Talk:Holography/Archive 2

Do holograms record the phase?
The assertion by Danh that both the intensity and the phase relative to a reference beam are recorded is an old, hard-to-die, idée reçue. I imagine that this is because it is an easy answer, given to annoying questions, by teachers who had not understood how a hologram works. Holograms do not record the phase as there is no means to record a phase. All light sensitive surfaces or devices (retina, photographic emulsion, photodiode, photomultiplier, etc) are sensible to intensity of light. Phase is just a difference in timing between two waves. You cannot record these differences in time with a photosensitive surface or device. The only thing you can do is transform these differences of phase in amplitude, adding the two waves. But even then, the only thing you get is something like $$\scriptstyle{A\cos^2(\phi_1-\phi_2)}$$. You get something related to de modulus of the phase difference (the sign of the difference is lost). However, as the squared cosine is multiplied by the amplitude, you cannot know if a zero is due to phase difference of 180° or to a zero of amplitude. An hologram is just a diffraction image recorded on a photosensitive support. Would the same teacher as above say that the diffraction image of Young slits or Fresnel biprism has recorded the amplitude and the phase? No, because now the teacher has really understood the problem and does not need evasive (and incorrect) answers. If holograms recorded the phase, so would all diffraction images, including current photographic images that are Fraunhofer diffraction patterns of incoherently illuminated scenes. User Danh also wrote When reconstructed by illuminating with the appropriate light, the resulting light field is identical (up to a constant phase shift invisible to our eyes) to that which emanated from the original scene. This is wrong. Neither the amplitude nor the phase, are the same. The phase of light exiting the hologram is identical to the phase of the illuminating beam (only the amplitude is modulated by the hologram). This is not the case when recording the hologram, where the phase is the result of the sum on the reference beam plus the light coming from the scene. Another proof that the reconstructed light is not identical to the original, is the formation of real (in the optical meaning) images in the wrong side of the hologram. This is the reason why the normal illumination is seldom used. The more common "of-axis holograms" separate real from virtual images. Real images are always there but not in the same line of sight. As I wrote (and Danh "corrected"), the reconstructed wave front are similar to the originals, but they are far from identical. I tried to explain the working principle of holograms in the paragraph so named (the two images are computed, not draw). I am afraid that I did not succeed. I will not restore what Danh wrongly "corrected". This is the inconvenient of wikipedia. Anyone who thinks to know the truth can "correct" you without any verification or reading of a good book (as Jenkins & White "Fundamentals of optics" 4th ed. McGraw-Hill 1981 for example). I will not enter a guerrilla of correcting corrections. LPFR 12:39, 17 September 2006 (UTC)


 * Hi LPFR. As I stated in the edit summary, your correction were technically absolutely correct. Just, this is the first section that explains the working of a hologram. It should do it as simply as possible, so that also an interested layperson gets out some information. Sorting out the details here makes it only more difficult to understand, for those that do not know it yet, what a hologram is. A better location would be a bit down in the section "Hologram engraving" or in "Holographic recording process", which BTW duplicate each other and should IMO be merged.
 * For the things you call "wrong", they are mostly compromises between rigorosity and usability for explaining. Of course Newton's second law is wrong, and perhaps even general relativity. But they are nevertheless very useful for understanding.
 * So let's resolve the things, if I make an edit, it doesn't mean you are not welcome any more to contribute. a) The phase: I think we agree that the important thing is only the relative phase, this lets you see in 3D. And the relative phase of two points you get looking at a hologram is similar to that of the real image. So what do you think about changing both the intensity and the phase relative to a reference beam are recorded to a more general both the intensity and some phase information are recorded? Keep in mind that "recorded" is intended in the sense "can be obtained back", not that it is physically present unencoded in the hologram. b) Identical: this was the wording of before and I don't like it either. Proportional (not really correct)? Simililar I wouldn't recommend, because it would include also distorted or morphed images. Anyway, the meaning should be something like "retaining the intensity proportions and the relative phase". Suggestion from anybody? --danh 22:49, 18 September 2006 (UTC)

I think I'll venture a comment, although this is a fiendishly difficult question where it is easy to get things mixed up. I tend to agree with Danh and disagree with LPFR, but here are a couple of important things I think we all agree on: a) The phase is not, and cannot ever be, recorded. Only the intensity of a wavefield is recorded. If I talk about the phase being recorded, I really mean that it can be recovered. b) The "absolute value" of a phase is not important, only relative phases need be considered. One can always change the origin and get whatever absolute value one wishes. When I talk about the phase, I am referring to the relative phase.

With this in mind, I believe that the wavefield exiting the hologram after reconstruction does contain the phase of the original object wave. This following is adapted from A. Tonomura's book on electron holography (Springer-Verlag 1993): We record the interference pattern from a refrence wave $$\phi_r$$ and the wave scattered from an object (the object wave) $$\phi_O$$. These waves have, of course, both amplitude and phase, but the recorded interference pattern has only the intensity $$I=|\phi_O + \phi_r|^2$$, recorded e.g. in a film. If this film is subjected to the (known) refrence wave, the transmitted wave will be

$$T=I\phi_r=|\phi_O + \phi_r|^2\phi_r=(|\phi_O|^2+|\phi_r|^2)\phi_r + |\phi_r|^2\phi_O + \phi_r^2\phi_O^*$$

As we see, the two last terms contain the original object wave and its conjugate. These can be separated in off axis holography. Since the refrence wave is known, we now have reconstructed the original object wave, including its phase. If you read Gabor's original paper (Nature, vol 161 pp. 777-778, 1948) this is as he intended: "the new principle provides a complete record of amplitudes and phases in one diagram". So, in conclusion, I believe that the wavefront of the original object, including its phase, is recovered when the hologram is illuminated by the refrence wave. O. Prytz 14:32, 19 September 2006 (UTC)
 * Hi DANH. There is a frontier between deep simplifications and false statements. Second Newton's Law is not rigorously exact but it is not wrong. "Holograms record the phase" is wrong, and not because of lack of precision but just it is untrue. I do not think that propagating false "idées reçues" as explanations is a good thing. If you cannot respect the verity when giving an explanation, it is better not to give an explanation at all. I wrote "but some information related to phase is recorded", this is as far as you can go respecting the truth. When I added the paragraph "working principle ...", I did not erased or corrected the paragraph "technical description" - I do not like to modify other's work. I hoped that the author would correct it himself. As this did not happen, I corrected the text, trying to conserve as much as I could of the old one.


 * At the right, you can see the reconstructed wave fronts from the hologram. As you can see, they have nothing to do with the original wave fronts. When I wrote "similar" this was as far as I could go. When you write "identical", you do not know what you are talking about. You can see the formation of the real image and, at the far right, the wave fronts of the lecture beam, but the wave fronts of the virtual image are not even visible.
 * You seem to think that the most important thing is phase. NO, it is not. If it where so, just a tilt or a bend in a hologram would ruin the reconstructed image. The angle between the hologram and the reconstruction beam do not need to be exactly the same as the original. If the holograms deforms, you get still an image. The phrase "both the intensity and some phase information are recorded?" is still too far from reality. What an hologram record is the places where the phases of the light from the scene and the light from the reference beam where near. And this record of places is modulated by the amplitude. You do not record both of them. You record just the product of them, as I wrote. The "catch" in the holograms is not the phase but the place where the phase "was OK". This record allows - in the reconstruction process - to create wave fronts that are very different (not identical, not proportional) to the original wave fronts. However, they create a virtual image of the scene plus a bothering real one. LPFR 14:49, 19 September 2006 (UTC)


