Talk:Holography/Archive 3

3D holographic projection

Following technology should be mentioned: http://www.eyeliner3d.com/ —Preceding unsigned comment added by 87.66.54.18 (talk) 10:56, 3 July 2009 (UTC)

As far as I can see this technology projects an image on a semi-transparent foil. In that case the holographic in their name is mostly for marketing. --Danh (talk) 07:26, 6 July 2009 (UTC)

Agreed, seems to have nothing to do with true holography. BobKawanaka (talk) 23:26, 6 July 2009 (UTC)

Holography in fiction

Do we really need every single mention of holography in every SF film or TV series since 1980? I thought the idea was to limit refs to major or central usage, which would seem to exclude everything but the EMH or Vic Fontaine. TREKphiler ^{any time you're ready, Uhura} 20:06, 4 June 2010 (UTC)

I totally agree that adding the hundreds of films with a hologram inside is a bad idea. Until August 2009 we had a small paragraph about holography in fiction, and a comment in the source urging not to add every film. Ironically, after even that got deleted, a long list is now popping up. What do you think? Should we change it back to a paragraph? Should we put the never-ending list of films with holograms in a separate article or is it not encyclopedic enough? --Danh (talk) 15:24, 6 June 2010 (UTC)

I don't oppose lists, except for them making it easy to add every trivial use. I'd suggest a 'graph like this:

Holograms have been a staple of science fiction since [first use, suitably sourced & dated]. Since then, their use has expanded to information displays & communications devices (both becoming increasingly common), and even characters, such as the EMH (the first holo character [if true, cited]) & Vic Fontaine. The increased use is mirrored by improvements in special effects and real world holographic technology.

I wouldn't exclude examples of displays & comm tech, but IMO, they aren't essential, unless, & except if, a first use can be cited reliably. TREKphiler ^{any time you're ready, Uhura} 16:18, 6 June 2010 (UTC)

I don't personally think that this section should be included. One would not have a 'Lenses in fiction' or 'Lasers in fiction'. At most, it should be a separate article, with a link from the main article, with an introduction as defined by TREKphiler above. I don't know when the first mention of holography in fiction occurred nor do I want to research it, so perhaps a devotee of the subject could provide this information in a new article Epzcaw (talk) 18:54, 29 March 2011 (UTC)

An unregistered user recently removed this section, and user:Rangoon11 restored it. My own opinion (above) is that it should not be included, certainly not as a long list of books and films. The other comments above support this view. I have grave doubts about whether all the items listed actually do refer to holography (e.g. Jules Verne - but I haven't got the time or energy to check them all. It would be much better to have a separate article which covers this topic in more detail.

The same applies to the "Things that are not holograms" section

Epzcaw (talk) 16:32, 29 August 2011 (UTC)

An unregistered user has removed this section, but it has been restored byLutzL. I have refrained from removing it even though I don't think it should be there as such a move requires some consensus, but most of the comments here support its removal. Epzcaw (talk) 18:35, 12 November 2011 (UTC)

I also think that the list 'Holography in fiction' should not be included. But since this section is pretty much the only one the casual reader cares to edit, it seems to be read. I would therefore just move it to a separate article. --Danh (talk) 22:33, 13 November 2011 (UTC)

I restored it, because, as can be seen from the history, someone will always add those trivia. I believe that a short list of good examples could act as 'lightning rod', in that it deters some (and hopefully most) people from adding stupid examples. Stupid examples are, among others, such where only the name 'hologram' is used for some deux-ex-machina. Good examples are, of course, uses of the actual technology, and where the application is technologically believable (the holodecks of star trek barely fit the latter class). I didn't hunt for it, but the above described state of a paragraph and a short list sounds good.--LutzL (talk) 15:49, 14 November 2011 (UTC)

Discovered vs. invented

Hi, this is not very important in the grand scheme of things but this article states that holography was discovered by Dennis Gabor whilst his biography states that he invented holography. Which is correct? Can one discover something that was not pre-existing? —Preceding unsigned comment added by Quirkius (talk • contribs) 07:19, 5 June 2010 (UTC)

What holograms are not

Wouldn't it be helpful to explain what holograms are not? Even after reading this wikipedia entry, many people's idea of holograms will still be purely in the realm of sci-fi. I've seen many news articles(in science sections no less) that state that "holograms are 3D projections into air". This is simply not the case but I see it all the time. It's no wonder that when people see the CNN "hologram", or Musion Eyeliner, or the touchable "hologram", or many other things which are just video reflections off glass, that they are fooled into thinking that they are witnessing the latest hologram technology. Anyways, just a thought.Laserlight1234 (talk) 21:33, 31 August 2010 (UTC)

I don't see the point of this section. In any article about X, one could include a very long list of what X is not, but this seems pretty pointless. If the subject is explained properly by the article, then it should not be necessary to say what it is not. If this is not clear, then the article needs to be re-written. Epzcaw (talk) 18:58, 29 March 2011 (UTC)

Theory section

Instead of being a section about the theory of the subject, it is a step-by-step explanation of the problems faced by the original holographer.

