Yes, that's what i meant. 5% AD (w/w of gelatine) seemed to me to be a good value with 5-6um thick coatings and 405nm. 2-8mJ/cm2 was sufficient for such plates.
PFG04's coating is 16-17um thick and as these plates are optimised for the blue-green region of the spectrum i would expect them to absorb too much light at 405nm. With such thick coatings even 5% AD would be too much for Denisyuk style holograms i guess.
Holography Noob....Questions
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onyx86
Holography Noob....Questions
So should I use 532nm instead?
Btw, I have constructed a holography table today using the method described here:
http://www.youtube.com/watch?v=TiJ7XvlFmuo
Btw, I have constructed a holography table today using the method described here:
http://www.youtube.com/watch?v=TiJ7XvlFmuo
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dave battin
Holography Noob....Questions
Yes you should use the 532 laser as the 407nm laser will play havoc on your first attempt. the green is much more managable. @ 5% AMDI should work fine to start with, later on you will want to find you maximum ammount of dichromate you can put in the gelatin befor it reaches a crystalization effect when the film dries, the more dichromate in the gelatin, the more sensitive the film is :think:onyx86 wrote:So should I use 532nm instead?
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onyx86
Holography Noob....Questions
Ive tried several attempts on the isolation table, and I still can't seem to get an image. All I get is a dark spot on the glass where the cone of the laser beam hits. This spot forms a small diffraction grating it seems, but no 3D image.
I have the plate going through a concave lens to try and widen the beam. The plate is leaning against the subject (a metal VW bug model) and is about 12" away from the laser. I'm exposing the plate for about 2-3min. Afterward I dip the plate in an alcohol bath- 50%, 70%, 90% and blow the plate dry with a small hair dryer.
The lens seems to only produce a small 0.25" size spot that I can see where the light first passes through the plate. Should it be made larger?
I have the plate going through a concave lens to try and widen the beam. The plate is leaning against the subject (a metal VW bug model) and is about 12" away from the laser. I'm exposing the plate for about 2-3min. Afterward I dip the plate in an alcohol bath- 50%, 70%, 90% and blow the plate dry with a small hair dryer.
The lens seems to only produce a small 0.25" size spot that I can see where the light first passes through the plate. Should it be made larger?
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dave battin
Holography Noob....Questions
it sounds like you need to locate your laser and lens further form your film plate, the laser's beam needs to cover the plate completely and evenly. i would suggest you place your plate on top of some coins to insure there is no movement between object and plate. as far as the post processing you need to get intouch with some hobby photographers to find where they get processing chemicals from(kodak rapid fix). could you post your location and name in your profile so i know what to call you?
and how long do you let the film plate settle befor you shoot?
and how long do you let the film plate settle befor you shoot?
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onyx86
Holography Noob....Questions
These are premade Slavich PFG-04 plates. They're old, but i'm told they should still work. I already have some Kodak Rapid Fixer.
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Joe Farina
Holography Noob....Questions
Onyx86, overall there might be quite a few problems with your equipment and methods, but I will try to give a few honest comments in order to try and help. First, I saw that video with the isolation table. I wouldn't use a table like that. I would just get a concrete paving slab (it needn't be big) and rest it on a small inner tube on a concrete floor (like a garage floor). If you need to raise it up a little off the floor, you can use those cinder blocks to raise a paving slab up, then put an inner tube on top of that, and place another paving slab on top of that. Then place 3 coins (all of the same type) on top of the slab, and place your PFG-04 plate on top of the three coins (the plate should rest stably, and not rock back and forth on top of the coins).
Place your 75mW laser (532nm) somewhere away from the table. It would be preferable to use a tall tripod as a support for the laser head, so you can raise it up, so that it can shine downward on the plate. Do not use a concave lens to expand your laser beam. Use a convex lens. The convex lens will first focus light to a point, then it will expand after that. No spatial filter is needed. The light must expand and cover the entire plate. But to conserve light, don't expand the beam too much. Just enough to cover the plate, with a little spillover on the 4 sides.
I have not used the Slavich dichromate material, PFG-04. I don't know how sensitive it is at 532nm. And I don't know how this material ages. I guess we are assuming that it's not too old.
Now the laser will almost certainly mode-hop (very few 532nm lasers are well-suited to holography), but for these early experiments, I don't think that's a big deal. (The image will likely have light/dark bands.)
Expose some plates with different times (or bracket some exposures on a single plate). Then fix, rinse with water, then go into one or more alcohol baths (I suggest using 99% for the last bath), and blow dry with hot air from a hair dryer.
There are quite a few potential problems here, especially for a beginnner, but that's the best advice I can offer.
Place your 75mW laser (532nm) somewhere away from the table. It would be preferable to use a tall tripod as a support for the laser head, so you can raise it up, so that it can shine downward on the plate. Do not use a concave lens to expand your laser beam. Use a convex lens. The convex lens will first focus light to a point, then it will expand after that. No spatial filter is needed. The light must expand and cover the entire plate. But to conserve light, don't expand the beam too much. Just enough to cover the plate, with a little spillover on the 4 sides.
