Newbie on DCG holography

[MilanKarakas]

Hello, everyone.

Recently (July, 16th exactly), someone on lasers mailing lists sparked interest on holograms (mentioning 'Litiholo'). I mean, practical part (theory is more or less known), but I wanted to try it myself - with great doubt that I am able to do that. I chose DCG, don't know exactly why (perhaps the easiest one).

First tried G307 formula because I have only weak laser (cca. 15 mW @ 532 nm). Recently tried 'classical', or 'plain' KDi, just to see the difference.

My first 'hologram' was actually just border effects (some rainbow), where light enter glass plate and made multiple reflections (September 7th). This was first sign of anything at all. Later had trouble with everything; from gelatin (only two kind of gelatin available: Dr.Oetker and Podravka's Dolcela), coating method (tried veil, mold coating, Meyer's bar), and dip'n'shoot soaking (remaining drops on emulsion), to laser instability (mode hopping, wrong pumping diode alignment).

Next issue is how to get potassium dichromate at first place - the 'heart' of the DCG. After contacting five distributors for chemicals in my country (Croatia), nobody wanted to sell it me, because of strict government regulations. Finally, bought 100g KDi from Oxford chemicals, and after a lot of begging custom officers, they allowed it to reach my hands (not exactly bare hands ).

Even alum is restricted, and got only small stick for after shaving purpose. Tried to make my own aluminum sulfate, but pretty high amount of sulfuric acid remains. Does anyone know whether aluminum sulfate is better than alum (potassium aluminum sulfate) for G307?

Troubleshooting bit by bit, and got some decent results, although far from 'perfect'. 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.

That is all for my introduction. I am happy to get on this forum (Thanks, Ahmet).

Here are some of my recent holograms I made:

G307 problem with drops remained on the emulsion. Later solved that problem with additional water bath with two drops of dish detergent.

The same plate as above, but this time captured macro of small part, this time reconstructed on 532 nm diverged laser beam.

Small cigarette lighter, chosen wrong incident angle - not Brewster. G307 formula

'Plain' KDi in gelatin. Exposure time: 60 minutes @ 15 mW, 532 nm.

Still 'fighting' with this object - so far, the most difficult one. 'Plain' KDi in gelatin. Exposure time over 200 minutes (planned 120 minutes, but fell asleep) @ 15 mW, 532 nm.

For first two holograms (first three photos), I forgot exposure time. Much shorter than with plain KDi (somewhere between 5 and 15 minutes).

That's all for now, more when get something.

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Milan Karakaš
Vinkovci, Croatia

[Johnfp]

Welcome. Good to see a new face. Keep up the good work.

I chose DCG, don't know exactly why (perhaps the easiest one).

ROTFLOL. DCG, or making any of your own plates for that matter only throws another variable you need to control into the mix. Any "store bought" plates for holography would have surey been easier. DCG gives exceptionally bright images for SBR holograms, that's why most who use it choose to use it.

Anyway, glad to hear from you.

PS. As far as the Aluminum sulfate vs Alum for G307, Jeff Blyth should be able to answer that....JEFF???

[MilanKarakas]

Welcome. Good to see a new face. Keep up the good work.

Thanks.

I chose DCG, don't know exactly why (perhaps the easiest one).

ROTFLOL. DCG, or making any of your own plates for that matter only throws another variable you need to control into the mix. Any "store bought" plates for holography would have surey been easier. DCG gives exceptionally bright images for SBR holograms, that's why most who use it choose to use it.

The problem is that I have very little or no money. 100 g KDi cost me 100 Croatian kuna (cca. $17 US). Aside that, things what I bought in order to start is 99% IPA, alum, many containers, gloves, and few other (minor) things. Everything else I already have, or made. I had plenty of 2 mm thick glass plates, bought many years ago and planned to make HV capacitors for nitrogen laser (337.1 nm for pumping dye lasers at various wavelengths, depend of dye used).

Generally, the rule right now is NOT to buy anything which is not necessary. Saving money for some 445 nm diode (that part will be very 'painful' - $$$), and will made my own version of feedback to get single mode, current/voltage controller, and assembling optics as well as other things (spatial filter(s)/pinhole(s), power meter, more thermometers, etc.).

Aside all of that, long time ago (maybe over 30 years ago), making zillions B/W photographs (okay, didn't made emulsion, but anyway), so some chemical processes and precision of temperature measurements, exposure time, and other related things are not strange to me.

Hehe, only 'confusing' part is difference between B/W photos and holograms is that films needs developer, THEN fixer - DCG need first fixer, then the rest - but no developer.

Anyway, glad to hear from you.

I am glad to join such extraordinary group of people with much more knowledge that I can imagine (as I saw many works of you, people).

PS. As far as the Aluminum sulfate vs Alum for G307, Jeff Blyth should be able to answer that....JEFF???

This information will be very helpful. Thanks.

