Newbie on DCG holography

[MilanKarakas]

Hello Milan,

Hello, Ahmet.

With outer housing i meant the part around the brass cylinder, so what i was proposing is exactly what you have. What you could try is to further reduce the power, maybe you can find a more stable operating point for your laser. At lower power the lasers are usually more stable. In addition very small changes in the power settings can make a big difference concerning stability.

Yes. Right now just finished building of fresnel lens with three 1W white LED (one LED missing) for easier work with small parts. But, this lens is disappointing, just 3x magnification. Oh, well. I will add some more lens. My diopter is +3.5 and seems not good enough.

One thing what I need to do first is mount one big mirror (even second surface mirror should work), and expand beam across room and back to screen close to me in order to see fine details of the interference pattern. That way I can closely monitor change in the behavior of the laser. Right now, if I mess with laser close to me, then I can't see what happening on spot side. Too far away to see anything precisely.

Yes, power is not issue for now (unless one day begin to work with big holograms, but that day is far from now). Currently using 8x10 cm plates, but all plates has only 6x8 active area (due to mold coating, or Meyer's bar method). It is better to have border - anyway many times I put my gloves or fingers close to the edge of the plates and leave some fingerprint, or just screw up emulsion.

I hope today or this evening to begin work on my laser. Priority... two things: clear polarity and stability, without mode hopping.

Thats all for now. More news when something appear.

Best--
m--

[holomaker]

Hello Milan, do you have any green photo polymer holograms? These are great to use as a test set up, if you do contact copies of this hologram, the coherent length of the laser will not matter and will cut down on your exposeuer times greatly. Allowing you to continue your DCG testing ................

[Joe Farina]

Still troubleshooting many things, mostly high amount of dust. After improvisation of laminar flow hood, result is much better with less 'craters' on it, but still not perfect since fan is too weak and any movement of my body cause dust coming in.

Hello Milan,

Improving a laminar flow area is something that can be done on a limited budget. I built three, and all worked very well. Only rarely does dust get in. I don't know how yours is constructed, but the "grill" or "honeycomb" structure is something that can be improvised from local materials (I mean the part which causes air coming off the hepa filter to come "straight" out in a laminar way: I use a large quantity of plastic drinking straws from a local restuarant-supply store).

The air flow doesn't have to be very strong, but it has to be "laminar" with no swirls or eddies of air that cause air to go back inside the enclosure. To test this, I light an candle and move it around over the entire opening area. If the candle flame "bends" and does not flicker at all, then you are ok.

Another couple things: I wear a windbreaker (tends to repel dust and can be wiped down with a wet towel) and nitrile or latex gloves. I also use clear packaging tape to wrap around my wrists where the gloves and sleeves meet. The tape is easily removed from the windbreaker and gloves. All of this reduces the chances of dust getting in the enclosure when I put my arms in to make the coatings.

I have done Mayer bar coatings mostly, but have recently tried the molding method. I do like the mold technique in certain circumstances. This has the advantage that when dust settles on the emulsion (and it defintely will unless done under a laminar flow) it is incorporated into the emulsion, instead of laying on the wet surface (like in Mayer bar or veil) and sucking up the gelatin. But it would still greatly improve the quality of the mold-coated plate if it's done under a laminar flow.

[MilanKarakas]

Still troubleshooting many things, mostly high amount of dust. After improvisation of laminar flow hood, result is much better with less 'craters' on it, but still not perfect since fan is too weak and any movement of my body cause dust coming in.

Hello Milan,

Hello Joe.

Improving a laminar flow area is something that can be done on a limited budget. I built three, and all worked very well. Only rarely does dust get in. I don't know how yours is constructed, but the "grill" or "honeycomb" structure is something that can be improvised from local materials (I mean the part which causes air coming off the hepa filter to come "straight" out in a laminar way: I use a large quantity of plastic drinking straws from a local restuarant-supply store).

That is very nice idea to use straws. I have no access to such supply store. Can I use something else instead straws? Currently running with HEPA filters (actually medical masks, found that it does it's job nicely), before air enter this area, six or seven layers of additional electro-statically charged material added - which slow flow even more.

