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How do 3d holograms work exactly? I read that there is a laser in use, but how are the multiple perspectives generated and how is the light trapped? in a certain area to create the effect?

Furthermore, how do you generate different colors? Is it still using multicolored projectors or is there something special? What kinds of lenses are used?

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Start here: en.wikipedia.org/wiki/Hologram –  anna v Apr 10 '12 at 4:36
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wiki isn't enough??? –  Vineet Menon Apr 10 '12 at 4:54
    
You may be interested in this question and answer. –  Andrestand Mar 7 at 11:04

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up vote 4 down vote accepted

The Wikipedia article that Anna mentioned is an excellent description of holography and I'm not going to try and compete with it, but since I'm guessing that you're not a physicist the following might help make things clearer.

When you "see" things, you see them because they enter your eye, get focussed by the lens and hit the retina. In addition you see 3D because the image recorded by your left and right eyes are slightly different, and the brain can reconstruct a 3D image from the differences.

So if you're looking at a mouse (to use the example from the Wikipedia article) it's the light reflected off the mouse that the eye uses to "see" the mouse. Suppose you could come up with some clever trick to remove the mouse but still send the light to your eyes as if it had come from the mouse. Your brain couldn't tell the difference because your eyes are still receiving the same light as when the mouse was there. This is what a hologram does.

A hologram is a pattern of light and dark areas. When you shine a laser onto a hologram the light and dark areas scatter the light by a process called diffraction. The clever bit is that the light is scattered in exactly the same way as if there were a mouse there, so your brain sees light that looks as if it has come from a mouse, so you see a mouse. It appears in 3D because the hologram scatters light differently depending on the angle you're looking at it, so your left and right eye receive differently scattered light just as they would from a real mouse.

You might think it would be tremndously difficult to make a hologram to scatter light in just the right way to make it appear as a mouse, but actually you make a hologram from a real mouse i.e. it's just a type of photograph.

It's hard to make multicoloured holograms because to "see" the hologram you have to shine a laser on it, and lasers are just a single colour. You could use three lasers, e.g. a red, green and blue laser, but annoyingly the hologram scatters different coloured light in different ways and your multicoloured hologram would be very blurred.

I hope this helps - to get any further you'll need to work through the Wikipedia article, and also understand what diffraction is.

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ok! I'm reading the wiki article. I'm wondering how did they make this person for concerts since it uses a variety of colors and moves pretty fast. Seems like a technology feat to me. –  Eiyrioü von Kauyf Apr 10 '12 at 13:50
    
From a quick look at your links I'm pretty certain that is not a hologram. Yes, the L. A. Times article said it was a hologram, but I suspect that's just the journalist not knowing what a hologram is. –  John Rennie Apr 10 '12 at 15:29
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You say the hologram scatters light in different directions, so that means that the hologram (a surface?) is not just two-dimensional, right? –  NikolajK Apr 10 '12 at 20:03
    
I would have to check, but I'm fairly certain a hologram is a plate of glass (or whatever) and it does have a 3D structure i.e. the pattern varies as you go through the thickness of the glass. –  John Rennie Apr 11 '12 at 6:05
    
From 'Things often confused with holograms' on the Wikipedia page linked above: 'In 2010, there was a series of concerts ... which included Hatsune Miku ... performing on stage as a "holographic" character. This effect was actually achieved through a special method of rear projection against a semi-transparent screen.' –  ptomato Apr 11 '12 at 14:07

If you have a laser (highly parallel beam of) light, make it go through a pinhole and it emerges on the other side forming a cone of light distribution(in varying directions withing the solid angle). if then you place a detector(screen or eyes or CCD chip) anywhere within this region, it will capture an instance of the wave-fronts http://www.khanacademy.org/cs/superposition/1245709541, both intensity of light and the phase. if there is an object between the source and detector, every point on the object acts as a point source (by scattering some of the light just like a pinhole) and the detector records the interference(a hole where both incident and scattered waves phases match) from all these sources(superposition of incident and object waves). This is the inline geometry and is the simplest. If this was recorded on a holographic plate, on shining light of similar wavelength as the light used to record the hologram, every hole on the hologram acts as a point source and scatters the light to form exactly the same 3D scene that was recorded (reconstruction) on the other side of the hologram. The main difference between Holograms and 2D images is that holograms have additional phase information about the object waves recorded in them. Images just have the intensity. It is the phase variation that gives the 3D geometry of the object in the image plane. The process of reproducing the image from a hologram is reconstruction and in the case of digital world, its mathematically computed. I have made matlab simulations of holograms, and reconstructed them at different distances, but only for simple cases. Different reconstruction algorithms are used for different geometries of recording.

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There is multiple ways holograms work, 1. A laser going into a half mirror going into 2 more mirrors that brings out the hologram... Or they get a plain price of glass and have either a projected or lots of lasers to build up the hologram...

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could you be more specific and/or put more detail into your answer because it is a bit short and not very clear. You could describe a bit and put a link in, for example –  tom Dec 13 at 22:16

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