When I came to read the theory section I hoped to gain insight about how the holographic recording happens. What I found out was that the original holographer's first problem was X, which he solved and then bumped into problem Y, and so on. That's not theory, it's more like History of Holography Problems and Solutions

Sadly I don't understand the subject. 89.139.165.171 (talk) 15:03, 25 September 2010 (UTC)

I agree. I have removed all the stuff about pinhole cameras and Dennis Gabor's early work as I think it obscures the explanation. But not sure it explains how the holographic process work in the new form. This is not easy. Taking the sound analogy - early phonographic recordings were made by converting the amplitude of the sound pressure waves at a microphone into hills and valleys on a wax surface (recording). In themselves, these give no indication of what the sound is like. But they can be converted back into sound waves by running a stylus on the hills and valleys, and converting the motion of the stylus into air pressure waves (reconstruction). The holographic recording is a seemingly random pattern on a holographic plate (there is photograph of one further down in the article). When a laser beam is shone onto the hologram, it recontructs the original beam which formed the hologram by diffraction. Does this help? Epzcaw (talk) 19:09, 26 March 2011 (UTC)

Moving Holograms research

Research at the University of Arizona

http://uanews.org/node/35220 —Preceding unsigned comment added by 86.136.215.148 (talk) 10:10, 5 November 2010 (UTC)

This is now included as a reference. --Danh (talk) 19:09, 5 November 2010 (UTC)

Rewrite?

I am by no means a physicist, and upon reading large portions of the article I was left wondering, 'wait, what?' I had to re-read several sections multiple times to get even the foggiest idea as to what is being talked about. Large sections can also be simplified to explain the mechanism of how a hologram works. The specifics of the mechanism do not need to be mentioned, these only serve to confuse people who are not familiar with the terminology. For example, this is confusing; "Mechanical stability is also very important when making a hologram. Any relative phase change between the object and reference beams due to vibration or air movement will cause the fringes on the recording medium to move, and if the phase change is greater than π, the fringe pattern is averaged out, and no holographic recording is obtained". That section can be shortened to something like "mechanical stability is also important because, even tiny vibrations can reduce or eliminate coherence between the object beam and the reference beam. If coherence is lost due to vibration, an image might not be captured."

X64ghost (talk) 08:17, 8 February 2011 (UTC)

It would not be helpful to use the term 'coherence' here as it has a very specific meaning in optics Coherence (physics), and is not reduced or eliminated when the object beam vibrates with respect to the reference beam. What happens is that the holographic recording, which is an interference pattern, moves across the field of view, so that is first blurred, and then averaged out altogether. The effect is similar to taking a photograph of a moving grid - if the grid moves by one spacing or more while the photograph is being taken, then the grid will not be visible in the photograph. Epzcaw (talk) 18:29, 26 March 2011 (UTC) epzcaw

I have re-organised most of this article, removed some parts, and re-written several parts. I hope it makes it easier to understand what holography is, and welcome any comments, suggestions etc. Epzcaw (talk) 12:20, 30 March 2011 (UTC)

In practice

Mention Nasser Peyghambarian and his team at the Iniversity of Arizona, aswell as the system they made. Ref= http://www.uanews.org/node/35220 91.182.193.178 (talk) 17:09, 27 April 2011 (UTC)

hatsune miku

i read this article about hatsune miku and it suggests that hatsune miku was not projected on to a black screen, but was an actual moving-in-3-dimensions, strutting hologram. i tried to write about it, but then someone deleted it saying that hatsune miku's hologram was just an image projected on a black screen and not an actual hologram. here is a link to the article and the concert video. please have a look at it and include it in the article. http://www.dailymail.co.uk/sciencetech/article-1329040/Japanese-3D-singing-hologram-Hatsune-Miku-nations-biggest-pop-star.html http://www.youtube.com/watch?v=DTXO7KGHtjI StewDaDa (talk) 06:34, 29 April 2011 (UTC) i have added the article back, please dont delete it. hatsune miku is an actual hologram and not a projected image

Are you sure? At the frames at 0:00 and 2:41 of the youtube video you link one can in my opinion clearly see a semitransparent screen, which reflects the audience in front of it. According to [1] the technology used is Musion Eyeliner, which uses a conventional projector and a screen (see http://www.youtube.com/watch?v=HtVcN0q-A08 for how it works). --Danh (talk) 14:17, 29 April 2011 (UTC)

Fidelity of the recorded hologram

From Hariharan, Optical Holography. page 88

"With any practical recording medium, its MTF will, in general, affect the resolution as well as the intensity of the reconstructed image."

