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[quote="Ed Wesly" post_id=72686 time=1649429637 user_id=2186]
The curve in the post above is not exactly the true picture, as it is a graph of [u]relative[/u] sensitivity, not absolute, unlike this curve, from Agfa Technical Information Bulletin 21.7271(688)LI, the rest of the bulletin available here: [url]http://edweslystudio.com/Materials/AgX/Agfa/Holotest217271688.PDF[/url]
[/quote]

Relative to what? Could you define 'relative sensitivity' , as opposed to 'absolute sensitivity'. Generally, plots such as these are normalised to unity, so that the maximum ordinate is, in effect, 1. Thus, if you're measuring intensity from some source, and I₀ is the maximum intensity, the ordinate is in units of I/I₀, making the maximum =1 (when I = I₀). In these cases, the ordinate is relative (normalised) to some constant. However, these curves don't specify any normalisation.

[quote="Ed Wesly" post_id=72686 time=1649429637 user_id=2186]

The absolute sensitivity never falls to zero,
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Not entirely so. The sensitivity of silver halide is mostly in the uv/blue region. Silver halide film for photography/holography is infused with dye(s) to extend the sensitivity into the vis. The basic mechanism is a two-electron excitation process, whereby the dye molecule is excited by the radiation and the excited dye molecule passes an electron into the conduction band of the silver halide. However, because the actinic process whereby the dye gets excited occurs over a limited range, any individual dye has a limited range, so different dyes are used for different areas, such as X-Rays for dental photography. For holography, any given emulsion, with it's concommitant dye has a sensitivity over a limited wavelength range.


[quote="Ed Wesly" post_id=72686 time=1649429637 user_id=2186]

The -2 on the ordinate (vertical axis) could be translated as 100 microJoules/cm^2, and the -3 as 1000 microJoules/cm^2 or 1 full milliJoule/cm^2, since the axis is logarithmic. These figures are again borne out in practice, as 100- 200 microJoules/cm^2 is usually the bracketing point when I make test exposures at red wavelengths.
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The scale actually states "Log S(S = m²/mJ). " Log(-2) = 1/100. So. S = 1/100 m²/mJ, or 100 mJ/m² (not cm²). Translated to μJ/cm², this comes to 10 μJ/cm², since 10⁴ cm² = 1 m²

From "Topics in Applied Physics, vol 20: Holographic recording materials"
[attachment=0]biedermann.jpg[/attachment]

The curve in the post above is not exactly the true picture, as it is a graph of [u]relative[/u] sensitivity, not absolute, unlike this curve, from Agfa Technical Information Bulletin 21.7271(688)LI, the rest of the bulletin available here: [url]http://edweslystudio.com/Materials/AgX/Agfa/Holotest217271688.PDF[/url]

[img][attachment=0]8E75HDSensCurve.jpg[/attachment][/img]

The absolute sensitivity never falls to zero, just varies over the spectrum, with that area that is the borderline between blue and green, cyan, where the 488 nm line of the Argon laser reigns supreme, is where it dips to its lowest value. The guidelines were put in place to show that the difference between the sensitivity at the He-Ne red of 633 nm is about an order of magnitude greater than that at 488 nm, almost 10X, or about 3 or 4 photographic stops, which are binary orders of magnitude, which is borne out in practical experience.

The -2 on the ordinate (vertical axis) could be translated as 100 microJoules/cm^2, and the -3 as 1000 microJoules/cm^2 or 1 full milliJoule/cm^2, since the axis is logarithmic. These figures are again borne out in practice, as 100- 200 microJoules/cm^2 is usually the bracketing point when I make test exposures at red wavelengths.

Comparing the 2 graphs, the shape of the curve is the same, but the numbering of the relative's ordinate, which is also logarithmic, starts at zero, and ascends as powers of 10, and once again it can be seen that the sensitivity difference between the 2 lambdas is an order of magnitude off. The drawback to the relative graph is that it gives an impression of absolutely no sensitivity, but the zero in a log axis is 10^0 = 1, so that dip is used as unity, the standard of comparison, not as an exposure suggestion.

[quote="John W" post_id=72680 time=1647997897 user_id=2211]
Hi Jody

Have you tried exposing the old red sensitive plates to green laser light?

Obviously they don't have the correct dyes to be sensitive to green but given modern green lasers are fairly powerful I wonder if the emulsion would respond anyway?

