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Hologram ?

  1. Jun 28, 2010 #1
    So when they make a hologram they use a laser and it gets shot out and goes through a beam splitter and the one beam bounces off a mirror and then the object they want to make the hologram of , and the other beam bounces off a mirror and when the two beams meet they interfere and then hit the plate made of silver halide . So when i shine light on the hologram it diffracts off of it and i see the image because off diffraction . But I'm having trouble with
    when you cut the hologram in half , each half still produces the image just smaller , is this because when it was made and the light interferes with itself,and it scatters the light in all different directions so it encodes the information all across the hologram .
    Any input will be much appreciated .
     
  2. jcsd
  3. Jun 28, 2010 #2

    jtbell

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    Staff: Mentor

    Looking through a hologram is like looking through a window. If you cut the window in half, you can still see the entire object behind it, you simply have to move your head around a bit, and/or get your eye closer to it. The object doesn't appear to become smaller when you make the window smaller. Similarly, the image doesn't become smaller when you cut a hologram in half.

    Each point on the hologram receives light waves from all parts of the object that are visible from that point.
     
  4. Jun 28, 2010 #3
    This forum needs a FAQ. Weren't we just talking about that? I think I mentioned the NOVA episode where I saw it demonstrated.
     
  5. Jun 28, 2010 #4
    jtbell is absolutely correct; however, another way of thinking about it is just to record the hologram with a smaller piece of film the same size as your "dissected hologram". That small piece receives the same field distribution as the dissected piece, does it not?
     
  6. Jun 28, 2010 #5
    so your saying record the image with a smaller silver halide plate , at the same distance from the beam splitter , and the interference pattern will be recorded on the plate ,
    Can we think of it like a double slit setup , the smaller plate will record lets say the central bright spot and the two next to it , and the larger one will record 5 brights spots as opposed to 3 , is this correct or incorrect .
     
  7. Jun 29, 2010 #6
    It's far easier to think of it as a window. A window at the original scene looks exactly like the resulting hologram recording. What happens if you cover up half of the window?
     
  8. Jun 30, 2010 #7
    ok but what i said about the double slit is that correct ,
     
  9. Jun 30, 2010 #8
    Well it's not wrong, but I don't immediately see how it relates to your original question.
     
  10. Jun 30, 2010 #9
    when they make the hologram and the light interferes between the 2 beams , the interference pattern is recorded on the silver halide plate , so i was using the double slit interference pattern as the interference between the two beams and it sends the light in all different directions , and the bright spots from the double slit are equally spaced and the bright spots would be recorded on the silver halide plate , so when the two beams interfere to make the hologram the diffraction pattern is symmetric and the information from the image they are trying to make a hologram of is scattered to every part of the silver halide to make the reflective hologram . does this make sense
     
  11. Jun 30, 2010 #10
    So I guess you're saying that regardless if you have a screen or not, you will still have the same interference pattern throughout a given plane, so that when you place a small screen at different locations in that plane, you record the interference pattern for that location.

    Yes, that's correct, and is essentially what's happening in the hologram. I don't really know how helpful that picture is, but if it works for you then great!
     
  12. Jun 30, 2010 #11
    that was the only way i could make sense of it , i dont know if i understand the window thing ,
     
  13. Jul 1, 2010 #12
    Look out a window so the house across the street or some other object pretty much fills it. If you took a static picture of that, and cut it in half, you would only have half the house showing.

    But if you close one curtain, covering half the window, and remain in your same spot, again you cover half the house. But if you move to the side, you can see the whole house, in the half of the window that is available. If you continued covering up parts, you could still claim that the whole house was still visible, even once you got down to a little peep-hole.

    The hologram is exactly the same. If you took a laser "snap" of the scene, with the photo plate where the window is, and then took the developed plate to an empty warehouse with the correct laser light for viewing, you would see the house exactly as you did through the window.
     
  14. Jul 1, 2010 #13
    ok i got ya ,
     
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