If the scene being recorded consists of two point sources which produce essentially Young's fringes, and if the spacing of these fringes is well below the resolution of the recording medium, then no fringes will be recorded, and no image will be obtained. Any feature in a complex scene with the same separation as the point source will likewise not be reconstructed. Epzcaw (talk|) 23:32, 18 May 2011 (UTC)

Hi, thanks for the quick reaction. I don't doubt your quote of him, but I cannot possibly see how this would be the case. I cannot possibly see how a reduction in the modulation would change the resolution of the image formed by it. It would change the strength of the diffraction (thus the brightness of the image). A film that recorded lower spatial frequencies and not higher spatial frequencies would record images at a small angle with respect to the reference beam and would attenuate images at larger angles from it. Isn't that sort of obvious? It would not affect the ability of the hologram to separate two nearby points both near or both far from the reference beam. It is not interference between two close points that's involved, after all (and indeed if it were, then closely spaced points -- "high resolution" -- would be EASIER to record since they'd produce a lower spatial frequency on the film, so that would make even less sense!). I really really think that author simply wrote that in error (as we all do sometimes). I cannot possibly see how this would be true, whereas the following paragraph tells how you can REALLY lose resolution within a holographic image: by limiting the extent in the frequency domain -- the hologram -- thus losing resolution (frequency response) in the spatial domain. Doesn't what I say make sense?? Or am I really missing something? -- Interferometrist (talk) 01:02, 19 May 2011 (UTC)

I am off on holiday for a week, so have time only for a quick response.

Consider a single point source as object and a plane reference beam. The hologram will consist of a series of curved fringes of varying spacing. A faithful reproduction of the point source will only be obtianed if the whole of the wavefront from the point source is recorded so there will be some 'fuzziness' which will be increased as the size of the recording is reduced (I think we agree on this). If the MTF of the recording medium is unable to resolve the finer fringes in the interference pattern, then some of the spatial frequencies in the object beam will not be reproduced in the re-constructed beam, and the effect of this on the reproduction will be more 'fuzzinss' - excuse the inexact term! If you don't agree, what effect do you think the loss of spatial frequencies will be on the reproduction?

If I have a chance on holiday, I will put together a more analytical argument. But in the meantime, thanks for the suggestion - it is always useful to have one's views questioned, and you may be right, but I don't think so!!Epzcaw (talk) 08:00, 19 May 2011 (UTC)

Just before I go - Hariharan also provided a refereed journal reference - Kozma A & Zelenka JS, 1970, Effect of film resolution and size in holography, Journal of the Optical Society of America, 60, 34-43. Epzcaw (talk) 08:31, 19 May 2011 (UTC)

Alright, thanks for that reference, which I will try to look up when I have the chance (I'm a bit tied up right now too, though sadly not due to taking holidays.). But I still can't see the justification for the claim. Let me go over what you said:

A faithful reproduction of the point source will only be obtianed if the whole of the wavefront from the point source is recorded so there will be some 'fuzziness' which will be increased as the size of the recording is reduced (I think we agree on this).

Yes we agree here. Though it doesn't even have to do with holography in particular but just the viewing angle (acceptance angle of the optical system) that is really at issue. If you look at a small object 10cm away (which could be as well be the image generated by a hologram) and must view it through a 1cm hole, you could not resolve it with a resolution better than 10 wavelengths using any possible optical system. If it were a 1mm hole then 100 wavelengths resolution. If the hole were huge and you had a microscope with a huge (>10cm diameter) objective (with a 10cm FL so you could use it 10cm away) then you could get near diffraction limited resolution. So the size of the "viewing window" (the size of the hologram) limits the resolution in principle, but for ordinary viewing that would only be a limitation when the size becomes smaller than the pupil of your eye. (You can try this at home. Make a small pinhole in a piece of thin cardboard or aluminum foil and look through it. Look at anything in the room or preferably outside where it's sunny since everything will be dimmed. You will see everything fuzzy due to diffraction by the pinhole. The smaller the pinhole, the fuzzier. The angular resolution you observe is equal to lambda/D.)

