My first really bright DCG hologram!

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Thieu

My first really bright DCG hologram!

Post by Thieu » Thu Aug 05, 2010 8:33 pm

Well, here it is, finally something I dare to post in the gallery section. I think a little bit of his enlightened spirit radiated onto the hologram.. :wink:
first bright dcg hologram with 445nm diode.JPG
my first bright 445 nm dcg hologram
first bright dcg hologram with 445nm diode.JPG (36.06 KiB) Viewed 3393 times
and a video:


5 minutes exposure at about a meter distance from the 445nm diode, current set at around 250 mA (+/-30 mW)

Thanks a lot for all your helpful suggestions!I wouldn't have been able to make it without them.

dave battin

My first really bright DCG hologram!

Post by dave battin » Thu Aug 05, 2010 8:50 pm

good job Thieu ! This was a long exposuer! was this using TEC unit?

Joe Farina

My first really bright DCG hologram!

Post by Joe Farina » Thu Aug 05, 2010 10:25 pm

dave battin wrote:This was a long exposuer!
Wow, I'll say it's a long exposure, and no banding :!: Last I saw, he was using passive cooling only. Incredible, for a diode. I'm imagining what might be possible with more power....

Superb job, Thieu

Thieu

My first really bright DCG hologram!

Post by Thieu » Thu Aug 05, 2010 10:52 pm

No indeed, everything without a TEC, just the simple heatsink that I showed in an earlier post. And I was a little impatient, the diode hadn't been on for that long, maybe only an hour or so. This may be the reason that the buddha's head (being more at the back) is a bit dimmer than the rest, there may have been a small loss of coherence due to a slight wavelength drift. But as long as the current is in the right interval, there's no mode hopping or switching to multimode, I check the spectrum continuously on the webcam. So banding is never an issue.

The exposures are indeed long. I have no optics whatsoever in the beam and because it's so elongated more than 90% of the area of the beam is lost. I'm working on a FAC to improve this.

JohnFP

My first really bright DCG hologram!

Post by JohnFP » Fri Aug 06, 2010 10:29 am

Excellent job!!!
Gosh I miss holography.

Joe Farina

My first really bright DCG hologram!

Post by Joe Farina » Fri Aug 06, 2010 11:23 am

JohnFP wrote:Gosh I miss holography.
Well John, now would be a good time to return :wink:
Based on what Dave and Thieu have done, it looks like all you need is a $50 diode and a very modest driver/power supply. Also, if you refrigerate your DCG plates, you can use them for at least a month with no problems. For me, it would be extremely impractical to always coat and shoot within a couple of days. If a little refrigerator is used to store the plates, all you need to do is have your laser warmed up, take a plate out of the fridge, let settle/equilibriate, expose, soak in warm water, dehydrate in 99% IPA, and blow dry. With Knox gelatin, I needed no fixing when the plates had been stored in the fridge for a while.

dave battin

My first really bright DCG hologram!

Post by dave battin » Fri Aug 06, 2010 11:40 am

Joe Farina wrote:[

all you need to do is' expose, soak in warm water, dehydrate in 99% IPA, and blow dry. With Knox gelatin, I needed no fixing when the plates had been stored in the fridge for a while.

I have got to try this joe! i have always used a liquid fixer :doh:

Joe Farina

My first really bright DCG hologram!

Post by Joe Farina » Fri Aug 06, 2010 12:04 pm

Hi Dave. Let me elaborate on this. In my opinion, refrigeration of the plates "enables" DCG. Without this, it usually requires at least 2 or 3 full (8-hour) days to make any progress. That's very demanding. And after this kind of session, other obligations pile up, and this makes us reluctant to have another go. Maybe a week or two goes by, and no time is spent in the lab at all.

With refrigeration, we can work 3 hours a day for a month or more, from a single batch of plates, if enough are made. The hardening due to ageing in the refrigerator is no big deal at all, simple adjustments can be made during exposure/processing.

Joe Farina

My first really bright DCG hologram!

Post by Joe Farina » Fri Aug 06, 2010 12:23 pm

I forgot to mention that the plates need to be kept in airtight containers in the fridge. I use lock & lock containers. Also, when coming out of the fridge, water will likely condense on them, like it does when any cold thing comes out of the fridge. There are a couple ways to deal with that. The whole container can be taken out, and allowed to reach ambient temperature, before taking the plate out. This takes considerable time, so I don't do it. Instead, I open the container while still in the fridge. With my other hand, I hold a hair dryer set on high, blowing cold or warm air, and have it turned on and going. Then, immediately after pulling the plate out of the fridge, I apply the forced air to the emulsion side. I try to get the maximum airflow to the emulsion, and hold the hair dryer close, maybe a couple of inches from the surface. Condensation doesn't get a chance to form.

a_k

My first really bright DCG hologram!

Post by a_k » Fri Aug 06, 2010 3:53 pm

Well done, Thieu. The exposure would be about 4mJ/cm2. The thermal drift of the blue LDs is supposed to be considerably lower than for the red ones. It won't take long until we see the first 1m^2 DCG holograms i guess :)

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