450 nm transmission DCG, some progress

[MilanKarakas]

Hello.

I tried to run Osram PL450B in free running mode, and got some results. At about 40 mA, it gives me 21 mW (~450 nm). And some coherence length, not sure exactly, but at least 3 cm.

Here are some videos of reconstruction of (really bad emulsion) of this hologram:

http://www.flickr.com/photos/milan_kara ... otostream/

projection with green laser

http://www.flickr.com/photos/milan_kara ... otostream/

projection with blue laser (recording laser)

http://www.flickr.com/photos/milan_kara ... otostream/

reconstruction with green laser

http://www.flickr.com/photos/milan_kara ... otostream/

reconstruction with blue laser

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Setup: single beam transmission.

Mixture: 1/4 of 100:12:3 (25:3:0.75), but:

Later realized what is bad with the gelatin and with emulsion: usually I filter gelatin after mixing with coffee filter. This time lot of gelatin 'stuck' onto filter, while most of the water and dicrhomate goes through. The result (mould coating) resulting in crystalizing of the dicrhomate on the surface. After spending all molds, the rest I poured over glass plates (veil coat), and this plates went okay, but with uneven coating (I should to practice this procedure). It puzzles me why dicrhomate does not crystalize on veil coated plate, but slowly dried mold coated plates get frosty look at some places.

At least, my first few transmission holograms are visible to some extent (better visible in person than on videos or pictures.

Best--
milan

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[Tony DCG]

Hi Milan,

Thanks for your update.

Is there anything in particular you need help with?
You mentioned crystalization of AmDi. This is from my understanding the result of the ratio of AmDi and gelatin. Now if you are freezing the mold plates then perhaps that might be a factor.

If you wish more input please provide a bit more info.
Gelatin type
AmDi to gel ratio

When you say crystalize do you mean preexposure or post process.

Help is here if you need it.

Tony

[MilanKarakas]

Hi Milan,

Thanks for your update.

Thank you too, Tony.

Is there anything in particular you need help with?

Not at this moment, thanks. I think I found the source of the problem and that is filtering method. Earlier I had no such problem but then I did gelatin mix on high temperature (60C even close to 70C), and emulsion is pretty okay, but has some other problems related with too high temperature. This time at 45C it has problem with viscosity: good part of the gelatin remains on filter side, while liquid (mostly water and KDi) pass through. So ratio while mixing was 100:12:3, but who knows what was ratio after filtering.

Now I got nylon stockings and will try filter with it, and will repeat exactly the same procedure but with this filtering method. I will report here how it goes. Past few days found myself posting onto facebook instead on this forum. I am sorry for that.

You mentioned crystalization of AmDi. This is from my understanding the result of the ratio of AmDi and gelatin.

If IIRC, AmDi is more soluble than KDi (I have only KDi), but that is not issue (I think). I can go lower than 100:12:3, perhaps 100:12:2 or less, but will insist to first one - exactly because I saw this blob of the gelatin stuck (something like glue) on top of the coffee filter.

Now if you are freezing the mold plates then perhaps that might be a factor.

Not this time. Only noticed that it require longer time when amount of gelatin is low. For example, 100:15:xx gelling faster than 100:12:xx. My earlier attempt to make dilute gelatin (100:6:xx) failed because of too short gelling time.

In meanwhile I tried one test with blank gelatin: first mixing the same ratio (100:12) then let to gel. Then freeze, and after thawing let some amount of water to leave, then melt it again. Now, gelling time is much, much shorter. Probably high amount of water acting as a barrier for helices to arrange (no matter triple helices or doublet or singlet), but it working very slow. Just need to investigate role of the gelling temperature vs. gelling time. I think that plates were okay first time when I was so slow, and part of the gelling occur at room temperature even before refrigerator. Later I 'pick up the speed' and this lead to fast (maybe too fast) process of applying gelatin mix onto plates and thus less time on room temperature to allow partially gelling before cooling.

