First DCG, Please, Help me find the problem.

This is a forum to share experiences and ideas about holography.
Kiffdino

First DCG, Please, Help me find the problem.

Post by Kiffdino » Sun Sep 05, 2010 1:48 pm

The waterbaths have room temperature. Thats 20°C at the moment.

What do you mean with transition point exactly ?
You mean the temperature at which the plate turns milky ? Or from good to bad ?
Sorry didnt get it.

I still have some heatingpads somewhere ill get them and run some tests.
I will also increase the dichromate percentage because i think that this will improve things.

Dutchelm05

First DCG, Please, Help me find the problem.

Post by Dutchelm05 » Sun Sep 05, 2010 2:06 pm

It looks to me just looking at the photo that you are under fixed and under exposed.
I would fix it until the film goes green then you will most likely be dim (and green)
Then increase exposer until it brightens.
John likes to see a little "burn in" on the hologram meaning when looking through the glass you can see a bit of the image burned in.
Danny uses a piece of black tape and by looking on how black the black is can determine exposure and fix
Although I think the best choice is to walk over to Dave's house and see how a master does it :D
Keep at it, don't be afraid to go extreme on fix and exposer to give you an idea on where you are

Thieu

First DCG, Please, Help me find the problem.

Post by Thieu » Sun Sep 05, 2010 3:55 pm

Indeed, with the transition point I mean the point at which fog/milkiness sets in. If your water baths are at room temperature now, you definitely need to harden and/or expose more. If you do, you'll find that at room temperature you'll get a dim image, but the plate is completely clear. Then you can start to increase the temperature of the water bath one degree at a time. The image will get brighter until milkiness sets in again. It will set in at a higher temperature. Somewhere in between the image will be bright.

From what I read and heard, as I understand it, the theory of DCG is roughly as follows, I use "dissolves" instead of "swells and forms cracks with air voids"" to make it a bit simpler.

Depending on the amount of crosslinking by exposure, the temperature at which the gelatin dissolves varies. If it's exposed a little, it may dissolve at 20C, if it's exposed a lot, maybe it'll dissolve at 40C. What you want is:

1. the gelatin to dissolve in the least exposed parts, the dark parts of the fringes.
2. the gelatin that remains in the bright fringe parts to be more or less rigid, depending on how broadband you want the hologram to be.

In this case, you'd "develop" at 30C and what remains is gelatin with "dissolves at 40C"-degree of hardness.

What's probably the case now, is that your bright fringes are like "dissolve at 22C" and the dark fringes are like d.a. 20C. When you water bath at 20C, you get an image, but the bright fringes are only of d.a. 22C hardness. They are too soft, the structure collapses causing the hologram to become milky.

If you harden more, you'd probably get d.a. 25 in the dark parts and d.a. 30 in the bright parts of a fringe. If you water bath at 27 now, the gelatin will dissolve in the dark parts and the remaining structure at d.a. 30 will be rigid enough to remain up and the hologram will be bright.

Suppose you harden even more, like d.a. 30 and d.a. 50. You can dissolve at 40, but the remaining fringes will be hard. So hard that they don't collapse at all. You will get a hologram in almost the same color as the laser, but dim, because only a small band of your reconstruction light can form an image.

So the trick is to harden just enough to keep the structure up, only letting it collapse just a little to get broadband.

This is kinda how I've come to see what happens in the gelatin, maybe the pro's can correct any flaws.

Dutchelm05

First DCG, Please, Help me find the problem.

Post by Dutchelm05 » Mon Sep 06, 2010 3:19 pm

Interesting approuch Thieu,
I understand the theory and that Fixing hardens the film enough to withstand soaking in water. I have not played around with the interplay between fix time and water temperature.

Is it possible to see this paper you saw this at?

I am not aware of any of the pros using water temperature to tune brightness, rather using fix time and exposure. Sometime they use hot water to reprocess dim holograms which I guess is the same idea. There are no doubt many ways to do this. Perhaps this will work although it seems a little more complicated for my blood.
:)
Good luck to you!!

Joe Farina

First DCG, Please, Help me find the problem.

Post by Joe Farina » Mon Sep 06, 2010 5:17 pm

The temperature of the water which precedes the alcohol has a big effect on final brightness. Warmer water will cause more swelling, colder water less. In DCG, the layer is swollen to a certain size with water, the water is replaced with alcohol, and then it's quickly dried (sometimes called shock-dried). For some reason voids pop up in the softer (unexposed areas). The degree of swelling has a big impact on how effectively the voids will form.

