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How holography works (entire explanation)

  1. Jan 13, 2006 #1
    Would someone, PLEEEEAAAASSSEEE, explain here how holography actually works.

    ...I mean - I know (I've already read about it times and times again) - I know it has to do with interference patterns (interaction between two components of light (object and reference light)), I see it has to do with difraction (the characteristic of light that it can diverge path if the "hole" is comparable to the wavelength (...or something))... and phase of light (actually what is the definition of "light phase"?!?), and coherence of the light itself (ability to interfere (with itself))...

    I've tried to find an essential explanation about how holography ACTUALLY works on many places (unsuccessfully every time) - still I can't quite figure it out... (and it seems interesting enough (and more!) to bother myself with this even further) I tried to find topics about it even on this forum - no luck...

    Can someone give a full and definite explanation please?

    (no mathematic formulae, just an explanation on how things LOOK like - there on a holographic plate - in relation on how it creates a diferent picture depending on an angle of view)

    I mean - what all those things have to do with the fact that you view a different intensity of light on some/any point of the (two-dimensional) plate of a hologram?!?

    Is starting with the physical apearance of the surface of the holographic film under strong enough microscope a good way to explain how it all works?

    PS: have you seen those true color holograms!!? That stuff is amazing!! (Imagine that you have a true color FULL ZIZE holographic picture of yourself, put it there on your wall - so it looks as if the picture is actually a door to another room - and there you stand (wow! generations to come could ACTUALY see EXACTLY how you looked like - THE original of yourself! Wow, wow, wowy, wow...))
     
  2. jcsd
  3. Jan 13, 2006 #2
    Since when do we have amazing holographs?
     
  4. Jan 13, 2006 #3
    Last edited: Jan 13, 2006
  5. Jan 15, 2006 #4
    I don't understand your question. (...and who mentioned "amazing holographs", I spoke of the holograms...)

    On this link you can see a picture of an example of a true-color hologram and an object that was holographed (near the botom of the page):
    http://www.holographer.org/articles/hg00007/hg00007.html
    I preety much think that stuff IS amasing.
     
    Last edited: Jan 15, 2006
  6. Jan 15, 2006 #5
    Yes. As a matter of fact about six months ago I was searching for a term "hologram" on howstuffworks.com (from where else to start...). There I've found that link you posted here - I was amased too (further more, I've even made some engravings myself (first some simple ones to figure-out the details on how to make them (my initials (simple), then a first letter of my name - huge outlined) - when I did that I made some serious ones: my handwriten signature, and a really complex thing - a drawing of a head of a creature I "invented")). I was searching for the right materials and tools until I've finaly given up and used the things I've find around me to make the first ones (back surface of the transparent plastic CD casing, a regular pair of compasses (I sticked a pin instead of grafitt, and used a piece of plasticine to fix the angle...) - you can't get more rudimental than that...).

    BUT STILL(!): we are diverging from the sole subject of this topic!!! WHAT YOU MENTIONED IS NOT A HOLOGRAM - pictures you get are STEREOGRAPHIC, NOT HOLOGRAPHIC (you see a reflection of the light on the curves you made with a pair of compasses; YOUR EYES see a 2D(!!) object from slightly different angles, it's not a vision of 3D object from different perspectives (same 2D images in both eyes, not changed by an angle of view) - so it is just a simple ilussion of space (you can draw it on a piece of paper...), and a cube you see from diferent angles is actualy - two 2D pictures (both made intentionaly by you (not reconstructed as in real hologram)))...

    ------------------------------

    Now: back to the topic.
    How holography works (I'm sure it can be explained in one sentence - it's basic principal at least) - they mention fringes and how light behaves on them when you view a hologram, but I don't understand it - I want an explanation.
    What interference has to do with it?
    Does someone have a picture of hologram surface under a microscope?
     
  7. Jan 15, 2006 #6
    Reference waves + object waves + interference waves + brain = hologram.
    Our brain creates holograms because it doesn't know how to assemble the information it receives from our eyes. The interference waves confuse our sight/recognition process and our brain assembles what we see the best it can.
    See: http://www.holostudios.com/holohelper/ for more.
     
    Last edited: Jan 15, 2006
  8. Jan 16, 2006 #7

    vanesch

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    I don't think that this is correct. You can take a picture of a holographic object, and then view the (normal) picture, and you will STILL see the object, in the same way as you would have seen it if you would have put your eye in the place of the camera taking the picture.

    Holograms reproduce the EM wave that was reflected from the original object (and not simply the intensity pattern, which is what a normal picture is about). As for our eyes, or for our camera, the EM wave is all we receive from the object, if the EM wave is the same, it looks the same. But holograms are NOT visual deceptions. The true EM wave is restored (well, up to a point).
     
  9. Jan 16, 2006 #8
    I have always found it illustrating to cosider a hologram of a single point.
    The interference pattern created on the photografic plate by the object beam
    and the reference beam will be a series of concentric circles of different
    width. If you calculate the diffraction of light (monocromatic)
    passing thorough the same series of concentric cirles you will find that the
    "picture" created will be that of the original point at the same distance from
    the photografic plate.

    For more complex objects, one use the fact that they are all composed of
    single points.
     
  10. Jan 16, 2006 #9
    OK, but how come photons (when interfering) create CONCENTRIC CIRCLES?

    Everywhere they say that there are two theories regarding light - particular (photon), and electromagnetic theory (waves) - I mean - we don't really know what is light, yet we use its phenomenons to create something cunning as a hologram!

    I think I've read or heard somewhere that they dismiss ether theory regarding the "upset" ether actually being the light (also I saw something in news on TV - they showed a water tank with wavy water, and how it projects shadows of the waves on the bottom of the tank, conclusion being that ether theory can't be (the problem being that I tunned in just to hear "...and that's why ether theory is impossible.")).