 * Hi O. Prytz. You do not need a formula to know the phase of light exiting the hologram. If the hologram is a classical photographic one, that is, and amplitude-modulating plate, the only thing the hologram does to the light is modulate its amplitude. Then the phase is the same as if the hologram where not there. The phase is that of the illuminating beam. No formula can change this fact. This demonstrates that you do not get the original phase. LPFR 15:28, 19 September 2006 (UTC)


 * Ok, perhaps it's bit dangerous for me to venture into this, as it's been about 10 years since I've studied holography, but I think you're getting a bit semantic here, LPFR. I could say the same thing about an amplitude grating: it only modulates amplitude leaving the phase unchanged. But then how does the effect of a grating manage to look so much like a linear phase? Well, I think the answer is that a grating is like two linear phases in cojugate pairs, which is why an amplitude grating has at least two diffraction orders, one positive and one negative. (Which I think is analogous to the issue you guys have discussed above regarding the reasons behind off-axis holography.) But in the case of a grating (which can be considered a very simple hologram) if you restrict yourself to looking at just one order, the effect of the grating in the far field is indistinguishable from a linear phase applied to the illuminating field. So what I'm trying to say is this: (a) when you modulate the amplitude of a field, you ARE changing the far field phase, and (b) if you restrict yourself to the right diffraction order it is fair to say that the phase information was preserved. I think you're getting caught up in semantics by insisting people not say that phase information is recorded or that the field isn't perfectly reconstructed. Sure, there are complicating issues like the fact that the reconstruction also includes spurious fields, but if the phase wasn't recreated in the virtual image, holography wouldn't work. When you bend a holograph, it DOES mess with the image. It's just that bending shifts all the phases in a given region together, resulting in a distortion but not complete destruction of the image. At least when it comes to monochromatic holography, i think it is very fair to say that the phase information is recorded. Recording just means the information is there, and says nothing about reconstruction or accessibility. I'm interested in your response to this. Birge 19:19, 19 September 2006 (UTC)


 * LPFG, here you talk about the absolute phase of the reconstructed wave. O. Prytz was talking about the relative phase between two points in the hologram. This is what we want (and for this a hologram with one point cannot tell anything). --danh 20:14, 19 September 2006 (UTC)


 * LPFG, most of your objections come your interpretation of the term "recording", which is different to that of the original author, O. Prytz's and mine. So, let's change its meaning to your stricter one, like in "In a hologram, information from both the intensity and the phase is recorded." or use a totally different word.
 * Anticipating further comments, with "reconstructed hologram" we refer to just the virtual image, not the real image term, the transmitted or the halo terms, which are always present too. I think it's acceptable. For a homogeneous intensity of the recording reference beam, the same reading reference beam as the recording one, a linear recording material, this term is (up to a constant factor) identical to the original image. But tell this to someone who wants to know what a hologram is :-). --danh 20:14, 19 September 2006 (UTC)


 * Hi, I wish to remind the subject of this talk. It is about "How a hologram works" and about two assertions: "A hologram records the phase" and "The hologram reconstructs the wave fronts as they where at the recoding time"
 * First a wish to tell DANH that I am not as dumb as to confound relative and absolute phases. Incident closed.
 * To BIRGE I said that, for the simplification of the talk, I do not think a good idea to replace a diffraction grating by "two linear phases in conjugate pairs". The phrase "Recording just means the information is there, and says nothing about reconstruction or accessibility" reminds me an 30 years old hoax of a technical datasheet of a "write-only" memory. I do agree that a hologram is the same thing as a diffraction grating. The difference is that a hologram is not a periodic pattern, but the reconstruction process is the same. The sentences about folding a hologram where just to remind DANH that phase is not the most important thing in life.
 * I am no sure that you read what I wrote. What I said is that a hologram does not record the phase but the places where the phase of the light coming from the scene is near the same as the phase of the reference beam. In this way, in the reconstruction phase, only the light that has the "correct" phase is allowed to pass. This, I tried to demonstrate in the paragraph "Working principle ..." with the images I computed. Secondly, I maintain that the hologram does not reconstruct the wave front as they where at the recording time. I demonstrate this in three English sentences (see above, my answer to O Prytz). I computed the wave fronts created by the hologram (see image above) to convince you that the wave fronts are very different from the original ones. Is this not suffice as a demonstration, I am afraid that I cannot do any more to convince you. In science, when someone gives a demonstration, either you accept it or you demonstrate that the demonstration is erroneous. LPFR 12:41, 20 September 2006 (UTC)
 * I think you talk about different things. Birge refers to the virtual image (which has the same phase as the original image, up to a constant shift), while your demonstration contains all other terms too. If you subtract the real image (nicely visible in front of the holographic plate), the transmitted plane wave and the halo term, you recieve the original wave (up to a constant phase shift and a reduced intensity). --danh 14:32, 20 September 2006 (UTC)
 * Hi, LPFR. Thanks for the response. I think I see one point of contention. When you talk of the hologram "recording where the phase is correct" I understand what you're saying, and agree. But that's only a *binary* hologram, where the material response is either on or off. And in that case, I agree that there will be significant differences, for the same reason a square wave introduces harmonics not present in the sinewave it approximates. But in a continuous hologram, there is a lot more being recorded that just "where the phase is correct". You're getting an analog recording of *how much* the phase is "correct" or not. And the bottom line is that if you're able to isolate the right diffraction order you get exactly what you put in. So, is what you object to that we are ignoring the other components in the reconstructed field, or is it that you disagree with the statement that within the correct diffraction order we exactly reproduce the phase and amplitude of the writing field? I agree that science must rely on demonstration, but I think we're still sorting out where we differ. I'm not sure we disagree as much as we misunderstand each other. Birge 18:21, 20 September 2006 (UTC)
 * I thought you where old enough to understand the phrase "where the phase is correct" as a shortcut for $$\scriptstyle{A^2\cos^2(\phi_1-\phi_2)}$$, as I wrote above a few times. Sorry. LPFR 18:45, 20 September 2006 (UTC)
 * Mon dieu! Il n'y a pas raison pour que vous soyez si français. It just seemed like you were suggesting information was ALWAYS irretrievably lost because of the translation into a pure amplitude modulation, and it's not always the case. That was my reason for the simple example of a sinusoidal amplitude grating (and whether you like it or not, such a grating does produce two new plane waves with conjugate linear phases relative to the illuminating field). Personally, I think that's a pretty good example of how an amplitude modulation can look just like a phase modulation under certain restrictions. It's entirely anologous to how a signal can be entirely reconstructed from the amplitude of its fourier transform if you are able to make certain assumptions about its support in the time domain. You seem caught up in the fact that it's POSSIBLE for the reconstructed hologram to include spurious fields (as in your illustration) but your illustration is not a correctly done hologram that anybody would ever use. Again, though, I think we all pretty much understand what's going on, and I think we need to agree on how to best explain holography while making it clear that the real situation is complex and care must be taken for the hologram to truly reproduce the original field, and only at certain angles, etc. Would you be happier if we said something along these lines? I agree with you that we shouldn't state things simpler than they really are, but on the other hand I don't think we can go into academic detail about exactly which conditions must be satisfied for the holographic reproduction to equal the original field. Birge 21:08, 20 September 2006 (UTC)


