Newbie on DCG holography

[MilanKarakas]

Hello Milan,

Hello, Ahmet.

For such extremely long exposures like 200 minutes you need an extremely stable laser + table + a very quiet and also otherwise suitable location. I'm not sure that your laser is sufficiently stable to be used like that. Even if there were no mode hops, this doesn't mean that the wavelength of the laser is rock solid. Slow changes of the frequency won't be visible as mode hopping but can still be large enough to get in your way when recording holograms. Why don't you try smaller formats first, like a few cm^2 so you can minimise the exposure time and the problems associated with stability.

You are right. Something come in my mind, and today tried capture time lapse video (30 photos, 1 minute apart, each 15 second exposure). This test is intended to show me how much interference fringes move due to temperature change. Just two glass plates, laser beam bounced first from one to another, then screen.

Not only that fringes constantly moves during 30 minute (or more) period, but suddenly fringes reversing! Is that mode hopping? Look at video:

[youtube]http://www.youtube.com/watch?v=kbHdw27JsWo[/youtube]

(something is wrong with my 'programming' on this forum), if embed option doesn't work, try:

http://www.youtube.com/watch?v=kbHdw27JsWo

This is maybe reason why I need so long time of exposure. Actual sensitivity of plain dichromate is maybe good, but if fringes reverses bright <-> dark (constructive <-> destructive interference) too often, it actually cancels out the final result.

With the cracked lens of your module you are lucky that it lases at all. I think that your laser could be the cause of a good part of your problems. If the module is pointer style it might also have thermal problems like so many of that kind. If you haven't done yet, i would remove the module from the outer housing because usually there is insufficient thermal contact between the too and this leads to heating of the module, making it unstable. Maybe you could stick the module into a metal block for better heat dissipation.

The module is inside heatsink since first day (okay not exactly first day, I broke it first day or two ).:

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Edit: Do you mean to remove diode, lenses and crystals from barrel? I am not sure what is 'outer housing'? There is just brass barrel, and everything inside stacked each after other, whole part no longer than 2 cm. This laser working few hours without sign of overheating. Actually it is close to room temperature, cold by touching.
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Drilled hole inside CPUs heatsink, and module placed inside. Ugh, still lazy to use that LM317 to make 3 V PSU (current regulation is already next to module). Part of stability problem is due to voltage change when batteries lose it's capacity.

I admire the intensity with which you are conducting your work.

Ahmet

Thanks. I hope it will remain that way. I don't want to 'cool down'.

Best--
m--

[holomaker]

Hello Milan, i suggest you get rid of that laser and get a decent one to replace it, this laser will cost you way too much time ....................

[MilanKarakas]

Hello Milan, i suggest you get rid of that laser and get a decent one to replace it, this laser will cost you way too much time ....................

Hello, Dave.

I wish. But no money, maybe something next spring. Even then it is in question. My pension is cca. $370 monthly. All bills for electricity, water and other thing... this amount is just barely enough to cover all of that. I can't afford buying expensive stuff any more.

[Joe Farina]

I can't afford buying expensive stuff any more.

No problem. Obviously (and from the pictures), you are learning a tremendous amount with the resources you already have. I have found that when life closes one door, another opens. It looks like you have a modest facility and plenty of time, I would continue to make the most of them. But as Dave said, if you do establish a holo-piggybank, I would write "for a better laser" on it.

[holomaker]

If your good at hacking electronix i can suggest a couple lasers contained in laser pico projectors, these little lasers put out an easy 50mw of 530nm have a ton coherents, i purchased three "non working" models for $100 each unit (all 9 lasers worked) ........... PM me if you want details.

[MilanKarakas]

I can't afford buying expensive stuff any more.

No problem. Obviously (and from the pictures), you are learning a tremendous amount with the resources you already have. I have found that when life closes one door, another opens. It looks like you have a modest facility and plenty of time, I would continue to make the most of them. But as Dave said, if you do establish a holo-piggybank, I would write "for a better laser" on it.

Hello, Joe.

You are right. But life closes the wrong door.

Well, facility... my home is not yet my. It belongs to firm my father had. Firm closed, my father no more in good shape, and firm has some debt, and if not solved, it can be lost.

Yes, plenty of time. At least something.

Well, better laser, that is the question. I will try repair my laser again, but it is risky business. It turns out that it gives me more power than I judged by eyeballing. Some 25 mW. So, at least filtering out unwanted polarization will decrease that power. Spatial filtering - that is tricky part, but not impossible. At end, if I get decent 10 mW - I will be happy. Frequency stability... oh, I can't do much about that (can't put etalon intracavity, because Nd:YVO4/KTP crystals are glued together, and mirrors are directly coated onto crystals). Only perhaps controlling temperature of the module.

Best wishes,
m--

[MilanKarakas]

If your good at hacking electronix i can suggest a couple lasers contained in laser pico projectors, these little lasers put out an easy 50mw of 530nm have a ton coherents, i purchased three "non working" models for $100 each unit (all 9 lasers worked) ........... PM me if you want details.

Yes, most of the time hacking everything, from the electronic to the chemistry (actually most of the things). There are some stuff I can't hack, and that is potassium dichromate (no raw material).

I tried convert CrIII to CrVI with NaOH, and it turns out that it works. At least it change color from green or bluish to orange, depending how much sulfonic acid added in solution. Spent dichromate turns blue after converting old plate's spent dichromate into CrIII by adding 5% sulfonic acid (H2SO3). It works the same way as sodium metabisulfite (I have one liter sulfonic acid, but only gram or two of SM). Just need to re-crystallize recovered dichromate and try to use on new plates.

