I seen this a bunch of times in DCG and wanted to post it but with so few DCGers out there I put it off.
This is a subset of my brigthness fetish.
Sometimes when I remove a plate out of the water bath I will see a fanit hologram image. Not so much to see the object clearly but a rainbow of sorts along with the a dim outline.
I am guessing that the there is a difference between crosslinked and non crosslinked areas that makes an image. As we try to break down the process and isolate the various baths as to which contrube to max brightness I thought I share this and see if anyone else has seen it.
Thanks
Tony
H2O Image
H2O Image
I have not seen this. I'm still at the infant stage, taking baby steps with my DCG attempts, but I have yet to see fringes coming out of the water bath. Always in the 100% IPA, sometimes in the 91%, but never earlier.
World's worst holographer
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Johnfp
H2O Image
I have seen this with most holograms that have a little too much burn in or have exactly enough burn in. Some of my brightest hologram have burn in. Some may say it detracts from the hologram but I disagree as you can only see the burn in when you are out of the viewing window. When you are within the viewing window the burn in is not evident.
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Tony
H2O Image
Thanks guys.
So John you think it might be more of an indicator of exposure? Or a combo of exposure and fix?
js this is not neccessarly an indicator of a good hologram but it is important to try to observe what is happening during your processes. There are small clues out there. Freaks of nature where a hologram is exceptional. Any clues that led up to that is pretty valuable as well was when the process goes completely south, There are plenty of those too.
I haven't looked if there is any going on after fixing, the transistion between fix and water is pretty fast. I will have to look some time.
Later guys
Tony
So John you think it might be more of an indicator of exposure? Or a combo of exposure and fix?
js this is not neccessarly an indicator of a good hologram but it is important to try to observe what is happening during your processes. There are small clues out there. Freaks of nature where a hologram is exceptional. Any clues that led up to that is pretty valuable as well was when the process goes completely south, There are plenty of those too.
I haven't looked if there is any going on after fixing, the transistion between fix and water is pretty fast. I will have to look some time.
Later guys
Tony
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Johnfp
H2O Image
Indicies of refraction
1.0 = Air
1.33 = Water
1.38 = Gelatin
1.5 = Crosslinked Gelatin
So, we have a DCG layer that has an approximate Index of refraction of 1.38 (gelatin).
We get some crosslinking in the exposed areas of about 1.5
We finish crosslinking in the exposed areas to get most of the gelatin at the 1.5 from fixing.
Then we swell the hologram in water which lowers the uncrosslinked somewhere in between 1.38 (glatin) and 1.33 (water).
Continuing past the scope of this discussion, we process the hologram in alcohol and air dry such that we replace the water in the uncrosslinked areas with air which has an index of refraction of 1.0.
So we can see, uncrosslinked (1.38) to crosslinked after exposure (1.5) but remembering not all gel is crosslkinked in the exposed areas, some of the Cr is in the IV state wating for the fixing to do more crosslinking. So lets say 33% of the gelatin is crosslinked in the exposed areas (This still may be too high) we get (1.5 - 1.38 = .12 .12 x .20 (20%) = .024 .024 + 1.38 = 1.4) So after exposure we may only have a differential of index of refraction of 1.38 and 1.4 which is .02
Now we fix and that 33% crosslinked may come up to 80%. Using the same methodology we now may have a differential of index of refraction of .1 (1.38 and 1.48)
Water swelling now takes the uncrosslinked down a bit, lets go on to say it swells nicely at 75%. (1.38 - 1.33 = .05 .05 x .8 = .04 1.38 - .04 = 1.34) So our differential is now 1.34 and 1.48
Now lets say after drying we have 75% air voids in the uncrosslinked areas (1.38 - 1 (air) = .38 .38 x .8 (80%) = .30 1.38 - .30 = 1.08)
So after exposure 1.38 (uncrossed) and 1.40 (crossed)
After fixing 1.38 (uncrossed) and 1.48 (crossed)
After water 1.34 (uncrossed) and 1.48 (crossed)
After drying 1.08 (uncrossed) and 1.48 (crossed)
Now of course these are hypothetical numbers and I am sure there is some loss in the crosslinked areas and some air in those sections also but it does provide us with a map of what is going on.