If the MTF of the recording medium is unable to resolve the finer fringes in the interference pattern, then some of the spatial frequencies in the object beam will not be reproduced in the re-constructed beam

Yes, and those would correspond to image detail at a large angle from the reference beam. A point 100 milliradians from the reference beam would produce a spatial frequency of .1 cycles / wavelength (period of 10 wavelengths). If that were near the MTF limit of the film, then an object at 200 milliradians away would produce little or no modulation at .2 cycles/wavelength (5 lambda fringe spacing) making it DIMMER (or absent).

, and the effect of this on the reproduction will be more 'fuzzinss' - excuse the inexact term! If you don't agree, what effect do you think the loss of spatial frequencies will be on the reproduction?

Suppose that at .15 cycles/wavelength the MTF of the film is down to 1/4. Compared to an image point at .05 radians, the point at .15 radians from the reference beam will appear 1/4 as bright. If there were a point at .15 radians and another at .1515 radians, then the recorded pattern would be two sets of ~ .15 cycles/wavelength fringes with a beat pattern (Moire pattern, in this case) of 100 fringes (.01cycles/fringe = .0015 cycles/wavelength), but what is being modulated after all is a frequency of .15 cycles/wavelength which is the aspect that the film can barely reproduce (no problem with the beat frequency!). Thus both points will be 1/4 as bright as they should be (if you had used perfect film) but both will be there and separated according to that outer beat frequency. Thus no reason for a decrease in resolution between those two close image points. That's the way I see it! -- Interferometrist (talk) 12:07, 19 May 2011 (UTC)

If you lose some of the information from the original wavefront, you lose the saem information in teh re-constructed beam, and by losing this, you will increases the spreading out of the beam compared with the original one, thus the image will be spread out, and the overall image will eb less sharp.

Consider the following scenario:

Assume we have a point source, and a plane wave bot illuminating the hologram plate normally. The hologram will be a sinusoidal zone pattern as in the Holography article, i.e. a series of circles whose spacing decreases with increasing distance from the centre. In the first instance, assume that all these fringes are fully resolved by the recording medium. We both agree that the resolution of the reconstructed beam is determined by the size of the holographic recording which acts as an aperture. If the recording is circular, the resolution will be defined by the Airy disk. The virtual image of the point source will no longer be a point but will have circular Airy rings. The diameter of the first disk in the image of the point source is inversely proportional to the size of the holographic recording. Now assume we use a holographic recording medium whose MTF is a step function, and falls to zero at a spatial frequency which occurs halfway out in the interference pattern, so no fringes are obtained after this. This reduces the effective aperture of the hologram by a factor 2 and therefore increases the Airy disk in the reconstructed beam by the same amount. Therefore the loss of resolution in the holographic recording medium results in a loss of resolution in the reconstructed beam, which is observed as an increase in the size of the virtual image of the point source. An off axis point source will give a different interference pattern, but nonetheless, will consist of curved fringes of decreasing spacing, some of which, again, will not be recorded because of the limited range of the MTF of the recording medium, so the aperture of the hologram is reduced and the size of the virtual image of the point source is increased compared with that which would be obtained if all the fringes were resolved. A holographic recording of a complex object can be considered to be made up of a set of point sources, each of which creates its own Fresnel zone structure, and therefore the reconstruction of each of these point sources will have a larger Airy disk than if all the spatial frequencies were fully resolved by the recording medium. This means that the image will be less well defined, and features closer together than half the new Airy disk size, using the Airy resolution convention, will no longer be resolved. Hence the image will be 'fuzzier'.

Of course, we don’t get step-function MTFs, but if we have an MTF for which a significant fraction of the Fresnel fringes are not recorded, or barely, recorded, then we expect to have reduced resolution in the reconstruction. And any falling off of the MTF mean that the amplitude of part of the re-construction is reduced, and this must mean that the resolution of the re-constructed beam is also reduced. I am sure that the paper which Hariharan quotes will do the mathematics to show this. If not, I will have a go when I get home next week.Epzcaw (talk) 16:09, 22 May 2011 (UTC)

