Holographyforum.org / holowiki.org

I found this free online from SPIE and thought there is just so much good information on holography in it I should put up the link again in case if hasn't been shared recently. Thanks TJ (missed by many) and Hans. Some "Light" reading.....


https://spie.org/Documents/Publications ... e%2008.pdf

I guess you wanted to share this link, Phil
https://spie.org/Documents/Publications ... e%2010.pdf

Anyway, the whole volume "Fundamentals of Photonics" is accesible here:
https://spie.org/publications/fundament ... cs-modules

"Maria works for a company that has received a new contract from a software firm for producing 1,000,000 small holograms to be used as security seals on all its products."
"She sets up the basic split-beam, focused-image, reflection-hologram configuration....."
"She then hands the image to her friend, another technician in the replication department, who treats the hologram as if it were an original object and makes a million copies of it using rolls of photopolymers."

Not yet! There's no one who can make a million copies of a reflection hologram on photopolymer. If Maria wants to make a million copies of a security seal, she should've made a rainbow master and replicated by making a shim in a nickel tank. If her customer wanted a million reflection copies, she would have to get 1,300,000 sheets of polymer, assuming ~30% loss (does anyone actually produce 1,300,000 sheets of polymer?). She would then have to expose each one separately. Assuming an exposure of about a minute, with about a minute to change the film in the holder, and taking into account that she probably needs some sleep, she would spend about 6 years shooting this, day in and day out, for 16 hours every day.

"Having been trained as a holography technician"
-Does one get the feeling that Maria should've had chosen a better technician?

"Now hold the emulsion side of the hologram on top of a cup of hot water (tea, coffee) and allow the steam to “swell” the gelatin. Observe the image again and notice that the color has been shifted toward red."
Keep observing and notice the image disappear into the infra red! The melting point of gelatin is about 35 deg C. Putting the gelatin above steam at, possibly, 60 deg C will swell the gelatin into the IR, then it will become viscous and slew off.

"If a transmission hologram is broken into pieces, each piece will give a complete perspective of the original scene."
Not so! This is an old misconception. It depends on how far the image is behind the image plane. If the image is too near the image plane, it's no longer visible

"In the areas where the light waves from S are in phase with those from S1¢, the total amplitude is doubled."
But, the intensity, which is what's being recorded, is quadrupled, assuming equal intensities:

I(t) = I(1) + I(2) + 2√[(I(1)I(2)]cos(φ)

If I(1) = I(2) = I, and φ = 2nπ, then
I(t) = 2I + 2I = 4I (Does this violate conservation of energy? After all, recording with two units of light produces a disturbance of 4 units of light.)

"Suppose a 1.0-mm-thick CD can store 1.0 gigabyte of information in the form of digital data. All these data are stored in the top 1.0-micrometer-thick layer. How much information can this CD store if it can record over its entire volume at the same information density?
Answer: 1.0 terabyte"

CD's store information as a series of lands and pits on the surface, not within it's volume. This is why the read laser can access the data.

etc etc etc

Thanks Petr, I have no idea how I copied the wrong link! No clue....I found the volume 1 by accident. Lots of good stuff for people starting out. Phil

142laser wrote:Lots of good stuff for people starting out.

It's only good stuff if it's correct. Some of it is, and some of it is not.

I sometimes wonder how our knowledge of the world would be if physics were taught by the same modality. That is, if physics were taught by canonizing old physicists, as holography is taught by making catholic saints out of old holographers.

I think TJ himself would have wanted holography to progress, not be stuck in ca 1968. I'm pretty sure that TJ, as an educator, would have thought (and taught!) that progress was more important that himself.

"If a transmission hologram is broken into pieces, each piece will give a complete perspective of the original scene."
Not so! This is an old misconception. It depends on how far the image is behind the image plane. If the image is too near the image plane, it's no longer visible"
Not completely sure about the term, "if the image is too near the image plane." I made numerous pulse portrait holograms with Rob Munday (Hi Rob!) at the Royal College of Art in the mid 1980's. Some of those included images where the subject (me and my father) reached out and were touching the film creating some areas where the film recorded no fringes because of the shadow they caused. However, when I light up any part of those transmission holograms with the laser beam, even at the finger tips, then a complete image is projected on the wall.

Din wrote: ↑Thu Jul 12, 2018 8:04 am "If a transmission hologram is broken into pieces, each piece will give a complete perspective of the original scene."
Not so! This is an old misconception. It depends on how far the image is behind the image plane. If the image is too near the image plane, it's no longer visible

This point of view appeared in early years of holography. As light coherence was very low (no lasers were available), the objects were just flat images such as transparencies, or nearly flat objects such as thin microscopic specimens. The holograms were recorded in on-axis configuration. The object-plate distance was big. A transmission hologram recorded in this way could produce real image of the original object. Indeed, any reasonably big piece of the hologram could reconstruct the whole object.

This idea does not hold for holograms of 3-D objects. For example, when making a tabletop hologram of a box, each part of the holograhic plate "sees" the top of the box, but the left side of the box is seen just from the left part of the plate. Thus, if you take a right part of the hologram, there is no way how to reconstruct the left side of the box.

Yes, and this idea that a hologram contains "the whole image in every part" (the literal translation) also contributed to this misconception. What's not reealised, I think, is that the word 'hologram' meaning 'The whole image in every part' followed because of the misconception. The word followed the misconception, not the other way around. Originally, it was 'wavefront reconstruction', not 'hologram'.

In fact, David Bohm started the whole "holographic universe' concept because of this misconception of the 'whole image in every part'. He asked the question: "Why are all the laws of the universe in every part of the universe?" That is, Newton's Laws are valid in every part of the universe, given existing conditions. We know this because light and elementary particles reach us from distant parts of the universe, and behave exactly like light and particles here on earth. So, because Bohm thought that a hologram contains 'the whole image in every part', he used this as a metaphor for the universe. That is, the universe contains 'all the laws in every part'. This theory has become part of string theory. But, this string theoretical construct has nothing to do with actual holography. String theorists and cosmologists have simply used Bohm's idea of 'the laws in every part', just ta hologram has 'the whole image in every part'. In other words, Bohm and cosmologists had the wrong idea from the beginning. However, this misconception of the being able to tear up, or break up, a hologram and see the image in every part still persists.

You can determine how much of any image exists in any broken or torn part by simply taking the broken piece, of dimension d, and creating a cone which subtends a solid angle at some point, such that the cone includes the image. Then, the angle subtended by the plate to this point, say at some distance r, is ~ d²/r, while, if the image, or part of it, has dimension i and is at some distance r' from the hologram, the solid angle subtended by the image is ~ i²/(r - r'), Thus, the part of the image still visible is given by:

i² = d²(r - r')/r.

Agreed. And I have always assumed that when people talk of a part of the laser transmission hologram can reconstruct the whole image that they naturally mean the whole image as seen from that perspective only which in its simplest form is seen as a projected 2D image when a laser beam is pointed at the hologram at the reference angle. This is what I meant when relating the information about the pulse portraits I made.

Moreover, a hologram can be seen as a perfect, diffraction-limited record of an object. When I take a tiny part of the hologram, it still contains "the whole image", but diffraction limitation becomes critical. In other words, a tiny part of the hologram contains "the whole image", but the signal to noise ratio is much worse than for the whole hologram.