    So: what is light?
    I mean - it's a little strange to imagine the wave in nature as they usualy graphicaly represent it (a wavy line).
    Or is light a spiral, but when you watch it from side you see it 2D (a wavy line) - that sounds strange too.
    Or is photon just rotating at some speed in itself?

    I, personaly, prefere to compare it to sound: when something makes a sound (a bee while flying for example) it tickens (compresses) and decompresses air all around it - so it spreads radialy - so where ever you stand you can hear it; it compresses and decompresses air repetedly and very quickly - the frequency of sound is actually a speed of compression-decompression (membrane in your ear is affected by that air - that's sound) - so: that small-little-tinsy-winsy bee actually affects the air meters and meters away by compressing/decompressing it! Then why shouldn't it be possible that when electron dislocates in an atom it spreads in similar ways waves in ether - the difference being that ether cannot change volume - so it's like a watter in a pipe (as soon you open a valve watter exits on the other side (pushing the water already in pipe)) - which explains why light waves shoot-out at maximum speed possible in vacuum of space (the pure ether in thet case) - the only constant is time - or else the speed of light would be indefinite; and it also explains why there is particular and wave aspects - the particle of ether are affected by electron's displacement (wave) - the same way air is affected by objects in motion (vibration); AND it also explains polarisation - on the position of the electron in relation to atom's core depends the way waves spread (electron's oscilation toward and away from the atom's core is the same frequency, but it's not the same weither electron on atom is directed toward your eye (at the observed moment of emission), or it's on the top of the atom and jumps up and down from your point of view)...

    So - what's the truth about light?

    How interference makes the light beam form those circles (or whatever) that make diffraction patterns which are so crucial for holographic effect?
     
  11. Jan 16, 2006 #10
    ...I guess the best way for someone to explain how holography works is to make a computer 3D animation of photon particles in wave, their interference, and the moment when they hit the emulsion on holographic plate changing its optical characteristics (imprinting the hologram)...

    ...It's like a simulation of what could be seen under some hypotetical "hyper-microscope"...
     
  12. Jan 16, 2006 #11
  13. Jan 17, 2006 #12

    vanesch

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    In order to understand holography, all you need is the classical theory of light (classical electromagnetism). In most applications of holography, you do not need to switch to the photon picture.
    That doesn't mean that the *correct* application of quantum electrodynamics to a holography problem would give wrong answers ; on the contrary, it would coincide with the classical response. But because often the "photon picture" is *incorrectly* assumed to be a kind of "bullet" version of light as tiny light-dust particles or whatever, if you do not have a correct understanding of the theory of photons (quantum electrodynamics) will only lead to confusion - confusion which is not necessary, because the problem can nicely be handled with classical optics.

    As an analogy: Newtonian gravity is sufficient to understand the motion of the moon and its tidal effects on the earth. General relativity allows you to explain the effect too, using the bending of spacetime. But if you think that "the bending of spacetime" is having the earth and the moon roll on a rubber sheet, and try to deduce a tidal effect from that, you'll get highly confused. And this confusion is not necessary because Newtonian gravity can do the trick.
     
  14. Jan 17, 2006 #13
    I'm going to be doing a project in holography in a few weeks.

    pinestone: That holography helper resource is very useful-- thanks!
     
  15. Feb 2, 2007 #14
  16. Feb 2, 2007 #15
    Are the properties of the actual 3-dimensional object fully retained in the holograph? I thought I read somewhere that in theory, you could rederive the entire 3-dimensional object from the holograph but my perception is probably distorted.
     
  17. Feb 4, 2007 #16

    Claude Bile

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    To the OP - Are you questions directed toward how holography in general works, or holographic imaging specifically?

    For example, are you interested in the fundamentals that underlie holographic data storage?

    Claude.
     
  18. Feb 5, 2007 #17
    Who's OP?

    ---
     
  19. Feb 5, 2007 #18
    Nice.
    ("How it's made" in general is a great show for 'inquireing minds' (actualy, that was the name of the fist show on this 'how does it work?' theme; even before I comented that such TV show must be made - so people can see technical stuff on all kind of things))

    But, at the begining the presenter said: "Sounds mysterious? Not for much longer."

    Well... it still sounds mysterious. (it didn't answer the fundament of my question)

    Just like I said - what I ask is: how does a hologram look under a strong enough microscope. I mean - the surface of it... Are there some dots or concentric elipses or circles or closed complex shaped curvatures? Do they intersect or not?

    I mean: simple pair of split laser light that's intersected after shows interference fringes because when light waves are in phase they add to eachoter, and when they are completely out of sync they cancel eachother out, and that's the bacis of it - because every picture is a play of light and dark in all of the individual "pixels" its made of (and, it's all black and white - even the color ones because there are three layers: Red, Green and Blue (RGB), so in every layer you have just that change (between light and dark) (so it's enough to make light on the hologram you view cancel on reinforce in every point of the hologram's surface)). But what I ask is: how does it actualy look there on the surface of a hologram?
     
  20. Feb 5, 2007 #19
    Ideas are popping in my mind.
     
  21. Feb 5, 2007 #20

    Integral

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    If you looked at a hologram under a microscope you would see the grain of the film used, is this surprising?

    The pattern on the film is the interference pattern created by the reflected beam and the reference beam. If you create a hologram of nothing, that is just the image beam and the reference beam you get a series of lines, this is the Fourier Transform of 2 point sources (your 2 beams). What you get on the film is the Fourier Transform of your image, only when the image is very simple can we know what this will be.

    A lens is a form of analog computer, it transforms a interference pattern in the focal plane to an image. When you create a hologram you capture a interference pattern.
     
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