Whatever Became of Holography?

[Din]

https://www.americanscientist.org/artic ... holography

An article in American Scientist by Sean Johnston; some of you may know him as having received a grant to write the history of holography, he was a presence in a lot of the conferences about 10 years ago ( https://global.oup.com/academic/product ... us&lang=en&).

It's about 25 pages in large script, but I estimate it's about 200 words. A lot of us here already know most of the story. However the last section (Modern Holography) might be interesting, since Johnston lays out his thesis on what happened to holography in this last section. I thought a few quotes were interesting:

"During the late 1960s....Conductron’s founder Kip Siegel touted an impending commercial future for holograms of all kinds. To shareholders, employees and potential investors, he promised that the United States would have the only holographic television, cinema and home movies within a decade"
And here we are, some 60 years later, still waiting

"Siegel’s portrayal of holography as a future consumer industry relied on an implicit faith, widely shared by many of his contemporaries, in scientific, technical and economic progress. Yet his claims far exceeded the capabilities and expectations of his engineers, and the commercial predictions diverged widely from the most optimistic technical extrapolations. "
I seem to recall I said this on many an occasion.

"These scientists, engineers, artists and artisans began to identify themselves as holographers, and they proselytized for the new field."
Yep! Actually, I don't think scientists, the engineers and the actual artists proselytized the new field. I think it was the artisans who seemed to think of themselves as artists, who did the proselytizing. These artisans also seemed to want to own the subject - their mantra or expulsion, accompanied by much anger!

"But by the late 1980s, the artform’s popularity was beginning to wane. Ironically, the falling appeal was associated with holograms’ widespread availability and the consequent trade-offs in quality."
Several actual artists I've talked to, particularly Ron Olson, have complained about this.

"In the same way, holograms had a commercial trajectory that started as a gallery phenomenon, then became an art form for the home and eventually were relegated to children’s sticker books. [Holography] shared a pattern of popular acclaim, declining interest, niche novelty and transformation for the juvenile market. Cultural memories endure longer, but not necessarily with accuracy."

[Joe Farina]

In terms of display holography, a person who is, first and foremost, a "holographer" may be a thing of the past.

Display holograms had something of a mainstream presence in the 1980's and into the first half of the 1990's. Unfortunately, holograms were presented to the public as a novelty. The public consumed the novelty for a certain period of time (for a surprisingly long period, in my opinion). When the novelty factor wasn't enough to make the product commercially viable, it basically disappeared. By 2023, display holography appears to be largely forgotten.

This is all for the best. A person can say "love me because I'm a novelty" for only a certain amount of time. It will work, but only for a short while.

I have always felt that "holography" should only be considered a method (or tool, component, etc.) for a much more general purpose. When a person sees a hologram, and says "what is it?" the answer should be ___________ (fill in the blank, something other than "it's a hologram!"). The hologram is part of the process which enabled ____________.

By the way, I don't like the word "hologram" to begin with. It's a false and arrogant word, because it most certainly isn't the "whole picture."

[Din]

I have always felt that "holography" should only be considered a method (or tool, component, etc.) for a much more general purpose. When a person sees a hologram, and says "what is it?" the answer should be ___________ (fill in the blank, something other than "it's a hologram!").

A technique in optical engineering that enables compact, novel optical applications that cannot be undertaken by conventional optics. SPIE, the organisation that hosts conferences on optical science and technology, has a section they call "Business Development" (or something similar). It's aimed at corporate executives who are not scientists and engineers. Various speakers address the group of about 100 or so on future possibilities in optical technology to keep these corporate executives abreast of new technologies that may affect markets. About 5 years ago, Seth Coe-Sullivan who was VP of technology at Luminit (where Joy was an optical engineer at the time) asked me to give a lecture on applications in holography that may be exploited for new products. I gave the lecture pointing to the vast scope and flexibility of holography by creating new optical functions where none existed yet, as well as streamlining conventional optical engineering by making product lighter, smaller and cheaper. I was followed by Bernard Kress, head of the Microsoft Hololens project, who told the audience that they should take heed of what I'd said, because the potential for holographic engineering was vast.

