1st time on DCG Project

Dichromated Gelatin.
Zeta
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1st time on DCG Project

Post by Zeta » Wed Jan 10, 2018 11:03 am

Hello, I'm new here and try to work on DCG for my College special projects.
I just bought a potassium dicromate gelatin and some safety equipment. I wonder which laser do I choose? In my country, I can find Red Laser 1mw 5mw 20mw 1000mw, Green Laser 5mw 20mw 1000mw, Blue Laser 1000mw 3000mw 5000mw or which type of Laser suit best and how long for the exposure time? And how do i calculate?
This is my testing setup using cheap Red laser 1mw https://www.picz.in.th/image/0jiEJD and at the background https://www.picz.in.th/image/0jRDbN is it good or not?
For the emulsion I will use 362:68:8 formula.

Any tips and tricks ? Thanks :D

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admin_jsfisher
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Re: 1st time on DCG Project

Post by admin_jsfisher » Wed Jan 10, 2018 9:28 pm

Oh, dear. This gets complicated really fast.

Holography requires a stable light source. Without getting into details, gas lasers of the Helium-Neon variety are usually sufficiently stable in all the ways that matter; argon-ion lasers, not at all. The lasers you mentioned I would assume are all diode (or diode pumped solid state, DPSS). Diode lasers are terrible for holography. Low-power diode lasers (say, 25 mW and below) may be ok, but the exposures need to be kept short (as in seconds, not minutes).

Silver halide holographic plates (like you might get from Integraf) and many low-power red diode lasers work fine. Silver halide is reasonable fast at reacting to the red light. DCG, on the other hand, is not fast nor sensitive to red at all. (There is some special chemistry you can use to improve the red sensitive, but the chemicals are difficult to get; even then, the exposure times aren't all that short.) DCG is sensitive to ultraviolet and near ultraviolet, so a low-power "blu-ray" diode laser (25mw at 405nm) might work. The frustration will come when the gelatin shrinks and the replay from the resulting hologram shifts into the invisible.

DCG has a little green sensitivity. Unfortunately, for green, no pedestrian laser will work for you. Exposure times will be in the 5-10 minute range, and your laser will need to be rock solid stable over the entire time. The Coherent 315 laser at 100mw or so is the preferred choice for many holographers, but now you are in the price range of many, many hundreds of dollars. Same story with blue, but if you can find a low power (50mw or below) 455nm diode laser, it might be work playing with because the laser could be stable enough for the required exposure. Good luck finding a low power diode laser in that color of blue, though.

I don't know how you came up with that gelatin formula, but it seems way to heavy on gelatin and dichromate. (I assume you mean either ammonia dichromate or potassium dichromate. Sodium dichromate is not much use.) It you are want to play with a 405nm diode (or 455nm, if you can find a suitable low power laser), I'd suggest 300-30-2 (with a preference for potassium dichromate).


By the way, I am a rank amateur. If someone else posts in complete contradiction to me, they are probably right.

pluto
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Re: 1st time on DCG Project

Post by pluto » Thu Jan 11, 2018 3:37 am

If you're going with DCG, here are some lasers you might want to look out for:

Coherent Compass C215/C315 - 10-150mW - 532nm

Coherent Sapphire LP/HP - 10-300mW - 458/460/488/514/532/552/561/568nm/588nm/594nm

JDSU uGreen - 5-50mW - 532nm

JDSU uBlue - ?mW - 473nm

Melles Griot 58-BLD-605 - 50-400mW - 473nm - combined power, dual beam output

Coherent Verdi - ?-8W+ - 532nm

Coherent TracER - 8W - 532nm - this ones actually for forensics but OSPL so very likely to operate SLM, laser output is through some kind of fiber-optic wand as a thick possibly diverging beam. $10k+

Crystalaser - any part number that ends with 'S' for SLM. also these guys say they offer every wavelength under the sun: 262, 266, 349, 351, 355, 375, 405, 440, 445, 447, 473, 488, 523, 527, 532, 542, 555, 561, 593 638, 642, 655, 660, 671, 685, 785, 780-980, 808, 852, 946, 980, 1030, 1047, 1053, 1064, 1080, 1313-1342, 1444, 1550

Zeta
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Re: 1st time on DCG Project

Post by Zeta » Fri Jan 12, 2018 8:42 am

So, low-power blue diode lasers might work.
I found this on ebay does it work and does it ready to use or I need other thing to operate it?
https://www.ebay.com/itm/Coherent-Laser ... .l4275.c10
And, is this the cheapest laser from the list?

pluto
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Re: 1st time on DCG Project

Post by pluto » Fri Jan 12, 2018 10:01 am

Zeta wrote:So, low-power blue diode lasers might work.
I found this on ebay does it work and does it ready to use or I need other thing to operate it?
https://www.ebay.com/itm/Coherent-Laser ... .l4275.c10
And, is this the cheapest laser from the list?
Does it work? It appears to be emitting green light in the photo, but whether it's SLM? Probably but impossible to say for sure. It would need a power supply but is otherwise complete.

Huge credit to Coherent by the way, if their lasers are working and the output is good and stable, there's a pretty good chance they're also SLM. This applies more to Compass, but also the Sapphire. Lots of cool scanning and auto-calibration going on inside these laser heads that make sure they're still useful to us holographers 10, 20 years later when they hit the surplus market :)

If you're looking for a laser, here's a 50mW system for just a little bit more cash: https://www.ebay.com/itm/Coherent-Compa ... SwZQxW50go

Generally though I recommend buying the most powerful laser you can afford. You will be able to make small (3x2") holograms with 50mW of 532nm, but I think you will quickly want more power to make larger holograms with shorter exposure times.

DCG is also not very sensitive to green light, you want to get as close to 405nm as possible.

