im trying to get caught up in info--dichromates- leds-laser diodes April 27 2003 at 3:01 PM
Danny Bruza (no login)
ok first q
1 most of them show (dichromate)sensitivty at uv-512
what about (532)?
2 ther are some leds that are (strong) uv,being leds would they have any coherence? and has any one use led diodes to do holograms?
3 mabe if you plused the diodes (leds) to get a single plused wave?
Re: im trying to get caught up in info--dichromates- leds-laser diodes
April 27 2003, 9:21 PM
"1 most of them show (dichromate)sensitivty at uv-512
what about (532)?"
I made a 1 cm2 DCG with a100mW DPSS. I had to expose for ~ 30 sec.
2 ther are some leds that are (strong) uv,being leds would they have any coherence? and has any one use led diodes to do holograms?
A couple of years ago I made a - dim - transmission grating (contact copy) with a filtered red LED.
3 mabe if you plused the diodes (leds) to get a single plused wave?
Probably not.
I'm going to try to put up a graph of DCG sensitivity. The graph is from "Topics in Applied Physics vol 20 - Holographic Recording Materials":
Only half the picture seems to show in the preview. If that's all you see, the 532 sensitivity is right at the bottom, in line with the 'T' of the word 'Transmission' on the vertical axis.
Anyway, graph 1 is before exposure, the others are absorbtion curves after exposure and after development. Graph 1 is the one to note. As you can see, the sensitivity at 532 is almost non-existant. As far as I know, dyes do not transfer up, ie, you can't go from 532nm up towards blue. I might suggest using SHSG techniques. Hans gave a talk at SPIE last year where he claimed very high efficencies. I have all the papers on SHSg but there are about 8 pages of the stuff! Too many to post. If you want I can mail them or fax them.
"It has been found that by substituting the dye eosin Y for methylene blue one can produce bright green reflection holograms at an exposure level of ~50 mJ/cm2 of 514-nm light." have you tryed this
No, I've never tried shooting DCG with dyes added. I assume this quote is for DCG's. Also, what does .."at an exposure level of 50 mJ/sq cm" mean? Either it means that the sensitivity is 50 mJ/sq cm or that you have to compensate for the weaker sensitivity of the dye to get an exposure that you would have gotten by exposing at 514 with 50 mJ/sq cm.. If so, what is this compensating factor? If not, then adding the dye seems to have increased the sensitvity, which seems funny. I've never tried any dyes, but it seems that adding a dye should decrease sensitivity, not increase it. As can be seen from the curve, the sensitivity at 532 is about 1/5th of that at 514. Since the sensitivity at 514 is about 100 mJ/sq cm (less for display, more for HOE's), the sensitivity for 532 should be about 500 mJ/sq cm. So either this figure of 50 is a typo, or you need a compensating factor, or the dye actually increase sensitivity, which I find hard to believe since dyes are not particularly efficent at transferring energy.
The advantage of DCG for display is the extreme brightness. However, unless you can get this brightness with 532+dye, it seems better to go with Silver. You might try exposing on Silver (both Slavich VRP and Colourholographics have 532 sensitive materials) and then converting to DCG using SHSG. This is where you convert the Silver grains to dichromate and then develop it just like a DCG hologram. You end up with the best of both world!
I am still working on this. Here is some information from my web page.
SHSG for PFG-03C and PFG-03M
from: Transmission and Reflection SHSG Holograms - Kim, Choi, Choi, Kim, Kim, Bjelkhagen, Phillips - SPIE
and SHSG processing for three-wavelength HOEs recording in Silver Halide Materials - Kim, Choi, Bjelkhagen, Philips - SPIE
I have made some assumptions about their process. Please read the source if you are serious about this process.
Prehardening 6 min
Develop G282C Diluted 1 to 3 to 1 to 5 3 min
Rinse Running Deionized Water at least 3 Min
Stop
Wash?
Bleach (diluted 1:3) 15 min
Warm water bath (60C) 10 min
Wash?
Dehydrate 50% IMS 3 min
100% IMS 3 min
Dry in 45C oven 5 min
Vapor harden with Formaldehyde 25 min
or 50% glutaraldehyde vapor 25min
Fix 2 Min
Wash
Dehydrate 50% Isopropyl 10 min
100% 10 min
100% 70C 2min
Dry in 45C oven.
