanisms of reflection, indicating that multiple competing perspectives remain without consensus on these points.

Contextual Notes

There are unresolved assumptions regarding the interaction of electromagnetic radiation and the specifics of reflection mechanisms, as well as the implications of destructive interference on energy measurements.

cyber stealth
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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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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.
 
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.
 
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?
 
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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