I think Jeff Blyth was the first person to discuss the "yield point" in detail, see the complete description under "processing" at:

http://cabd0.tripod.com/holograms/id4.html

Dutchelm05

First DCG, Please, Help me find the problem.

Post by Dutchelm05 » Mon Sep 06, 2010 7:22 pm

Thanks Joe,
I don't tend to vary my water temperature but perhaps should look into it a bit more.
Hope your enjoying the long weekend

Thieu

First DCG, Please, Help me find the problem.

Post by Thieu » Mon Sep 06, 2010 7:28 pm

Indeed Jeff talks about it in detail, looking through my papers I also found a paper by T. Kubota, T. Ose, M. Sasaki, and K. Honda "Hologram formation with red light in methylene blue sensitized dichromated gelatin" that says:

"...some slight modifications about the processing temperature were made to get optimum
results with good reproducibility.
(1) Wash in running water at 23C for 20 min.
(2) Soak in hot water at 43C for 3 min.
(3) Soak in 70% isopropyl alcohol-30% water mixture for 3 min.
(4) Soak in 100% isopropyl alcohol for 1 min.
(5) Dry in hot air flow for 1 min.
The optimum development temperature in step (2) was found to be about 43C near the gelatin gel melting
point. High diffraction efficiency could not be obtained at temperatures between 20-35° C due to insufficient
swelling of the gelatin layer, while a milky white appearance and deformation-like folds of the
gelatin layer were often observed at higher temperatures than 50C. This fact shows that the development
temperature is a very important factor in producing a good hologram as pointed out by many authors."

Kiffdino

First DCG, Please, Help me find the problem.

Post by Kiffdino » Tue Sep 07, 2010 1:23 pm

Thankyou guys for all this New Information.
I will Coat some New plates and keep postifng hopefully Better results.

Kiffdino

First DCG, Please, Help me find the problem.

Post by Kiffdino » Sat Oct 16, 2010 3:59 pm

Hey guys. Heres an update. Ive been doing lots and lots of testing. Changing pretty much all paremeters.

My Coatings are getting better and I have tried out various Gelatine concetrations.
I had the best results with 14g of Gelatin dissolved in 100ml of Water.
I obeserved that thicker gelatin layers can take higher Kdi concentrations, but the Holograms come out dimmer.
Still shooting green with my cohrent 315m, even though i had to turn the power down to 80% output power because for some reason the laser is unstable at full power.
The ready light at the analog controller goes of all the time an it never stabalizes, thats a new problem. Havent figured out why it does that.
Doing Vail Coating.
I coat first, put them in the fridge after 4 hours drying and sensetize the plates before I shoot.
Kdi Concentration @ 3.75g in 100ml of water.

So these are the last ones i made, everything at room temperature, except the laast alcohol baths is heated to about 30°C.

settle 13 min
Exposure 3 min
dark 5 min
chemical fix 1 min until all yellow gone
2 Waterbaths each 1 min
ISO standard, high diffraction in last bath
hairdryer 5 min
oven 10 min

The plate that has the blue II written in one corner has received an aditional light fixing after the dark reaction.
50 Watt halogen light at 80cm distance for 1 min.

On both plates, cristilization is visible. I didn't have these problems with the thicker coated plates. I'll try to fix that with more soap in the sensetization bath.

Your last comments havent been unnoticed. I tried changing the temperature of the washing bath on a test a week ago. But i didnt control the temperature closely. I just heated it until it felt warm.
The result was a VERY milky plate with enormous noise, hologram was barely visibly but the layer was extremely bright. Maybe if i find a way to fine tune the temperature in the water baths, i will achieve higher brightness levels.
Attachments
P1010153x.jpg
P1010153x.jpg (14.7 KiB) Viewed 2749 times
P1010133x.jpg
P1010133x.jpg (23.02 KiB) Viewed 2749 times
P1010149x.jpg
P1010149x.jpg (5.51 KiB) Viewed 2749 times

Dutchelm05

First DCG, Please, Help me find the problem.

Post by Dutchelm05 » Sun Oct 17, 2010 2:26 pm

Hey great progress Kiff,

As far as your expreiment with warm water.
You'll need more fix time if the gel is to withstand that great of a shrinking during the IPA baths.
The mixture of your IPA % may need to be looked at as well as there temp.
Also consider that if you bloom strenght is low you will have a softer film and therefore more whitening.

I think you are very close to making some nice stuff!

Good luck

Locked