This is the available developer for millimask plates in the US. I think the D8 is the replacement for g282c but I need to call and ask again.
I talked to Hans about this and he suggested that it would require adjusting all of the rest of the process to change developers. Of course he is looking for the highest efficiency possible for HOE work and the difference between 92 and 97% efficiency probably won't matter much to a art holographer.
I used AAC using Hans' first paper on transmission holographyand started with gratings. I got an efficency of about 10%. I haven't worked on his second (reflection) paper yet.
"Since the sensitivity at 514 is about 100 mJ/sq cm (less for display, more for HOE's),
the sensitivity for 532 should be about 500 mJ/sq cm. So either this figure of 50 is a
typo, or you need a compensating factor, or the dye actually increase sensitivity, which I
find hard to believe since dyes are not particularly efficent at transferring energy."
Compared to traditional "pure" DCG technology at 514nm, yes, the dye seems to increase
sensitivity (actually, it is based on a dye and an electron donor). Thinking of the red
sensitive MB-DCG system, I guess it might rival DCG, exposed at 514 nm . Remember what Jean
Dufrasne reported here at this forum. If I am not misled he mentioned 5 min. exposure for
a 4 x 5" with a 50 mW diode at 650 nm.
Besides SHSG there is yet another silver halide/DCG hybrid:
Mazakova et al. bathed gelatin layers in weak AgNO3 and KBr solutions in order to form
very small silver halides. The emulsions were then sensitized in an ammonium dichromate
solution to which a spectral sensitizer had been added. "If small quantities of silver
halide are present in the layer, besides the photoinduced dichromate reduction on
exposure, silver halide photolysis takes place. If the resulting photolytic silver is
oxidized by the dichromate, leaving Cr3, this could lead to more effective reduction and
hence to better hardening of the illuminated areas of the light-sensitive layer. This
process can be further stimulated by the presence of an optical sensitizer. (...) Thus the
presence of silver halide catalyzes the reduction of the dichromate and makes possible an
increase in the light sensitivity of the dichromated gelatin. The silver halide crystals
must be superfine and in a quantity such as not to deteriorate by scattering the contrast
of the recorded interference pattern or the signal-to-noise ratio of the reconstructed
image." (Mazakova, Pancheva, Kandilarov, Sharlandjiev, "Dichromated gelatin for volume
holographic recording with high sensitivity. Part I", Optical and Quantum Electronics 14,
1982, p. 311-312. Apropos, thank you, Joe Farina, for sending me that paper!). The
Bulgarian research group reported a 10x increase in speed.
Yes, you're right. My holo-Coins was shoot at 650nm for 5 min. exposure.
It's probably true that dye increases natural sensitivity of DCG. In fact, even pure DCG has sensitivity to 'red light' but very low and requires high power.
Thank you for the info about Mazakova paper. Looks interesting! (once again, something to try )
Thanks for the Mazakova paper. As I read this, I thought, "I thought of that 10 years ago!" But when I read the date, I realised that I only thought of it about 1997 and did nothing about it. I did not realise work was being done in this direction.
Can you point me to a source on how dyes in holography actually work? You mention "electron donor". I thought that dyes absorbed at one wavelength and emitted at another, a fluorescent effect. But unless there's some kind of Raman effect going on (in which case the sensitivity would be bl*o*ody low!), the dye cannot transfer energy 'up'. However, as you say, a dye will make DCG red sensitive. Presumably the dye does not absorb red and re-emit blue which then causes the photolytic reduction of the dichromate.
"Can you point me to a source on how dyes in holography actually work? You mention "electron donor". I thought that dyes absorbed at one wavelength and emitted at another, a fluorescent effect."
In my point of view the dye absorb the photon energy gets in the excited state and, on dependence of your oxi-reduction potential can donate or receive an electron via triplet state to another molecule (dye oxidation) or receive an electron from an electron donor (cause reduction), this is the natural mechanism of electron transfer encountered in photosyntesis and silver halide photography.
If the dye has a high "trap" triplet effect, the dye does not fluoresce efficiently but can donate a electron efficiently, this is why MB sensitized dichromate gelatin works so well. In polymer science, dye sensitization works well with couple agents that donate electrons for the dye and your oxidized state (co-initiator) generates radicals that initiate polymerization, this mechanism is used in DuPont photopolymer and other materials.
But unless there's some kind of Raman effect going on (in which case the sensitivity would be bl*o*ody low!), the dye cannot transfer energy 'up'."