 * Hi Birge. Usually French physicists favor formulas instead explanations and understanding. I hope it is no my case. First, there is a big difference between the interference pattern of a periodic structure and a non-periodic one. In a periodic structure, as a grating, the number and the amplitude of primary, secondary, etc. depends on the "shape" (with, binary, sinusoidal, etc.) of the slits. I am not sure (that is, I cannot assert) if the diffraction pattern of a non-periodic structure depends also on the "shape". I guess that it is not the case. The case of a sinusoidal grating is a particularly very well behaved one.
 * Long time ago, I read that you can make diffraction gratings and holograms that just modify the phase and are 100% transparent. The result is about the same as with amplitude gratings or holograms. The way to do this is to use light sensitive gelatin that swells with light. The drawback is that they are not dimensionally stable. Let us come back to the main talk.
 * I would really like that you read the paragraph "Working principle ... ". I think that I explained the working principle simplifying as much as decency allows but with all the caveats about the explanation and stating that this type of thin hologram with on-axis illumination is not of practical use. If I missed other important caveats, just add them.
 * Your sentence "for the hologram to truly reproduce the original field" shows that you still believe that a hologram MUST reproduce the original field. A Hologram doest not reproduce the original field. At least, not truly. The demonstration is:
 * ''If the hologram is a classical photographic one, that is, and amplitude-modulating plate, the only thing the hologram does to the light is modulate its amplitude. Then the phase is the same as if the hologram where not there. The phase is that of the illuminating beam. In the same place, the phase of the original field was the result of the addition of the illuminating beam and the light coming from the scene and diferent from the phases of the reference beam. Then, the phases are not reproduced as they where. This is valid for any amplitude modulating hologram and not only for thin on-axis holograms.
 * If the phase at the hologram level are not the same, the far field or the interference pattern can not be the same. This comes from Huygens principle (wavelets). Then, amplitude holograms DO NOT truly reproduce the original field.''
 * But it is not necessary to "truly reproduce the original field" to obtain something related to the original image. When you look (just with one eye!) a picture, you see the same thing as the original scene, and the light fields are different (yes, I know about color. Just illuminate the scene and the picture with monochromatic light).
 * As I said, in science either you accept a demonstration or you demonstrate that it is erroneous. If you think that my demonstration is false, just prove it.
 * As for a reasonable simplified explanation of how works an hologram I think that you could say: As phase cannot be recorded, the hologram record the places where the phase of the light coming from of the scene is near (squared cosine if you prefer) the phase of the reference beam. These places are favored by the amplitude of light coming from the scene and by the similitude of phases. When observing the hologram, the places where the phase was the near that of the illuminating beam transmit more light than the others do. This does not reproduce exactly the originals wave fronts (or light field), but is enough to create wave fronts similar to the original. I do not mind exact wording, as long as there are not assertions like the phase is recorded or the light fields are exactly reproduced. LPFR 09:26, 21 September 2006 (UTC)
 * Hi, LPFR. I would agree with those changes, and I think you should feel free to make them (I don't want to take credit for your work). For the record, I don't think you ever got my point that the hologram CAN exactly reproduce the writing field under certain restrictions, and therefore that ALL of the phase information was preserved modulo a constant. But I also don't disagree with your wording because, in general, you are right that the reconstructed field is not the same. Birge 12:25, 25 September 2006 (UTC)

Birge, it is also my understanding that the virtual image (the third term in the rhs of the equation of O. Prytz) contains all the phase information (modulo a constant). LPFG, I like your changes, but I have a few comments: in The hologram reproduces the original light field accurately: FALSE you treat holograms as synonym of amplitude holograms. I think phase holograms are much more important than amplitude holograms (at least in science), so I would welcome if you included them too. The second thing is that I don't really agree with the statement :-). I mean, O. Prytz's equation demonstrates that the virtual term is proportional to the original light field $$\phi_O$$ if the intensity of the reference wave is homogeneous. Do you agree with that equation (up to a complex constant)? Do you call all 4 terms as the hologram or does just the virtual image qualify too? --danh 04:37, 26 September 2006 (UTC)


 * Hi Birge. I posted my last paragraph (True or false?) at the same time as you wrote your comment in this talk. Anyway, as all this talk does not suffices to convince physicists like Danh, I think that we can keep it as it is, at least for a time.
 * To Danh I say that I read the "O. Prytz's equation" $$\scriptstyle{T=I\phi_r=|\phi_O + \phi_r|^2\phi_r}$$ as "The light $$\scriptstyle{T}$$ exiting the hologram has the same phase as the illuminating light $$\scriptstyle{\phi_r }$$, and its amplitude is modulated by the transparency of the hologram $$\scriptstyle{|\phi_O + \phi_r|^2 }$$".
 * Yes, I did not read the rightmost expression, but as there is an equal sign, the meaning of the last expression must be the same as the meaning of the second one. The interpretation made by O. Prytz is erroneous. Writing an equation in a different form does not allow you to extract terms that are not in the first one. I also think that "O. Prytz's equation" should be written with different names for the engraving $$\scriptstyle{\phi_{re} }$$ and the reading $$\scriptstyle{\phi_{rr} }$$ reference beams. In this writing, the third expression is very different and O. Prytz's would not have been misled.
 * Yes, I do not consider other holograms than amplitude ones. The length of this talk proves that even amplitude holograms are not that simple to understand. When the explanations for amplitude holograms will be so clear that everybody understands them, we can consider adding explanations for other types.
 * I am almost sure that "phase holograms" are not the same thing for you and me. Would you please tell me what do you mean by "phase holograms" (and if possible, how you record them)? LPFR 08:22, 26 September 2006 (UTC)


 * Ok, it seems we'll have to do this in some detail. The following is a more detailed examination of the recorded intensity which follows from simple complex calculus:


 * $$I=|\phi_O + \phi_r|^2 = (\phi_O + \phi_r)(\phi_O + \phi_r)^* = (\phi_O + \phi_r)(\phi_O^* + \phi_r^*) = (\phi_O\phi_O^* + \phi_O\phi_r^* + \phi_r\phi_O^* + \phi_r\phi_r^* = |\phi_O|^2 + |\phi_r|^2 + \phi_O\phi_r^* + \phi_r\phi_O^*$$


 * If we assume $$\phi_O=A_Oe^{i\theta_O}$$ and $$\phi_r=A_re^{i\theta_r}$$, we can write the recorded intensity as:


 * $$I= A_O^2 + A_r^2 + A_Oe^{i\theta_O}A_re^{-i\theta_r}+A_Oe^{-i\theta_O}A_re^{i\theta_r} = A_O^2 + A_r^2 +2A_OA_rcos(\theta_O-\theta_r)$$


 * The two first terms are just the intensities of the object and refrence waves, while the third term is the interference of these two and contains phase information. In fact, the recorded intensity must contain at least some phase information, think of diffraction: how else should we account for systematic extinction of reflections if not by knowing that there is a phase difference of $$\pi$$. But the genius of holography is that we treat one of the waves as known, and therefore we can fully retrieve the object wave:


 * $$T=I\phi_r=|\phi_O + \phi_r|^2\phi_r= (|\phi_O|^2 + |\phi_r|^2 + \phi_O\phi_r^* + \phi_r\phi_O^*)\phi_r = (|\phi_O|^2+|\phi_r|^2)\phi_r + |\phi_r|^2\phi_O + \phi_r^2\phi_O^*$$


 * which is my original statement from sept 19. I hope you are satisfied with the mathematical validity... I should certainly note that reconstructing the original wavefront exactly probably is impossible due to experimental difficulties (lens aberations if nothing else). But in principle it is certainly possible.O. Prytz 09:35, 26 September 2006 (UTC)


 * The term $$\scriptstyle{A_O^2 + A_r^2 +2A_OA_r\cos(\theta_O-\theta_r)}$$ contain as much information about the phase as a Young slits diffraction picture. That is, you know when they are in phase or out of phase. But, as the term is multiplied by the amplitude, if you do not know the amplitude you do not know much about each of them.
 * If you see a Young interference pattern you can say where the waves where in phase or in opposition. However, when the diffraction pattern is not periodic, you cannot tell, given the light level in a point, what the phase or the amplitude was.
 * In your formula you are using the same beam to record and to read the hologram $$ \scriptstyle{\phi_r} $$. This is the case when you use holograms built by non-linear effects for phase conjugate mirrors and the like. I suspect that your formula comes from a text about phase conjugate optics. In the holograms recorded on a sensitive surface, the two $$ \scriptstyle{\phi_r} $$ are not the same. Try to name one of them $$ \scriptstyle{\phi_{re}} $$ and the other $$ \scriptstyle{\phi_{rr}} $$ and start again with your math. All the information that you can extract from your formula is already in the left term. You do not need lenses to record or observe a hologram? LPFR 15:12, 26 September 2006 (UTC)