The air flow doesn't have to be very strong, but it has to be "laminar" with no swirls or eddies of air that cause air to go back inside the enclosure. To test this, I light an candle and move it around over the entire opening area. If the candle flame "bends" and does not flicker at all, then you are ok.

Checked, and flame just barely bends, and it flicker. Tried to capture video of laminar flow setup, but decide to show my whole lab (kitchen). Lot of blather (sorry for that), and my English speech is not the best (also, I am not prepared, so more blather and errors). Here is video (it is unlisted, only one who get over this forum can see it).:

http://www.youtube.com/watch?v=o1M-E2hLXpA

Yes, I am sleeping in kitchen. That is because preparing to winter time (sort of 'survival mode') - can't afford enough wood for heating any other bigger room. So, there is lab _and_ bedroom. I not use kitchen for making food, just for coffee (eat at girlfriends place, different house down street), so no worry about mixing toxic stuff and food.

Another couple things: I wear a windbreaker (tends to repel dust and can be wiped down with a wet towel) and nitrile or latex gloves. I also use clear packaging tape to wrap around my wrists where the gloves and sleeves meet. The tape is easily removed from the windbreaker and gloves. All of this reduces the chances of dust getting in the enclosure when I put my arms in to make the coatings.

That is really good idea. All I have for now is two type of latex gloves (white, not so strong, and yellow - much stronger), and hair hood (for medical purpose). Windbreaker is very good idea. Tape is another good point.

I have done Mayer bar coatings mostly, but have recently tried the molding method. I do like the mold technique in certain circumstances. This has the advantage that when dust settles on the emulsion (and it defintely will unless done under a laminar flow) it is incorporated into the emulsion, instead of laying on the wet surface (like in Mayer bar or veil) and sucking up the gelatin. But it would still greatly improve the quality of the mold-coated plate if it's done under a laminar flow.

I also noticed that after mold coating, film looks much better. There are chance for scatter, but as you said - no big craters (sometimes up to 5 mm in diameter). Meyer bar has another one problem: I have only one flat surface and even this one is hard to level, so warm gelatin tend to flow at one corner or somewhere else. With mold coating, I can make many plates (much, much more than with bar), put in the fridge (5C - 10C) then removing mold. The result is fantastic! With Meyer bar, some amount of gelatin always remains (in this case, few plates prepared for veil coating).

Also, I think this way coating is more even - without much variation in thickness, depending of flatness of the glass surface of mold and plate.

BTW, about gelatin preparation. After more than one hour, small bubbles present in the beginning begins to clear. While stirring (gently by hand), on occasion some big bubble appear, but most of the time I see very small bubbles (maybe micron or so in diameter).

I suspect that such bubbles are due to gasses present in water prior to adding gelatin. Will try first heat water until boiling, then allowing to cool down to the room temperature again, and then add gelatin to see the difference. Maybe this is sign of something different, perhaps additives in gelatin? Will post result on the forum.

More later...

[Joe Farina]

Hello Milan,

Awesome video, thanks.

Your DCG lab is quite complete and impressive, except for two (or maybe three) things: a good laser (and also preferably a reliable power meter to keep track of its output) and a good laminar flow area.

I am wondering if those medical masks are true hepa-type filters? If they are, then they should be ok. Also, I'm wondering why you're using 7 layers of pre-filter material. Shouldn't one be enough? I don't use any pre-filters, just the hepa. Your flame isn't bending -- it needs to bend. It should be easy to find a cheap fan that is strong enough, if your current one isn't.

Of course, you can use any kind of honeycomb structure other than straws. John Pecora uses a grille that we often see under fluorescent light fixtures that is white plastic in the shape squares. I'm not sure if he uses just one, or multiple sheets glued together to form a longer honeycomb, more than one seems better to me. But this item may not be easy to find. You will have to use your own ingenuity here (which I see is considerable -- homemade doubling crystals, wow). The grille must be clean, and not friable (i.e., it must not generate dust). If the material is friable, it can probably be made non-friable by coating with varnish or shellac.