The hologram is part of the process which enabled ____________.

Phase reconstruction. Since Zernike invented the phase contrast microscope in 1932, the ability to manipulate phase has been a vital tool in optical engineering. However, only holograms can record phase variations.

By the way, I don't like the word "hologram" to begin with. It's a false and arrogant word, because it most certainly isn't the "whole picture."

It was never meant to be the "whole picture". Gabor coined the term 'holography' or 'holograph', not hologram. It was meant to show that, unlike previous methods of capturing light (photography, light meters, the human eye etc) which could only capture intensity, holographs can capture both intensity and phase. Light can be described by three parameters: intensity, phase and frequency (or wavelength). Ignoring wavelength for the moment, any equipment to capture light, from photography in the mid 19th century to photomultiplier tubes, capture only intensity. Phase information was discarded as unimportant. Gabor was troubled by the inability for an electron microscope to reach it's theoretical resolution because of lens aberrations. In a flash of insight (on a tennis court, reputedly) Gabor realised that you could do away with lenses altogether if you could capture the wavefront itself. However, the shape of the wavefront was based on the phase of the wavefront at any position. So, Gabor realised, he'd need to find a method to capture not only intensity, but also phase; in other words, he needed to capture the "complete (whole) picture" - phase and intensity. The word 'picture' in this sense is a metaphor for information. Unfortunately a sub-group of display holographers has swallowed the idea of picture meaning an actual picture of a cat, for example, and get pretty nasty when the idea of 'picture' in the scientific sense of information is broought forward.

[Joe Farina]

Unfortunately a sub-group of display holographers has swallowed the idea of picture meaning an actual picture of a cat, for example, and get pretty nasty when the idea of 'picture' in the scientific sense of information is broought forward.

I don't know if you're referring to me or not, Din, but I'm not getting nasty. You seem to think that "display holographers" are against you. If some are, then I'm sorry to hear that. I've got nothing against you whatever. In fact, I have a lot of respect for you as a scientist. I have learned a great deal from your posts, and I'm grateful. But, I still think "hologram" is an incorrect and arrogant word, because it's not the "whole" message or picture. You yourself can point to long list of hologram characteristics which do not meet the criteria of "the whole message." I don't have anything against Gabor, but if he originated the word, I have to say I don't like it. It's not a holo-gram. It's a partial-gram, or maybe a 90%-gram. However, I think this partial-gram is sufficiently miraculous to spend much of my life working with it.

I think you're mistaken about Gabor not coining the word "hologram." I could point to a long list of sources which say otherwise. You can see these for yourself if you google "origin of the word hologram." Or, you can show me where the word came from, and I will admit my mistake.

[Din]

Unfortunately a sub-group of display holographers has swallowed the idea of picture meaning an actual picture of a cat, for example, and get pretty nasty when the idea of 'picture' in the scientific sense of information is broought forward.

I don't know if you're referring to me or not, Din, but I'm not getting nasty. You seem to think that "display holographers" are against you. If some are, then I'm sorry to hear that. I've got nothing against you whatever. In fact, I have a lot of respect for you as a scientist. I have learned a great deal from your posts, and I'm grateful. It's not a holo-gram. It's a partial-gram, or maybe a 90%-gram. However, I think this partial-gram is sufficiently miraculous to spend much of my life working with it.