 * So the difference is that LPFG talks about the whole wave $$\scriptstyle{T}$$, while I talk only about the virtual image $$\scriptstyle{|\phi_r|^2\phi_O}$$ .  $$\scriptstyle{T}$$ has the phase of $$\scriptstyle{\phi_{r}}$$, while $$\scriptstyle{|\phi_r|^2\phi_O}$$ has the phase of $$\scriptstyle{\phi_O}$$. But $$\scriptstyle{T}$$ in itself has no useful properties, the 3D image that looks exactly like the original image is the virtual image.
 * I find the first two "true or false" at least misleading, since, whatever you call a hologram, it yields a virtual image that can accurately reproduce the original light field (even with the relevant phase information).
 * About phase holograms: In the equation above, the transmission function of the hologram is set to be the intensity $$\scriptstyle{I}$$. This is a very limited case. In general
 * $$T=H(x,y)\phi_r $$,  with $$H(x,y)=|H(x,y)| \exp[-i\varphi(x,y)]$$ a complex transmission function. If $$\varphi(x,y)$$ is constant you have an amplitude hologram, while if $$\scriptstyle{|H(x,y)|}$$ is constant you have a phase hologram. You get phase holograms whenever the holographic material does not change the absorption in response to light intensity, but the refractive index. The table in the holography article displays the most common recording materials.  --danh 17:04, 26 September 2006 (UTC)


 * Hi, Danh. I made a question about what phase holograms are for you, because I am not sure that you are aware that the information recorded in phase holograms is the (squared) amplitude of the light field and NOT the phase of the light field. You can spare the formulas. In physics, you do not need formulas to explain or understand. You need formulas to calculate.
 * I wrote the demonstration that the light field exiting the hologram is different from the original field. In science, either you accept a demonstration or you prove that the demonstration is erroneous.
 * You say that a part of $$\scriptstyle{T}$$ creates the virtual image. Fine! We agree. This is what I wrote as "... similar enough to create front waves similar to the original..."
 * You wrote "$$\scriptstyle{|\phi_r|^2\phi_O}$$ has the phase of $$\scriptstyle{\phi_O}$$". Yes, but if you are taking the formulas of O.Prytz you will see that this term appears added with others terms and there is no way to isolate $$\scriptstyle{|\phi_r|^2\phi_O}$$. The two equations in each side of an equal sign contain the same information. You cannot have more information in one side and less in the other one. Math does not add physics.
 * I wrote to O.Prytz, that "his" formula was not appropriate for the holograms we are talking about, but for phase conjugate holograms. In "his" formula, he uses the same beam to write and to read the hologram. This is not the case when reading a previously recorded hologram. Instead of using $$\scriptstyle{T=I\phi_r=|\phi_O + \phi_r|^2\phi_r }$$, he should have written $$\scriptstyle{T=I\phi_r=|\phi_O + \phi_{rw}|^2\phi_{rr}} $$, as the write and the read reference beams are not the same (they are the same in conjugate phase devices). LPFR 11:36, 27 September 2006 (UTC)


 * Hi LPFR. The demonstration and the "=" sign apply to T and not to the virtual image. In normal 3D holograms (off-axis holograms) the virtual image is well separated from the other three terms (and therefore you can see it).
 * What we call "O. Prytz's equation" is the equation for normal holographic readout, not for phase conjugated readout. And adding a different readout wave than the recording wave just complicates things, without changing them much. The image is somehow distorted, but can be reproduced without distortions by the right wave. It's a bit like looking a photo with say blue light: the colours you see will just be different than what they should be. --danh 14:12, 27 September 2006 (UTC)


 * Let's stop calling it "O.Prytz's" equation, ok? :) It's not my equation, and since it in reality is the only equation used in this discussion, simply "the equation" should suffice.


 * You are quite right, LPFR, that math does not add more/new physics. However, it can help us understand the physics that is already there, without having to resorting to the vagaries of ordinary language. In this case, if you accept the left side of the equation you must also accept the right side, given that my derivation is correct (I make no guarantees, please check the math).


 * I do not understand why you maintain that the refrence and reconstruction waves cannot be the same. There might be something I'm missing, but could we not for example use the same set ut that was used to record the hologram, and just block the object wave before it reaches the previously exposed film? Anyway, I believe that using a different (known) wave would just result in a predictable distortion of the image (e.g. magification).


 * What I believe we have demonstrated (mathematically) is that the reconstructed wave consists of three parts: the object wave (multiplied by a constant) $$\scriptstyle{|\phi_r|^2\phi_O}$$, the conjugate of the object wave (multiplied with a constant and with its phase shifted I guess, "the conjugate image") $$\scriptstyle{\phi_r^2\phi_O^*}$$, and the refrence beam multiplied by a constant $$\scriptstyle{(|\phi_O|^2+|\phi_r|^2)\phi_r}$$.


 * Now, as danh states, in off-axis holography the virtual and conjugate images can be separated, so this should not cause a problem. However, I must confess that I don't know how one usually handles the fact that you have a contribution to the wavefront from the refrence beam (multiplied by a constant). (I'm an electron microscopist, and I believe that in nowadays in electron holography one rarely reconstructs the image with a physical refrence wave. It's usually done digitally, and since the refrence wave is know it can be subtracted?) In this light LPFR may be correct that the reconstructed wavefront is not equal to the original object wave, since it contains at least two contribution, only one of which is the original object wave. I will, however, maintain that the original phase is retained in the virtual image. O. Prytz 16:38, 27 September 2006 (UTC)


 * Hi O.Prytz and Danh. The reference and reconstruction beams are not the same because they are not coherent. Even if you use the same experimental setup, for the beams to be the same would ask for a coherence time of a few hours (needed to develop the film) or a few years if you examine the hologram later. From a mathematical point of view, the term that would be different in "the equation" is $$\scriptstyle{\phi_{rw}\phi_{rr}}$$. If the two $$\scriptstyle{\phi}$$ are coherent, the mean value will be non-zero as $$\scriptstyle{\cos\omega_1t\cos\omega_1t }$$. If they are incoherent, the mean value is zero as $$\scriptstyle{\cos\omega_1t\cos\omega_2t }$$. As you know, holograms can be read with beams that do not have the same wavelength as the recording beam. Then, "the equation" should work also for different beams. Rework "the equation" with $$\scriptstyle{\phi_{rw}}$$ and $$\scriptstyle{\phi_{rr}}$$ and you will see that you cannot extract more information from the right side of the "=" sign than from the left side.
 * I do not understand what O.Prytz mean by "the original phase is retained in the virtual image". Neither have I seen the link with my assertion about light field issuing the hologram.
 * I wrote the demonstration that the phase of light issuing the hologram is different from the phase at the recording time (I do not care if you fraction this light in a number of components). Either you accept my demonstration as true, or you prove that my demonstration is false. Until you prove that my reasoning has a glitch, my demonstration holds. LPFR 08:52, 28 September 2006 (UTC)


 * The reference and reconstruction beams don't have to be coherent relative to each other since they never appear together. They just have to be close enough in frequency and fairly monochromatic. The absolute phase of light never matters in linear optics. Birge 16:21, 28 September 2006 (UTC)

Ideas for changes or additions
I have seen a special in which, I believe it was, a japanese researcher used knowledge of how the auroras cause open air to fluoresce, to make a machine which could create a pyramid of dots in the open air with some strange combination of lasers, ultrasonic sound, microwaves or something. I just can't find it again but it would be a great addition to this article as the next wave of open air holography if someone DID find it. —Preceding unsigned comment added by 75.64.211.12 (talk) 12:08, 28 January 2011 (UTC)

Good article. My physics teacher asked us if anyone knew how one was made when I was about 17. Despite loving laser from the age of 11 (Sams Laser FAQ), I didn't understand the theory of it. Now a fair amount older and having a lot more money, equipment and knowledge to hand, I may have a go at making my own at some point. But I don't fully 'get' some of the analogies made in the article.