Code: Select all

405 nm	5 mJ/cm2
442 nm	15 mJ/cm2
475 nm	40 mJ/cm2
488 nm	60 mJ/cm2
514 nm	125 mJ/cm2
532 nm	200 mJ/cm2
As you can see, DCG is about 40 times more sensitive to 405nm than 532nm. That means a measly 10mW 405nm laser would be equivalent to 400mW of green! I've read that noise starts to become an issue as you start approaching UV, but I imagine that this can be corrected for pretty easily.

However, you don't see lasers of this wavelength all too often in commercial laser systems that operate in a single longitudinal mode. [Edit: Not on the surplus market at least]

Going with the Coherent Sapphire affords you a lot of flexibility, as the controller can drive a variety of laser heads which go as low as 458nm.

It's a little bit more expensive though, so by all means go with the $300 50mW system -- it'll be great fun and rewarding to make holograms. Just expect to want to upgrade a few months into your holography career :)
Last edited by pluto on Wed Jan 17, 2018 1:12 am, edited 1 time in total.

Zeta
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Re: 1st time on DCG Project

Post by Zeta » Tue Jan 16, 2018 4:30 am

Thanks alot Pluto
Can you give me more information about power supply does it has to be a specific one to work with the laser you gave me the link or which type I should looking for?

pluto
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Re: 1st time on DCG Project

Post by pluto » Tue Jan 16, 2018 9:54 pm

Zeta wrote:Thanks alot Pluto
Can you give me more information about power supply does it has to be a specific one to work with the laser you gave me the link or which type I should looking for?
Here are the power requirements for the Coherent Compass 215M/315M/415M (from Sam's Laser FAQ)
The DC power supply must be correct. THEY ARE NOT THE SAME for the C215M, C315M, and C415M:

C215M: 5 VDC +/-5% only, 40 W max. Applying more than 5 VDC to a C215M controller will smoke it as the semiconductors sacrifice themselves to protect the internal 7 A fuse.

C315M: 12 to 28 VDC +/-10%, 100 W max. The power consumption listed in the C315M spec sheet is 100 W max and the recommended power supply rating is 150 W. I think the maximum would only be needed under the worst case ambient conditions at maximum output power and possibly only momentary or a surge rating since there is a 10 A fuse in the input which implies 120 W max at 12 V. Thus, something in between will probably suffice. The power source can be either a linear or switchmode power supply or a pile of dry cells. :) Or, you could run it from a fully charged 12 V auto battery (so the voltage doesn't drop below 12 V!).
However, I've heard of power supplies that would have seemed to have adequate specifications resulting in erratic behavior. For example, the laser shutting down shortly after the head LED or green output comes on. I have used a 75 W (15 V, 5 A) switchmode power supply on dozens of C315M laser heads over hundreds of power cycles without any trouble, though an LED across the 15 VDC line does flicker with some specific C315M laser heads indicating a momentary power dip from excessive current. I currently use an 80 W (12 V, 6.6 A) supply and haven't seen any problems either. But, a power supply with at least a 100 W continuous rating is probably a good idea if you have a choice.

C415M: 24 VDC +/-10% only, 125 W max. The DC power supply provided by Coherent is rated 300 W!
For the C215M which I linked to, it seems to want 5VDC with a stability of +/- 5%. This means that the voltage must never drop below 4.75V and never exceed 5.25V regardless of power draw.

Precision 5V and 24V power supplies are quite common and shouldn't cost too much. Keep in mind that they must be able to provide 40-150W output, depending on which laser you get.

The only other consideration is the connector type. For the C215M, you will have to attach a P4 connector, which looks like this:

Image

I'll need close-up pictures to confirm that this is the right one. This connector is very commonly used in desktop computers in order to provide power to the motherboard and PCI(e) peripherals.

I wouldn't worry too much about it as far as the Coherent Compass lasers go. Once you buy a laser, I can give you some more detailed information via PM.
Last edited by pluto on Tue Jan 16, 2018 10:51 pm, edited 1 time in total.

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admin_jsfisher
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Re: 1st time on DCG Project

Post by admin_jsfisher » Tue Jan 16, 2018 10:35 pm

Zeta wrote:Thanks alot Pluto
Can you give me more information about power supply does it has to be a specific one to work with the laser you gave me the link or which type I should looking for?
Just to be clear, between laser module and the power supply is the control module. The control module does all the magic of keeping the C215 (for example) stable.

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Re: 1st time on DCG Project

Post by admin_jsfisher » Tue Jan 16, 2018 10:40 pm

pluto wrote:I'll need close-up pictures to confirm that this is the right one. This connector is very commonly used in desktop computers in order to provide power to the motherboard.
That is the correct one for the C215. One important point, though: If you clip that connector and leads from a defunct PC power supply, be aware that the +/- arrangement for the PC is different for the C215 controller. You'll pair a yellow and black to +5 and a yellow and black to ground. Make sure you choose wisely.

Zeta
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Re: 1st time on DCG Project

Post by Zeta » Fri Jan 19, 2018 1:37 pm

Hello, I just ordered laser in the link it should be delivered to me around 5-10 February. Now I'm practiseing my coating skill (veil coating and will try mold coating as well). My emulsion look like a water should it be thicker? (100-12-3) And what good plate should look like before exp and after developed?

When I developed first my 3 plates it came out full of crystal tree, milky in the edge whith a little rainbow and cloudy in the middle, cloudy all over the plate.
I use ilford rapid fixer 1:5 -> Water -> ipp 54% 58% 75% 80% 100% -> heat gun (all bath at 22°C) Exp 10 min with 8$ 5mw pointer laser 12hr dark reaction.

Hope the laser come soon so I can practise whith a suitable laser. :D :D

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