Joe,
I'm not referring to you at all! If I gave that impression, please accept my apologies. I am referring to a group of perhaps 4 display holographers/artisans (call them what you will, I call them The Gang of Four) who seem to want to dominate all of holography, and codify it's interpretation and structure into a dogma of their own. They're incredibly egotistic and narcisstic, I find, and come out with abject nonsense that has no bearing on the technical literature on holography. Stating that the diffraction efficiency of a hologram is dependent on some sort of polarisation variable is abject nonsense, not supported by any of the literature, including the defining paper by Kogelnik on the Coupled Wave Theory. When you state that this is nonsense, they become nasty. When you ask for references, they become even nastier! A holographer in the past stated this "fact" without references, then proceeded to give an equation for the efficiency of a hologram without any variable for polarisation!. The most elementary level of physics states that if you think that a variable is important to an effect, the equation determining that effect must include a variable for it! One of them stated publicly that holography has nothing to do with wavefront reconstruction ! The first papers by Gabor, Leith and Upatniks and other initial workers specifically refer to holography as a method of wavefront reconstruction. Other examples proliferate. However, when I mentioned that one of my professors in physics won the Nobel in Physics, one of the Gang of Four actually said that the Nobel Prize was meaningless!!! One presumes that his ego had to state that, since he himself had not won one! They also will not tolerate dissent, any disagreement with any of their statements is met with harsh and nasty responses. And, it's not me alone; several prominent holographers, including a very prominent artist and a very prominent physicist, has said to me that this Gang of Four tries to dominate holography but is very ignorant, but they say they don't want to be drawn in. I just wish that more of the technical group would stand up and be counted when bizarre nonsense such as holography has nothing to do with wavefront reconstruction is stated.

As I've stated many times, you don't need theory to make a hologram. But, if your ego demands that you set forth nonsense as theory, someone needs to call that out. I'm not against actual artists, but this dogma has permeated the world of display holography because of the Gang of Four's demand for absolute loyalty! Both Joy and I promote education; we've been to classrooms and given talks on holography, we've been invited by STEM associations to give presentations on holography, and Joy has been asked by STEM and by SPIE to give talks to young girls on future careers in optics. But, a lot of this outreach to students, STEM and SPIE career talks to young girls is damaged by ignorant, egotistic people promulgating nonsense!

I'm all for reasoned debate on a civil level, but not for nastiness. If you state something remarkable, include a reference. Or, as Sagan put it: "Extraordinary claims require extraordinary proof"

But, I still think "hologram" is an incorrect and arrogant word, because it's not the "whole" message or picture. You yourself can point to long list of hologram characteristics which do not meet the criteria of "the whole message." I don't have anything against Gabor, but if he originated the word, I have to say I don't like it. I think you're mistaken about Gabor not coining the word "hologram." I could point to a long list of sources which say otherwise. You can see these for yourself if you google "origin of the word hologram." Or, you can show me where the word came from, and I will admit my mistake.

As always, if you make a statement, it's necessary to give references. I'm afraid that the internet itself feeds off itself, insofar as that if one apparently prominent person makes a claim, everyone else follows suit without examining the literature. In the technical field it's well known that the "complete picture" refers to the recording of phase and amplitude. It's stated in lecture notes to physics and engineering students. Here, for example, is the lecture notes from the University of Illinois, where it states that "complete" refers to phase and amplitude (http://light.ece.illinois.edu/ECE460/PDF/Holography.pdf):
"In 1948, Dennis Gabor introduced “A new microscopic principle”, which he termed holography (from Greek holos, meaning “whole” or “entire”, and grafe, “writing”). The name was chosen to indicate that the method records the entire field information (i.e. amplitude and phase) not just the usual intensity.".

Also, Gabor's Nobel acceptance lecture speech (which you may not value, according to one of the Gang of Four, who thinks that the Nobel prize is meaningless!). In it ( https://www.nobelprize.org/uploads/2018 ... ecture.pdf ), he states (page 13, second para):

"After pondering this problem for a long time, a solution suddenly dawned on me, one fine day at Easter 1947, more or less as shown in Figure 2. Why
not take a bad electron picture, but one which contains the whole information, and correct it by optical means? It was clear to me for some time that
this could be done, if at all, only with coherent electron beams, with electron waves which have a definite phase. But an ordinary photograph loses the
phase completely, it records only the intensities."
Again, he states whole information, not whole picture.
I think at some point in the past, display holographers, not understanding the concept of phase, misinterpreted "picture" to mean an actual, literal picture rather than "information". But, you're right, he did use the word "hologram".

