Very Sexy 3 color DCG

[Johnfp]

Right now, I'm being asked to take dcg to it's limits in colour control - well beyond the visible - can I use this technique?

Actually in thinking about this you could use a second wavelength to control your shift as that will tell you what the one is that you can't see.

So lets say you shoot with 457 and 514. You process your hologram with a shink of about 17%. That process makes 514 to be about 427nm which you can see and measure. This will give your 457 shrink to 379 in the non visible.

If you shoot with lets say 532 and 442 then you can get the 442 even further in the UV while still seeing the 532 shinkage.

You could use your longer wavelength as a control as a small circle up in the corner of your hologram such that it does not interfere with the "main" non visible hologram.

I guess you should use the same technique into the enfrared but you would need something like a ruby laser and possibly one of those "yellow" lasers and make the DCG red sensitive. But that is just a thought, I have no experience with red sensitive DCG, although I may be trying it soon.

[Dinesh]

So lets say you shoot with 457 and 514. You process your hologram with a shink of about 17%. That process makes 514 to be about 427nm which you can see and measure. This will give your 457 shrink to 379 in the non visible.

Actually, dcg doesn't shrink, it expands. I've got countless spectrophotometer plots demonstrating this! I wish it would shrink, it'd make life so much easier for me! Note also the fact that a dcg display hologram shot with 488 replays at orange (for us, the way we process). This means that fringes recorded at 488/2 have ended up at around 590/2, or, in other words, the replay has red shifted - expansion - from the recording wavelength. Silver halide shrinks, so a hologram recorded with a 633 (red) laser replays at orange or green, ie the replay is blue-shifted from the recording wavelength. This is because you've removed silver from the gelatin matrix, causing "holes" in the gelatin matrix and so a collapse of the matrix. The actinic reaction in silver affects something - the grains - inside the gelatin matrix. In dcg, the actinic reaction affects the gelatin matrix itself.

The point I have a problem with is this figure of 17% (or any percentage, for that matter). For example, your blue, which I judge to be about 470 seems to have become green, which I judge to be about 520. Naively, this seems to be an expansion of (520 - 470)/470 = 10%. However, the bandwidth of the blue has to be different to the bandwidth of the green. So, which figures do you use to calculate the swell factor? The arithmetical average? A weighted average? Three percentage figures for the extremes and the center frequency? The FWHM? There are many possible figures you can use, so a statement that the film "swells (not shrinks) by m%" has to be carefully justified.

I guess you should use the same technique into the enfrared but you would need something like a ruby laser and possibly one of those "yellow" lasers and make the DCG red sensitive. But that is just a thought, I have no experience with red sensitive DCG, although I may be trying it soon

Thanks for the suggestion, but no need. I have a different technique. I just shot a hologram in dcg at 700nm yesterday using 514 for recording. IR is relatively easy, but UV is the problem. Hence my earlier remark that if dcg did shrink, life would be golden!

Actually in thinking about this you could use a second wavelength to control your shift as that will tell you what the one is that you can't see.

This is an interesting technique for different reasons. I'm presently working on a theory of aberrations in focused holograms. That is, if you record a hologram to focus light at some specific position in dcg ( a simple converging lens), after processing it focuses at another point. What other point? Is the other point wavelength dependent? I have a vague mathematical structure for this work, but no way to experimentally justify the math. Your technique may give me a way to test the equations experimentally.

[Tony]

I just shot a hologram in dcg at 700nm yesterday using 514 for recording. IR is relatively easy, but UV is the problem

A little confused I thought it was easier to go blue than red? Can you elaborate a bit Dinesh?

John this is fasinating stuff, I hope to try it one day and will hopefully pick your brain. A long list of wanta trys, can't wait untl I retire Or should I say when my wife let's me retire

Can you talk about post exposure processing a bit? Did you alter your IPA baths or fix times?

[Johnfp]

Yes, I could go bluer with reprocessing.

Well, I would have to look back in my notes which are burried somewhere in plastic tubs after the move out of the garage lab but...

I shot with 514 to get a orange/red that looked close to the color I wanted from the color triangle. I believe I used 35, 50, 70, 90 and 100 % alcohols. All were room temp ( maybe 75 F) except the last bath which was heated (prob about 90 F.) Fixer was room temp. The rincse water was luke warm and was about same temp as room temp.

I tweeked the replay wavelegth and bandwidth by exposure time and did not try to compensate with chemical processing. A longer exposure gave me a shift toward the red and made the hologram more narrow band.