Best wishes,
m--

[Ed Wesly]

Pretty impressive for some first trials! Keep up the good work, and keep touching base with this forum, as there are plenty of experts here!

I am not one when it comes to DCG, however!

[MilanKarakas]

Pretty impressive for some first trials!

Thanks, Ed.

Maybe only three weeks or so, but day/night experimenting by trial and error. In meanwhile reading old and new forum about everything, as well as googling around. Theory of the holograms is relatively simple, but practice is completely different story.

Behind that 'first trials', there are lot of bad holograms (by 'bad', I mean really bad - just one or two visible patches of the object visible), lot of re-processed glass plates (some badly scratched), and lot of frustration. What missing here is good sleep.

Literally 'overnight' I become addicted to holographic work (okay, now I made camera obscura - dark room).

Lasers are not new for me, photography (old one, not digital) also. What is new is the beauty of the result, no matter how much is visible. I have two old books about holography, and I was pretty disappointed with it's content. For example, they mentioned range of prices for HeNe lasers from cca. $100 US, to few k$. And that is from 0.1 mW up to maybe few milliwatts or so. One book is mostly about masers (microwaves) and sound, and very little about lasers.

One thing what holding me back all that years is fact that split beam holograms is much more difficult than single beam (reflection). Noticed that even black plastic holding object is not good for thermal/vibrational stability if plate is on separate holder. Once in good 'connection' plate/object, hologram may be made even if laser move slightly (tried it intentionally, and still got something resembling hologram).

What is the problem - chemicals. Even gelatin is not the same in many countries, so reading posts from someone who made success with one brand, does not means that I should follow recipe to the finest details.

My first troubles started on overheated gelatin (up to 50C or more) with dichromate in it. I am not sure, but G307 and separate gelatin is much more forgiving.

Keep up the good work, and keep touching base with this forum, as there are plenty of experts here!

Yes, I will. I noticed great amount of knowledge posted on forum. Not just a theory, but really working recipes, advices and guidances. Only problem is with me; at first I mixed up bit of everything together. Tried G307 mix in hot gelatin, and it failed - some stiff gum formed almost instantly inside bottle. And many other mistakes.

I am not one when it comes to DCG, however!

Oh, I don't know. I did not paid enough attention who posted information, just wanted information.

Right now is time for some sleep. After that, more rainbows.

Best--
m--

[Joe Farina]

I agree with Ed, that's excellent progress for your first couple months.

DCG is always the same. Everyone has a lot of struggles in the beginning. Sometimes it's a very minor thing that causes a lot of trouble, and the problem can't be identified. (This is happening to me at the moment, by the way ) Your own experiments and experience are the best way to make progress, but everyone needs help once in a while. So I wouldn't hesitate to ask questions about any difficulties, and provide a photo if possible. The photo is the thing which enables others to see the issue clearly. There's a lot of combined DCG experience on this forum, and people willing to share it.

It looks like you're off to a flying start!

[MilanKarakas]

I agree with Ed, that's excellent progress for your first couple months.

It is maybe beginner's luck. At first, I am in rush to get my first hologram. Now come time to slow down and troubleshoot bit by bit.

First at all, I should to 'debug' my small DPSS laser module. Polarization ratio is terrible. When pumping diode is at proper angle, it gives more power out, but polarization ratio is not the best. If slightly misaligned, polarization is bit better (and less mode hopping as well), but it shows two beams overlapped, each polarized differently. Since I can't put anything intracavity, only option is to put some polarizer at output, and lost up to 50% of my poor laser.

Here are few pictures for comparison:

HeNe laser, oriented vertically (P plane), so that at Brewster angle reflect NOTHING from the glass surface(s).

HeNe P-plane.jpg (45.12 KiB) Viewed 5610 times

HeNe laser, oriented horizontally (S plane), and even at Brewster angle reflecting something (maybe up to 15%) from the glass surface(s).

HeNe S-plane.jpg (48.68 KiB) Viewed 5610 times

I did the best orientation possible (supposedly P plane), but ratio of polarization is very poor.

(BTW, does anyone know how to properly attach photos? I have trouble with it. I did the same thing for all three photos, but bottom one looks okay, and two upper pictures are in some sort of frames. All pictures 450x600 px.)

DCG is always the same. Everyone has a lot of struggles in the beginning. Sometimes it's a very minor thing that causes a lot of trouble, and the problem can't be identified. (This is happening to me at the moment, by the way ) Your own experiments and experience are the best way to make progress, but everyone needs help once in a while. So I wouldn't hesitate to ask questions about any difficulties, and provide a photo if possible. The photo is the thing which enables others to see the issue clearly. There's a lot of combined DCG experience on this forum, and people willing to share it.

It looks like you're off to a flying start!

Yes, I am. Just at start.

