DCG split beam holography.

Dichromated Gelatin.
Grayham
Posts: 40
Joined: Wed Feb 11, 2015 12:56 pm
Location: Hampshire, UK

DCG split beam holography.

Post by Grayham » Sun Oct 30, 2016 5:33 am

Hello

I have a coherent 315 100mw putting out a 100mw. I'm just in the process of setting up my "lab" and wondering which way to go, DCG or Silver.
I intend to make my own plates which ever direction I choose.

The question I have is, is it practical to attempt split beam transmission masters and white light reflections in DCG with just 100mw?
I know you can make some beautiful single beam reflections with 100mw but don't want to limit myself.

I'm thinking if I have to expose for an hour or more then movement is going to be a problem.
Is there a way to make the DCG more sensitive to the green?

Grayham

Grayham
Posts: 40
Joined: Wed Feb 11, 2015 12:56 pm
Location: Hampshire, UK

Re: DCG split beam holography.

Post by Grayham » Sun Oct 30, 2016 11:09 am

I just found this :)

http://holowiki.org/wiki/G307_DCG_Formula

I'm thinking it should do the job :)

Grayham

Din
Posts: 224
Joined: Thu Mar 12, 2015 4:47 pm

Re: DCG split beam holography.

Post by Din » Mon Oct 31, 2016 12:45 pm

In general there are a lot of factors, such as emulsion thickness, softness of film, dcg formula etc. However, as a general rule of thumb, at 532 (I assume the 315 emits at 532), the exposure is about 70 mJ/cm^2. The exact time of exposure depends on the light on your plate, which in turn depends on the size of your plate and your optical paths. But, your exposure for most reasonable shots should be in the 3 - 7 minutes region

Grayham
Posts: 40
Joined: Wed Feb 11, 2015 12:56 pm
Location: Hampshire, UK

Re: DCG split beam holography.

Post by Grayham » Mon Oct 31, 2016 2:58 pm

Din wrote:In general there are a lot of factors, such as emulsion thickness, softness of film, dcg formula etc. However, as a general rule of thumb, at 532 (I assume the 315 emits at 532), the exposure is about 70 mJ/cm^2. The exact time of exposure depends on the light on your plate, which in turn depends on the size of your plate and your optical paths. But, your exposure for most reasonable shots should be in the 3 - 7 minutes region
Hi Din

Are you referring to green sensitised DCG when you say around 70mJ? I've read standard DCG is around 200mJ which I could see as a problem for anything large.

I have read DCG was more sensitive than originally thought to 532nm but I'm unable to test this out just yet.

Grayham

Din
Posts: 224
Joined: Thu Mar 12, 2015 4:47 pm

Re: DCG split beam holography.

Post by Din » Tue Nov 01, 2016 1:11 pm

Hi Grayham, I've inserted the sensitivity curves for dcg. Curve 1 in the lower picture is the sensitivity of dcg before exposure, and the one to use to determine exposure. If you look at the 488 point and the 532 point, you'll see that sensitivity at 532 drops by about 20% odd from the 488 point, or, in other words, at 532 it's about 5 times slower. As a reference, when I shoot 4in x 5in ( 10cm x 12.5cm) in a split beam setup from an 8in x 10in (20cm x 25cm) H1 master, I generally need an exposure of about 1 - 5 minutes. This is based on an exposure of roughly about a 25 mJ/cm^2 exposure. But, this is terribly dependent on how good your H1 is (the weaker the H1, the weaker is the object beam and the longer the exposure), how hard the dcg is and other factors.

DCG doesn't really have an "exposure" as such because you're hardening the emulsion by exposure, or rather, you're increasing the modulation. So, for example, for a HOE, I sometimes go to hundred of mJ/cm^2, which is apparently the number you heard. However, this only applies to HOEs, for display you don't need to go that high.
dcg_sensitiity008.jpg
dcg_sensitiity008.jpg (38.32 KiB) Viewed 2812 times
Edit: This figure is from "Topics in Applied Physics, vol 20. Holographic Recording materials"

BobH
Posts: 338
Joined: Tue Jan 06, 2015 10:26 pm
Location: Mesa, AZ

Re: DCG split beam holography.

Post by BobH » Thu Nov 03, 2016 9:27 am

I wonder why people don't use 364nm. Look at the sensitivity. Same argon ion laser. I'd be interested to see imagery shot in the UV. HOEs are easy at that wavelength, once one is accustomed to working with it.

Din
Posts: 224
Joined: Thu Mar 12, 2015 4:47 pm

Re: DCG split beam holography.

Post by Din » Thu Nov 03, 2016 1:38 pm

BobH wrote:I wonder why people don't use 364nm. Look at the sensitivity. Same argon ion laser. I'd be interested to see imagery shot in the UV. .
Well, for hobbyists uv is probably not easy to get. You need the uv optics in the Argon, which is probably not easy to get and not easy to install. You and Joy could probably do it, but I doubt very many could. Professional imagery? Well, with our processing for display, we start at 488 and end up at about 580 - 590, ie a 100nm upshift. Therefore, assuming all things equal, anything shot at 364, would end up at about 460, This may be a bit too blue for the general public, since you're now talking rod vision, and the scotopic at that wavelength is very low. Another point is that there are no more professional holographers! I honestly think we're the last of the breed still practicing; well us and maybe Jason Sappan. We don't really do display anymore, except when friends and artists want to play. Colin came here last week and spent two days playing here.
BobH wrote:HOEs are easy at that wavelength, once one is accustomed to working with it.
There's the rub! Umpteen watts of invisible coherent light bouncing around gawd-knows-where scares the beejasus out of me. I remember Pierre once told me that he uses a business card to track the beam. Thank god, I've never been asked to shoot in uv!

Grayham
Posts: 40
Joined: Wed Feb 11, 2015 12:56 pm
Location: Hampshire, UK

Re: DCG split beam holography.

Post by Grayham » Fri Nov 04, 2016 4:45 pm

BobH wrote:I wonder why people don't use 364nm. Look at the sensitivity. Same argon ion laser. I'd be interested to see imagery shot in the UV. HOEs are easy at that wavelength, once one is accustomed to working with it.
Availability really. I've been looking at 405nm upwards to about 488nm but it's the cost that holds me back in that region.
I do have an ALC 60X waiting for a refurbish though I'm not sure what it would take to get it good for holography though. An intercavity etalon I think but I don't know how to achieve that just yet.

I have been looking at frequency stabilised laser diodes at around 405nm. $3000 for a diode only, ridiculous.

What I did find was a recipe from Jeff Blythe to increase the sensitivity of 532nm in DCG. Only takes a little glycerine in the mix and I read brings the exposure down to 20-50mJ which is more than doable. I have a 100mw 315@ 532nm so probably best to utilise that until i can get some blue.

I am considering creating an ECDL setup for the blue but have quite a lot to learn on the subject first.

Grayham

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