What's the consensus on optical tables?

[holomaker]

Transmission holograms can be viewed in white light if they're done properly, multitudes of colors and lots of depth can be made with one laser

[lobaz]

Does the laser itself require the same level of vibration dampening? How critical is keeping the laser head motionless?

It is not very critical. You should not walk around with the laser in your hands, of course. But once the beam splits to the reference and the object arm, is must be motionless.

I was also wondering if it's possible to use two different lasers for the same exposure.

Try it
You understand well that it is possible to use e.g. R, G, B lasers to produce a colour hologram. Each wavelength creates its interference pattern, and they do not interfere with each other. So far so good.
But there are reasons why I did not try it.

First: you can record several mutually incoherent interference patterns on the plate, but the hologram brightness drops quickly with each added pattern. In the RGB setup, there is hardly anything you can do with it because you need several independent patterns; in your case (you want to combine lasers of the same wavelength), you will end with dimmer hologram.

Second: if you make a reflection hologram, then you usually suppose you will display them using a point white light source. Let us assume it and let us assume you are making a single beam reflection hologram.
You have two choices when making a hologram:
a) You use single reference wave. Here it means you need combine two beams together before they pass a spatial filter (or just a lens). But how? If you use e.g. a 50/50 beam splitter, then 50 % of each beam goes to nowhere, so you end with the same amount of light as if you used just one laser. Moreover, it will be a mix of two incoherent beams, which makes things worse. In multicolor (RGB) setup you can combine the beams using a dichroic mirror, so almost no light is lost. It is not possible here. I don't know any way how to combine two beams of the same colour without loosing power.
b) You use two reference waves, i.e. you simultaneously illuminate the plate from different directions. But as we are going to display the hologram using single point light source, you will probably see two overlapping reconstructions that are shifted a little bit from each other. Unless it is an artistic intention, it degrades the image significantly.

Anyway, you can try it. If theory tells you it won't work, it does not mean it really won't.

So what is the advantage of other types of holograms?

First of all, reflection holograms require very fine recording materials, which means long exposure times. Transmission holograms can be made with less fine material (but still very fine compared to photographic), i.e. shorter exposure. I would consider common you can expose 10x faster when making transmissions (or even faster).

Second: depth of reflection holograms (illuminated with white light) is limited to about 20 cm; then the image gets blurry. You can go to several meters with transmission holograms (illuminated with laser). You can think about illuminating a reflection hologram with a laser, but you need very careful processing. (More about this later if you are interested).

Third: It is common to make copies of holograms (called transfer holograms or simply H2's). It is advantageous to prepare the master hologram (called H1) as a transmission and the H2 as a reflection or a transmission, depending on your intent. Then you have the best from both worlds. However, making H1 transmission -> H2 reflection copy is a bit advanced technique and requires very stable setup. You also need large optics.

Fourth: Transmission holograms are often brighter, especially if they have limited parallax (e.g. rainbow holograms).

Fifth: Some techniques such as pulsed holographic portraiture require very sensitive material, i.e. transmission is the only choice.

Maybe (read: most likely) there are other reasons.

[Din]

Maybe (read: most likely) there are other reasons

Well, take a look at your credit card.To make the quantities required to put holograms on credit cards you need to make hundreds of thousands, up to over a million holograms. This cannot be done one at a time as Denisyuks.

In the larger picture, I don't think that Pluto (named after the planet or the dog?) realises how widespread is the world of holography. Pluto's interest is in making display holograms in a cheap manner as a hobby. In this situation, perhaps Denisyuks is the best way to go. After a little experience, Pluto may want to progress to more advanced holograms, for example rainbows or multiplex/lenticular for motion. It's been my experience that most people start with single beam Denisyuk's because they're simple and cheap. At some stage, they either abandon holography altogether, or continue on to more advanced stuff. If the latter, I would strongly suggest that Pluto visit an exhibition, so as to answer his question. There's some excellent work out there that'll really show the difference between Denisyuks and other types. There's an exhibition of work by Rudy in New York: http://holocenter.org/news/the-floating-world

But, as I mentioned, holography has a much, much wider reach. There are holograms for security and brand ID, such as on your credit card, there are Holographic Optical Elements, usually called HOEs, for technical holography, such as in the HUD used by the Air Force, and several of these AR applications, and there are large scale projects such as the Holorad "Talking Monkey" (https://www.youtube.com/watch?v=BiXSAkcAu5c ).

So, my answer to "Why make other kinds of holograms?" is that it's a matter of taste, style and application. I still wonder why people eat broccolli!

If theory tells you it won't work, it does not mean it really won't.

Petr, How can you say this! When we theoreticians tell you it can't be done, it can't be done. And, if you manage to do it, you'll get a Nobel Prize!