By carefully adjusting amount of sulfonic acid, it is possible to get CrIII, CrIV, CrV, and finally CrVI (judging by change in color), but I might be wrong. Will consult my friend chemist (he is just 16 years old, and he is 'expert' in chemistry already) .

BTW, PM sent. Just for details, right now no money available. Thanks Dave.

[Tony DCG]

Some very interesting work MilanKarakas
Look forward to seeing more

Since there are lots of variables here I would seriously consider small plates, like 2x2(inch) plates. Reduce that exposure time. Work for now just on making good film. Smaller plates allow you to try many different things. One large plate can yield many plates with about the same thickness and should be pretty consistent. Keep the object simple like a coin. It’s boring but you get good ratios and doesn’t move. Also if you coherence length is crappy or if the laser mode hops you will still get a decent image. Once you reached the point where you understand your film you can decide if you want to invest more money into a laser.

The guy who would be able to help you the most here regarding chemistry is John FP. He’s not a chemist but has done a lot of empirical work in DCG. Not that others here are knowledgeable about DCG here but John did a lot of work in this area. Perhaps send him a private message and see how much help he can give you.

Good luck
Tony

[MilanKarakas]

Some very interesting work MilanKarakas

Thanks.

Look forward to seeing more

I am working now bit slower - first working on 'cleaning' laser beam. I got into multiple difficulties. First observed that my laser has more power than anticipated (by remembering it's brightness before damaging some parts). Decided to make simple power monitor too see in which direction laser goes (more or less power), not real power meter. Tried to calibrate it anyway with small DPSS 532 nm laserpointer, and after making attenuator, something strange happens: my big laser - no reading at all! Small laserpointer, microampermeter's pointer indicate exactly where is set. By looking at brightness, big one is stronger. Something else is wrong.

What I discovered is that cheap chinese pointer has bad or no IR filter at all!

Nowadays, they probably doesn't bother to put IR filter at all on their green DPSS laser pointers. On picture, green beam is attenuated by piece of brown (by naked eye) VHS tape.

Something else is interesting. On it's label says: "...class III laser, <20 mW.". What this means? Total output power, 532 nm + 808 nm + 1064 nm?

This messing delayed my work on lasers. Then desk lamp with lens collapse down (broken plastic holder). Then I tried to make wooden frame for big fresnel lens, but sawing blades are smashed, blunt. Rushing to hardware store to buy new one, but they haven't currently. Driving bike like crazy around town and finally found one. More delay.

In meanwhile, when already in town, bough one cheap red permanent marker, and one black. Tried to see which will be better for painting edges of the glass plates to prevent green laser entering. Then made simple poor-man's approach of chromatography, and by accident - one stripe with red marker fell into alcohol. To my surprise, it begins to glow faintly on incandescent bulb. Bring longwave UV lamp, and WOW, found new cheap source of yellow/orangish fluorescent dye.

Pretty bright fluorescent dye from red permanent marker (illuminated by 532 nm pointer). This marker by itself is not fluorescent!

One of two brands of red markers show solubility in water, so cheaper one is not 'permanent' at all. But, that dye - may be used instead Rhodamine 6G (which is just slightly soluble in water), or Rhodamine B (which _is_ soluble in water), and as far as I can tell, it's brightness is much better than both known dye (maybe this is subjective, because wavelength is close to green where eyes are mostly sensitive).

Comparison of RhB, Rh6G, and this new, unknown one.

Since there are lots of variables here I would seriously consider small plates, like 2x2(inch) plates. Reduce that exposure time. Work for now just on making good film. Smaller plates allow you to try many different things. One large plate can yield many plates with about the same thickness and should be pretty consistent. Keep the object simple like a coin. It’s boring but you get good ratios and doesn’t move. Also if you coherence length is crappy or if the laser mode hops you will still get a decent image. Once you reached the point where you understand your film you can decide if you want to invest more money into a laser.

That is good advice, thanks. I will do that immediately after make laser with decent polarization. It is futile to get clean hologram if interference fringes come from bad polarization and cover whole surface. I can compare making holograms with photographing: good camera is equally important as good film. So, here 'good camera' is actually point-like coherent source of light - laser.

Making film has another difficulty: dust. Somehow manage to get clean glass surface, properly prepared (cleaned, attacked with HCl for better sticking gelatin to surface). But no matter which method use (veil, mold coat, or Meyer's bar), there are lot of craters and other scattering stuff which may ruin the hologram.

Stability of laser and object is separate issue. Laser _can_ move slightly around it's point-like source, exactly at spatial filter/pinhole. But, whole construction must be stable - not moving it's position. That part is yet to solve.

Object end of the room (laser -> object distance is about 4.5 m) is on the floor (at Brewster angle from laser shining from above, on the shelves), and not only stepping on floor cause movement's of the fringes, but also temperature change during exposure time.

So, most important part; object/emulsion is not stable, or it is just enough stable to get bigger diffraction patterns, but no finest one - responsible for fine and deepest details.

Anyone doubt in my last statement, please make simple setup of double slit experiment. Then move away two slits (as laser beam width may provide) and observe interference fringes shrinks - that part is counterintuitive. Whole overall look of the spot remains the same, but inside it - more fringes closely spaced appears.

The guy who would be able to help you the most here regarding chemistry is John FP. He’s not a chemist but has done a lot of empirical work in DCG. Not that others here are knowledgeable about DCG here but John did a lot of work in this area. Perhaps send him a private message and see how much help he can give you.

This part will be my next challenge (for example, messing with MBDCG, etc.), but first to solve the main issues. Thank you for that advice, too.

Good luck
Tony

Thank you, Tony.

Best--
m--

[a_k]

Hello Milan,

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.