Epzcaw

Your new Holography intro

Thanks for working on the Holography intro. Good to learn that I'm not the only one who thinks it could be improved.

I'm no expert on the topic, so I didn't really dare to rewrite it myself, and I can't really judge whether your version is really correct. Nonetheless, I have some comments and questions: -My main concern was that artificial holography exists and in that case the result is not really "recorded" and the image is not a "reproduction". Your version keeps using those concepts. -Whatever a holographic recording device is called, I suppose a "hologram" is the result of it, not the device itself. However, maybe a hologram can be seen as a device that generates a holographic image? -holocenter.org (referenced in your new version as well as in the current one) states "A hologram is a physical structure that diffracts light into an image." I suppose this can't just be plagiarized onto wikipedia, but it seems a good starting point. However, the definition seems to say that a truly holographic (laser) projection can't be called a hologram. Nonetheless, holocenter continues as follows: "The term ‘hologram’ can refer to both the encoded material and the resulting image." How "physical" is that image? (yes, it contains photons, but that's still not as tangible as the word seems to suggest) Also: is this "structure" always a pattern encoded on a 2D surface (as your text suggests), or can that pattern also be encoded on more or less 3D surfaces?

So, how about this version? It is mostly based on your text, but heavily edited and rephrased in several places: A hologram is a representation of diffracted light that forms a three-dimensional image, with depth cues such as parallax and perspective that change realistically with the relative position of the observer. A hologram can be a recording of light scattered from actual objects, or it can show a computer-generated holographic virtual view.

A hologram contains a very fine encoded speckle pattern of the interference between the waves of the depicted light field and of a light source reference beam. The actual pattern shows no immediately discernible relationship to the light field, but when suitably illuminated, it diffracts the light into forms that can be viewed from different angles.

Holography produces truly three-dimensional light images, rather than a limited illusion of depth. It is thus distinct from lenticular and other autostereoscopic 3D display technologies, which can produce superficially similar results but are based on conventional lens imaging. Images requiring the aid of special glasses or other intermediate optics, stage illusions such as Pepper's Ghost and other unusual, baffling, or seemingly magical images are often incorrectly called holograms.

Maybe these (relatively slightly edited) parts can be used in other sections: The holographic process is analogous to a CD audio recording where the audio signal is encoded as a series of indentations in a reflective surface that are read by a laser light in a CD player. Holographic recordings are generally made using laser light; the object whose light field is being recorded is illuminated and the scattered light is combined with a second laser beam to form the interference pattern. The first holograms were recorded using photographic plates, but nowadays other materials are also used. The recorded light field is reproduced more or less exactly when the recording is illuminated by a light beam identical to the reference beam used in the recording, although in practice laser illumination is often avoided with acceptance of the resulting loss of image quality.

Holographic portraiture often resorts to a non-holographic intermediate imaging procedure, to avoid the hazardous high-powered pulsed lasers otherwise needed to optically "freeze" moving subjects as perfectly as the extremely motion-intolerant holographic recording process requires.

Hopefully I managed to keep what you wanted the text to say in a more compact form. Please let me know what you think. Would you like to put it in the article like this, or in the talk page, or does it need more work? Joortje1 (talk) 17:26, 13 August 2020 (UTC)

Good to have a discussion about these things.

The problem that arises in writing these articles is that if you make it really simple, you are likely be inaccurate. If you make it more detailed to improve accuracy, you are criticised for making it too hard to understand (see comment which has been at the top of the holography page for several years!!)

Firstly, a hologram does not form an image. It forms a light wave which can be formed into an image by a camera or a human eye.

Next, your first statement:

A hologram is a representation of diffracted light that forms a three-dimensional image

is not accurate. Not all holograms are designed to produce images. Supermarket bar-scanners have holograms which diffract an input laser beam into a range of output laser beams travelling in different directions - see Holographic optical element. This means that your second paragraph:

"A hologram contains a very fine encoded speckle pattern"

is not correct - holographic optical elements will have very clearly defined fringe patterns - if the optics are clean enough, or indeed if the hologram is computer-generated, there will be no speckles.