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John,
I think that the red emulsion would respond to green laser light because the sensitivity never actually goes to zero. But, the sensitivity falls quite a lot. Below, the sensitivity curve for 8e75, and you can see it does fall to zero at 500nm, but still has sensitivity at 514 ( Argon) or 532 (Yag). I also had a quick look at the sensitivity of Slavich's pfg-01; in that film, there's fall of about 2 orders of magnitude for green. So, if Jody is finding a loss of sensitivity to almost 5 orders of magnitude in red film for red lasers, I'd suspect that there's be a further loss of 2 orders of magnitude, or more, when using a green laser. This is assuming that the dyes have not decayed, or there is no dark reaction, in which case the fall in sensitivity may be even more. Therefore a powerful enough green laser would record on a red sensitized film. But, with a fall of several orders of magnitude, you'd need a [i]very [/i] powerful green laser, or, a long exposure, with the associated stability issues.
[attachment=0]getImage.cfm.jpg[/attachment]

Hi Jody

Have you tried exposing the old red sensitive plates to green laser light?

Obviously they don't have the correct dyes to be sensitive to green but given modern green lasers are fairly powerful I wonder if the emulsion would respond anyway?

And a similar thought.... Were you ever to experiment with adding dyes back in to the emulsion... it might be worth thinking about adding green dyes in to a plate that was originally sensitized to red, which would allow you to use the more powerful green lasers with those old red plates.

Petr & Dinesh,
Definitely odd that you had the opposite experience with Agfa materials vis a vis red vs green & thanks for the suggestion re a cheap blue pointer.

Re the blue pointer, I’m old school in the sense that whether or not a plate can be exposed (or not) and turn dark in developer, the only proof to me is if it can record a hologram. I was almost ready to throw out my red sensitive Ilford early in these tests since I was literally getting nothing. It was only after realizing that maybe a comparably MUCH larger exposure might be necessary for the Ilford, based on my prior successful tests in the sequence with the Agfa 10E75, that I finally got a result.

Re your opposite experience red vs green decrease/loss of sensitivity, in my tests with the red sensitive materials, large loss of sensitivity held true, to a greater or lesser degree, across manufacturers, i.e., Agfa, Ilford, HRT BB.

If/when you have time, download the spreadsheet with data about the 24 test plates and open it in Excel on a computer.

Other users of 8E75HD have also told me of a noticeable, if undefined, loss of sensitivity.

Regardless, I agree that storage conditions probably have a significant effect on people’s varying experiences with these legacy materials😊.

[quote=lobaz post_id=72676 time=1647798508 user_id=2217]
Hi Jody,
a few years ago I had exactly the opposite problem: red Agfas (more than 20 years old) worked perfectly, while the green ones were completely dead.

Petr
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Petr's observation makes me think it could be caused by random events. If so, this could be due to double random walk ("drunkard's walk") events. This seems to indicate that dark reaction is (probably) the cause.

Hi Jody,
a few years ago I had exactly the opposite problem: red Agfas (more than 20 years old) worked perfectly, while the green ones were completely dead.

[quote=jrburns47 post_id=72672 time=1647572481 user_id=4407]
You could be correct about trying a blue laser, assuming one has an appropriate blue laser with which to test.
[/quote]

You don't need a SLM one for testing plate sensitivity. A blue pointer for a few USD will be enough.

Petr

[quote=dannybee post_id=72671 time=1647563291 user_id=2167]
thanks Din, so if the dye because age or heat becomes bleached, why not just dye it again there by restoring the dyes ability to transfer energy to the silver? mm nice info :P
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I suppose you could. This was brought up recently. I think you'd have to choose your dye carefully; it must take in the laser wavelength and transfer some of the energy to the silver halide molecule, so the quantum efficiency of the dye at the laser wavelength determines the appropriate sensitivity.

Dinesh,
The point of testing the 660nm laser was that it’s a red laser to expose red sensitive legacy materials. You could be correct about trying a blue laser, assuming one has an appropriate blue laser with which to test. That’s a whole other technical rabbit hole to go down that takes me away from the direction I’m trying to go in - use the red sensitive materials to make good finished display holograms. There’s a sub infinite number of ways to NOT make finished holograms now🤪😂. That’s certainly one of them😊.

Dannybee,
As far as re sensitizing a several decades old gelatin emulsion with fresh red dyes - that sounds like another interesting experimental rabbit hole to go down. Have you tried this yourself? After an interesting email back and forth with Mike Medora (BB plates), it sounds like red dyes are a whole interesting sub genre by themselves. John Wiltshire, co-author of an interesting book about optical display holography with Martin Richardson, turns out to be an expert in silver halide emulsion development for holography. It would be interesting to hear his take on this.

thanks Din, so if the dye because age or heat becomes bleached, why not just dye it again there by restoring the dyes ability to transfer energy to the silver? mm nice info :P