Hello everyone.
Yesterday i started testing a 405nm LD for DCG. Much to my surprise I got a hologram (denisyuk) of a 4cm deep scene with the very first plate.
The LD had been extracted from an PHR-803T sled. It has a nominal output of about 100mW but seems to be capable of up to 170mW when cooled sufficiently. The LD was installed in a cylindrical metallic housing with the dimensions 30mmx11mm (Aixiz module).
During my tests i found a quite broad stable operation region with currents around 70-90mA, which corresponds to an optical output of 60-75mW. At this currents the LD produces clear and strong fringes, similar if not better than what i'm getting with a 650nm LD (Sony SLD1239JL-54).
Unfortunately i didn't have suitable collimating optics for 405nm yet. So a cheap plastic optics had to be used, which seems to be coated for 650nm and did cause considerable loss of power. The net power after the lens is supposed to be around 30mW.
The first DCG mixture was prepared with 2g gelatine, 0.085g Amdi and 16.5ml H20. The beam was expanded to 10cm and the exposure times tried were 8, 12 and 30 secs, which correspond to roughly 2 - 12mJ. The 30 sec exposure turned out to be too long. With 8 and 12 sec the holograms could be seen extremely bright in the last IPA bath. After drying the replay color was indigo/blue/green. A day later the colors had changed to violet/indigo.
I'm trying to achieve a longer replay wavelength. As i have no previous experience with DCG (except MBDCG) i don't know which factors favour a red shift.
I tried a 15% citric acid solution so far but had no success because the coating separated from the glass. Next i want to try a lower concentration as well as a gelatine solution for post swelling.
What are other's experiences with 405nm LD's? Any hints how a substantial red shift can be achieved with DCG?
405nm DCG
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JohnFP
405nm DCG
How did you coat your plate? How big is your plate? How long did the plate set before exposing? What kind of gelatin did you use? What were temps of water bath and alcohol baths? What % IPA were each of your alcohol baths? How did you blow dry?
The reason I ask is that it seems your hologram is red/gold near the edges and it is only near the center that it seems the fringes collapsed. This indicates you are very very close to getting a nice bright gold hologram and need to only change one variable very, very slightly to get an even bright hologram.
But to answer you question;
Did you really mean "2g gelatine, 0.085g Amdi and 16.5ml H20"? That equates to a 100:12:.5 formula (water, gel, AmDi). It seems pretty low for the AmDi. If you meant .85g AmDi then that would be 5 grams per 100 water and thus I would lower it to 2.5 grams for red shift.
Also, if you use KDi instead of AmDi you will notice a redder hologram.
A shorter exposure also yields a redder hologram.
A younger plate yields a more broad band hologram and thus a gold hologram
A little warmer water and alcohol baths also increase broadband tendencies.
Here are some variables you can play with.
http://www.holowiki.com/index.php/DCG_Variables
The reason I ask is that it seems your hologram is red/gold near the edges and it is only near the center that it seems the fringes collapsed. This indicates you are very very close to getting a nice bright gold hologram and need to only change one variable very, very slightly to get an even bright hologram.
But to answer you question;
Did you really mean "2g gelatine, 0.085g Amdi and 16.5ml H20"? That equates to a 100:12:.5 formula (water, gel, AmDi). It seems pretty low for the AmDi. If you meant .85g AmDi then that would be 5 grams per 100 water and thus I would lower it to 2.5 grams for red shift.
Also, if you use KDi instead of AmDi you will notice a redder hologram.
A shorter exposure also yields a redder hologram.
A younger plate yields a more broad band hologram and thus a gold hologram
A little warmer water and alcohol baths also increase broadband tendencies.
Here are some variables you can play with.
http://www.holowiki.com/index.php/DCG_Variables
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a_k
405nm DCG
Hello John
The plate is 6x10cm, and veil coated. I made exposures after 4hrs and 16hrs. This plate was exposed 16hrs. after coating with roughly 3mJ/cm2. The gelatine used was 290 Bloom photo-gelatine (Gelita, low ion content). All baths were room temp. First alcohol bath was 96% Ethanol, second 99.x% IPA.
The picture was taken after very briefly blowing away the alcohol, before the hologram had a chance to shift to blue and beyond. I wanted to include a second picture after the plate had dried better, but it had gotten too dim to take a picture. The color of the hologram, two hours after the processing is a uniformly deep violet. The camera would have trouble reproducing that color and record blue instead.