Alright, you indeed were able to think of a case where the MTF of the film reduces the active size of the entire hologram and for that reason decreases the possible resolution that could be observed using a very special optical setup. Is that what this was all about though? I would never have guessed it! Most of the article implied looking at holograms using your eye, not a large aperture optical system. What's more, normal holograms are off-axis so you don't have to look directly into the laser beam (though even in that case I can see that a limited MTF of the film could cause the modulation to fall off toward one side of the film, again making the effective size of the hologram smaller). And if the object were at infinity rather than nearby, this effect wouldn't apply at all. I find it hard to believe that this was the situation that was at issue because it is rather far-fetched. If it was, then you'd really need to lay out the conditions for what is really a problem that is never likely to be observed in practice (i.e. unless you were trying). In other words, including the statement in the article is more misleading than helpful to the average person. And I still doubt it is what the author was thinking when he wrote that -- is it? - Interferometrist (talk) 20:07, 22 May 2011 (UTC)

I wrote that section and it was based on my own experience of making holograms some years ago. We used special photographic plates for making holograms which had very fine resolution, and correspondingly low sensitivity, so that several minutes exposure were required using a 5W argon laser to provide sufficent illumination to produce a working hologram. These plates were expensive, and also very high mechanical stability was required because of the long exposure time, so we wouldn't have been using them if we could have used standard black and white film. If you look at the article cited in the Holography article from 'How Stuff works' you will see that it says "Holographic film: Holographic film can record light at a very high resolution, which is necessary for creating a hologram.". Look at this website - http://www.holo.com/holo//book/book.html#thholo and you will again find they say that very high resolution special film is required to make a hologram. You will find similar statement in any other article which discuss the practical aspects of making holograms. If you look at this web-page http://www.kodak.com/eknec/documents/59/0900688a80300559/EpubBW400CN4036.pdf you will see the MTF fo rprofessional Kidak black and white emulsion starts failling off at 50 lines/mm, so you would have no chance of proudcing a holgram with this, becuase most of the interference pattern which makes up the holgram would not be recorded and therefroe teh reconstructed beam would contain very few of the object beam spatial frequencies. If you did get an image, it would be extremely blurred. It is not at all misleading, therefore, to say that the resolution of the reconstruction is reduced if the resolution of the recording medium is limited as anyone who is embarking on making a hologram needs to know the importance of using a high resolution film (or whatever) to make a hologram. Maybe that needs to be stated more explicitly, i.e it should start by saying that special very high reoslution film is required to make a hologram, as otherwise most of the information in the object beam will not be recorded etc. etc. I will provide the mathematical explanation in a few days when I get home.Epzcaw (talk) 08:35, 24 May 2011 (UTC)

I have now modelled this using Mathcad. I have calculated the amplitude distribution where a point source located at a distance of 2000mm is focused with a lens of focal length 100mm, and an aperture of 2mm. There are three plots (a) w(p) - all the fringes fully resolved (b) y(p) - efficiency falling off from the centre withe the square of the distance from the centre and (c) z(p) - a sharp cut-off half way across. Clearly, the spreading of the point increases, and therefore the resoution of the viewed image is degraded. I will modify the text but stand by the statement that the resolution of the hoographic image is affected by the MTF of the recording medium. Epzcaw (talk) 17:06, 28 May 2011 (UTC)

Removal of the word 'random'

An unnmamed user has removed the word 'random' from the phrase

"The hologram itself consists of a very fine random pattern, which appears to bear no relationship to the scene which it has recorded."

The object beam in a hologram is nearly always derived from an object with a rough surfaces, so that the light scattered onto the hologram plate is a speckle pattern.

In the introduction to the book, "Laser Speckle, Topics in Applied Physics", 1985, Springer Verlag), Prof. Chris Dainty says:

"The random intesity distribution that we now call a speckle pattern is formed when fairly coherent light is either reflected from a rough surface ....!

The objects recorded by holograms nearly always have random rough surfaces, and therefore produce speckle patterns on the holgram plate. The only circumstances under which the object beam would not be random is if the object had a reflecting surface, and such an object would illuminate only a very small part of the hologram unless it was a flat mirror. Such a holgram would not be of much interest.

I propose to re-instate the word 'random', perhaps prefacing it is 'normally', unless the author can provide a convincing argument for not doing so. Epzcaw (talk) 13:44, 11 June 2011 (UTC)

Virtual image

The image which is seen in a transmission hologram is known as a virtual image - see 'Optical Holography', P Hariharan. Cambridge University Press, 1996 - pages 16, 19, 29. Or see http://www.holostudios.com/holohelper/faq.htm. (Also, ask anyone who makes holograms!!). I have therefore undone the removal of the reference to virtual images in the text.Epzcaw (talk) 09:46, 27 June 2011 (UTC)