(I should mention that I spent some years trying to produce quite complicated holographic optical elements so I have a special interest!)

So before proceeding any further, perhaps you would consider this point. Is it being too pedantic to include the more general definition of a hologram, or is it important to tell the whole story?

Regards. Epzcaw (talk) 19:14, 13 August 2020 (UTC)

Glad you like the discussion. If those are the only inaccuracies, it shouldn't be too hard too hard to create a decent new version. If there are many more, we'll have to see whether it's useful for me to work on this. I think I understand your concern about accuracy vs simplicity. But since I'm hardly grasping how holography works and am learning more about it while trying to get this text right, I might be able to tell when it gets too complicated, detailed or pedantic for the average reader. I believe it's possible to tell a more or less complete story in accurate and understandable terms, without too many details.

My new thoughts: -I checked several other definitions and descriptions in online dictionaries (and other sites) and most seem to agree that a hologram is a three-dimensional image. Merriam-Webster adds that it's also "the pattern of interference itself". No definition I saw seems to describe it as a device. I suppose holography can indeed be used for other purposes than images, but maybe in those cases it's not totally accurate to describe the resulting light field (or its carrier, or its holographic optical element) as a hologram (or is it just less common?) Maybe it can even be argued that a "diffracted range of output laser beams travelling in different directions" still forms a 3D image, albeit an abstract one (and possibly one with infinite lines)? -We seem to have lost the term "holography" (the official title for the article), so it might be a good idea to use it in a new short paragraph about holographic techniques that don't really create images, like those supermarket bar-scanners (and cd-players?)? Something like, "Apart from imaging processes, holography is also applied in..." -I missed your use of the word "generally" in that second paragraph. Maybe it can be changed into something like "A hologram contains a very fine encoded pattern (generally a speckle pattern) of the interference between the waves of the depicted light field and of a light source reference beam."? Would a description of exceptions fit in the new short paragraph suggested above? -Is it more accurate to define it as "A hologram is a representation of a diffracted light field as a three-dimensional image" than the way I wrote it before?

By the way, it may be worth noting that I'm not a native speaker of English. It's quite possible that I'll make some mistakes or construct sentences awkwardly.

Regards.Joortje1 (talk) 21:40, 13 August 2020 (UTC)

It is really good to be able to discuss things and disagree in a friendly way.

Your English is several orders of magnitude better than my use of the two languages I learnt at school, and the other three that I attempted to learn along the line!!

I agree with you that since the article is entitled "Holography" the first sentence should define holography. I've noted about ten definitions of holography from the internet. I've listed them here and added my opinions:

Holography is a technique for recording information about an optical wavefront by interfering it with a reference coherent wave

Essentially my definition, but too technical for an introduction.

Holography is the science of making holograms which are usually intended for displaying three dimensional images. It is a physical structure that diffracts light into an image.

I’m fairly happy with this one though could so without the “science” bit. I have the impression that you do not agree that the hologram is a physical structure – but a computer generated hologram has to be “printed onto a film or a mask” - see Computer-generated holography

Holography is a technique by which the image of a three dimensional object is recorded on film so that upon reconstruction, or playback, the constructed image of the object is three dimensional.

OK, but assumes that all holograms are recording three dimensional objects

Holography is a method of reproducing a three-dimensional image of an object by means of light wave patterns recorded on a photographic plate or film.

OK, but again assumes all holograms are recording 3d objects

Holography, means of creating a unique photographic image without the use of a lens.

Disagree – need a lens to create the image!

Holography is a process that creates three-dimensional images called holograms using laser beams, the properties of interference and diffraction, light intensity recording, and illumination of the recording

Disagree – I don’t agree that the image is a hologram but...

Holography is a way of making three-dimensional (3-D) picture made with a laser.

Disagree – (1) Don’t need a laser to create – can use computer – (2) Don’t need a laser to view

Holography is "lensless photography" in which an image is captured not as an image focused on film, but as an interference pattern at the film.

Disagree – the image is created by a lens

Holography is the creation of three-dimensional images called holograms. The process is similar to that of photography except that rather than recording an image, it captures light fields

Disagree – if the hologram is the physical device with the interference patterns on, then it is not a three dimensional image.