You mentioned that the top cover was removed. It does need a top cover, and also covers for both sides (you're using the tabletop for the bottom cover which is fine). The area in front of the hepa/grille needs to be box-like, this is the clean area where the coatings will be made. Also, importantly, the front opening of the box always needs to be covered when not in use, to prevent dust from getting inside and corrupting your grille. I use a piece of rigid plastic film with magnetic adhesive tape around the edges. The front of my box also had magnetic adhesive tape, so that it "mates" with the magnetic tape on the plastic film.

By the way, I saw your solution of Rhodamine 6G. R6G can increase the sensitivity of "classic" DCG to green light. If you don't already have that paper, please PM me your email address, and I will scan and send it to you.

[MilanKarakas]

Hello Milan,

Hello Joe.

Awesome video, thanks.

Your DCG lab is quite complete and impressive, except for two (or maybe three) things: a good laser (and also preferably a reliable power meter to keep track of its output) and a good laminar flow area.

Whole day and whole night spent making 3 V stable PSU, power meter, power indicator (not real power, just to see whether power increase or decrease), finding the best operating point of the laser module (this took me many hours, too much), and other things.

Laser now running on 3V, 470 mA, giving stable 42 mW (okay, reading tolerance maybe '/- 5%, not sure my power meter is properly calibrated). But it working stable without mode hopping. Found that at 440 mA or less, it begins hopping frequently, as well as at or above 480 mA. So, I found 470 mA is the best. Tomorrow will setup improvised interferometer to see true stability.

Seems that all my problems with laser's instability is due to one small transistor close to 808 nm laser diode:

When this transistor overheats, beam brightness begins to cease and make mode hopping.

I remove this transistor, solder three wires, and put two transistors (darlington pair) outside module. Laser works much more stable now.

Also, make one toy: 'polariscope'.:

It is essentially two Brewster's plate, each for separate polarization, angled 90 degrees each to other. Working well.

This 'toy' showing that this laserpointer has very bad polarization ratio. If polarization is okay, just one of two side beams should be visible.

Tried to remove rest on unwanted polarization with BGO crystal (haven't any suitable polarizer, except for photography - too much attenuation):

Lost about 50% of incoming beam, but it is much better than 'raw' beam. Ratio of polarization is much better. Note small spot on top of polariscope - almost invisible.

At Brewster angle, small amount of wrong polarization remains. Even this small amount can make troubles. Note how much on top of polariscope remains. I want to remove this, but haven't proper polarizing beamsplitter. Tried BGO crystal (it has high refractive index, and reflecting cca. 40% 'good' polarization). How it works is shown on previous picture (above).

What I found with my 'polariscope' is that all my holograms are made with misaligned polarization by 30 degrees (too much, trusting polarizing sunglasses - too bad idea). So, part of my problem with unwanted interference fringes at plates are due to this issue. Now, some fringes remains, but much less visible.

I am wondering if those medical masks are true hepa-type filters? If they are, then they should be ok. Also, I'm wondering why you're using 7 layers of pre-filter material. Shouldn't one be enough? I don't use any pre-filters, just the hepa. Your flame isn't bending -- it needs to bend. It should be easy to find a cheap fan that is strong enough, if your current one isn't.

Not sure either, only know that there are three layers, and middle one is electret (electro-statically charged), and that this layer actually doing it's job. Only thing what I don't know is how it is effective.

7 layers of pre-filter is because without that it causes turbulent flow (I had no clue how this device actually looks like). About fan: I will try to do something about that.

Of course, you can use any kind of honeycomb structure other than straws. John Pecora uses a grille that we often see under fluorescent light fixtures that is white plastic in the shape squares. I'm not sure if he uses just one, or multiple sheets glued together to form a longer honeycomb, more than one seems better to me. But this item may not be easy to find. You will have to use your own ingenuity here (which I see is considerable -- homemade doubling crystals, wow). The grille must be clean, and not friable (i.e., it must not generate dust). If the material is friable, it can probably be made non-friable by coating with varnish or shellac.