I have not used the Slavich dichromate material, PFG-04. I don't know how sensitive it is at 532nm. And I don't know how this material ages. I guess we are assuming that it's not too old.
Now the laser will almost certainly mode-hop (very few 532nm lasers are well-suited to holography), but for these early experiments, I don't think that's a big deal. (The image will likely have light/dark bands.)
Expose some plates with different times (or bracket some exposures on a single plate). Then fix, rinse with water, then go into one or more alcohol baths (I suggest using 99% for the last bath), and blow dry with hot air from a hair dryer.
There are quite a few potential problems here, especially for a beginnner, but that's the best advice I can offer.
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onyx86
Holography Noob....Questions
Thanks for your honesty Joe. I already have the table built though. It seems to work nicely and gives me a 4 x 4 foot surface to set up my laser and optics. It's using 4 inner tubes as the suspension device, then has the concrete tiles as the mass for the table.
I'll try the coins tonight with a convex lens and see if that works. What is the best angle to hit the plate?
Oh and there will be mode hopping. I've noticed when I leave the 75mW on for a while, the beam starts to shift between dim and bright. It's only meant to be powered on for 110sec max, so I'm pushing it at about 2min exposure with about 1-2min warm-up / setup time.
I've ordered a JDS 1145P with power supply from Phil (142laser) and also have a holokit coming from Integraf, so I can try how I should have started in the first place with HeNe. These high powered pointers have no heat sinks to protect the diode from overheating and causing damage.
I will probably still play with the 405nm 10mW and these DCG plates though, since it can be left on pretty much continuously, and hey I've got the plates so...
I'll try the coins tonight with a convex lens and see if that works. What is the best angle to hit the plate?
Oh and there will be mode hopping. I've noticed when I leave the 75mW on for a while, the beam starts to shift between dim and bright. It's only meant to be powered on for 110sec max, so I'm pushing it at about 2min exposure with about 1-2min warm-up / setup time.
I've ordered a JDS 1145P with power supply from Phil (142laser) and also have a holokit coming from Integraf, so I can try how I should have started in the first place with HeNe. These high powered pointers have no heat sinks to protect the diode from overheating and causing damage.
I will probably still play with the 405nm 10mW and these DCG plates though, since it can be left on pretty much continuously, and hey I've got the plates so...
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a_k
Holography Noob....Questions
The dimensions you gave for the green laser suggest to me that it is a thin pen style pointer, is that correct? The flickering after a short period of operation, together with your remark that it is not meant to be on longer than 120sec indicates to me that the laser is operated over spec (pot modded). If you can spot the potentiometer which regulates the lasers power, i would lower the power, until the laser does not overheat when run in a constant mode. It is important that during the exposure of the hologram the laser should be as stable as possible and if you can even see it flickering it is not stable at all.
What kind of batteries are you using (i know they are AAA)? I would make sure to use the best possible quality of batteries - they should be able to deliver the current needed without large fluctuations of the voltage. You could also use a stable 3V power adapter or large external batteries.
Now for the plates. According to Slavich's data sheet the sensibility of the plates for green (514nm) is 250mJ/cm2 and their shelf life is 1year when stored in a fridge. As your plates are 2 years old and you are using a laser with 532nm, the sensitivity will be lower and a higher exposure will be needed. Let's be optimistic and assume 300mJ/cm2.
If the size of the plates you are using is 63x63mm / 2.5*2.5", the light beam needs to have a diameter of at least 90mm to cover the entire plate. With a sensitivity of 300mJ/cm2 and with a power of 75mW, this would result in an exposure time of 6 minutes or more.
There are quite a few uncertainties like the laser, the plates, the new table and very little experience with the processing. Therefore i would stick to the simplest and safest procedures. By that i mean:
- Make sure your laser is running as stable as possible (batteries/power supply/additional passive cooling/reducing the output power)
When the laser is turned on, it's power will fluctuate until it reaches a thermal equilibrum, which can take a couple of minutes, sometimes much longer. Because at 75mW you can't let your laser run for extended periods of time, it won't be able to stabilise itself. So reducing it's light output, using appropriate batteries/power supply and using an additional passive cooling could all help to improve the lasers stability.
You could also try not illuminating the whole plate but only part of it. That way the intensity of the beam would increase and the exposure time would decrease accordingly. A shorter exposure time could result in more stability. For each square cm you would need an exposure time of about 4 sec, so if the beam has a diameter of 2cm, the exposure would be about 12sec.