[pluto]

Thanks for the replies, lots of great info. Named after the greek god, by the way

I would love to visit a hologram exhibition! I have never actually seen a proper hologram in real life. After reading your post, I looked at the back of my credit card... It is a hologram, but with no parallax! How boring.

I live near Vancouver, BC so the NYC exhibition is out of the question, haha. There have been holograms on display at the Vancouver Art Gallery before I believe, but I don't think it's very common occurrence. It might just be the case that the first hologram I see in real life is one I've created!

My laser should arrive early next week at the latest The tracking has been stuck for nearly 4 days now... I must have checked the tracking status a hundred times today. Holomaker was nice enough to include a photodiode for measuring laser power, some AmDi and a beam spreader lens! Thanks Dave. This will allow me to fail at holography way ahead of schedule

Getting back to the topic of optical tables, I will use a granite slab on top of four bags of sand to begin with. I think I will set up an interferometer and try different setups and see how easy they are to disturb. It'd be great to find a cheap, easy and lightweight solution to stabilisation.

This may sound stupid, but I'm amazed by how "simple" holography is in essence. I understand that the process is hard to master due to vibrations and all the variables, but the concept itself is startlingly simple... even the emulsion is simple. Potassium dichromate and Jello. I really like the idea of being able to produce holograms at virtually no cost. Maybe one day we'll (aka some smart chemistry minded holographer) find out how to make a cheap emulsion with the sensitivity of AgX.

Thanks again for your help guys. I have never come across a forum as warm, friendly and generous as this one.

[lobaz]

It'd be great to find a cheap, easy and lightweight solution to stabilisation.

If you find some, take a picture and post it, please! Even if you think it is a very basic idea - new beginners in the forum will appreciate it!

[lobaz]

When we theoreticians tell you it can't be done, it can't be done.

Such as rotating polarization with a pair of mirrors? That was a long thread!

[Ed Wesly]

Going back to the basic query of this thread, yes, you can shoot on the floor! And get incredibly good results, as evidenced in this photo of real time fringes generated when replacing the processed Holographic Optical Element in the set up on the floor!

FoFRealTimehf.jpg (238.24 KiB) Viewed 3529 times

For details, go to: http://edweslystudio.com/Research/FunOn ... Floor.html

[Ed Wesly]

"It'd be great to find a cheap, easy and lightweight solution to stabilisation."

"If you find some, take a picture and post it, please! Even if you think it is a very basic idea - new beginners in the forum will appreciate it!"

Here is a cheap, easy, lightweight, portable solution in vibration isolation, called the Big Beam:

BBSu08hf.jpg (193.52 KiB) Viewed 3528 times

Some details here: http://edweslystudio.com/Pedagogy/7SBP/ ... e7SBP.html

[Din]

When we theoreticians tell you it can't be done, it can't be done.

Such as rotating polarization with a pair of mirrors? That was a long thread!

To tell you the truth, I was really trying to understand why the polarisation ended up as it did. I fully accept that rotating mirrors will change polarisation, I just don't have an instinctive understanding of the final state. Why does it got from one to the other? Or rather, which way does it go if the mirrors are rotated a particular way and the polarisation starts in a particular state before the first mirror? No one seemed to be able to explain why, they simply repeated, "It does! It does!" As is probably well known by now, I don't accept statements that simply say <This happens> without some explanation besides "Hans B says so" or "Mike Klug says so" or "Rallison said so" or any "famous expert" says so. I need an explanation in terms of physics or mathematics. Just for the record, I use the model that Feynmann writes about, in which the final state of polarisation is based on the oscillations of the outer electrons (in case of confusion, I didn't say "Feynmann says so". I said that Feynmann provides a model that I can apply to different situations). But this model is difficult to apply in case of glass, since glass is a homogenous liquid.

Thanks for the replies, lots of great info. Named after the greek god, by the way

Ah! Did not think of the god! I assume it's a personal preference, and not a statement about Vancouver?

This may sound stupid, but I'm amazed by how "simple" holography is in essence.

Well, everything is simple in essence. To make a particle accelerator, you simply place magnets around a ring and launch super-heated hydrogen into it. To make a moonshot, you simply place large amounts of fuel in the other end and light it. Your statement reminds me of the story about Feynmann and the nuclear submarine. In his book, he says that after his work on the Manhattan Project, he was asked for some industrial applications of nuclear power. he says the question was a bit obvious, since there were so many. He says, for example, place a nuclear pile in a submarine and use it to propel the submarine. He apparently said this as an off-hand comment on the obvious nature of the question. But, he was amazed years later when he found he was listed on the patent for nuclear submarines!

In the case of holography, anyone can make a hologram; you don't need an isolation table or a laser. You can make a hologram on your kitchen table with an led. But, to make a decent hologram...now that's a different story!

Anyway, we have a large inventory of dcg holograms. If you want one, PM me your address.

[Wackhaus]

Hi pluto whats up
Where do you live/what do you consider affordable