mbdcg from last weekend

[Joe Farina]

Hopefully i'm beginning to get a toe-hold with mbdcg. I won't mention how long it's taken to get this far (which isn't very far) because it's too embarrassing. Anyway, some details are as follows:

Jeff Blyth's mbdcg, except with boric acid (per Hans) to get the pH down
Age of plate was one week after coating, stored at room temperature
Exposure time 22 minutes, using HeNe with about 20mW incident on the 5 X 5 inch plate
A little post-exposure reducing/hardening with a dilute mixture of sodium metabisulfite and aluminum sulfate (per John Pecora's research)

[MilanKarakas]

WOW! How beautiful golden color!

It looks good to me. Congratulations!

Best--
m

[Joe Farina]

Thank you Milan. By the way, how's the work going with the 450nm diode?

[MilanKarakas]

Thank you Milan. By the way, how's the work going with the 450nm diode?

Well, it working somewhat good. I tried to use very thin glass (0.1 mm cover), and god different issues. On the one hand, it gives me better shape of the spot, but on the second hand, stability is not the best. And I ruined few lenses - too much dust, and attempted to clean it ... scratched and now I have even worst situation.

When changed setup, from 40 mW it rises to some 50 mw, sometimes close to 60 mw, but I am not sure whether it is worth increasing power any more. I tried to use pinhole, but id can't make spot more clear (feedback plate is already in focus, so additional foil can't be exactly at the same place. And I got somewhat better spot, but power drop to maybe 10 - 20 mW, and shows another set of irregularities, so I removed spatial filter. As-is. At least I have working laser with decent coherence length.

Last nigh planed to make another batch of the plates, but spent too much time messing with this laser. Now I am exhausted, and did not sleep past few days... too much things bothers me. And, I still can't sleep, so maybe will make this plates... will see. I don't want to begin work on emulsion and fall asleep, which happened once.

Best,
milan--

[Joe Farina]

Thanks for the update Milan. When using 450nm for DCG, things will begin to fall in place. Of course, the laser needs to be coherent over the length of the exposure, else banded holograms will result. But even banded holograms are ok, since experience can be gained with other parameters of DCG, such as coating and processing. One quick suggestion though. Blue-exposed DCG needs much less dichromate compared to green-exposed. Rallison recommends 3-30-200 for "red" holograms, meaning that he's exposing in the blue (like you will be doing) and after processing, the layer will tend to expand and reconstruct more towards the red end of the spectrum. I have used this formula with 457nm and it works well. (The above ratio is 3 grams dichromate, 30 grams gelatin, and 200ml water.)

[Ed Wesly]

Joe: Maybe you could bring these things with you if you visit my Home and Studio when Hans Bjelkhagen is staying and I have a little get-together on Sunday, January 10th!

[Joe Farina]

Thanks for the invitation, Ed, but i will be stuck in New Buffalo. One of these days, i would like to spend some time at your place, so you can teach me about holography -- lately it seems i know next to nothing.

[Ed Wesly]

Don't kid yourself, you know plenty, and have super clean technique! None of this stuff works for us on even the fifth or sixth time!

[MilanKarakas]

Thanks for the update Milan. When using 450nm for DCG, things will begin to fall in place. Of course, the laser needs to be coherent over the length of the exposure, else banded holograms will result. But even banded holograms are ok, since experience can be gained with other parameters of DCG, such as coating and processing. One quick suggestion though. Blue-exposed DCG needs much less dichromate compared to green-exposed. Rallison recommends 3-30-200 for "red" holograms, meaning that he's exposing in the blue (like you will be doing) and after processing, the layer will tend to expand and reconstruct more towards the red end of the spectrum. I have used this formula with 457nm and it works well. (The above ratio is 3 grams dichromate, 30 grams gelatin, and 200ml water.)

Hello, Joe.

This sounds right to me, 3-30-200, or 100:15:1.5 (somehow I always prefer water first, because utilizing in this order). Someone recommend me using just 6% gelatin, and I tried. No matter what, always got wrong result. Such low concentration of the gelatin has very low viscosity at elevated temperature, and it looks like water when applying to the glass plates. Higher amount of the gelatin behave more like sirupy stuff.

But, now found one plate applied with this low concentration (6%), and emulsion looks pretty clear. All mistake I did during this batch is connecting several plates together by scotch tape, where every plate is slightly tilted differently, and gel mix tend to slide off of the plate. I think one by one plate coat will gives me more consistent result (providing good leveling).

Found one flat aluminum plate (about 5 mm thick) and will try to make TEC heater/cooler for quick heating before Mayer's bar applying, then quick cooling until gels (then moving this plate to drying place, and put new one onto this surface). Just need to build simple temperature controller.

Best--
milan

---

[MilanKarakas]

Of course, the laser needs to be coherent over the length of the exposure, else banded holograms will result.

Yes, that is strange. I am using simple interferometer (two piece of microscope slides), and on one occasion got hologram without bands, and on other banded hologram.

Seems that I can't avoid messing with scanning Fabry-Perot interferometer. While this simple way described above gives me some insight about coherence, it did not answered me to the question whether there is single wavelength or more than one. But, building scanning interferometers means more delay in doing holography.



Best--
milan