I will try to find my notes when I get a chance and let you know. Hopefully I was accurate with them.

The thing is, it is almost impossible to duplicate someone elses work unless every single variable is taken into consideration with DCG. So really, I can give exacts but your results may varry. I am sure you can get a nice orangish/red hologram with 532. So just add the second wavelength and process the same as the orangish/red for 532.

[Tony]

The thing is, it is almost impossible to duplicate someone elses work unless every single variable is taken into consideration with DCG. So really, I can give exacts but your results may varry. I am sure you can get a nice orangish/red hologram with 532. So just add the second wavelength and process the same as the orangish/red for 532.

Right I understand, I would be using 532 and 457nm so my color range would be limited. I know Dinesh and Dave use other techneques in shifting color using swelling as well.

I would not be all that intested in duplicating the object exactly what is useful for me is the fact that there is a color diference which adds interest to the piece.

Thanks John for posting this and thanks for being a good sport in addressing many of the slings and arrows. I think in most cases it is a heathy thing and makes for good reading. Funny how days worth of posting could be resolved in a 5 minute face to face conversation

[Dinesh]

I just shot a hologram in dcg at 700nm yesterday using 514 for recording. IR is relatively easy, but UV is the problem

A little confused I thought it was easier to go blue than red? Can you elaborate a bit Dinesh?

Yes, it's easier to go blue than red, if you shoot in blue to begin with.. If you shoot in blue-green (488) you'll get orange. Start with green (514) and you'll get yellow. The final image always shifts to longer wavelengths. You can mitigate this by being careful with processing, so shooting at 488 can give you a green at about 500, but not below. Really careful processing will not cause a shift at all and the image reconstructs at around the same wavelength as you recorded it with.

For display holograms, if you shoot in silver halide, you can shoot the hologram with any laser from HeNe (633) to HeCd (440 odd) with appropriate dyes in the emulsion. However, whatever wavelength you shoot at, you will either get an image of the same wavelength as the recording wavelength, or you'll get a wavelength that's shorter. So, shooting in silver halide with a HeNe will produce an image that's either red or it's orange or even green, depending on processing, while shooting in silver halide with an argon set to 514 will produce a green image or a green-blue image. Notice the replay wavelength always shifts to the blue end, if it shifts at all. It's true that there are swelling techniques that will enable you to shoot in green with an argon and shift the image to red, or to shoot the image in red and shift the image to infrared, but that's not easy to do and not easy to maintain. Generally, with silver halide, there's a shift of the image to lower (bluer) wavelengths. The whole technique of pseudo-colour enhances this blue shift by exacerbating the blue shift. So, to get green using a HeNe, you could preswell with TEA (for example), or you could throw in some sodium sulphite in the developer.

However, if you shoot in dcg, the shift goes the opposite way. If you shoot a dcg with an argon set to 514, the image will end up in the yellow-orange region, a shift to longer wavelengths. You will not get a blue image if you shoot in green, as you would have done with silver. If you shoot in deep blue, with an argon set to 457 or HeCd at 442, then the image comes up in a longer blue, green or orange, again a shift to longer wavelengths (however note xomment above about really careful processing). There is a common error i which areas of the image or emulsion turns a vibrant blue, known commonly as 'blue-ies'. These are caused by errors in coating and cannot be controlled. Well, maybe they can if you really put your mind to it, but it ain't going to be easy! In a similar vein, there are also areas where the emulsion goes a milky white - 'whit-ies', also caused by errors in coating.

The reason for all this is that when you shoot in silver, you're altering a specific set of elements in the gelatin matrix - the grains. I wrote up something about how the actual actinic reaction goes when you hit silver with light and I think Colin put it up in some knowledge base. Basically, the grains are tiny elements that go from white to black, but the gelatin itself is not affected (actually, it is slightly, but that's another matter). So, when you process, you remove some of the grains - or make them smaller than they originally were - leaving behind 'holes' in the gelatin. The forces within the gelatin then cause a collapse of the gelatin and so shifts the Bragg structure towards the lower wavelengths. The result is a blue shift.

In dcg, the whole gelatin matrix is affected. The entire mass of gelatin alters as a result of the light, not specific elements within the gelatin. Now, processing this, you first swell the gelatin by putting it in water. This gelatin expansion causes the Bragg structure to expand and so you shift to longer wavelengths - a large redshift. As you put it in the various alcohols, you remove some of the water, but not all of it. This then causes a shrinkage and so mitigates the redshift caused by the water expansion, but the emulsion never quite shrinks all the way back to the latent image. In the end, there's an overall redshift towards the longer wavelength.

