How do you make Agfa 8E75 T3 HD sensitive to GREEN light

John Sonley · Post by **John Sonley** » Wed Oct 17, 2012 6:55 am

Maybe you can't - but I'd welcome any advice the Forum could give me on the practical steps of how to sensitise red sensitive Agfa film to green/blue laser light. I seem to recall ages ago reading that the reason 8E75 is sensitive to red is that after AgX deposition, it is soaked in a dye that renders the film red sensitive. Can this stuff be washed off and replaced with another dye to render it green sensitive?

holomaker · Post by **holomaker** » Wed Oct 17, 2012 7:14 am

Hi John, if the dye can be removed the film should naturally be sensitive to the green blue region ..............

John Sonley · Post by **John Sonley** » Wed Oct 17, 2012 7:27 am

Any idea how you go about removing the dye - a simple water wash, what temperature - or will something like methanol / ethanol be effective?

holomaker · Post by **holomaker** » Wed Oct 17, 2012 7:44 am

I gave Danny a shout, he'll post im sure as soon as he wakes !

Dinesh · Post by **Dinesh** » Wed Oct 17, 2012 8:09 am

John, the process by which AgX works is that light energy causes a breaking of the ionic bonds that bind the silver to the X. This causes tiny amounts of native silver to be embedded within the larger AgX crystal and the developer "seeks out" those specific crystals that have specks of silver on them and proceeds to convert the entire crystal to native silver.The energy necessary to break the ionic bond roughly corresponds to light in the blue/UV region, therefore the range of natural sensitivity of AgX extends from roughly 350nm, peaks at about 370 or so and falls off at about 460 or so (these are rough figures). So, there's no real green or red sensitivity. In order to make it green and red sensitive, dyes are added that absorb the red and green light. The dye absorbs the red/green light and then re-emits blue light which then causes the ionic breakdown mentioned above. Blue sensitive film also has blue dyes in it to increase blue sensitivity in the blue region. I've written an essay on the subject that you may want to read ( http://www.triple-take.com/publications/grains.pdf ). However, the addition of dyes does not affect the sensitivity of the AgX to parts of the emulsion not "covered" by the dye. So, the red dye in the red sensitive film is not affected by any green dye added to the emulsion; there's no need to wash away the red dye. If you manage to find the right dye, your film will be both red and green sensitivity.

The exact dyes you need are commercially available. Danny has done a lot of work in adding dyes to AgX to alter the sensitivity of red film and he probably can give you a list of appropriate dyes and procedures to introduce the dyes into the film.

dannybee · Post by **dannybee** » Wed Oct 17, 2012 8:18 am

the simplest way is to add a dye I use Rhodamine B, I will try to look for the paper and post it, also hans talk about even a better dye.. il see if I can find that.

John Sonley · Post by **John Sonley** » Thu Oct 18, 2012 1:57 am

I've just read and now printed off copies of the two papers you've attached - very clear and interesting reading.
The Bruza/Padiyar paper certainly gives the detail of how I could move forward - and for Kodak SO-173, I assume I could transpose Agfa 8E75 T3 HD. I wonder how easy it is to get that Sigma Aldrich dye in the UK - and at what price. The concentrations of IPA seem very precise ... I wonder how much tolerance there is and are those % figures v/v or w/v

Danny - I'd like practical details of the rhodamine method, particularly if the chemistry is easier and doesn't use flammable solvents. My holography lab is in a basement without fume cupboard or simple ventilation facilities

Dinesh · Post by **Dinesh** » Thu Oct 18, 2012 7:39 am

John Sonley wrote:I assume I could transpose Agfa 8E75 T3 HD

Yes, you can use the Agfa film. The difference between the two films is in the difference in hardness of the two emulsions which alters the rate of absorption, so you may have to tweak the times and concentrations. Danny did the work for that paper and I correlated his results and wrote them up. I also helped design the experimental protocol. As I remember, Danny used the Kodak because that's all he had on hand. Any red sensitive film would have done.

John Sonley wrote:I wonder how easy it is to get that Sigma Aldrich dye in the UK - and at what price.

I don't know about the UK, but I've been hearing that it's not easy to get anything form Sigma Aldrich here in the US. I believe they want you to have a corporate account. It's probably worth trying to call them and find out. However, these dyes are probably available on Ebay.

Jeffrey Weil · Post by **Jeffrey Weil** » Thu Oct 18, 2012 8:33 am

The classic "need corp account" problem!

It's really not a problem. When those companies ask for a corp account they don't check anything out. They just keep going on the order form.

Next time a company like that asks who you are just make up a company name. Seriously, this will work.

So don't say, I Jeff W need some chem, you say, I from J.W. Holography Inc. need that chem. Problem solved just that easy. Sometimes they will ask for an email or fax on company letterhead......Microsoft office is your friend.

Jeff W

Ed Wesly · Post by **Ed Wesly** » Thu Oct 18, 2012 9:33 am

It is sensitive to green light, just not as much as it is to red. Check out the Agfa brochure at http://nlutie.com/ewesly/AgfaBrochure.PDF

Here is a close up of the curve. It looks like there is almost an order of magnitude difference between 633 nm and 532 nm response for the 8E75HD, like maybe 2 or 3 stops in photographic terms, 4 or 8 times more exposure. For the 10E75 it looks like 2 or 4 times more exposure is necessary for that silly little 100 nanometer difference.

I recently shot 532 exposures on the 10E75, and it worked fine, but it was only gratings. Many moons ago I shot some two beam back lit reflection holograms on 8E75 using 633, 514 and 476 nm beams, and the 8E75HD worked, not really great, but did record all those 3 lambdas. But the 8E75HD failed to make single beam reflections at anything other that the red zone.

So instead of screwing around with re-dyeing the film, just try it with longer exposures at the green!

Methanol is a solvent for the dye in these films.