Yes, more efficiency is obtained with a trigger system in that photon energy starts an electron transference from or to other potentially favourable substance. Direct energy transfer is less favourable to do "something".
"However, as you say, a dye will make DCG red sensitive. Presumably the dye does not absorb red and re-emit blue which then causes the photolytic reduction of the dichromate."
I think it uses a sequencial electron transfer to perform a dichromate reduction?
Regarding red sensitive MB-DCG, the basic principle behind seems to be - according to Jeff Blyth - that red light is absorbed by methylene blue. The excited dye oxidizes the electron donor (TMG). At the same time that electron donor recovers its electrons from the dichromate which thus gets reduced to Cr3 (the part that causes gelatin hardening).
"The effect of red light absorption on MB is to make it an excited molecule with a
transitory existence as an oxidant seeking electrons. Certain types of amine can provide
electrons to photoexcited MB via the transitory formation of a charge transfer complex
which is believed to be produced. The MB is thus turned into a colorless form known as
leucomethylene blue. This is a reactive reducing agent able to gradually return to the
colored form of MB by reacting with oxygen from the air."
(Jeff Blyth, "Methylene blue sensitized dichromated gelatin holograms: a new electron donor for their improved photosensitivity", Applied Optics, Vol. 30, May 1991, p. 1598)
Ok. I think I understand the mechanism. Basically, the dye absorbs a photon, goes into a higher state(s) and, depending on the reaction energy - the electropotentials of the triplet state that Sergio mentions - donates an electron that then reduces the Cr[2]O[7] to Cr[3], as Martin states. Presumably, the energy of the released electron must be just right so that the probability cross section of capture of the electron by the Cr[2]O[7] is high. Sergio has indicated that this is a standard method of polymerisation. If this is so, can the polymerisation of the gelatin take place directly without the necessity of the Cr[3]. Presumably, the reason for the Cr[3] as a catalyst is that the Cr[3] itself then acts as an electron donor to enhance the polymerisation of the gelatin. Why then can't we find an appropriate dye that creates such a donor electron directly?
"... can the polymerisation of the gelatin take place directly without the necessity of the Cr[3]."
In the case of methylene blue, yes, there is evidence that MB alone provides some degree of hardening. Solano (C. Solano, "La sensibilisation des couches de gélatine utilisées pour le traitement des images en holographie conventionnelle et polarisée", Ph.D. Thesis, U. Laval, Quebec, 1985) showed that methylene blue sensitized gelatin - in absence of dichromate - provided sufficient crosslinking to form a hologram.
Dinesh mentions the probabilistic cross section of Cr[2]O[7] absorb the transferred electron? This is a probabilistic model? It is stabilished that this transfer is made by collision interaction between molecules, I guess.
In the gelatin structure the Cr[2]O[7] after reduction really cross link it and the Cr[3] takes part of gelatin, increasing the refraction index a little and make it prone to the Shankoff phase shift enhancement. If you could graft an acrylated photoinitiator (Acrylated benzophenone from UCB chemical USA)with gelatin,(not acylates) maybe you could with others water soluble monomers get such gelatin crosslink with a visible photoinitiator, at high efficiency. This is an alternative to current DCG model, giving the same final result, I think the Cr[2]O[7] still plays an important hole here, perhaps some dye produced (photopolymer)radicals can reduce the Cr[2]O[7] as it usucally do with cationid initiators? Usually CIBA Irgacure 184, sensitised by dyes, forming radicals to work in polymerization could obtain the reduce potential to work with Cr[2]O[7]?
I was talking about the quantum mechanical capture cross section, the probability amplitude for capture of the electron by the Cr[2]O[7]. I was wondering whether the electron released by the dye had other reaction possibilities. In particular, what is the probability amplitude of Cr[2]O[7] reduction with this electron as opposed to the probability amplitude of direct polymerisation of the gelatin? If there is a probability of direct polymerisation of the gelatin (even if it's small), can you use the law of reaction kinetics and increase the concentration of gelatin to favour the gelatin polymerisation reaction? In particular, my interest in direct polymerisation of the gelatin without Cr[2]O[7] is that it might be possible to get around the "dark reaction" of DCG and thus extend the shelf life of a DCG-type material.
"I was talking about the quantum mechanical capture cross section, the probability amplitude for capture of the electron by the Cr[2]O[7]."