Yes, the formula used is 100:12:.5; 0.085g Amdi were used. I had 2 rasons for using so little Amdi. First i was hoping to get more shift towards red this way. Second the sensibility of the plates for 405nm is very high, even with so little Amdi.
One of the plates had a thicker coating and that plate had very little transmittance for 405nm. I think for denisyuk style holograms with a violet source it would be difficult to use much more Amdi because the beam ratio would not be optimal anymore.
I would love to use KDi but it's almost impossible to get here; it has been banned for private use not long ago.
I'll try shorter exposure. I'm sure 2mJ/cm2 is not the lower limit. And also increasing the temperatures to maybe 25°C.
Thanks a lot for your suggestions.
The plate is 6x10cm, and veil coated. I made exposures after 4hrs and 16hrs. This plate was exposed 16hrs. after coating with roughly 3mJ/cm2. The gelatine used was 290 Bloom photo-gelatine (Gelita, low ion content). All baths were room temp. First alcohol bath was 96% Ethanol, second 99.x% IPA.
The picture was taken after very briefly blowing away the alcohol, before the hologram had a chance to shift to blue and beyond. I wanted to include a second picture after the plate had dried better, but it had gotten too dim to take a picture. The color of the hologram, two hours after the processing is a uniformly deep violet. The camera would have trouble reproducing that color and record blue instead.
Yes, the formula used is 100:12:.5; 0.085g Amdi were used. I had 2 rasons for using so little Amdi. First i was hoping to get more shift towards red this way. Second the sensibility of the plates for 405nm is very high, even with so little Amdi.
One of the plates had a thicker coating and that plate had very little transmittance for 405nm. I think for denisyuk style holograms with a violet source it would be difficult to use much more Amdi because the beam ratio would not be optimal anymore.
I would love to use KDi but it's almost impossible to get here; it has been banned for private use not long ago.
I'll try shorter exposure. I'm sure 2mJ/cm2 is not the lower limit. And also increasing the temperatures to maybe 25°C.
Thanks a lot for your suggestions.
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Joe Farina
405nm DCG
Nice job. That looks like a pretty brilliant DCG hologram. I don't know of anyone else reporting those kind of results using a blue diode, thanks for posting the photo. By the way, are you sure there was no banding? I saw a few areas which suggested banding, but couldn't tell just from the photo. If there was no banding, then that's superb.
To get redder holograms, yes, the first thing I would do is lower dichromate concentration, like you did. Also, based on a paper I have, it might be possible to raise the temperature of the last IPA bath slightly, and get some red-shifting, without inducing a broadband result. But after that temperature is reached, it might become broadband quite quickly. If you're content with broadband DCG, that might be a way of "red-shifting" the final result, in a manner of speaking.
It's a problem to get the water out of the final DCG layer without inducing a blue-shift, especially when recording at that short wavelength. If you have a visible hologram (like in the photo) I would suggest drying in the microwave oven. That might dry and stabilize it without causing a blue shift.
Red-shifting has historically been hard to do in DCG. Tony (Dutchelm05) did a successful series of experiments recently (as reported on the forum) based on some work originally done by Jeff Blyth. He used succinic acid mainly, although he did some tests with citric acid also. He encountered the same kind of gelatin-lifting problems you described. I have the feeling that if this gelatin-lifting problem can be resolved, then the succinic or citric acid method will have tremendous potential for red-shifting DCG. It already works to a certain extent, but if we could get the gelatin to really stick to the glass, we could use higher concentrations and longer soak times, which would probably result in large red-shifts. On Jeff's website (as I recall) he gives directions for using a certain kind of silane to enhance the adhesion of MBDCG to glass. Unfortunately, this chemical, along with many others, is difficult or impossible for some holographers to obtain.
I would suggest looking into ways of getting the gelatin to stick to glass while using succinic or citric acid baths, because a substantial amount of red-shifing would be very helpful when shooting at 405nm. Tony and I were discussing a few ideas to accomplish this, but I don't think any real tests have been done so far. Personally I find TSP a good degreaser for glass, for one thing. I have also heard of putting glass into an ultrasonic cleaner. It might take a rather robust approach, however, to get gelatin to adhere to glass during long acid baths. Maybe Jeff's silane would do the trick. Earlier, John had suggested using ordinary tape along the edges. This might be worth trying, but I would suggest aluminum tape (used for ductwork) because it will hold its shape around the edges of the glass better than plastic-backed tape. Presumably, the gelatin peels off at the edges of the glass first, so if this can be stopped, maybe it will solve the problem. Tony suggested coating this juncture with nail polish, that might be worth a try also. Hope this helps.