 * "The person looking through this captured "window" would see the image in 3D by virtue of each of his or her eyes seeing the scene from a different viewpoint."

This doesn't explain why they don't see the effect looking through a smaller window; like a pinhole.


 * ''"The resulting pattern is the sum of a large number (strictly speaking, an infinite number) of point source + reference beam interference patterns."

''
 * This is simply because you cannot see through the pinhole with both eyes.

I know that the wavelength will usually define the resolution of a light source, but that here we have a continually varying diffraction pattern, is this the source of the infinite data points? If so, maybe that could be clarified a little, as I expect others are wondering how the finite resolution of a wavelength becomes an infinite number of points.
 * One still has a finite resolution (given by the wavelength), so the infinite number of points in the article was misleading, since one cannot resolve all of them. I've changed that.

I'd like to see some discussion of 'fake' holograms, the kind of holographic rainbow film seen on gift wrapping or the discs you can spin and watch the pattern change. The article discusses the use of a reference beam to illuminate the hologram again, but there are of coarse those 'holograms' that can be viewed under normal sunlight.
 * That should definitively be expanded. And sunlight is actually a good reference beam for most holograms (since although it is not temporally coherent, it is at least spatially coherent). For the holograms from Rabbitholes, they indeed seem very nice (but I've seen only their preview videos). Probably they would be best mentioned in the article about computer generated holography. --Danh (talk) 15:41, 26 July 2010 (UTC)

I also saw an excellent site recently called RabbitHoles who produce animated holograms. The one with the picture of a Medusa like woman on it is particularly impressive when the video is viewed, as she appears to float into view with her hair snaking into it's full complexity. They're trying to use this idea to capture sections of video from films to use as promotional material. I believe they can store up to around 10s worth of footage on them at present. —Preceding unsigned comment added by 82.24.47.178 (talk) 13:06, 24 July 2010 (UTC)

Inconsistent due to bickering...
Due to the arguments taking place, this article presently contradicts itself about phase. And someone might want to correct errors like "Holograms record de phase" while they're at it. I don't really want to venture into editing because I don't know enough about the rest of the subject. Queerwiki 02:23, 28 September 2006 (UTC)
 * Well, I did, and this gave raise to this (very long) argument. LPFR 08:52, 28 September 2006 (UTC)
 * Okay, well then let's a) get in some hard citations here, and b) put a dispute notice up until we've resolved everything. Oh, and I will correct c) "de" is not an English word!!! Queerwiki 15:59, 28 September 2006 (UTC)
 * Most of the bickering above comes from one of two things: how to interpret the verb record, and not understanding if the other is talking about the "virtual holographic image" or the whole wave transmitted by the hologram.
 * I think the record thing is now solved. Using it in the sense of "stores in a coded form" or "allows retrieving" is ok.
 * And I hope also the other will not be confused anymore. The "virtual holographic image", $$\scriptstyle{|\phi_r|^2\phi_O }$$, is a part of the whole wave transmitted by the hologram, $$\scriptstyle{T}$$. The "virtual holographic image" has the phase of $$\scriptstyle{\phi_O }$$, and $$\scriptstyle{T}$$ has the phase of $$\phi_r$$.
 * The inconsistency of the paragraphs Holograms record the phase: FALSE and The hologram reproduces the original light field accurately: FALSE. comes from the fact, that they speak only about the whole wave transmitted by the hologram $$\scriptstyle{T}$$. This reflects the viewpoint of (only) LPFR, that $$\scriptstyle{T}$$ is the important wave. But the virtual image that possess these holographic properties, retaining the original light field and its phase (and thus its 3D appearance). And if one speaks of holographic image one certainly thinks of the virtual image and not of the whole wave $$\scriptstyle{T}$$. So the two statements above do not hold and both paragraphs should go away. Does anybody agree (or disagree)?
 * BTW, citations were asked:
 * "The unique characteristic of holography is the idea of recording the complete wave field, that is to say, both the phase and the amplitude of the light waves", Optical Holography: Principles, Techniques and Applications, p. 1, by P. Hariharan (readable on Google Books).
 * After describing photographs, "Holography also records the intensity distribution of a wavefront; in addition, the local propagation direction (or phase) is recorded through the process of optical interference.", Handbook of Optics, Vol.II, p.23.3, by OSA.
 * --danh 20:13, 28 September 2006 (UTC)


 * I agree with your statements above. I would also like to say that regardless of who is correct about the phase being reconstructed, I find the "true or false" section of this article inappropriate for an encyclopedia.


 * With regard to citations, I'll just repeat the one I gave earlier where Gabor talks of holography ("the new principle"): "the new principle provides a complete record of amplitudes and phases in one diagram". Nature, vol 161 pp. 777-778, 1948. There are tons of other citations where he and other pioneers talk of the object wave being "reconstructed", but I guess those are too vague to use in this discussion. O. Prytz 08:11, 29 September 2006 (UTC)

Farewell
As no one seems to share my ideas, I infer that it is people, as Danh, who wrote:
 * "In an hologram, both the intensity and the phase relative to a reference beam are recorded." (sic) and
 * "the resulting light field is identical (up to a constant phase shift invisible to our eyes) to that which emanated from the original scene" (sic),

who have really understood how a hologram works, and not me. In consequence, I am withdrawing all the explanations and demonstrations that wrote in the article, because they are in contradiction with Danh conceptions. Please be kind enough not to restore partially any of my writings. Farewell. LPFR 11:33, 30 September 2006 (UTC)
 * Thanks for removing the two contended paragraphs. The rest was an unprovoced decision. --danh 19:16, 30 September 2006 (UTC)

some thoughts
the way i was taught to think about holography was this: if you throw a stone into a pond waves ripple out from the center. if you throw two in then two circular wave patterns emerge. now if you take a "slice" across the surface where the waves meet you get a standing pattern. if you record that pattern you get a water-wave-hologram. if you place that in the water and then trow one stone in, the "slice" will bend, shape and redirect the waves from the first stone and recreate the pattern that the second stone would have created. in terms of holography the first stone is your normal light source when viewing the hologram and the second wave is the laser used to illuminate the scene.

Yes, this is exactly what I talked about in my "holograms as diffraction gratings" section! Nice analogy, maybe using this will allow people who haven't heard of diffraction gratings before, to understand my explanation. What do you think? Quantumcat 06:50, 19 August 2007 (UTC)

interestingly what really blew my mind (and is used in airplane HUD setups) is that if you take a hologram of a lens the hologram will allow you to send and focus light through the virtual holographic lens. —The preceding unsigned comment was added by 82.108.42.194 (talk • contribs) 09:43, 22 November 2006 (UTC)

Hologram store data in 3d space?
well... AFAIK, hologram store image information in 2d. I mean, the interference information is still recorded on a surface and not in a volume, right? So why in the first paragraph in the holographic storage section it said "The advantage of this type of data storage is that the volume of the recording media is used instead of just the surface."?
 * There exist both types, but only with volume holograms you can record more data than on a magnetic hard disk, see Holographic Versatile Disc or InPhase Technologies. --danh 00:59, 25 November 2006 (UTC)

perspective, moving left/right and cutting film
When viewing a hologram, you can move and see the image as it looked from your new position.