Yes, the electron transference to Cr[2]O[7] is probabilistic too and related to redox potentials.
"I was wondering whether the electron released by the dye had other reaction possibilities. In particular, what is the probability amplitude of Cr[2]O[7] reduction with this electron as opposed to the probability amplitude of direct polymerisation of the gelatin?"
Much more to direct Cr[2]O[7] reduction, due the less gelatin amino acids "affinity" with reduction..
"If there is a probability of direct polymerisation of the gelatin (even if it's small), can you use the law of reaction kinetics and increase the concentration of gelatin to favour the gelatin polymerisation reaction? In particular, my interest in direct polymerisation of the gelatin without Cr[2]O[7] is that it might be possible to get around the "dark reaction" of DCG and thus extend the shelf life of a DCG-type material."
I think the right way is find another simple reduction mechanism with perhaps ferric nitrate or other salt that may become stable? Another mechanism is modify the pH with some heat development that release acids or superacids to the gelatin, even a photoinitiated acidic release can be obtained, this would be useful?
Thank you. The idea of releasing acids to increase pH had not occured to me. This gives me ideas for photolytic production of [H] ions. I understand that the halide acids, eg HBr, release [H]+ photolytically. I haven't done any chemistry since school so I'm trying to learn photo-chemistry very fast!
Right, 1,3-dichloro-2-propanol can release acid under thermal "development", apropos, very strong acid (HF) can be obtained with the cationic photoinitiator type Sartomer CD1012, used for cationic polymerization it can be adapted for other systems.this stuff can be sensitized with dyes very efficiently in GREEN by naphtacene.
With the gelatin the problem is find a crosslink reductible agent to work with. May be interesting try. As for my english salad,sorry, I'm learning as fast as I can too!
"If not, then adding the dye seems to have increased the sensitvity, which seems funny. I've never tried any dyes, but it seems that adding a dye should decrease sensitivity, not increase it."
A photon absorbed by a dye can start interesting reactions that would deliver more energy (or radicals) with associative synergistic molecules to the system, multiplying in some way the sensitivity to start the polymerization or holographic latent image, even on silicon material this effect can be pronlogated after exposure to light, most of "development" is made after exposure and greatly enhance by heat (cationic polymerization).
> A photon absorbed by a dye can start interesting reactions that would deliver more energy (or radicals) with associative synergistic molecules to the system, multiplying in some way the sensitivity to start the polymerization or holographic latent image, even on silicon material this effect can be pronlogated after exposure to light, most of "development" is made after exposure and greatly enhance by heat
(cationic polymerization).
Such effects do not necessarily maintain a molecular locality. If for instance a cascading free radical stream propagates spherically, then silver halide or other dipoles on either side of a source node will be triggered thereby,... not only lowering the overall resolution of the gel matrix eigan, but also adding 'noise' to the defining fringe structure.
Imagining a better world with Electronically pre-Biased HoloFilm:
It would be nice to be able to specifically trigger each speck in a way where there would be no migration and an adjustable sensitivity. Maybe this could be accomplished using a trigger stimulation that could ramp the sensitivity in db increments! (Perhaps in the stated semiconductor model there is room for polymeric organo-metallic pelloids that be stimulated by a Jacobs ladder style, transmission line RF burst through the bulk of the dielectric with transparent conductors incontact along the planes of the pelloid, or encapsulant via conductive index matching fluids, or a special plate holder with temporary charging surfaces, or a seperate machine to precharge the film in some way, or. some method which has very high first order characteristics and no reflection pulse.) Then the 'electronic bias' could be added by a source that raises the sensitivity threshold of the emulsion in a way that does not impart its own coherent optical noise, scatter and/or drift?!
Then of course some have tried optical pre-bias pulses and standard emulsions:
Since the response curves of silver halides are non-linear,... in some cases pre-biasing the matrix with photonic energy in a homogeneous field exposure can ride the curves to their peaks and would add little noise since the burst would be incoherent and homogeneous. Adjusting the chemicals, temps. and times would then provide for an increased responsivity to a 'select exposure', that of the Holographically coherent wave front, which occurs post pre-bias burst.
This sounds like some kind of Silver Halide/Thermoplastic mixture with highly locaclised activation. You might be able to get this "ladder" effect by varying either the Silver/Thermoplastic ratio linearly across the plate or by varying the electric field.