So I never really thought about this with numbers but it seems replacing the air in the gelatin is more important that the crosslinking alone. Which makes sense why you really do not need to see a hologram until most of the water is replaced with air.
Back to the question at hand. I doubt you will see any fringe structure after exposure unless you really get a lot of crosslinking during that time.
You may see some fringe structure in that water after fixing if you get a lot of crosslinking in the fixer.
So you want to get that just a little bit brighter hologram, Do the final alcohols and air drying in a Helium environment. Then seal it while in the Helium environment. LOL!
That was a fun exercise, thanks Tony. Hope all is well.
Peace,
John
1.0 = Air
1.33 = Water
1.38 = Gelatin
1.5 = Crosslinked Gelatin
So, we have a DCG layer that has an approximate Index of refraction of 1.38 (gelatin).
We get some crosslinking in the exposed areas of about 1.5
We finish crosslinking in the exposed areas to get most of the gelatin at the 1.5 from fixing.
Then we swell the hologram in water which lowers the uncrosslinked somewhere in between 1.38 (glatin) and 1.33 (water).
Continuing past the scope of this discussion, we process the hologram in alcohol and air dry such that we replace the water in the uncrosslinked areas with air which has an index of refraction of 1.0.
So we can see, uncrosslinked (1.38) to crosslinked after exposure (1.5) but remembering not all gel is crosslkinked in the exposed areas, some of the Cr is in the IV state wating for the fixing to do more crosslinking. So lets say 33% of the gelatin is crosslinked in the exposed areas (This still may be too high) we get (1.5 - 1.38 = .12 .12 x .20 (20%) = .024 .024 + 1.38 = 1.4) So after exposure we may only have a differential of index of refraction of 1.38 and 1.4 which is .02
Now we fix and that 33% crosslinked may come up to 80%. Using the same methodology we now may have a differential of index of refraction of .1 (1.38 and 1.48)
Water swelling now takes the uncrosslinked down a bit, lets go on to say it swells nicely at 75%. (1.38 - 1.33 = .05 .05 x .8 = .04 1.38 - .04 = 1.34) So our differential is now 1.34 and 1.48
Now lets say after drying we have 75% air voids in the uncrosslinked areas (1.38 - 1 (air) = .38 .38 x .8 (80%) = .30 1.38 - .30 = 1.08)
So after exposure 1.38 (uncrossed) and 1.40 (crossed)
After fixing 1.38 (uncrossed) and 1.48 (crossed)
After water 1.34 (uncrossed) and 1.48 (crossed)
After drying 1.08 (uncrossed) and 1.48 (crossed)
Now of course these are hypothetical numbers and I am sure there is some loss in the crosslinked areas and some air in those sections also but it does provide us with a map of what is going on.
So I never really thought about this with numbers but it seems replacing the air in the gelatin is more important that the crosslinking alone. Which makes sense why you really do not need to see a hologram until most of the water is replaced with air.
Back to the question at hand. I doubt you will see any fringe structure after exposure unless you really get a lot of crosslinking during that time.
You may see some fringe structure in that water after fixing if you get a lot of crosslinking in the fixer.
So you want to get that just a little bit brighter hologram, Do the final alcohols and air drying in a Helium environment. Then seal it while in the Helium environment. LOL!
That was a fun exercise, thanks Tony. Hope all is well.
