Improvement on my project

Dichromated Gelatin.
Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Improvement on my project

Post by Zeta » Wed Apr 25, 2018 1:45 am

Hello, my hologram is visible but still some problem.

I am using Lasos 50 mW lasers with 5 MHz linewidth

This is my setup
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56degree
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Area
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Size 7"x 9" Exposure time is 90 minute, 10 minute in Dark, 3 minute Fixer, 5 minute water, 2 minute 59%ipp, 2 minute 84% ipp, 3 minute 99% ipp

I can see diffraction after put the plate in 84% for 2 minute and full plate in 99% for 10 sec but after I dry the plate the top part disappear but the emulsion still there.
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Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Wed Apr 25, 2018 1:58 am

As you can see the right part has no image on it
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Is this call burn in effect cause of over exposed?
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This one is fade on the left
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Is my exposure time too long? 51mw size5”x7”in 7x9plate

My image still blure is it because they have some movement occur while exposing?

Also my image has limited view cannot see from the side.

pluto
Posts: 94
Joined: Fri Feb 05, 2016 2:06 am

Re: Improvement on my project

Post by pluto » Wed Apr 25, 2018 9:09 pm

Please post links to videos, it's hard to diagnose a picture of a hologram. I recommend making smaller holograms as well.

But if you want to calculate the exposure for 5" x 7" inch (17.78cm x 12.7cm) hologram:

17.78cm * 12.7cm = ~225cm^2

50mW / 225cm^2 = Each cm^2 gets 0.222mW per second, or 0.222mJ

DCG sensitivity @ 532nm is 200mJ/cm^2

200mJ/cm^2 / 0.222mJ = ~900 seconds = 15 minutes

To compensate for light losses, add 25%, so say 20 minutes.

I think I did the math correctly?

Log all your developing steps (amount of time, temperature, concentration, etc.)

Making sure your subject doesn't move for such a long amount of time is difficult. Start small and work your way up.

Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Thu May 03, 2018 1:23 pm

Hello

Last time is not going well.So I go back to basic the Coin, I start with 30min but it not that good
https://www.youtube.com/watch?v=jC6fdj_2hM8
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Today I decide to do a test strip 20 30 50 70 90 100 min
https://www.youtube.com/watch?v=NeoPNOh8QN0
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I choose 60min to be my next exp time.
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but the out come is not very impress, compare to the small one. brighter and sharper
https://www.youtube.com/watch?v=x8As5vZkGeU
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Last edited by Zeta on Thu May 03, 2018 1:30 pm, edited 2 times in total.

Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Thu May 03, 2018 1:29 pm

This Is my set up
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My object
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My out come 60min
Super dim and only top of the lens is visible
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Does the subject material affect exposure time?

lobaz
Posts: 234
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Improvement on my project

Post by lobaz » Fri May 04, 2018 5:19 am

My first guess is poor stability of the setup. If anything slightly wobbles when you touch the setup, then forget 60 minutes exposures. Avoid plastics. The wooden board looks too thin. Avoid tall legs freely standing on a surface. Try to put the glass on four rather than three pins and fix it somehow. To avoid air currents, put the whole stack made of the object and the glass into a box with wide enough window that lets laser light in.

Steven
Posts: 33
Joined: Sat Jan 31, 2015 8:14 pm
Location: Cornwall, UK

Re: Improvement on my project

Post by Steven » Fri May 04, 2018 1:03 pm

Some points:

Your reference beam is "dirty" as indicated by light and dark banding.
I assume that your beam steering mirror is first surface coated and not just a normal mirror???
Otherwise the banding may be caused by inter surface reflection in your lens beam expander.

You may be better off replacing the lens beam expander with a small first surface coated concave mirror.
One other advantage of using a concave mirror, is that you will have less light loss, but you will have to find the sweet spot for a clean beam.

I assume that you have done some basic checks on your laser using a simple interferometer setup, to find out how long it takes to warm up?

Settling time:
You must give enough time for both the plate and object to get to a stable state before making an exposure.
For the long exposures needed for DCG, temperature is going to have the biggest influence on stability, assuming the laser is stable.
Mechanical stability is relatively easy and inexpensive to achieve.

I usually set up the objects 24 hours before making an exposure.
This is to allow enough time for any heat that has been transferred from my hand to the object to dissipate into the environment.
It also helps to have the objects stored in the same room that the exposure takes place, several days in advance.
Wearing a pair of lint free gloves, or using tweezers to place objects helps to reduce heat transfer.
I also wear the gloves when placing the plate on the setup. I normally allow a couple of hours for the plate's temperature to normalize before
exposure. Oh, and as lobaz said above, avoid using plastic objects. They are not stable enough for the long exposures used for DCG.

I assume that the "setup" - object stand and plate mount are stable?
I guess that the "wooden board" is made of aluminium or steel and just looks like wood due to the light and dark banding.
It's on the thin side, but it should work, mine is made of 8mm thick Aluminium.
It would be better if you could isolate it from any vibrations if you can, but much depends on the noise environment.
The advantage of using a thicker base plate, apart from its better mechanical stability, is that it takes longer to contract and expand with changing air temperature.

My setup is sitting on a large 11mm thick steel plate that is isolated from the coffee table that it sits on, with a couple of partially inflated bicycle inner tubes. I guess that the steel plate weighs 25Kg or more. You could do something similar, but on a smaller scale.

"Does the subject material affect exposure time?"

Yes. I normally aim for about 150mJ or so total exposure (ref+obj beams).
I don't over worry about this though, but if I'm shooting a bunch of bright coins, I can reduce the exposure time.

HTH,
Steven.
Success through failure - the amateur DCG holographer's path to enlightenment.

Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Sun May 06, 2018 11:49 pm

Update

This time 20 min

https://youtu.be/zvC81IgO_QA
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60min is dimmer
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I have change the mirror and the banding pattern is change rotate mirror banding is also change 90 is like a wave ~~~~ 45 //// 0 ||||
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Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Sun May 06, 2018 11:51 pm

Before mirror
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After mirror
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pluto
Posts: 94
Joined: Fri Feb 05, 2016 2:06 am

Re: Improvement on my project

Post by pluto » Mon May 07, 2018 1:13 am

By the looks of it, you're not using a first surface mirror. There should be no gap between your fingernail and the reflection.

I'm not 100% sure what the consequences of not using first surface mirrors is, but it can't be good!

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