- Make sure to use the most stable setup for the exposure e.g. plate lays on top of a flat object, like a coin, and let the setup rest (like 1minute or more)
- Make sure that the plates have sufficient time to adapt to the room temperature/humidity
- Use a simple processing procedure. The simplest and most basic way would be to:
- let the exposed plate sit (in the dark) for 5-10min
- put it in a dish with water for 30-60sec, agitate to make sure the AD is washed out of the plate
- put it in concentrated alcohol (>90% or 95%) for 1min or longer
- use a hot hair dryer to quickly forced dry the plate, at which time (latest) a hologram should become visible
The alcohol bath can have room temperature but the temperature of the water bath is important. If the water is too cold, there is either no visible hologram or only a weak one. If the water is too hot, the plate becomes milky everywhere. The water temperature is about right, if the unexposed parts (assuming that not the whole plate was illuminated) are milky and the exposed parts are still clear or just getting a bit milky. As your plates are not that fresh any more, you will need a higher than usual temperature for the water bath. I would start with 25°C. If after processing the plate is clear throughout not everything is lost. You can reprocess the plate: let the plate cool down, increase the water temperature (maybe 2-3°C each time) and repeat the entire process (water/alcohol/drying) until you get a satisfactory result. You can stop the reprocessing loop and give up for that particular plate as soon as the stepwise increased water temperature has caused the whole plate to become milky (with or without hologram) because going further will be of no use.
I got good results with this $27 green laser, btw., it runs stable for hours, it delivers true 30mW and there are no sliced-bread holograms with it:
http://www.dealextreme.com/details.dx/sku.10557
Good luck.
Ahmet
What kind of batteries are you using (i know they are AAA)? I would make sure to use the best possible quality of batteries - they should be able to deliver the current needed without large fluctuations of the voltage. You could also use a stable 3V power adapter or large external batteries.
Now for the plates. According to Slavich's data sheet the sensibility of the plates for green (514nm) is 250mJ/cm2 and their shelf life is 1year when stored in a fridge. As your plates are 2 years old and you are using a laser with 532nm, the sensitivity will be lower and a higher exposure will be needed. Let's be optimistic and assume 300mJ/cm2.
If the size of the plates you are using is 63x63mm / 2.5*2.5", the light beam needs to have a diameter of at least 90mm to cover the entire plate. With a sensitivity of 300mJ/cm2 and with a power of 75mW, this would result in an exposure time of 6 minutes or more.
There are quite a few uncertainties like the laser, the plates, the new table and very little experience with the processing. Therefore i would stick to the simplest and safest procedures. By that i mean:
- Make sure your laser is running as stable as possible (batteries/power supply/additional passive cooling/reducing the output power)
When the laser is turned on, it's power will fluctuate until it reaches a thermal equilibrum, which can take a couple of minutes, sometimes much longer. Because at 75mW you can't let your laser run for extended periods of time, it won't be able to stabilise itself. So reducing it's light output, using appropriate batteries/power supply and using an additional passive cooling could all help to improve the lasers stability.
You could also try not illuminating the whole plate but only part of it. That way the intensity of the beam would increase and the exposure time would decrease accordingly. A shorter exposure time could result in more stability. For each square cm you would need an exposure time of about 4 sec, so if the beam has a diameter of 2cm, the exposure would be about 12sec.
- Make sure to use the most stable setup for the exposure e.g. plate lays on top of a flat object, like a coin, and let the setup rest (like 1minute or more)
- Make sure that the plates have sufficient time to adapt to the room temperature/humidity
- Use a simple processing procedure. The simplest and most basic way would be to:
- let the exposed plate sit (in the dark) for 5-10min
- put it in a dish with water for 30-60sec, agitate to make sure the AD is washed out of the plate
- put it in concentrated alcohol (>90% or 95%) for 1min or longer
- use a hot hair dryer to quickly forced dry the plate, at which time (latest) a hologram should become visible
The alcohol bath can have room temperature but the temperature of the water bath is important. If the water is too cold, there is either no visible hologram or only a weak one. If the water is too hot, the plate becomes milky everywhere. The water temperature is about right, if the unexposed parts (assuming that not the whole plate was illuminated) are milky and the exposed parts are still clear or just getting a bit milky. As your plates are not that fresh any more, you will need a higher than usual temperature for the water bath. I would start with 25°C. If after processing the plate is clear throughout not everything is lost. You can reprocess the plate: let the plate cool down, increase the water temperature (maybe 2-3°C each time) and repeat the entire process (water/alcohol/drying) until you get a satisfactory result. You can stop the reprocessing loop and give up for that particular plate as soon as the stepwise increased water temperature has caused the whole plate to become milky (with or without hologram) because going further will be of no use.
I got good results with this $27 green laser, btw., it runs stable for hours, it delivers true 30mW and there are no sliced-bread holograms with it:
http://www.dealextreme.com/details.dx/sku.10557
Good luck.
Ahmet
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The_Stranger
Holography Noob....Questions
Sorry to go offtopic, but do you mean you actually made holograms with that laser? Did you modify it in any way?a_k wrote:I got good results with this $27 green laser, btw., it runs stable for hours, it delivers true 30mW and there are no sliced-bread holograms with it:
http://www.dealextreme.com/details.dx/sku.10557
Good luck.
Ahmet