There is, of course, no "correct" meaning of a word. Words mean what people believe they mean.The problem here is that there is a divergence of view about what "holography", or if you define it as "the art (science, process, technology or whatever") of making holograms, then there is a divergence of views about what a hologram is. I have several holograms, three of which feature in the Wikipedia article. I took the photograph of the detailed structure of a hologram by taking of a photo of the light passing through the photographic plate and

To me, the hologram is the physical object on which the interference is stored, and I'm confident that that would be the view of anyone who is in the business of making holograms. The three-dimensional image (but see my comment below about this) exists only when you are viewing the recorded pattern in the appropriate viewing conditions. I produced the photos of the detailed structure of a hologram in the Wikipedia article from a glass plate with developed photographic emulsion which I've had since about 1990. Two toy cars were used as the objects in the original recording. If you view the glass plate in ordinary light, you see a blackish mess! I put it in a microscope and took a photo of the microscope image, and there you can see the speckles which have stored the amplitude and phase of the light scattered from two cars. It is the simplest form of hologram and you can only see the cars if you shine an expanded laser beam (i.e. one that has passed through a lens) and then focus your eyes on an area behind the glass plate at the same distance as the cars were originally located. So my question to you is: if the glass plate with the photographic emulsion pattern on it is not the hologram, what is? Does the hologram only exist when you look at it in suitable laser light?

I also have problems with a "3d image". The photographs taken from the mouse hologram are 2d images as are the images in your eyes. hat the hologram does is enable you to see the object as is it were really there. But maybe I am being pedantic.

So how about this for the first sentence:

Holography is a method in which the image of a three dimensional object is encoded; this can then be decoded to produce a three-dimensional image of the object. Holography is also used to encode and decode other light fields.

If we can agree on the first sentence, we can go on to look at the rest!

There doesn't even seem to be that much of a disagreement (if you ask me), but it's indeed nice to discuss this complicated goal of finding a satisfactory description of holography in a friendly way. Let me address the problem I have with it being described as a physical structure. I accept that the word "hologram" is very commonly (and possibly most rightly) used for the physical carrier of the light field interference pattern. I believe we should definitely keep this use of the word in mind, but not as the only one. Now let's compare holography with photography. A photograph is no longer necessarily the physical object it used to be; it's more commonly an image on a screen. There will always be the physical reality of photons, but I think we'd be stretching the meaning of the words if we call the temporarily emitted lights from the pixels a "physical structure". Isn't anything similar already possible with holography, like holographic projection from an electronically created grid? Even if it's still totally sci-fi, the concept exists and may even entail the most common use of the word "hologram".

I have some similar problem with the use of "object" in your proposal. It seems to leave out less tangible subjects that I suppose can be computer-generated as a holographic virtual view (like a landscape with clouds or a rainbow), if not recorded in real life. Another problem is that you suddenly mention "other light fields" without having defined one before.

Let's break the issue down a bit more. The biggest problem seems to be that the word "hologram" is used to refer to both the carrier (a physical object with the encoded pattern) and its 3D image (the decoded light field pattern, non-tangible). I believe we could say the hologram is actually the pattern itself. This would avoid the problems with the two widely used different interpretations. So how about: Holography is the encoding of the interference pattern of a three-dimensional light field. Can you agree on that? It is rather technical, but I'd like to solve that with a very clear and simple explanation in the next sentence. Something like "It is commonly known as a 3D imaging technique, but the principle is also widely applied in different ways, for instance in holographic bar code scanners."

Cheers, Joris

Nearly there but

1) At least two light fields are required to produce an interference pattern.

2) All light fields are three dimensional

How about: Holography is the encoding of a light field as an interference pattern. It is commonly used as a 3D imaging technique, but the principle is also widely applied in different ways, for instance, to produce optical elements such as lenses.'

or

Holography is the encoding of a light field as an interference pattern which is generated by superimposing a second light field. It is commonly used as a 3D imaging technique, but the principle is also widely applied in different ways, for instance, to produce optical elements such as lenses.

