## Whatever Became of Holography?

Topics not fitting anywhere else.
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

### Re: Whatever Became of Holography?

Then quote those equations. Also, interpret those equations.
If you look at Hans Bjelkhagen's expression for the diffraction efficiency for a reflection hologram, you'll see it has no variable for polarisation. I can't attach the appropriate page because I'm told: "Sorry, the board attachment quota has been reached." when I try. However, Han's expression is:

η = tanh²{(πn(1)d)/(λcos(θ))} ( "Silver-Halide Recording Materials" by H. J. Bjelkhagen eqn 2.59, p 70,)

All the variables (n(1), λ, θ) are scalar variables, and therefore cannot be a vector variable, which is what is necessary for a variable encoding polarisation.

Joe farina asked what the difference was between display holography and technical holography.

Well, one difference is that in display holography, the end result is an image of an actual, physical object (be it a porcelain cat or a green gecko). In these terms, the output of a display hologram is photometric* in nature, ie designed for human perception. Holography has the peculiar nature of being radiometric in the recording and, in display holography, photometric in the output. In a photometric regime, the important factors are brightness, sharpness (resolution) and clarity. None of these characteristics have any connection to the diffraction efficiency in terms of the physics and mathematics of diffractive optics. Some display holographers may conflate efficiency with brightness, but there are photopic and scotopic limitations to this conflation.

In technical holography, the output is a diffractive wavefunction - a mathematical and physical (ie in the realm of theories of physics) concept - which is purely radiometric**. In technical holography, the hologram is part of a larger optical system and works with the optical system as a whole, along with lenses etc. In such a situation the efficiency of the whole optical system cannot depend on external factors, such as the focal length of a lens. The spec of an optical system must be absolute and dependent only on intrinsic factors. All specifications for the efficiency of a hologram are given without any reference to external factors upon readout; one does not put into the specs statements such: the focal length of a lens depends on the polarisation of light.

In other words, to design and evaluate a technical hologram requires 4 years of education in physics/mathematics/engineering. But, I find that display holographers who do not seem to have such an education keep trying to brandish technical terms with no idea of their meaning. Why? You don't need theory to make a display hologram. I've said this over and over again! So why pretend to understand concepts you cannot possibly understand without the aforementioned 4 years of education. A green gecko is not evaluated by radiometric means.

* Photometric refers to human perception, such as photographs or television
**Radiometric refers to an optical function for data or information transfer.
BobH
Posts: 441
Joined: Tue Jan 06, 2015 10:26 pm
Location: Mesa, AZ

### Re: Whatever Became of Holography?

Din wrote: Fri Nov 24, 2023 1:18 pm Then quote those equations.
How about you get the book?

"Also, interpret those equations."

How about you make an edge-lit grating and see for yourself?
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

### Re: Whatever Became of Holography?

BobH wrote: Fri Nov 24, 2023 1:35 pm
Din wrote: Fri Nov 24, 2023 1:18 pm Then quote those equations.
How about you get the book?
Normally, in an environment of physics/ mathematics and engineering, one does not quote a reference by insisting that one buys a book just for one section. Normally, in an environment of physics/mathematics and engineering, it should be possible to quote the relevant equations, as I always do. Note that I quoted the equation in Hans Bjelkhagen's book without insisting you buy the book!
I'm not sure what you mean by "how about...". Is this a technical phrase? It sounds like something rather antagonistic by someone uneducated in a bar losing an argument! Are we getting a touch edgy?
Din wrote: Fri Nov 24, 2023 1:18 pm How about you make an edge-lit grating and see for yourself?
Well, I have made edge-lit gratings, in particular as light guides, but I fail to see your point. A literature search shows the following paper: https://opg.optica.org/ao/abstract.cfm?uri=ao-42-5-778

if your point is that somehow there's a polarisation effect, there's nothing in this paper concerning any vector quantities. perhaps, you can quote reference a paper?
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

### Re: Whatever Became of Holography?

Oh, wait! I think I see your point. If an edge-lit hologram is recorded with TM polarisation, then r.s = 0, where r and s are the vector representations of the reference and signal waves, because r and s have an angular separation of π/2. Since we have M = k[r.s(cos(phase))], the modulation vanishes. One must, therefore record with TE polarisation. This is quite true. But, on reconstruction, such a dependance does not follow. Kogelnik does not have a theory of edge lit holograms, and, I believe, as yet, there is no mathematical thoery of edge lit holograms, so the various parameters relevant to the efficiency of an edge lit hologram have not as yet been specified (unless you have a reference for such a mathematical reference).
BobH
Posts: 441
Joined: Tue Jan 06, 2015 10:26 pm
Location: Mesa, AZ

