What's the consensus on optical tables?

[pluto]

Being new to holography, I've read through these forums quite a bit looking for a somewhat affordable optical table solution. I would much rather spend that money on a better laser if I can get away with it! I don't mind putting in some work if it means better bang for my buck, as long as I'm not shoveling tonnes of sand

It seems that most everybody agrees that sand tables are an unnecessary nuisance. I also read through a thread where it was recommended to focus on things other than the table first, with some claiming to have made DCG holograms on a basement floor. Elsewhere, I read that optical stability is crucial when doing DCG due to the longer exposure times.

I've come across quite a few people discussing the use of empty cans. Inner tube comes up pretty often too. I just recently read a post by BobH where he denounces air isolators! They seemed like a cheap and effective solution...

I think I need the wisdom of the masses -- I'd appreciate everybody's opinion on the matter.

[lobaz]

It depends on your environment. If you are lucky and live in a very calm area (no traffic etc.) and you have a very calm basement, you can work directly on the ground. Even then you must think about how to make the components stable - no rocking is allowed. If you can build an interferometer to check the stability, do it. Otherwise start with a shoebox of sand and the simplest setup you can build, and if you succeed in making a hologram, try -- very slowly -- if you can repeat the result with several small sandboxes (for holding the components), without sand at all...

[holomaker]

I would recommend as a beginner you start off with the small 12" x 12" marble slab ,later on if you advance you can utilize this is a tabletop to elevate optics or even lay this into your Sand table to put critical optics on. Put the slab on top of bubble pack ( vibration isolation ),and set up your object laying on its back , and epoxy or superglue three screws with their points up to place the 2 x 3 slide on . Then take that concave mirror and simply attach it or use plasticine clay to hold mirror in place ( on the wall ,pipe from the ceiling or your tripod , place your laser a good distance away from mirror(20 feet or so), Direct the laserbeam to the mirror , And adjust mirror to point to the plate.with Denisyuk configuration the only place you have to worry about movement is between the object and the film ,you could hand hold the mirror if you really wanted to !

[Joe Farina]

I agree with holomaker.

Don't shoot directly on the concrete floor. Place a large ceramic "field tile" (or a stone slab) on some kind of air support like an inner tube. This should rest on a concrete slab on the ground, like in a garage for example. Maybe put some coins (as your objects) on the ceramic or stone, then lay your glass plate on top of the coins. If you're using DCG, use a powerful 532nm laser like a Coherent 315M (100mW). Set the laser up some distance away as holomaker said (it shouldn't be on the isolation table, and doesn't require vibration isolation). Expand the beam by some means (concave mirror or lens). The expanded beam should angle downward to strike the plate. The size of the expanded beam should be (for example) 4 to 5 inches in diameter when it reaches the plate, but of course it depends on the size of the plate. Allow the plate/coins to settle for while, then zap it hard for a minute or two.

[BobH]

If you plan to do only the Denisyuk type of recording, you can do it on anything. The floor, the bathroom counter, even a shaky old card table will work because stability is only needed between the object and the recording plate. If using split-beam geometry for more complex object lighting, stability is needed over a larger area. Sand was an artist's improvised solution in the late '60s when super heavy granite tables and very expensive steel optical benches were all that were available. Yeah, it can be made to work but in 2016 there are sooooooooo many alternatives. I currently use a 2x3' 4" thick
newport steel table that was pulled from the dumpster. Watch Ebay for a cheap one near you. I've used a both 2" thick steel breadboard and 1/4" thick steel plate on top of tables built with cinder blocks on fork lift inner tubes in the past. The top is easier to handle and move that a full thickness optical table, and the rest of the table can be easily disassembled for moving.

[Joe Farina]

stability is only needed between the object and the recording plate

That is true, but there are a couple reasons why I suggested not shooting on a concrete floor. Concrete slabs can move or shake, for example my concrete slab will vibrate somewhat (which can shake or disrupt the object-plate relationship) when a train passes by a quarter-mile away. The same could probably happen when a large truck drives by. If the plate was somehow "locked" to the object, then it might not matter. But in most practical cases, and especially with longer exposures, I would say that the plate-object spatial relationship has a pretty good chance of being disrupted by underlying instabilities.

Since Pluto said that DCG is being contemplated, there is a more important reason to get off the floor: humidity has a tendency to collect there. Every lab will be different, but my garage-lab used to have a bare concrete floor, and the humidity was much greater in the first few inches. This can easily be checked by using a digital humidity meter.

[holomaker]

I amcurrently testing these 35mW. lasers out and thought I would use the Liti film ,this is technically not a denisyuk set up because the object light enters from the side, but it all takes place on the small

image.jpeg (608.67 KiB) Viewed 4807 times

isolated tile....

Also notice the "kicker mirror" on the right-hand side

[pluto]

even a shaky old card table will work because stability is only needed between the object and the recording plate

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

I was also wondering if it's possible to use two different lasers for the same exposure. I understand three lasers are required for true colour holography, so it should be possible, right? I'm just wondering if there are any "gotchas". It seems to me that it would be cheaper to buy two or three 100mW lasers than one 200 or 300mW laser. The main reason I ask is that I would like to keep using my existing laser if/when I upgrade to something better.

Last question. SBR holograms seem to be much easier to produce, contain a beautiful range of colour and are visible under normal white light. So what is the advantage of other types of holograms? Transmission holograms, for instance, are much more susceptible to vibration, are monochromatic, and can only be reconstructed by laser light. So why even pursue it?

Thanks!

[John Klayer]

Transmission holograms, for instance, are much more susceptible to vibration, are monochromatic, and can only be reconstructed by laser light. So why even pursue it?



I specifically use two beam transmissions because they have such great depth and complete parallax. Dirt cheap diode and dpss lasers can be used for reconstruction. I shoot most of my holograms in a cave which is naturally rock solid. When I'm experimenting on variations of my speleoholograpy contraption as I'm doing tonight I use a table made from soda cans and two steel plates.

[John Klayer]

Pluto also asked:
"I was also wondering if it's possible to use two different lasers for the same exposure. I understand three lasers are required for true colour holography, so it should be possible, right? I'm just wondering if there are any "gotchas". "


I tried. I failed.