However, my question is this: how far (left and right) can you move and still see the proper perspective? Is it the same distance as the size of the film used to record the hologram?

If that is the case, then, if I cut a piece of the film, I can still see the entire image, but what I lose is that I can no longer move left and right as far as I used to? Is that correct? Do you also lose resolution when the cut the film? Ariel. 01:04, 8 December 2006 (UTC)


 * Good question. For a recording process as shown in the article it is like you say, you cannot move as far to the right or to the left as you could before. You don't lose resolution other than that given by Fresnel diffraction (it's as if you see the object trough a window of the same dimension as the film). --danh 15:32, 10 December 2006 (UTC)

Added to Hologram Recording section
I added some explanation to the "Recording" section (after the diagram), as the existing explanation seemed a bit thin, especially for the lay person. Holograms are the kind of thing average people are curious about, as it seems amazing that a three-dimensional scene can be recorded on a (for all intents and purposes) two-dimensional medium; It's the kind of thing about which people exclaim, "How do they DO that?!?" Yet the existing explanation of the recording process is really not geared towards understanding by the average individual. I remembered reading that section a long time ago and coming away just as confused as when I started. Now that I have a better understanding of holograms and saw the section was still unchanged, I thought I would add something that I think would have originally helped me understand the concept better. Here's what I added:

"It is also important to note that these recorded fringes do not only directly represent their respective corresponding points in the space of a scene (the way each point on a photograph will only represent a single point in the scene being photographed). Rather, an individual section of even very small size on a hologram's surface contains enough information to reconstruct the entire original scene (within limits) as viewed through that point's perspective. This is possible because during holographic recording, each point on the hologram's surface is affected by light waves reflected from all points in the scene, rather than from just one point. It's as if, during recording, each point on the hologram's surface were an eye that could record everything it sees in any direction. After the hologram has been recorded, looking at a point in that hologram is like looking through one of those eyes.

To demonstrate this concept, you could cut out a small section of a recorded hologram; If you then view that cut-out section, you could still see most of the entire scene simply by shifting your viewpoint, the same way you would look outside from a small window in your house, for example."

This may still not be the best way to describe the concept to the lay person, not to mention I sacrificed some technical accuracy in exchange for easy reading, but I feel at least some kind of similar description is needed. I'm fairly new at this, this addition being my first major edit of an article, and I didn't discuss the addition before I posted it in the article; so I apologize if that's contrary to general practice here (I hope someone will tell me whether or not it is). If anyone has any comments or suggestions regarding what I added please let me know.

Thanks.

Equazcion 23:09, 18 December 2006 (UTC)
 * Hi Equazcion. Thanks for your additions, they are very welcome. It is fine to edit the article directly. Only for very controversial articles (like Israel or Bush...) I would first post to the discussion page. I hope we will see many more edits from you. --danh 23:13, 19 December 2006 (UTC)

Equazcion 06:58, 21 December 2006 (UTC)
 * Danh, I just noticed your use of the "window" analogy above in your response to Ariel. I honestly didn't see that before I wrote my addition; but nevertheless you did come up with it first, so I thought I should acknowledge that. I don't want you to think I'm trying to take credit for your words.   :-)


 * No problem. --danh 17:02, 21 December 2006 (UTC)

Window analogy
I've changed the window analogy wording back to the way it was, more or less, before Netjeff changed it. Here are the two versions:


 * Original: To demonstrate this concept, you could cut out a small section of a recorded hologram; If you then view that cut-out section, you could still see most of the entire scene simply by shifting your viewpoint, the same way you could look outside in any direction from a small window in your house, for example.


 * Netjeff: To demonstrate this concept, you could cut out a small section of a recorded hologram; you could still see most of the entire scene simply by shifting your viewpoint around the cut-out section. The effect is similar to the way you can see most of the outside world through a small window from inside your house.

While I agree that my wording could use some work, I think Netjeff's is worse (no offense), especially because it makes it sound like we're telling people to look at the hole in the cut-out hologram, rather than look at the cutout itself. If anyone has any thoughts on this or an idea for how to better word the whole thing please let me know. Equazcion 02:12, 17 February 2007 (UTC)


 * Now that Equazcion points out the possible confusion about vieiwing the hole, I agree that my edit might be no better. No offense taken.  I think the difficulty is somewhat caused by the future/passive voice like "you could".  How about this version?


 * If you have a recorded hologram you don't mind damaging, you can demonstrate this concept by cutting out and viewing just a small piece; you can still see most of the entire scene simply by shifting your viewpoint around the small piece. The effect is similar to the way you can see most of the outside world through a small window from inside your house.


 * Does the more active voice help with the example? Is the style still appropriately encyclopedic? netjeff 01:48, 18 February 2007 (UTC)


 * If we already are at it, let's add a few details. What about the following? --Danh 01:29, 19 February 2007 (UTC)
 * To demonstrate this concept, you could cut out and look at a small section of a recorded hologram; from the same distance you see less than before, but you can still see the entire scene by shifting your viewpoint laterally or by going very near to the hologram, the same way you could look outside in any direction from a small window in your house. What you loose is the ability to see the objects from many directions, as you are forced to stay behind the small window.


 * Needs to be edited for encyclopedic tone though, Manual of Style. Femto 12:53, 19 February 2007 (UTC)
 * I think Danh's version is perfect. It's written in the second person because this is an example to illustrate a point and make it easier to understand, rather than explaining the facts, which we've already done, correctly and in the third person. Equazcion 13:17, 21 February 2007 (UTC)


 * Then my job here is done. :-) netjeff 23:39, 21 February 2007 (UTC)

Holonomic brain theory
I've replaced the discussion of "holonomic brain theory" with a sentence and a link to the main article. This is an old, speculative idea that seems to have gained no traction in the modern neurosciences, and adds nothing to the understanding of holography per se. The section had a "cleanup-confusing" template on it. —The preceding unsigned comment was added by Harold f (talk • contribs) 08:44, 9 May 2007 (UTC).

Recent addition by 130.56.65.25
A large section on diffraction gratings was added by user 130.56.65.25 recently. This section uses chatty, second-person language throughout and is accompanied by lots of external links to images. This really needs heavily cleaned up to follow Wikipedia's style guidelines. Chris Cunningham 10:35, 9 May 2007 (UTC)


 * I see this has been discussed above. I strongly disagree with the tone used. It's too directly instructional. Chris Cunningham 10:37, 9 May 2007 (UTC)


 * Hi there, I'm sorry if I didn't do it right, I am new to wikipedia. It's just that I recently did an assignment on holograms and was keen to share my understanding with others about how they work. Unfortunately, the text you have removed makes the whole section make no sense whatsoever. I know it must be tidied up, but can you tidy it up without stopping it from making sense? I didn't know how to put images in hence the external links. If an expert out there could redo my diagrams so they look nice, put them into the page, and tidy up the text that would be really good... I'll figure out blank out the section so that people don't have to read something that doesn't make sense, until it gets put back in (I think it is a valuable addition by the way, it shouldn't be removed forever?) 130.56.65.25 14:25, 9 May 2007 (UTC)


 * Thanks for replying. The information is indeed useful; at the moment the article needs a lot of copy-editing, but the added information is available in the article's revision history and I imagine it'll find its way back in at some point. Chris Cunningham 15:17, 9 May 2007 (UTC)


 * Hello again, I fixed it up, and figured out how to upload the images. There should no longer be any problem with my choice of langauge, but perhaps the format can be improved slightly. I hope what I've done is acceptable. Quantumcat 03:18, 16 May 2007 (UTC)

Holograms as trademarks
Duh!! I am lost in all the scientific jargon, but I guess most people (like me!!) encounter holograms in CDs,tickets etc as an anti-forgery/trademark measure. A section on how these principles work to ensure that you cannot forge holograms would be nice.