### Re: Whatever Became of Holography?

Din wrote: Fri Nov 24, 2023 3:05 pm ... so the various parameters relevant to the efficiency of an edge lit hologram have not as yet been specified (unless you have a reference for such a mathematical reference).
I provided the reference above. You just don't want to acquire it on your own. And I don't want to scan it for you, only to have you require yet another section of the book. Maybe the "very prominent artist" or the "very prominent physicist" has a copy you can borrow. Like you said, Kogelnik didn't address "edge-lit" angles in the late '60s. Syms did, twenty years later.
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

### Re: Whatever Became of Holography?

So, do you actually expect ALL of us to buy this book to follow your arguments? Are you then incapable of actually giving just a single equation, quoting a single paragraph?. Perhaps, since your author references Kogelnik, you can give us the equation that your author quotes? We ALL need to buy this book? Perhaps the moderator here can buy the book and allow us to examine your evidence? Evidence which quotes nothing is not evidence! It's just hearsay!
BobH
Posts: 441
Joined: Tue Jan 06, 2015 10:26 pm
Location: Mesa, AZ

### Re: Whatever Became of Holography?

If anyone else posts here wanting to see the section, I'll send it to them for comment. I don't think anyone else is interested. Essentially it says to disregard the boundary going from air to emulsion containing fringes. Assume the whole world is the index of the emulsion, and apply coupling theory to the fringes themselves during replay. When the angles are at Brewster's Angle to the fringes and polarization is parallel to the plane of incidence, DE falls to zero. During replay. Get the book if you want equations. Then, argue with the author or STFU.
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

### Re: Whatever Became of Holography?

BobH wrote: Sat Nov 25, 2023 9:26 am Essentially it says to disregard the boundary going from air to emulsion containing fringes. Assume the whole world is the index of the emulsion, and apply coupling theory to the fringes themselves during replay.
Not true. In equation 2 of the Kogelnik paper:

k² = (ω²/c²)ε - jωμσ

the relative dielectric of the medium is referenced; however, the magnetic permeability, μ, is assumed to be the same as that of air, which is usual, since most media are not magnetic. Your author may be confusing μ for ε. As any reasonable person knows, n² = ε, therefore the index is not the same in the medium as in air. Of course, as any reasonable person would realise, if the index of the medium was the same as that of air, there would be no modulation within the material! Only someone who opposes Bjelkhagen, Benton, Kogelnik and other educated researchers and who would insist they are all wrong would disagree.
BobH wrote: Sat Nov 25, 2023 9:26 am When the angles are at Brewster's Angle to the fringes and polarization is parallel to the plane of incidence, DE falls to zero.
Again, of course it does! If the reconstruction wave is TM polarised at Brewster's, no light goes into the medium. If no light goes into the medium, no light can go out of the medium. There is no coupling because there is no R wave. By the way, Brewster's angle is not relative to the fringes, but to the plate normal; the fringes may be (usually are) inclined relative to the plate normal, where the inclination angle is given by c(s) and c(r). But, of course Benton, Bjelkhagen, Kogelnik are all wrong and only you are the font of all knowledge!

Bob, you seem not to understand what DE is. The DE is given by SS*, assuming R = 1. If R = 0, then DE is also 0.

I'll try and make this simple enough that even you may understand it. Light has to go into the medium in order to diffract. If no light goes into the medium, there is nothing to diffract. I hope even you can understand this! I know it must be a difficult concept, but I'm confident that if you sit down and think deeply, understanding will come, even to you.
BobH
Posts: 441
Joined: Tue Jan 06, 2015 10:26 pm
Location: Mesa, AZ

### Re: Whatever Became of Holography?

Din wrote: Sat Nov 25, 2023 10:16 am
BobH wrote: Sat Nov 25, 2023 9:26 am Essentially it says to disregard the boundary going from air to emulsion containing fringes. Assume the whole world is the index of the emulsion, and apply coupling theory to the fringes themselves during replay.
I'll try and make this simple enough that even you may understand it. Light has to go into the medium in order to diffract. If no light goes into the medium, there is nothing to diffract. I hope even you can understand this! I know it must be a difficult concept, but I'm confident that if you sit down and think deeply, understanding will come, even to you.
This thread shows why you're banned from all the other holography pages and forums. You simply disregard what's written and spin off paragraph after paragraph of unrelated mathematical gobbledygook with personal insults added to nurse your bruised ego. This is also why nobody participates here anymore. I've made my point for anyone interested, and give you the last word.
Din
Posts: 408
Joined: Thu Mar 12, 2015 4:47 pm

### Re: Whatever Became of Holography?

BobH wrote: Sat Nov 25, 2023 10:57 am give you the last word.
Thanks!
By the way, does Hans Bjelkhagen know that you're accusing him of spinning "unrelated mathematical gobbledygook"