Home Optical Table

[Arturo]

I have not read this thread in a while, but the beauty of DCG is you do not need to create transmission masters if you don't want. DCG is efficient enough to make reflection masters, then a contact or proximity copy for your image planed holograms. Both of those holograms can be SBR's.

Thanks John. However I am not (yet) at a stage in which I would try doing DCG plates... Still trying with litiholo and AgX. But your comment also seemed interesting in this respect... you are implying that AgX reflection masters just aren't bright enough to make image plane copies? I had never read this before, but would explain a lot of things...

[Johnfp]

Well, if you made the master reflection with a split beam you could get it nice and bright enough to have good results. In fact I am sure some of the mass production techniques do exactly that. But if you try taking a SBR (Single Beam Reflection) in silver and use it as a master you will have difficulty. The key is there is no way to control light ratios.

[Arturo]

Well, if you made the master reflection with a split beam you could get it nice and bright enough to have good results. In fact I am sure some of the mass production techniques do exactly that. But if you try taking a SBR (Single Beam Reflection) in silver and use it as a master you will have difficulty. The key is there is no way to control light ratios.

And how DCG would change that for SBR? (excuse my absolute ignorance about the DCG world! )

[Johnfp]

I am not sure of the mechanics but DCG SBR are much easier to get really bright as compared to Silver SBR. Most DCS holograms you see out there are SBR and you can see how bright they are. Compare that to any SBR in silver. Most silver reflection holograms out there are made from masters to have more control over ratios to get bright holograms. I doubt any holograms out there are SBR in silver.

Now with that said, I have seen some promise in the newer films including full color that do great with SBR.

[Dinesh]

DCG holograms are brighter than silver holograms because they're broad band. Under laser illumination, this advantage disappears. The advantage of silver is that it's a lot more sensitive. However, you can make silver reflection masters as bright, under laser illumination, as dcg. It just depends on processing and some other techniques, for both silver and dcg. As far as split beam is concerned, you can get roughly the same brightness for both silver and dcg in white light. I put up a picture of both silver and dcg of the same image a while back and you can see they're roughly equal. Again, it depends on how you process and other techniques. The advantage of dcg is that the processing is a lot simpler than with silver (some people feel that processing dcg is more "intuitive" since they can "understand" what the emulsion is doing as the processing progresses) and, with the correct processing, it's a lot easier to tune the dcg to a desired wavelength and bandwidth. Also, the parameters in dcg are a lot more flexible, for example, dcg has an extremely large dynamic range, which allows for a large variation of ratio. Silver is a lot more particular. The loss of efficiency in silver is greater if you're off on a specific parameter than with dcg.

In the end, of course, it all depends on which you're most comfortable with. I've known dcg holographers who have been shooting dcg for over 40 years, who say that they'd never go silver because it's too complicated. I've also known silver holographers with similar experience who say the same thing about dcg. Since I shoot both, the emulsion that I use for a particular shot depends on the end use of the hologram.

[MilanKarakas]

In the end, of course, it all depends on which you're most comfortable with. I've known dcg holographers who have been shooting dcg for over 40 years, who say that they'd never go silver because it's too complicated. I've also known silver holographers with similar experience who say the same thing about dcg. Since I shoot both, the emulsion that I use for a particular shot depends on the end use of the hologram.

I have different set of issue: milkiness. And something that is not related with process temperature. No matter cold or warm first bath, holograms appear milky. Recently discover that after baking at 100C for 3 to 4 minutes, hologram is much more clear, but also lacking of diffraction efficiency.

Tried light fixing before exposure, light fixing after exposure, tried light fixing at emulsion side, glass side, both... no matter what I do, it is or milky or there is almost nothing on the plate.

And, my last batch of the plates are with too thick emulsion and too much dichromate in it (100:12:3), so for recording at 450 nm, often I am getting terrible UV shifting (I can't say blue shifting, because laser is already blue). Tried to skip 70% alcohol bath in order to get broadband reflection hologram, but what I got is just whole plate broadband, while object is really not visible. Transmission holograms are somewhat okay, probably because emulsion shrinking does less blue shifting. Not sure.

And, I wanted to post pictures of my 'optical table', but afraid to do that... It looks really terrible, and I am ashamed of it. It is actually surprise that I am able to get anything at all on such ... well, table.

Best wishes,
milan

---

[MilanKarakas]

Additional question about milkiness of the plates: Is that only present on DCGs, or the same thing appear on AgX emulsions as well? I mean, homemade ones?

[holomaker]

Hi Milan this question needs to be over on the "DCG" topic .... how are you drying the unexposed plates? these are mold-coated?

[MilanKarakas]

Hi Milan this question needs to be over on the "DCG" topic .... how are you drying the unexposed plates? these are mold-coated?

Uh, sorry for wrong topic.

No, this time it is veil method. I dried it inside laminar flow hood. Temperature was from 20C to 30C, but humidity is between 20% and 40% RH.

I gave up of mold coating... don't know what is wrong all the time. Tried many tricks, but got very rough surface when separating mold.


Best--

milan

[MilanKarakas]

Okay, I will post some pictures here of my optical setup. Table... it is ordinary desk table, nothing special. Only what is added on mirror beam separator is 8 mm thick glass plate beneath it. Two mirrors, one first surface, another concave; that two mirrors mimic beam splitter, separating one part of expanded beam onto plate, while the rest is focused onto object by second surface concave mirror.

As long as both mirrors does not move, holograms are possible.

So far, I have no problem with second surface mirror, but it projecting very weak interference fringes onto object, often not visible onto hologram.

Plate holder is stable as long as small test pieces of glass is used:

Improvised plate holder.

Beneath this holder is also 6 mm thick glass plate which prevent most of the thermal/mechanical movements between object and the plate. So far, I have no problem with stability of such setup, especially when shooting holograms after midnight, when traffic is low.

Right now I am focused onto two things; laser stability and getting plate clear.

Seems that I bought wrong blue diode; on eBay, there are two types with the same price: PL450 and PL450B. On PDF, for first one there is mentioned that this laser diode is good for holograms, while on second datasheet this is not the case. Difference is in power as well; PL450 is 50 mW laser diode, while PL450B is 80 mW laser diode (capable to run at 120 mW for brief period).

What is problem with PL450B is that it has many wavelengths at the same time, and I am using piece of glass to stabilize single frequency (not easy task, often it mode hops):

Lousy laser assembly.

and

I call it 'etalon', but it is just 1 mm thick glass plate...

Such feedback is provided at focal point of expanding lens. There are two main drawbacks of such approach: resulting laser spot has many impurities due to stray interferences caused by feedback mechanism, and there is not possible to put spatial filter. I tried to add pinhole, but got no improvements at all, just slightly cleaner beam, but far from perfect.

Regarding cooling fan; yes it produce vibrations so that whole desk vibrate, but such vibrations are minimal on that two glass plates holding mirrors and plate holder. Between glass plates and desk there are small felt-pads which serve as vibration dump. Seems that this works sufficiently good.
---

I wish I am able to do something better and more compact table setup and design, but I am afraid that my technical skill and current budget situation doesn't permit me build anything better than that. I am surprised that holograms are possible at all (exposure time from 1 - 5 minutes).

Best--
milan