stuck with DCG, always dim or foggy

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

stuck with DCG, always dim or foggy

Post by Thieu »

Hello guys,

Today I've been trying to make holograms on DCG with the casio blue laser diode. I'm monitoring the diode on my spectrograph while doing the exposures. During warm up it sometimes needs a little tweaking with the current to keep it single mode, but after an hour or so it's rock solid. So the laser seems to be ok.

The problem is, I'm still not getting good holograms. I do see the image, but it's always either dim or very foggy, never really good. The plates are mold coated with scotch tape spacers at around 45C with a 10% gelatin mixture. I sensitized them in cold AmDi 1g/100ml. They end up with a film that's seems to absorb about half of the light at 445nm, so that seems to be ok for Denisyuk I think.

I dont have hardener, so I use the lamp fixing method, 100W at 6 inches distance. I did 3 plates today, with 30,60,120 s exposure and 7,15,60s lamp fixing time respectively.

I usually start at a fairly low developing bath temperature and depending on what the result is, I reprocess at a higher temperature. Processing was 50%+99%IPA from spray bottles, so 100% fresh. As expected, the fast rise in IPA concentration gives a very broadband replay, almost white.

I see a progression, in the sense that temperature of the developing bath at which the clear+dim to bright+very foggy switch happens rises with the longer exposures. For the three plates above, the temperatures were 24,28 and 32 C respectively. But that's about it, no progression towards better holograms.

So I'm a bit stuck here, I don't know in which direction to go. Hope you guys can give me some directions which way to proceed or what things to check. Your help is very much appreciated.

Thieu
Joe Farina

stuck with DCG, always dim or foggy

Post by Joe Farina »

Hello Thieu,

Take a look at Dave's post in the gallery section, with the bright DCG hologram made with the 445nm diode.

I haven't done any transmission tests for my DCG plates at 457nm, but 50% absorption seems pretty high to me. In that case, the reference to object ratio could never be better than 2 to 1, and even that would assume the object is a mirror. The actual ratio for nomal objects would be much higher than that. The optimum ratio is 1 to 1. Maybe one of the other 457nm or 445nm holographers like Dave, Tony, or Danny knows what the blue transmission percentage is, for a good result in DCG.

If possible, I would suggest mixing the AmDi into the gelatin, rather than sensitizing after coating. The DCG holographers on this forum who use blue light do it this way. Basically I would follow Dave's exact formula, 2 grams AmDi/16 grams Knox gelatin/100ml deionized (or distilled) water. He exposed for 45 seconds with 20mW of 445nm light. Also, he used the veil method for coating. The coating method shouldn't make a difference, everything else being equal, but maybe your coatings are rather thick, perhaps explaining why the 445nm transmission is low. I suggest using Knox gelatin only because Dave, Tony, Danny, and myself use it, and we will have a better grasp of things if this variable is taken out. If you don't have it, please send me a PM with your address, and I will put some in the mail today.

You're the only person I know who uses spray bottles for processing. It's interesting, but for now I would use baths, because that's the norm, and it would take another variable out.

So, I would suggest using Dave's formula, Knox gelatin, and liquid processing, and see how that goes. As everyone has pointed out, DCG has a long learning curve, with plenty of ups and downs :wink:
Joe Farina

stuck with DCG, always dim or foggy

Post by Joe Farina »

I have checked my notes, and I used 1.5g AmDi/15g Knox gelatin/100ml distilled water for these holograms:

http://www.holographyforum.org/phpBB2/v ... f=4&t=5539
dave battin

stuck with DCG, always dim or foggy

Post by dave battin »

well said Joe ! the only thing i can add here is the coating method i use is a very fast turnaround time, and a thinner coat is also observed. coating/drying/exposing time in is as little as 15 minuets !
Thieu

stuck with DCG, always dim or foggy

Post by Thieu »

Joe Farina wrote:Take a look at Dave's post in the gallery section, with the bright DCG hologram made with the 445nm diode.
Hehe, I did.... still cleaning the floors :drool:

I think there is actually less amdi in my coatings than in both of yours, because the solution I used to sensitize contained only 1g / 100 ml amdi. So assuming that during sensitizing the coating completely saturates with the solution before it dries again, this would mean that it would contain as much as when I would have made it with 1/10/100. Unless the amdi somehow gets attracted to the gelatin but I doubt that. Still visually, just looking at the laser through the plate, I'd say that about half gets absorbed, so maybe they are indeed too thick. I'll see if I can measure a reflection spectrum with the spectrograph to determine their thickness.

I used veil coating in the past, but the perfect coating obtained with mold coating was love at first sight. And since I don't have a real lab but have to use my kitchen and fridge, doing all the messy gelatin stuff without amdi in the coatings is something I'm not keen to give up on. But I'm sure I can adapt both the coating and sensitizing so that I get coatings that are identical to directly loaded veil coated ones.

There must be someone else on this forum who uses spray bottles, because I got the idea from here. It appealed to me because of the 'always freshness' and because I think it also reduces the fire risk. The consumption may be a bit more, but it's not that bad considering some gets lost in setting up the baths as well. But I can go back to baths if needed.

Thanks for your suggestions, I sent you a PM about the gelatin.
Martin

stuck with DCG, always dim or foggy

Post by Martin »

Thieu wrote:There must be someone else on this forum who uses spray bottles, because I got the idea from here.
That's me - see: http://www.holographyforum.org/phpBB2/v ... f=2&t=6553
Using those spray pumps for dehydration does work nicely for thin layers (DCG, FEG or some other gelatin based void generating systems).
Thieu

stuck with DCG, always dim or foggy

Post by Thieu »

Thanks Martin for sharing that method there, it's very convenient for me. I feel a lot more comfortable spraying smalll quantities of flammable liquids over the plates than having several open baths.

In your post you also mentioned using denatured alcohol and acetone instead of IPA. Does it work as well as IPA or would you still consider IPA preferable?
Martin

stuck with DCG, always dim or foggy

Post by Martin »

Thieu wrote:Thanks Martin for sharing that method there, it's very convenient for me. I feel a lot more comfortable spraying smalll quantities of flammable liquids over the plates than having several open baths.

In your post you also mentioned using denatured alcohol and acetone instead of IPA. Does it work as well as IPA or would you still consider IPA preferable?
Meanwhile I completely abandoned acetone. Most of the time I use ethanol (called "Brennsprit" here, which is 96.5% ethanol plus 1% 1-butanol) since its by far the cheapest and safest way to dehydrate the gelatin layer. Contrary to general wisdom to be found in the DCG literature, I was unable to detect any significant difference between isopropanol and ethanol treatment. But maybe this is a "gelatin thing".
Moreover, I usually apply the above solution undiluted, right after the water bath (no 50/50% alcohol or alike).
Thieu

stuck with DCG, always dim or foggy

Post by Thieu »

I read your post and thought, what the heck, I'll try the shock treatment you described with 99% IPA right after the water bath on the holograms I made yesterday that were better than the day before but not so bright either. It caused a *huge* increase in brightness:

The hologram has been processed 20+ times, so it has suffered quite a bit from that. And there's quite some fog. And one of the pegs moved. But no banding and the brightest one so far. I'm happy, thanks!

PS: I'll do some tests with the several varieties of denatured ethanol available here. It would be really great if I can find one that works. IPA has become quite hard to obtain.
dave battin

stuck with DCG, always dim or foggy

Post by dave battin »

Thieu wrote:It would be really great if I can find one that works. IPA has become quite hard to obtain.

Thieu where do you live? i can aquire mine from the pharmacy, you need to request them to bring it in to the store, usually it arrives the next day ............
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