I wish I can found one document, and if I remember correctly, they do all gelling at room temperature, while just briefly cooling prior to releasing mold. Somewhere I buried this document in my folders, and can't dig out it right now.

If you wish more input please provide a bit more info.
Gelatin type
AmDi to gel ratio

Gelatin is Podravka's Dolcela, Croatian product:

http://translate.google.hr/translate?sl ... na&act=url

Although there is English, but when type on search window "gelatin" it did not showed me proper results. I have no any other info about this product. I called this company asking about bloom, but they said that: "...everything I should know about this product is already printed on the package...". Well, thank you Podravka.

KDi to gel ratio: 25% of dry gelatin (100:12:3). Actually, in order to save valuable potassium dichromate (achieved very hardly, begging custom officers to pass this chemicals, long story...), I made 1/4 of that amount (25:3:0.75). Even this amount is too much when applied by syringe to the plates (dimensions: 8x10 cm, with 'active area' of 6x10 cm, did not prepared enough amount of the molds). I applied 1.25 ml, but even this amount is too much, 1 ml suffice for 6x10 cm for whole surface.

Scotch tape is "invisible" type. Something like this one:

http://www.officemax.com/catalog/images ... 62i_01.jpg

It is 'invisible' only on paper, but very visible on clear glass plate. I love this tape because of its good mechanical properties, but it is maybe too thick. 55 micrometers (measured double tape, 110 um), without applied force on it. 37.5 micrometers with good force applied by micrometer.

Wow! Now I measured clear scotch tape, the same thickness (37.5 um) without applied force, and 25 um with applied force (micrometer pushed to the maximum). Some amount of air is trapped, so it has significant difference between relaxed and well pressed tapes. And some difference between brands. (I had somewhere one very thin scotch tape, but it get water and become not sticky any more)

Now tried to measure another brand of the scotch tape (previous one is more yellow, this one is more clear), and it shows almost the same values as 'invisible' one.

I have only washing clips, not paper clip. Perhaps it should be more firmly pressed for mold coating.

When you say crystalize do you mean preexposure or post process.

Pre-exposure. I did mistake after releasing mold - leaving to dry emulsion bottom with just 3-5 mm spacing. Most of the water vapor remains on the center, while crystallization occur near the edges. Later turned emulsion up, and then another plate (or two) begin to crystalize.

Two big plates which is cut later to smaller pieces did not show any crystals, but it is coated by veil method. I did not make perfect coat, because liquid did not slide down like veil, but more like separate drops of liquid. Seems that I did it too slowly.

Both; mold and veil coat is done after glass plates are pre-heated to 38C. Prior to that, gelatin mix is lowered from 45C to 38C to avoid thermal shock. Earlier time, I noticed when warm gelatin is applied to the cold plates, it leave unusual trace where liquid touches cold surface (room temp.). And it differ from the rest when both plates made sandwich. Here is one example:

http://www.flickr.com/photos/milan_kara ... 2309329634

Similar effect (even worst) got once when tried Mayer's bar:

http://www.flickr.com/photos/milan_kara ... 309329634/

Liquid is moved from left to right on this picture (toward me, but this glass is rotated 90 deg. clockwise on this picture). This time I made mistake when bar reached scotch tape, then I stopped for a moment, and continue to the end. I think 6 plates are connected together, 3 rows in 2 columns. I did only score on the glass, and wanted to break it later, but I dropped this plate onto desk and it breaks. So, I connected everything back with scotch tape.

My last batch of the plates (recently) did not showed such thermal shock issue - no trace of where gelatin mix is applied. Only the rest is bit wrong.

Help is here if you need it.

Tony

Thank you Tony. I think I can help myself with repeating coat until success. Trial and error is sometimes good teacher.

All what will change this time is filtering method, and will leave to gels on room temperature, then briefly cooling down prior to releasing. Actually, I can split this batch into two, and try half of the plate gel inside fridge (at 5C) and another half at room temperature, then briefly cool down prior to releasing mold. I am so curious about that.

This time will pay attention on drying orientation and will leave emulsion facing up.

Best--

milan--
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