[Johnfp]

Well, without readin DInesh's post after your first.

I would not be all that intested in duplicating the object exactly what is useful for me is the fact that there is a color diference which adds interest to the piece.

Agreed!!!

I knew I could never get the reds, greens, blues, yellow and whites had the model had them. But I think that hologram is more "interesting" as you say, then the same hologram that was just gold.

532 and 457 are 76nm apart. A very nice spread. So if you got your 532 to come out about 590 - 600nm, that would put your 457 at about 515 - 525. A nice reddish and greenish. And dont forget the yellow you would get.

[Dinesh]

So if you got your 532 to come out about 590 - 600nm, that would put your 457 at about 515 - 525.

Not so. The swell factor is a percentage increase from the present point, not simply an arithmetical addition. So, a swell factor from 532 to 595 indicates (595-532)/532= 0.11, or roughly an 11% swell factor. From 457 a swell factor of 11% would put you at 507. The important fact is that you can't simply arithmetically add the amount of swell and assume that all wavelengths will add by the same arithmetical amount.

More important are the factors of index modulation and spatial frequency. If the index modulation is very high, the bandwidth will increase and so will the centre frequencies, but not proportionately. So there will be a shift of the centre frequency wrt to the bandwidth.

In all of these statements, the importance of bandwidth has not been taken into account. Any shift caused by emulsion manipulation must take the bandwidth of the initial "colour" and the bandwidth of the final "colour" into account.

What I think needs to be said is that John has an interesting technique for adding colour to the hologram. Though, I don't know if you realise this, John, but Fred Unterseher was doing this sort of thing in the late 60s/early 70s. When I showed Fred some colour dcg holograms I made around 1998 he showed me some he'd made. Except, he used two or three lasers and I used just one. But, it's a display technique pertaining to those who wish to make images. It's effectively an algorithm for creating certain colour combinations. By throwing in these mathematical relationships, I think the waters are simply being muddied, because once you throw in mathematical relationships consisting of precise wavelengths and percentages, it gives the impression of mathematical accuracy. However, there is no accuracy unless the physical phenomena is properly modeled. The apparent profundity is lost to the inaccuracies of the model. The relationships pertaining to specific swelling of a dcg emulsion must take into account the fringe density, the index modulation, the frequency spread and other factors. It's a fairly complex system.

[Martin]

However, whatever wavelength you shoot at, you will either get an image of the same wavelength as the recording wavelength, or you'll get a wavelength that's shorter. So, shooting in silver halide with a HeNe will produce an image that's either red or it's orange or even green, depending on processing, while shooting in silver halide with an argon set to 514 will produce a green image or a green-blue image. Notice the replay wavelength always shifts to the blue end, if it shifts at all.

You can actually produce a wavelength shift towards red with AgX also. There are some bleaches that effect a "red" shift. E.g. copper sulfate bleaches may do that (maybe by some 20-30nm). And when you form a rehalogenating bleach with iodide instead of bromide, you usually effect a shift as well. Moreover, with certain emulsions (PFG-03 would come to mind) you can get large shifts by drying the layer in alcohol a la DCG.

[Johnfp]

I can't win. I give percentages and that’s wrong. I give a rough number as I didn’t have time to site down and work out real numbers and I am off by like what??? 10 - 15 nm and i get reamed... Thank you Dinesh for continually keeping me straight. Don't know what I would do without you.

Just for the record, I am not some scientist working in a sophisticated lab being paid for my work. For cryin out loud, I have a hollow steel door with rocks on it for my table. I'm in a third world basement. All my stuff is made from things I can put my hands on. I have a limited budget. I am an amateur holographer who likes to play and experiment with new stuff. That's all. But I do get things done. I don’t have a doctorates degree in math or physics. I have some college math and physics, enough to try to get my thoughts across but not enough to be paid as a physicist.

I really don't need to have every single little detail gone over with a fine tooth comb to say I am off by a few nm.

Dinesh, do you critique me while being paid by someone to do research, or is that your fun downtime?

No wonder no one posts anything new here. Probably afraid of being picked to pieces by the master.

It's a shame Dinesh didn't build Tony up instead, and offer some real practicle pointers and encourage him.

So from now on, when I post I will be sure not to include any numbers, percentages, mathematical relationships or precise wavelengths. NOT!

Dinesh, you do know this is a public amateur holography forum that consists of mainly amateurs. It's not a Havard physics/math discussion forum.

Increadable.

ROTFLMFAO!!!