 * The things you are talking about "CDs,tickets etc as an anti-forgery/trademark measures" are not actually holograms, they are examples of Lenticular printing.86.138.13.65 (talk) 19:01, 28 January 2011 (UTC)

Recent addition by 122.162.126.49
A large section was recently added to Holography. I think it was added to try to answer the question above about the use of holograms to prevent forgery, but as it stands, it's an unformatted mess. --Eyliu 09:43, 4 August 2007 (UTC)

Possible advertisement?!
The author (122.162.126.49) talks a lot about E-BEAM, this is a company. Is it possible that the information may be some kind of advertisement? --21:17, 15 October 2007 (UTC)

I concur, it says things like 'we offer', and 'we can provide'. Clearly copied from a company website. TimmmmCam (talk) 14:43, 19 November 2007 (UTC)

I'm an isomorph, not a telescope maker!
Aren't holograms able to function as lenses? If so, how? Hans Lippershey 18:57, 16 August 2007 (UTC)
 * See zone plate. —Ben FrantzDale 02:34, 31 October 2007 (UTC)

Possible advertisement?!
E-BEAM is a company

Hologram transform?
It seems to me that the formation of a hologram is an integral transform. Could someone verify this? In particular, it seems to that a zone plate is a hologram of a point. Suppose $$f(x,y,z)$$ is the intensity of a zone plate with a focal length, z, centered at the origin. Then it seems that the hologram of the scalar field I(x,y,z) is something like
 * $$h(x',y') = \int_{-\infty}^\infty\int_{-\infty}^\infty\int_{-\infty}^\infty f(x'-x,y'-y,z) I(x'-x,y'-y,z)\, dx\,dy\,dz$$

Which looks a lot like a convolution if you take $$f(\cdot,\cdot,z)$$ to be the kernel. Does that sound about right, at least for a source volume with isotropic radiance and no occlusion? —Ben FrantzDale 02:33, 31 October 2007 (UTC)

Hologram types
This discussion completely misses all of the Dichromate and Silver Halide holograms. While most money is in security holograms this is a grave oversite. I would call this article a stub for being highly incomplete. It needs to be expanded to discuss reflection and transmission holograms, volume and phase holograms etc.- Colin Kaminski —Preceding unsigned comment added by 67.122.252.166 (talk) 20:28, 28 December 2007 (UTC)

Prince Charles
Apparently he gave a lecture to an audience halfway around the world via hologram. There's a link here. Should it be in the article somewhere, or is it too irrelevant? 125.238.88.211 (talk) 22:21, 10 February 2008 (UTC)

Frank DeFreitas
Can anyone please assess the article Frank DeFreitas?

Is this person notable in the field of holography?

Thanks in advance. --Amir E. Aharoni (talk) 22:15, 4 March 2008 (UTC)


 * The content of the article seems correct, but states much that is not notable enough for inclusion in Wikipedia. Additionally many facts are referenced to Holoworld.com, his website.


 * My take is to streamline the article to the following: --Danh (talk) 01:53, 5 March 2008 (UTC)


 * Frank DeFreitas (born January 1th, 1956, Camden, New Jersey) is the maintainer of the popular website HoloWorld aimed at amateur holographers, and author of Shoebox Holography. He instructs people new to holography how to make simple holograms, for example using a laser pointer.


 * He started working on holography in 1983 with no formal training in science . He is a 2007 recipient of the International Holography Fund (IHF) grant award program, for the documentation of creative holographic artists through internet broadcasting and has provided laser & holography educational programs for schools, ranging from elementary to University level . Additionally he hosts an internet radio program, HoloTalk and has recently begun publishing a free companion e-zine.


 * References:

Major re-write
I have edited this article to make it easier to understand (I hope). I have changed much of the order, re-written some sections and added new material which I hope answers many of the questions raised in the discussions here. I have moved the section on Security holograms to create a new article. I plan to add more material soon

Comments/amendments welcome.Epzcaw (talk) 20:36, 12 May 2008 (UTC)
 * Thanks for the much needed rewrite of this article, especially removing the nonsense section "Hologram types". I think the sections on how to write and how to read a hologram should go before the explanation in terms of the interference. This would also put the two quality pictures (Holographic recording/reconstruction process) in front of the 4 interference figures, which in my view should be deleted altogether. --Danh (talk) 08:14, 13 May 2008 (UTC)

Thanks for this. I am not convinced that it would be logical to put the sections on reading and writing holgrams before the interference/diffraction part. I feel that 'simple holgrams' help to understand the 'complex' holograms. I used this approach in teaching the subject and found it worked well. You will see that I have split this inot sub-sections which maybe makes the logic clearer. I think you are maybe right about the other diagrams and I have removed them. I am planning to add a section giving the theory of how holography works after this one.

I have considered removing the sections entitled 'Dynamic Holography' and 'Combining Multiple Holograms' as they are a bit random. It may be that they fit in somewhere when I ahve done futher edits. What do you think? Epzcaw (talk) 17:06, 13 May 2008 (UTC)
 * I think 'Dynamic Holography' should be kept, but fits well where you put it. 'Combining Multiple Holograms' does not need a section. It would be nice to add a sentence that one can add (multiplex) holograms, but I don't find a nice place for it... --Danh (talk) 14:08, 14 May 2008 (UTC)

Holographic Interface
would it be possible to create a holographic interface? like being able to control a computer with holograms? —Preceding unsigned comment added by Ares Vallis (talk • contribs) 01:19, 16 May 2008 (UTC)
 * In theory yes. But while there exist computer-generated holograms, it is much to expensive in computer resources to compute such holograms in real-time, as would be needed for an interface. Think that you don't only have to compute the 3D picture for one point of view, but for all points of view. --Danh (talk) 07:56, 19 May 2008 (UTC)

Notable Holographic Manufacturers
Does this merit a section of its own? Shouldn't it be in 'External Links'? It seems like an advertisement for a company. —Preceding unsigned comment added by Epzcaw (talk • contribs) 22:51, 18 May 2008 (UTC)
 * It seems a big advertisement to me too. I don't think we should put the manufacturers of holograms in this article (there are a lot), put just one is even worse. Australian Holographics has a long Wikipedia article so they do not fit well under External Links. I recommend to remove it. --Danh (talk) 10:47, 19 May 2008 (UTC)

OK, will doEpzcaw (talk) 12:23, 19 May 2008 (UTC)

Resolution and aperture
An un-named contributor has added several paragraphs contradicting the statement that the resolution of the image from a hologram is made worse when the size of the hologram is reduced. He/she says that resolution is increased as the aperture of the lens is reduced.

I think there may be some confusion here - the lateral resolution of an imaging system is improved Ii.e more detail can be detected) as the aperture increases - see Airy disk. This is why telescopes use very large mirrors or lenses, and why optical microscopy is limited to how fine detail can be observed; the same effect applies to a holographic image - I will try to get photographs demonstrating this.  This is a diffraction effect.  The lateral resolution in many cameras may be limited by other factors, i.e. film or pixel resolution, lens quality (spherical or chromatic aberration), but even a 'perfect' lens or a 'perfect resolution' sensor will suffer from diffraction limited resolution.