To get redder holograms, yes, the first thing I would do is lower dichromate concentration, like you did. Also, based on a paper I have, it might be possible to raise the temperature of the last IPA bath slightly, and get some red-shifting, without inducing a broadband result. But after that temperature is reached, it might become broadband quite quickly. If you're content with broadband DCG, that might be a way of "red-shifting" the final result, in a manner of speaking.
It's a problem to get the water out of the final DCG layer without inducing a blue-shift, especially when recording at that short wavelength. If you have a visible hologram (like in the photo) I would suggest drying in the microwave oven. That might dry and stabilize it without causing a blue shift.
Red-shifting has historically been hard to do in DCG. Tony (Dutchelm05) did a successful series of experiments recently (as reported on the forum) based on some work originally done by Jeff Blyth. He used succinic acid mainly, although he did some tests with citric acid also. He encountered the same kind of gelatin-lifting problems you described. I have the feeling that if this gelatin-lifting problem can be resolved, then the succinic or citric acid method will have tremendous potential for red-shifting DCG. It already works to a certain extent, but if we could get the gelatin to really stick to the glass, we could use higher concentrations and longer soak times, which would probably result in large red-shifts. On Jeff's website (as I recall) he gives directions for using a certain kind of silane to enhance the adhesion of MBDCG to glass. Unfortunately, this chemical, along with many others, is difficult or impossible for some holographers to obtain.
I would suggest looking into ways of getting the gelatin to stick to glass while using succinic or citric acid baths, because a substantial amount of red-shifing would be very helpful when shooting at 405nm. Tony and I were discussing a few ideas to accomplish this, but I don't think any real tests have been done so far. Personally I find TSP a good degreaser for glass, for one thing. I have also heard of putting glass into an ultrasonic cleaner. It might take a rather robust approach, however, to get gelatin to adhere to glass during long acid baths. Maybe Jeff's silane would do the trick. Earlier, John had suggested using ordinary tape along the edges. This might be worth trying, but I would suggest aluminum tape (used for ductwork) because it will hold its shape around the edges of the glass better than plastic-backed tape. Presumably, the gelatin peels off at the edges of the glass first, so if this can be stopped, maybe it will solve the problem. Tony suggested coating this juncture with nail polish, that might be worth a try also. Hope this helps.
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Danny Bee
405nm DCG
John i dont think thats too low for AmDi, 1. gram for 457nm so I would also go for .5 . When I did my test for 405nm i used .5 100/12/.5 remember its really fast in 405nmJohnFP wrote:How did you coat your plate? How big is your plate? How long did the plate set before exposing? What kind of gelatin did you use? What were temps of water bath and alcohol baths? What % IPA were each of your alcohol baths? How did you blow dry?
The reason I ask is that it seems your hologram is red/gold near the edges and it is only near the center that it seems the fringes collapsed. This indicates you are very very close to getting a nice bright gold hologram and need to only change one variable very, very slightly to get an even bright hologram.
But to answer you question;
Did you really mean "2g gelatine, 0.085g Corel Paint Shop Pro and 16.5ml H20"? That equates to a 100:12:.5 formula (water, gel, AmDi). It seems pretty low for the AmDi. If you meant .85g AmDi then that would be 5 grams per 100 water and thus I would lower it to 2.5 grams for red shift.
Also, if you use KDi instead of AmDi you will notice a redder hologram.
A shorter exposure also yields a redder hologram.
A younger plate yields a more broad band hologram and thus a gold hologram
A little warmer water and alcohol baths also increase broadband tendencies.
Here are some variables you can play with.
http://www.holowiki.com/index.php/DCG_Variables
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Danny Bee
405nm DCG
John i dont think thats too low for AmDi, 1. gram for 457nm so I would also go for .5 . When I did my test for 405nm i used .5 100/12/.5 remember its really fast in 405nmJohnFP wrote:How did you coat your plate? How big is your plate? How long did the plate set before exposing? What kind of gelatin did you use? What were temps of water bath and alcohol baths? What % IPA were each of your alcohol baths? How did you blow dry?