[holomaker]

Hello Milan, you have made some good progress and im sure your learning curve will accelerate, now you have joined us. Can you tell us thr actual laser type? Have you tried to place a 1/2 wave polarising plate in front to see what it does ? if you dont have one ,i can send you a "seconds" 1/2 waveplate for no cost.....

when making your test objects keep it simple, coins, door keys, i used a photopolymer hologram and just did contact copies. By laying the film plate on the polymer hologram asnd shoot (no worries about movement),just to see all the chems/process were working correct. Initally keep it simple and be sure to use a bright backround, as you need as much light reflecting back as possible to give you a nice clean finished hologram.

good luck and lets see more pictures!

[a_k]

Hello Milan,

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.

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.

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

Ahmet

[MilanKarakas]

Hello Milan, you have made some good progress and im sure your learning curve will accelerate, now you have joined us. Can you tell us thr actual laser type? Have you tried to place a 1/2 wave polarising plate in front to see what it does ? if you dont have one ,i can send you a "seconds" 1/2 waveplate for no cost.....

My laser is small module, rated at 32 mW, but after few days it hits floor, and 808 nm diode focusing lens broke. I repaired it, and later original diode burned. Bought new 808 nm diode, but not sure in it's quality (9 mm dia.). I just estimated that it can put out half of the original power, maybe only 15 mW.

Long time ago built power meter (actually this is thermal detector, using Pelttier element), but there is something wrong with this concept. It is more sensitive to near and far IR than to visible light. Realized that I should put glass plate to prevent blackbody (continuum) radiation from my body to enter, else it read more from my own body than from laser. Another problem is when this glass become warm, it radiate heat - so it show something again, and glass cools very slowly. I

It is actually too sensitive, even room light show 0.2 mV, so I should measure it in darkness. It is not calibrated, but it has nichrome wire intended for calibration (heating this wire with known current and voltage, then calculate - mimic laser input power). Black absorbing surface is not so black at all, so glass surface reflect about 8% and this black part maybe 2-5%, so even if I success to calibrate it, always will be in great doubt whether to add some 10-15% to observed power or not.

WOW, now I did one test, and I am amazed, roomlight (+ my body heat) showing 0.2 mV, laserpointer 1.2 mV, and my holo-laser 5.2 mV. That may indicate five times stronger than pointer. If pointer is 5 mW, that means 25 mW I have for holography! That is AWESOME!

Some pictures of my poor-man setups:

I think IR filter is scratched due to often dust cleaning, and collimating lens just amplify this irregularity. Spatial filter/pinhole is next what should make.

HeNe laser (diverged), cca. 2 mW (power not known, only current - 3.7 mA... now measured voltage at DIY meter, and show 0.5 mV above background - half the value of green laser pointer, so maybe HeNe is actually 2.5 mW?!), and DPSS laser module on heatsink - on hanging shelves, facing down at Brewster angle (HeNe for testing).

Measured voltage with laser pointer 1.2 mV (1 V above background reading).

Background reading, 0.2 mV (room light + my body radiation). Peltier element serving as differential temperature sensor (between ambient and converted laser light into heat).

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Seems that HeNe lase has more power than I figured out at first glance. I got it for free long time ago. If someone know what power this laser may have, please tell me. Here is what is on label:

Techmet Company, 6060 Executive Bl., Dayton OH 46424, Model 40006, serial 3603-13699, V?, 3.7 mA. Dimensions of laser with housing is 2.7 cm diameter x 25 cm long.
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1/2 waveplate will be good to have. If it can't exclude unwanted part of the polarization, at least I can rotate polarization (once when it become clean). Thank you in advance. I have no much optics, just few red laserpointers, two green, and one BIG 25 mW(?) holo-laser.

If waveplate not working I should to something else to exclude wrong part of the polarization, and that will cost me up to 50% of that power I have. I have only polarized sunglasses, or maybe can use LCD display as a polarizer (split to half, because there are two polarizers, each 'steal' some power). Tried glass plate at Brewster angle, but no much difference. Tried one dichroic mirror, but at angle of relatively good polarization, it suppress even more 'good' polarization.

when making your test objects keep it simple, coins, door keys, i used a photopolymer hologram and just did contact copies. By laying the film plate on the polymer hologram asnd shoot (no worries about movement),just to see all the chems/process were working correct. Initally keep it simple and be sure to use a bright backround, as you need as much light reflecting back as possible to give you a nice clean finished hologram.

Yes, you are correct. Coins, PCBs, and everything close to the plate turns out the best.

My last hologram attempt is to make diffraction grating (by simply placing first surface mirror and holo-plate on top of it). But, failed. Too much unwanted interferences caused by light entering plate even at Brewster angle.:

Tried to make diffraction grating (by placing first surface mirror beneath plate). Failed due to too much unwanted interferences.

good luck and lets see more pictures!

Thanks. First need to debug laser and make object holder (something more stable than black pillow )

Best--
m--