I can vaguely envisage producing the equivalent of a holographic reconstructed light beam purely electronically, but you would not need to encode it. You could have an array of very small lasers where you could control both the amplitude and phase of the outputs of each laser (maybe they are working on this already!!) to generate the light field. A simple example would be a system producing a plane wave front. All the lasers would emit light with the same phase and amplitude, so they would act together to produce a plane wavefront (nearly). You could model the light which would be scattered from any object or scene you wanted to, and then drive your array of lasers accordingly. No interference of diffracction would be involved. Might, of course, still be called a hologram for historical reasons.

Cheers. Catherine.Epzcaw (talk) 16:36, 14 August 2020 (UTC)

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Happy to continue to received. I've amended the links. Epzcaw (talk) 19:09, 16 March 2021 (UTC)

Notice "Too technical" on page Holography

Hi Epzcaw. I've just seen now your note of August 2020. The "Too technical" notice is still there, and I like your suggestion to move Sections 3, 4, and 5 into a new page called Physics of Holography. I think it is better than just removing the notice, since the average user is indeed more likely interested to understand the concept than the exact physics. Danh (talk) 20:29, 21 March 2021 (UTC)

Great. I will get on with it. I started working on it a while ago on my Sandbox. Epzcaw (talk) 09:08, 22 March 2021 (UTC)

@Danh: I've now submitted a draft at Draft:Physics of Optical Holography. I will continue to work on it, as I see it can take up to five months to approve. Epzcaw (talk) 10:41, 12 April 2021 (UTC)

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Your submission at Articles for creation: Physics of Optical Holography (May 29)

Your recent article submission to Articles for Creation has been reviewed! Unfortunately, it has not been accepted because it included copyrighted content, which is not permitted on Wikipedia. You are welcome to write an article on the subject, but please do not use copyrighted work.

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I cannot leave this slur unchallenged. The material I was accused of copying was from an article which had copied it verbatim from the Wikipedia Holography article, much of which I had written. It had also copied a photograph which I had taken and submitted to Wikimedia Commons. There was no attribution given in the article. My article was published in Wikipedia in full - Physics of Optical HolographyEpzcaw (talk) 18:59, 25 December 2022 (UTC)

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I cannot leave this slur unchallenged. The material I was accused of copying was from an article which had copied it verbatim from the Wikipedia Holography article, much of which I had written. It had also copied a photograph which I had taken and submitted to Wikimedia Commons. There was no attribution given in the article. My article was published in Wikipedia in full - Physics of Optical Holography. There was extensive correspondence about this, but can't find it now. Epzcaw (talk) 19:06, 25 December 2022 (UTC)

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I've left a comment on your Articles for Creation submission, which can be viewed at Draft:Physics of Optical Holography. Thanks! Pbrks (talk) 18:16, 29 May 2021 (UTC)

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Thanks

Thanks for your thank-you for the correction I made to the holography page a while ago, but I think you are doing much more for that page than I am! I'm still trying to get time set aside regularly to be able to contribute usefully here.

I recently started a new job and was hoping to get regular 15-30 minute slots in my lunch break; but it's not working out like that :( The library's interesting though - there's a bunch of classic holography texts that look and feel as though they've never been opened (Jones & Wykes still has the paper dust jacket ... I don't think I ever saw that in any of the university libraries I got to visit at that time!). I appreciate they're a bit off-topic for the organisation, but it's sad how untouched they are. Louis Knee (talk) 16:08, 9 September 2022 (UTC)

I appreciate your input greatly. I realised that one needs to keep a permanent watch on a Wikepedia page to avoid it turning into a clutter and its much better to have a team than just one person.

I am the Wykes of Jones and Wykes.

Wow - I have a brush with fame at last! I spent some time (long ago) resurrecting a Vinten ESPI system, the optical system of which is a detailed diagram in the book (the pinhole through the mirror one).

I keep meaning to do some serious work on Speckle pages but haven't got round to it yet...

I've never looked at those; I have looked at digital holography and digital holographic microscopy, which are daunting enough unfortunately. Louis Knee (talk) 16:04, 19 September 2022 (UTC)

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