The reason I ask is that it seems your hologram is red/gold near the edges and it is only near the center that it seems the fringes collapsed. This indicates you are very very close to getting a nice bright gold hologram and need to only change one variable very, very slightly to get an even bright hologram.
But to answer you question;
Did you really mean "2g gelatine, 0.085g Corel Paint Shop Pro and 16.5ml H20"? That equates to a 100:12:.5 formula (water, gel, AmDi). It seems pretty low for the AmDi. If you meant .85g AmDi then that would be 5 grams per 100 water and thus I would lower it to 2.5 grams for red shift.
Also, if you use KDi instead of AmDi you will notice a redder hologram.
A shorter exposure also yields a redder hologram.
A younger plate yields a more broad band hologram and thus a gold hologram
A little warmer water and alcohol baths also increase broadband tendencies.
Here are some variables you can play with.
http://www.holowiki.com/index.php/DCG_Variables
-
a_k
405nm DCG
Joe, thanks for the tips. I wasn't expecting to get any usable coherence length. That's why i very thoroughly inspected the holograms for banding but there wasn't any banding at all. The artefacts that are visible are caused by the low quality optics and some dust particles on the lens.
I don't dare cleaning the lens, because they become unusable very quickly. Blowing off the debris from the lens was only a partial success. And any attempts of cleaning the optics have worsened things every time. I hope i'll find a better collimator soon.
Based on the deepest scenes used so far, i would think that the coherence length is at least 12cm if the LD is operated at a bit more than half of its nominal power. When the power of the LD was increased to 80-90mW, banding could be forced and the width of the stripes was about 3-4mm in this case.
It's very well possible, that a better coherence can be obtained with very small outputs or with temperature stabilization, but i didnt test that yet.
I played with higher IPA temperature (65°C) and got extremely bright mostly orange and green (and a little blue/violet), mirror-like looking areas. Unfortunately most of the hologram disappeared in milkiness. I'll try again with only slightly elevated IPA temperatures as you suggested. The direction of the color shift seems to be right. What remains is finding the upper temperature limit without causing too much unwanted effects.
Unfortunately i don't have a microwave here. Have you ever tried this? Which power level and for how long?
From what i read about succinic- / citric-acid on the forum it really seems to have a big potential if the coating stays on the glass. With MBDCG i once tried to replace the acetic acid with citric acid for pH adjustment and there the coating separated from the glass too.
Usually my coatings do stick very well to the substrate and sometimes its really difficult to strip the coatings off from the old plates, even with cooking water. I'll try silanating the glass if i can mange to get silane. In the meantime i'll try taping the edges and the nail polish.
Thanks a lot for all the ideas.
I don't dare cleaning the lens, because they become unusable very quickly. Blowing off the debris from the lens was only a partial success. And any attempts of cleaning the optics have worsened things every time. I hope i'll find a better collimator soon.
Based on the deepest scenes used so far, i would think that the coherence length is at least 12cm if the LD is operated at a bit more than half of its nominal power. When the power of the LD was increased to 80-90mW, banding could be forced and the width of the stripes was about 3-4mm in this case.
It's very well possible, that a better coherence can be obtained with very small outputs or with temperature stabilization, but i didnt test that yet.
I played with higher IPA temperature (65°C) and got extremely bright mostly orange and green (and a little blue/violet), mirror-like looking areas. Unfortunately most of the hologram disappeared in milkiness. I'll try again with only slightly elevated IPA temperatures as you suggested. The direction of the color shift seems to be right. What remains is finding the upper temperature limit without causing too much unwanted effects.
Unfortunately i don't have a microwave here. Have you ever tried this? Which power level and for how long?
From what i read about succinic- / citric-acid on the forum it really seems to have a big potential if the coating stays on the glass. With MBDCG i once tried to replace the acetic acid with citric acid for pH adjustment and there the coating separated from the glass too.
Usually my coatings do stick very well to the substrate and sometimes its really difficult to strip the coatings off from the old plates, even with cooking water. I'll try silanating the glass if i can mange to get silane. In the meantime i'll try taping the edges and the nail polish.
Thanks a lot for all the ideas.
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Joe Farina
405nm DCG
That's good news about the lack of banding. Out of curiosity, what does the raw beam look like when coming out of the diode (no lens)? Could you use it without the lens? By the way, I have a lot of small glass lenses and could send a few.