The depth of field (the depth over which the scene remains in focus) does, however, increase with decreasing aperture size, and a pinhole camera, in principle, has an infinite depth of focus. However, this model of imaging uses the ray model of light and fails when diffraction effect become significant. If the pinhole is small enough (of the same order of magnitude as the wavelength of light), then the image obtained would be extremely blurred.Epzcaw (talk) 08:17, 30 May 2008 (UTC)
 * No need to demonstrated that, it is clear. Thanks for reverting the misleaded anonymous edit.--Danh (talk) 11:31, 2 June 2008 (UTC)

To do: infobox "Ideas related to holography"
A rough prototype:

Justifications for the creation and existence of such an infobox:
 * 1) If it maps out and clarifies an actual (or notable?) relationship between ideas, it is good for us.
 * 2) Who is there to judge if some idea is now "permanently" outdated or not? Even if it is, the criterion that matters in Wikipedia is notability. The point of this monologue is that, thereby, I'm addressing in advance quite imminent challenges from other people in the following spirit:[Holonomic brain theory] (...) is an old, speculative idea that seems to have gained no traction in the modern neurosciences (...)—Harold f in  (9 May 2007)

In absence of such an infobox, I'm for example adding its planned content to the section "See also" in Logical holism . 6birc (talk) 20:16, 5 June 2008 (UTC)

Other issues to integrate somehow sensibly:
 * holism (of philosophy, metaphysics, epistemology):
 * semantic holism (of philosophy)
 * content holism / holism of the mental (of philosophy of mind)
 * epistemological/confirmation holism (of epistemology, of philosophy)
 * logical holism (of doctrine of internal relations, of epistemology, of philosophy)
 * alcoholism
 * ...all the other, too many, discipline-specific flavours of holism

Quite possibly, holography (the notion) ought to be represented as a particular manifestation of holism (the idea) rather than holism—of holography. But, then, holism is too broad an idea and the cozy concept-corner of holography can drown in it for the purpose of human perception. It doesn't deserve this fate, being notable enough on its own. 6birc (talk) 10:10, 7 June 2008 (UTC)

The infobox design style that appeals to me is in use at the bottom of [the] article Distilling. 6birc (talk) 10:27, 15 June 2008 (UTC)
 * Of course the infobox would have to use this standard. It is my impression that the optical holography described in this article has not much to do with holism, so I'm skeptical that adding an infobox that would link it very predominantly to it would reach consensus. --Danh (talk) 19:06, 15 June 2008 (UTC)

No mention of that use
How come there's no mention of their use in trading cards like baseball or Pokemon?--24.180.33.178 (talk) 06:59, 13 August 2008 (UTC)

CNN "holograms" taken out from the article
I transferred the following paragraph from the article to this page, since it is far away from being a hologram. Probably it is just a direction-sensitive superposition of two video signals. --Danh (talk) 10:05, 5 November 2008 (UTC)
 * On the night of the 2008 presidential election, CNN's Jessica Yellin was projected as a life-size hologram into the studio where Wolf Blitzer was being filmed, live. The two appeared to converse directly, although Yellin was in Illinois, and Blitzer was in New York. During the conversation, Yellin explained that she was enclosed in a special tent with 35 high-definition cameras that were filming her in a 360-degree fashion. However, it was not mentioned in the exchange whether she actually appeared to Blitzer three-dimesionally, or whether her appearance of standing in the room was merely added for television audiences much like a blue-screen projection, with Blitzer simply looking at a monitor showing her presence.


 * You could get exactly the same effect if you would synchronize the motions of two camera's, one filming the normal studio, the other one filming the "holographed" subject in front of a blue screen, the only innovation that was shown was this synchronization of camera's so that the "holograph" seemingly stayed at the same spot, even when the camera moved, but if you looked well you could see some errors in the positioning of the "hologram". Actually this has absolutely nothing to do with a hologram, and Wolf Blitzer was just acting that he saw someone, in fact there was nothing to see. Mahjongg (talk) 16:41, 5 November 2008 (UTC)

CNN during election night seemed to have holograms?


 * yeah it's true, and they did a very good job of it too. I was just gonna say that this should be montioned since me and every other american watching CNN saw these holograms and they were genius. So it should be added that holograms were used on CNN with very good success. AnthonyWalters (talk) 01:16, 6 November 2008 (UTC)


 * No, they used tomograms and called them "holograms". --Arctic Gnome (talk • contribs) 05:11, 6 November 2008 (UTC)

Isn't it worth mentioning in this article that CNN claimed incorrectly that they used holograms, and why this claim is wrong?--Xris0 (talk) 20:53, 6 November 2008 (UTC)
 * It might be worth mentioning that they misused the term, but the paragraph that keeps being added says that "Jessica Yellin was projected as a life-size hologram into the studio", which is wrong. --Arctic Gnome (talk • contribs) 15:55, 7 November 2008 (UTC)
 * There are many misusing the term, so I don't think it's worth to mention it. When these kinds of teleappearance become more widely used, they will surely all call them holograms.--Danh (talk) 08:09, 10 November 2008 (UTC)
 * Several people keep adding the CNN thing to the article, suggesting that even more people are coming here to read about it. I think it would be helpful to have a sentence redirecting those people to the proper article.  --Arctic Gnome (talk • contribs) 11:36, 13 November 2008 (UTC)
 * Its just a non remarkable publicity stunt, and has nothing to do with real Holography, let keep this encyclopedic, it does not belong in this article. Mahjongg (talk) 00:31, 16 November 2008 (UTC)
 * even if its somewhat relevant now for all the dunces, it should be taken out in a month or so, a simple stunt like this does NOT belong permanently in a technical article. Mahjongg (talk) 02:49, 17 November 2008 (UTC)
 * That's reasonable. The stunt will be non-notable in a month, but until then the section will be educational to many people who come here to learn about it.  --Arctic Gnome (talk • contribs) 02:52, 17 November 2008 (UTC)


 * Yes, and after that the article about Jessica Yellin still holds the details of the stunt. It is a far better place there than here. Mahjongg (talk) 08:48, 17 November 2008 (UTC)


 * We don't do "temporary inclusion". It's either notable or it isn't. This isn't notable, except insofar as Wolf Blitzer getting danced at by a CG Will.I.Am officially signalled the end of CNN's status as a semi-respectable new organisation. I'm removing this again; please do not add it back without estbalishing consensus to do so. Even if it is added back, secondary sourcing which indicates that this is a notable use of the term "hologram" which has captured public interest is essential to establish its worthiness - these were present in the original paragraph, but not in the reworded version just removed. Chris Cunningham (not at work) - talk 09:12, 17 November 2008 (UTC)


 * I have no problem at all with deleting, but (since I can't resist being advocatus diaboli), let me ask if it doesn't bear a mention on the basis of ignorance? I mean, people who think (or heard CNN say) it's a hologram, & don't know any better (not knowing not to believe your average media weenie on anything resembling technical matters, given a typical reporter couldn't tell a tank from an APC, or a Brink's truck, without chyrons and a producer whispering in his/her ear). Am I aiming too low?  TREKphiler   hit me ♠  09:58, 17 November 2008 (UTC)


 * As I said in the edit summary, this article has a lot of faults right now, but one of them is not "lack of a pop culture section containing barely-relevant one-off references". If there were reason to believe that this example had pervaded popular culture such that it ''won't have been totally forgotten by Christmas then there might be an argument for inclusion, but I don't see one. Chris Cunningham (not at work) - talk 12:52, 17 November 2008 (UTC)


 * As noted, I won't make an argument against deletion. Just a thought.  TREKphiler   hit me ♠  22:46, 17 November 2008 (UTC)


 * I would argue that temporary inclusion would be a useful policy given how many people use Wikipedia as a first-source for random stuff they hear on TV. As User:Trekphiler mentions, it would help rid the world of some existing ignorance.  But I guess this page isn't the place for broad policy proposals.  --Arctic Gnome (talk • contribs) 21:17, 18 November 2008 (UTC)