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Interference does not happen

  1. Mar 8, 2008 #1
    Why does laser light not interfere when the two split beams are directed toward another.

    All interferometers I've seen the interference forms where the beams are propagating in the same direction. But if the propagation direction is reversed (traveling from opposing directions) they no longer interfere.

  2. jcsd
  3. Mar 8, 2008 #2
    How would you measure that? Usually they are coming from the same direction so they can simultaneously be projected onto a single screen. A standing optical wave, (which I believe has been made), is basically interference of counterpropagating waves. Actually, there is a case of interference from waves in opposite directions. A reflection hologram is created by having the reference beam come from one side of the film and the image beam from the other.
  4. Mar 10, 2008 #3
    I used a clear screen. I tried a thin film and also a thick plexiglass.
  5. Mar 10, 2008 #4
    Hmm, I don't know. Have you gotten it working from the same direction? You are definitely using two halves of a split beam, not two different beams? How far do the two beams travel from split to recombination? Can you see light scattered on the screen?
  6. Mar 10, 2008 #5

    Claude Bile

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    They do interfere, counter-propagating waves will form a standing wave. This is readily observed as the longitudinal modes in a laser cavity or the transmission peaks of a Fabry Perot etalon.

  7. Mar 10, 2008 #6


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    Staff: Mentor

    With microwaves you can use a reflect a beam back on itself to produce a standing wave, and then move a field-strength meter back and forth along the beam direction to observe the maxima and minima of the electric field amplitude.
  8. Mar 11, 2008 #7
    It was a triangle setup.
    I don't know why this one does not interfere. One thing the beams only intersect at the screen and from opposite sides. From the beam splitter to the screen was about 10 cm for each leg.

    Sorry; I've got to drop this subject for a while. Too Busy at the moment.
  9. Mar 12, 2008 #8

    Sometimes it is easy to get fooled by what your seeing and mistake one thing for another.
    Physics has based the analysis of light waves from what water waves do in a ripple tank. This looks like one big error as I will show below.

    I’ve seen a lot of interference patterns and I’ve always tried to locate the center. Sometimes it seemed to be a bright fringe and other times it appeared to be a dark region. It was difficult to determine. So I strove to determine which one. Is Light or Dark the true center. Note: The two slit experiment is not adequate as the beams are not parallel and any number of fringes are possible although the center normally is bright.. I set up the below experiment to get to the root of the problem. In so doing, I discovered something unusual about light that is different from that of water.

    It made since to reduce the number of fringes down to the absolute minimum. What is the minimum? Without perfectly parallel beams there is no way to determine where the center of the pattern is. The fringes simply scroll from side to side depending on the alignment. Making locating the center of the pattern difficult. So in this setup the split beams are in perfect parallel. This results in only a single bright fringe in the center with a dark area on either side. Ergo, the circular spot from the simple lense becomes a single line.


    1. Michelson type interferometer
    2. REQUIRED: Cube type beam splitter.
    3. REQUIRED: At least one mirror must have a micrometer adjustment
    4. Standard front silvered mirrors and a simple lense.
    5. Laser light source. My choice: Polarized HeNe

    Setup the Michelson interferometer. Both optical path distances must be equal. My path length was 7 centimeters. Place the lense on the output path only. Align both beams into perfect parallel paths. (A cube type beam splitter insures this) One spot directly on top of the other. This is most easily done by blocking one side then the other. When the both beams are absolutely parallel a single constructive fringe will appear in the center only, with dark destructive bands on either side. Any misalignment will result in multiple fringes.

    The single center bright fringe is now four times brighter than the path from either single beam. This is not possible with water waves. In this case light waves and water waves do not relate. Water waves only double in height amplitude when two waves constructively interfere. Also, water waves will crash into another when their height is at maximum. i.e. when they are ready to break. In the controlled environment of a ripple tank producing small amplitude waves, they simply will pass through another. See, one difference is in the wave heights. A single photon always exhibits its maximum height based on a uniform sine wave. So it may instead be crashing, just like a full size water wave. Since it is nearly massless it would bounce. Something else however must be in effect. Why would two beams of light then pass through one another. The answer is related to the folding inward effect witnessed in this experiment. The waves dissociate then re-associate immediately after the collision. They fold back into place. (Swing or whip back and/or deform). (There is something else that could be considered here. I am not going into that yet.)

    This is the clue that light has something different and does not obey the rules of water waves. The question we should ask is; What could be occurring that produces a single constructive fringe that has four times the intensity of the split single beam.

    Since this does not relate to water waves at all. Something must be different.
    The conclusion I’ve made is that the beam is folding inward to the center. Wave collisions are occurring, not constructive and destructive interference. So light undergoes a type of elastic collision. The outer light folds into the center. No energy is lost through destructive interference. There is no destructive interference as previously thought. It appears to be interference, but is actually ‘waves bouncing into new directions’.

    This leads to some other very interesting conclusions which answer some unknowns in modern physics. This is enough for now. Try it for your self and try to figure out why its four times brighter. Where has the so called ‘destructive energy’ gone, and how does it get there?

    This leads to a spectacular understanding of magnetism, and gravity, as well as chemical bonding.
    Theory: Electromagnetic Waves of the Same Phase and Wavelength Collide.
    (Elastic collisions) This is a visual.
    Waves of differing sizes may interact but not so obvious, because they re-acquire their original paths. (requires a ‘net like’ concept) - see below.

    This is an excerpt from the book: (To learn more)
    <personal advertisement deleted>
    Last edited by a moderator: Mar 14, 2008
  10. Mar 13, 2008 #9


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    Em-waves also only double in amplitude when two waves constructively interfere. Any high school text should tell you, that the intensity of a light wave depends on the square of the amplitude. 2*2=4. No problem here.

    This depends on a lot more things. For example solitonic water waves will usually also simply pass through each other and are pretty high. Also the analysis of light waves is not based on what water waves do in a tank. It is a nice picture to visualize interference, but not a basis for any analysis as in water waves the effects of friction and gravity have to be considered.

    This sentence does not even make sense. What is the height of a single photon?

    What is destructive energy?

    Note to myself: Writing and selling crackpot books might be an easy way to earn money.
    Last edited by a moderator: Mar 14, 2008
  11. Mar 13, 2008 #10
    Ha Ha. Yea right! Go try and get rich selling a physics book you've written. Who got rich writing a physics book? Physics books are normally not best sellers.

    We could just throw punches...
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