Peace,
John
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Joe Farina
- Posts: 805
- Joined: Wed Jan 07, 2015 2:10 pm
H2O Image
DCG can have real-time effects with no development. Maybe 1% diffraction efficiency or more. See:
Real-time holography with undeveloped dichromated gelatin films, Calixto and Lessard, Applied Optics Vol. 23, No. 12 (1984)
Diffraction efficiency improvement of undeveloped dichromated gelatin gratings, Calixto et al., Applied Optics Vol. 24, No. 3 (1985)
Holograms in dichromated gelatin: real time effects, Newell et al., Applied Optics Vol. 24 No. 24 (1985)
Observation of a fast-formed absorption grating and a slowly formed phase grating in undeveloped dichromated gelatin, Lee et al., Applied Optics Vol. 40, No. 22 (2001)
In the Newell paper they say (p. 4465-6) "....when the recorded absorption gratings were stored in an atmosphere of higher relative humidity (RH = 50-60%), a phase grating with an efficiency of up to 15% appeared in the course of a few hours."
Real-time holography with undeveloped dichromated gelatin films, Calixto and Lessard, Applied Optics Vol. 23, No. 12 (1984)
Diffraction efficiency improvement of undeveloped dichromated gelatin gratings, Calixto et al., Applied Optics Vol. 24, No. 3 (1985)
Holograms in dichromated gelatin: real time effects, Newell et al., Applied Optics Vol. 24 No. 24 (1985)
Observation of a fast-formed absorption grating and a slowly formed phase grating in undeveloped dichromated gelatin, Lee et al., Applied Optics Vol. 40, No. 22 (2001)
In the Newell paper they say (p. 4465-6) "....when the recorded absorption gratings were stored in an atmosphere of higher relative humidity (RH = 50-60%), a phase grating with an efficiency of up to 15% appeared in the course of a few hours."
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Martin
H2O Image
I guess your 1.38 might qualify for wet gelatin.Johnfp wrote:Indicies of refraction
1.0 = Air
1.33 = Water
1.38 = Gelatin
1.5 = Crosslinked Gelatin
In a 1977 paper Meyerhofer quotes Shankoff with the following figures:
Material................................................................................Refractive Index
1) Gelatin.............................................................................1.5426
2) Gelatin + ammonium dichromate....................................1.5486
3) Gelatin + am. dich. exposed...........................................1.5572
4) Gelatin + am. dich. exposed, developend in IPA............1.5515
5) Gelatin + am. dich. unexposed, developed in IPA .........1.5488
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Dinesh
H2O Image
What you're probably seeing is a surface relief effect caused by the latent image.
In all holograms, there is always an initial latent image that forms after exposure and before processing that's about 1% efficient. The point of processing is to amplify the latent image. Also, every wet processed hologram is a combination of a surface relief hologram and a volume hologram - a combination of Raman-Nath diffraction and Bragg diffraction, no matter what the geometry. In a volume geometry with a volume material the volume effects predominate after processing is complete if the emulsion is thick enough. If not, then the surface effects will predominate. The exact thickness at which this occurs is a little vague, but there is a number, known as the Q number, whose value determines when the volume effects are stronger than the surface effects; Q > 10 is the "break point".
So, while processing, the latent image causes a surface relief grating to appear very early in the processing stage which predominates over the volume grating, hence a faint image but a clear rainbow. As the processing progresses, the volume effects - the Bragg effects - start to predominate.
In all holograms, there is always an initial latent image that forms after exposure and before processing that's about 1% efficient. The point of processing is to amplify the latent image. Also, every wet processed hologram is a combination of a surface relief hologram and a volume hologram - a combination of Raman-Nath diffraction and Bragg diffraction, no matter what the geometry. In a volume geometry with a volume material the volume effects predominate after processing is complete if the emulsion is thick enough. If not, then the surface effects will predominate. The exact thickness at which this occurs is a little vague, but there is a number, known as the Q number, whose value determines when the volume effects are stronger than the surface effects; Q > 10 is the "break point".
So, while processing, the latent image causes a surface relief grating to appear very early in the processing stage which predominates over the volume grating, hence a faint image but a clear rainbow. As the processing progresses, the volume effects - the Bragg effects - start to predominate.