Home Optical Table

[baja]

Hi,

I'm thinking about trying to make DCG holograms in my ground
floor apartment. I saw a youtube video,
http://www.youtube.com/watch?v=TiJ7XvlFmuo ,
on how to make a table with carpet, particle board and
inner tubes, but I wonder if would be stable enough to make
DCG reflection holograms? Does anybody have experience
with inner tube/particle board tables?

Thanks!

[Joe Farina]

Hello again Baja,

The type of floor you have is more important than the table. The first thing I would do is get a partially-inflated bicycle inner tube, and place that under a large concrete paving slab. Then set up a small interferometer on top of that, maybe with a red laser pointer or small HeNe. Take a long, careful look at the fringes. They need to be stable, especially for DCG. It may easily turn out that your floor is not stable enough, at least for DCG, which needs sustantial exposure (even with blue light).

[Gall]

I personally found a solution I like: a heavy board of any kind lying on bag(s) with sand. If this is not enough, partially inflated tubes under bags work fine.

I also made a portable version of this one: a wooden suitcase filled with a single big bag of sand. If open, a heavy wooden board covered with magnetic metal is exposed. I use it for making small transmissions.

[Johnfp]

Good morning Baja, if you are thinking of getting into DCG then the chances are you are going to be making Single Beam Reflection (SBR) holograms. If that is the case then you really don't need to concentrate on making some ellaborate, heavy table. Go out and get yourself a 18" by 18" concrete paving stone and place it anywhere you want (on a counter, table, chair, anything). I would paint the paving stone black.

What you need to concentrate on is keeping in mind that the object and plate cannot move with relation to one another. This is best accomplished by laying your object down on it's back on the paving stone and lying the plate directly on it. With this technique and provided the object does not move with exposure to energy (dont us plastic or rubber), you can have perfect stability for minutes of exposure.

http://www.holograms3d.com/Illustration ... Single.jpg

The supports if needed can be black painted washers, black painted nails, screws, whatever. Black tape the leading edge of the plate to stop light from coming in the edge. Although the diagram says sandwiched film, this is a perfect set up for any film, especially DCG for making SBR holograms.

Also look at: (proving fringe stability with laser off table)
http://www.holograms3d.com/Test_Researc ... search.htm

Once you have a grip on the DCG process (coating, exposing, processing, sealing), then if you want you can build a table if you want to make holograms other then SBR's.

Good luck and don't hesitate to ask for guidance here on the forum.

John

[BobH]

I agree with John. However, I'd forget about the tile or paver for the base of where you work. Making Denisyuk (single beam reflection) holograms can be done on any surface anywhere. All that's required is to be certain the plate and subject matter are interferometrically stable with respect to each other. That's it. No need for any kind of "stable base". Once one learns what "interferometric stability" means and requires, it's easy to achieve with simple objects found around the home. Focus on that instead of building a special table, learn all about preparation and handling of the recording materials, and get to the point of making a nice hologram that way. Then, you'll be all set to expand your capabilities by building a table, and you'll see why particle board and carpet are not very good choices for building materials. Yes, they'll work. Anything will work if configured properly and with a practical knowledge of "interferometric stability". That's the key to success with holography, not a stable table.

[holorefugee]

While the concept of "interferometric stability" is quite wise it is not very educational. Bob, are you willing to write a paper on "interferometric stability" and explain what the requirements and solutions are? This would be a valuable addition to beginning holography. While I understand "interferometric stability" it is because I have spent 100s of hours with interferometers. Summarizing this information is not a trivial task.

[baja]

Thanks to everybody for your advice. I think the idea of an interferometer is the best, and by interferometer I can probably just split a beam in two and direct them to the same spot, and magnify that spot to see the fringes. Most holography books show how to set up a Michaelson interferometer if thats the best way, so thats probably not a problem either. It looks like I'm best off just starting with inner tubes/heavy table on top right from the start so I think I'll build my test on something like that. I thought that car inner tubes were best but I can try bike tubes easier.

Thanks again.

[Dinesh]

Whatever setup you use, if you use an interferometer, the fringes need to be stable over the time of the exposure, which depends on the beam power at the plate. Roughly speaking, for a single beam Denisyuk, say one mirror and one lens, you might lose over half your power. So, for a 150 mW laser you're probably looking at about 50 mW/cm-squared. Normally for a dcg the exposure is in the range 50 - 80 mJ odd, so, in this case you're looking at a 1- 2 second exposure - not too bad. However, the more optics you put on the table, the more the beam power at the plate decreases and the longer the exposure. Also, for a single beam Denisyuk, the ratios are often poor, so you should check stability for twice this time - 2 - 4 secs in this case. Practically, for a single beam Denisyuk, if the fringes stay stable for about 30 seconds you're probably going to be OK. Be sure to test when you're going to shoot to take account of whatever the local noise situation is.

One other thing, you might want to put a mirror into your plate holder and use that as one mirror in your interferometric system. This checks the stability of the plate holder.

[djm]

and you'll see why particle board and carpet are not very good choices for building materials.

Can you expand on this? In what way are they bad to use? In several DIY table descriptions they suggest particle boards and carpets underneath a stiffer and heavier top. What options do you suggest?

[jsfisher]

One other thing, you might want to put a mirror into your plate holder and use that as one mirror in your interferometric system. This checks the stability of the plate holder.

Like many things, this becomes obvious only after it gets mentioned. Thanks for the tip!!