These days, small microwave ovens are pretty cheap, and I have one dedicated to DCG in my lab. It works very well for drying DCG without shrinkage, and I wouldn't be without it. I use a rather "high" setting for various time periods, but the time is not especially crucial. There is a lot of leeway when doing microwave drying of DCG. You can try 5 minutes, 10 minutes, 15 minutes, and so on. But I would only go in 5 minute intervals or less, and let the glass cool down somewhat before the next 5 minute cycle. The glass could overheat and crack. If you get a microwave, and would like more information, let me know, and I will email you a paper called "Microwave drying effects on dichromated gelatin holograms" by A. A. Andrade and J. M. Rebordao (SPIE 1051, 1989, pages 96-103). Tony has used microwave oven drying to good effect also.
The temperature of the final IPA bath might be important. If you like, I can send a paper called "Wavelength shifting and bandwidth broadening in DCG" by Corlatan et al. (SPIE 1507, 1991, pages 354-8). On page 358 they give two interesting graphs showing 1) how the central reconstructing wavelength shifts towards the red for IPA baths at 20, 35 and 40C and 2) how the bandwidth increases for IPA baths at the same temperatures. Regarding the red-shift, they report a change of over 100nm for samples processed at 35C as opposed to 20C. But at 40C the shift does not become any greater, although it does become more broadband. The second graph shows the bandwidth (FWHM) for IPA baths at 20, 35, and 40C. At 20C, the bandwidth looks like about 40nm, at 35C about 80nm, and at 40C it becomes larger still, about 160nm.
By the way, I have a lot of aluminum tape, and could send some if you want.
These days, small microwave ovens are pretty cheap, and I have one dedicated to DCG in my lab. It works very well for drying DCG without shrinkage, and I wouldn't be without it. I use a rather "high" setting for various time periods, but the time is not especially crucial. There is a lot of leeway when doing microwave drying of DCG. You can try 5 minutes, 10 minutes, 15 minutes, and so on. But I would only go in 5 minute intervals or less, and let the glass cool down somewhat before the next 5 minute cycle. The glass could overheat and crack. If you get a microwave, and would like more information, let me know, and I will email you a paper called "Microwave drying effects on dichromated gelatin holograms" by A. A. Andrade and J. M. Rebordao (SPIE 1051, 1989, pages 96-103). Tony has used microwave oven drying to good effect also.
The temperature of the final IPA bath might be important. If you like, I can send a paper called "Wavelength shifting and bandwidth broadening in DCG" by Corlatan et al. (SPIE 1507, 1991, pages 354-8). On page 358 they give two interesting graphs showing 1) how the central reconstructing wavelength shifts towards the red for IPA baths at 20, 35 and 40C and 2) how the bandwidth increases for IPA baths at the same temperatures. Regarding the red-shift, they report a change of over 100nm for samples processed at 35C as opposed to 20C. But at 40C the shift does not become any greater, although it does become more broadband. The second graph shows the bandwidth (FWHM) for IPA baths at 20, 35, and 40C. At 20C, the bandwidth looks like about 40nm, at 35C about 80nm, and at 40C it becomes larger still, about 160nm.
By the way, I have a lot of aluminum tape, and could send some if you want.
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Joe Farina
405nm DCG
It's a good sign that you're seeing those mirror-like areas. Judging from your photos, it looks like you're easily producing very bright DCG holograms. At 405nm I thought there might be some noise due to the short wavelength, but it doesn't look noisy to me. That's good also. Something might be going on with the very low dichromate concentration with regard to this lack of noise.a_k wrote:I played with higher IPA temperature (65°C) and got extremely bright mostly orange and green (and a little blue/violet), mirror-like looking areas.
My first objective would be to buy a small, cheap microwave oven, which should be well under $100, maybe as low as $60. I would use the microwave to dry the holograms so that they stabilize and don't vanish.
Then, I would work on shifting the wavelength towards the red. Even with broadband holograms, the brightest results would come from the center wavelength lying towards the center (or maybe yellow area) of the visible spectrum (I would think). Regarding succinic acid versus citric, I would definitely suggest using succinic (though I know it's harder to find) because Tony reported definite vanishing problems when using citric on DCG, plus the results seemed more erratic.
All in all, this is some really exciting work. Using 405nm in combination with red-shifting might open up a whole new approach to DCG.