Yes, I will try to find something which may serve for that purpose. Ah, homemade doubling crystals... not the perfect ones, but can double.:

http://www.milankarakas.org/pub/KDP/HomegrownKDP.html

You mentioned that the top cover was removed. It does need a top cover, and also covers for both sides (you're using the tabletop for the bottom cover which is fine). The area in front of the hepa/grille needs to be box-like, this is the clean area where the coatings will be made. Also, importantly, the front opening of the box always needs to be covered when not in use, to prevent dust from getting inside and corrupting your grille. I use a piece of rigid plastic film with magnetic adhesive tape around the edges. The front of my box also had magnetic adhesive tape, so that it "mates" with the magnetic tape on the plastic film.

I put top cover because it improves slightly cleaning ability (too weak flow). And, I will make some cover after using laminar flow hood. Magnetic stuff is good idea. Thanks for this advice.

By the way, I saw your solution of Rhodamine 6G. R6G can increase the sensitivity of "classic" DCG to green light. If you don't already have that paper, please PM me your email address, and I will scan and send it to you.

No, I haven't that paper, will send you PM. Tried once by guessing amount, but not working well. Maybe there should be some other additives?

Best--
m--

[msxc]

Hi Milan,

You report fascinating improvements(looking forward for experiments in my DCG darkroom-things do work better in the winter). And Yours web-page is also interesting- lots of nice experiments, and it seams that You know how to play with lasers.

This part sounds scary though:
http://www.milankarakas.org/pub/Eye_inj ... njury.html
Any improvements since 2005?
Greetings,
Msxc

[MilanKarakas]

Hello Milan, do you have any green photo polymer holograms? These are great to use as a test set up, if you do contact copies of this hologram, the coherent length of the laser will not matter and will cut down on your exposeuer times greatly. Allowing you to continue your DCG testing ................

No, I haven't (or don't know what is exactly 'green' photo polymer). I have many small holograms around,almost every valuable products has it (including money). Do you mean this one? If yes, then I will try it for sure.

Thanks.

[MilanKarakas]

Hi Milan,

Hi, msxc.

You report fascinating improvements(looking forward for experiments in my DCG darkroom-things do work better in the winter). And Yours web-page is also interesting- lots of nice experiments, and it seams that You know how to play with lasers.

Somewhat, yes. Not an expert, but study a lot about lasers and made lot of experiments.

This part sounds scary though:
http://www.milankarakas.org/pub/Eye_inj ... njury.html

Eh, yes. Very stupid idea. Still have small grey spot on left eye today. Much smaller than first days,... weeks, months, years.

Any improvements since 2005?

Yes, but too lazy to publish anything. I hate HTML, so rather publishing on flickr, youtube, or just send pictures to my friends. I waste too much time messing with nitrogen laser. The biggest problem is dielectric - or has too low dielectric constant, or has too low dielectric strength (easily punctured by HV).

Now, using only small lasers (maybe will made another doubling crystal and try it on holograms. First want to make decent setup, DPSS, shutter, spatial filter/pinhole, some housing if possible, plate holder for holograms, some stable platform, etc... many things.

Later will consider switch to dual color holograms (at least red/green, or maybe green/blue). Panchromatic holograms are difficult. At least in my case - no much money to spent on lasers, and material. I love to do anything myself, but sometimes good fabricated laser is the best choice for holography.

Greetings,
Msxc

Greetings,
m--

[Joe Farina]

Hello Milan,

Thanks for the update. If you have confidence in your laser and power meter, you should be ok. Around 40mW of green light is quite good.

The thing which reduces (and in fact should eliminate) turbulence in the laminar flow is the front grill or honeycomb. So if you have that, then you shouldn't need the layers is back, and this should greatly increase air flow. As a possible way to make a honeycomb, the following idea came to mind: cut many pieces (maybe a few hundred) of PVC pipe (say ~2 inches long), lay them flat, and glue together with PVC cement. Also brush the cement over surfaces (if they are dusty from being cut). The only question in my mind regarding this idea is that the thickness of PVC tubing (which is substantial) might conceivably cause a problem. But I doubt it.

Or use any similar idea with available materials.