"In 1948, Dennis Gabor proposed a novel two-step lensless imaging process which he called wavefront reconstruction [which, according to the Gang of Four, has nothing to do with holography] and which we now know as holography. Gabor recognized that when a suitable coherent reference wave is presented simultaneously with the light diffracted by or scattered by an object, then information about both the amplitude and phase of the diffracted or scattered waves can be recorded, in spite of the fact that the recording media respond only to light intensity"
- "Introduction to Fourier Optics", Joseph Goodman

"The unique characteristic of holography is the idea of recording the complete wavefield, that is to say, both the amplitude and the phase of the light waves scattered by the object. Since all recording media respond only to the intensity, it is necessary to convert the phase information into variations of intensity"
-"Optical Holography, Principles, Techniques and Applications", P. Hariharan

[Joe Farina]

OK, thanks

[BobH]

This is from R.R.A. Syms "Practical Volume Holography" (Oxford Engineering Scientific Series), Oxford Science Publications, 1990, page 184:

"Even for weakly modulated gratings, coupled wave theory predicts a considerable difference in diffraction efficiency between the two possible replay polarizations, perpendicular and parallel to the plane of incidence (Kogelnik 1969). This is because the coupling coefficients for the two polarizations are different, as discussed in section 2.6. In particular, coupling to a particular diffraction order can fall to zero through the Brewster effect, if the input beam and the order in question travel at right angles, and the polarization lies in the plane of incidence."

When the reference and object beams are in air, the replay polarization dependance is very small, and can easily be disregarded by inclusion with scatter, absorption and Fresnel reflections (which are seldom measured). When making "edge-lit" holograms, or HOEs where at least one of the beams is larger than the critical angle for the substrate, polarization dependance is obvious. Just sayin'.

[Din]

This is from R.R.A. Syms "Practical Volume Holography" (Oxford Engineering Scientific Series), Oxford Science Publications, 1990, page 184:

"Even for weakly modulated gratings, coupled wave theory predicts a considerable difference in diffraction efficiency between the two possible replay polarizations, perpendicular and parallel to the plane of incidence (Kogelnik 1969). This is because the coupling coefficients for the two polarizations are different, as discussed in section 2.6."

There is no section 2.6 in the Kogelnik paper. Perhaps if your author could give the relevant equations.

When the reference and object beams are in air, the replay polarization dependance is very small, and can easily be disregarded by inclusion with scatter, absorption and Fresnel reflections (which are seldom measured).

The diffraction efficiency, according to Kogelnik, assumes a unit intensity reference entering the hologram. The diffraction efficiency is then given by the modulus of the signal beam, S, modulated by the obliquity factors (section 2.2, eqn 40). In other words, any light that does not enter the hologram, whether due to Fresnel reflections at the surfaces or scattering in the air does not affect the efficiency, in terms of Kogelnik. If this were so, the presence of dust in the lab would affect the efficiency. Only light entering the structure has a bearing on the DE.

[Din]

When the reference and object beams are in air, the replay polarization dependance is very small, and can easily be disregarded by inclusion with scatter, absorption and Fresnel reflections (which are seldom measured). When making "edge-lit" holograms, or HOEs where at least one of the beams is larger than the critical angle for the substrate, polarization dependance is obvious. Just sayin'.

Insofar as absorption is concerned, Kogelnik addresses absorption loss in section 3.2 : "Lossy Dielectric Gratings" (section 3.3, eqn 47). In this section, he defines a Loss Parameter, D, in terms of the reconstruction angle,

D = αd/cos(θ)

where α is the absorption grating, and d is the grating thickness. This, however, is the expression for non-slanted gratings. His expression for D, including slant, is given following equation 48 in section 3.3:

D = αd/c(R)

There is no mention of polarisation in either of these loss equations. Fig 8 in the Kogelnik paper givges the loss in efficiency as a function of slant (I'm unable to post the diagram).

Again, loss in the Kogelnik model is based purely on loss after the light has entered the medium. Any losses of the beam intensity before it's entered the medium (Fresnel loss, scattering etc) is not considered as part of any efficiency calculation. As I mentioned previously, the efficiency is given by the modulus of the S wave, assuming a unit R wave. If the R wave is not unity, then efficiency is given by the modulus of the S wave divided by the modulus of the R wave.

[BobH]

There is no section 2.6 in the Kogelnik paper. Perhaps if your author could give the relevant equations.

The author gives the relevant equations in section 2.6 of his book.