405nm- any progress

[msxc]

Hi Holographers!

After studying resources of old forum I found very interesting topic which maybe could be continued?
http://holoforum.org/oldforum/viewtopic ... cb22d9555d

Some time ago out of curiosity I've checked the 405nm laser pointer for DCG, and indeed there is such a nice increase of speed of DCG exposure. Resulting hologram was quite green after developing in hot IPA, and thus well visible and (not surprisingly), the depth of hologram was not impressive(1-2mm). It would be so tempting to make experiments when amount of Dichromate is so minute and exposure can be cut to few seconds. The problem seams to be with availability of stable SLM 405nm diodes(when raw diodes are very cheap nowadays). I've even dared to ask Toptica abouth their system but that was just sort way of "teasing curiosity", knowing that the price will depress me a bit (http://www.toptica.com/products/diode_l ... 05_nm.html). Wouldn't that be a dream laser though ?

So to the questions:
-Did anyone tried the feedback stabilizing the 405nm diodes?
I know experiments by Wler on 405nm laser (http://redlum.xohp.pagesperso-orange.fr ... -test.html), but it is unclear weather resulting laser is truly SLM (or what would be its coherence length).
After reading how glass plate can help in stabilizing 445nm lasers- would that help with the 405nm diodes as well? Real ECDL system is complex, but if "glass plate version" would work, even bellow say 20mW then exposure times are still "slightly better" than with 532nm

-Experiments of a_k reported on the old forum looked so interesting and promising- It would be nice to read about follow up of them.

Greetings,
Marcin (msxc)

[jsfisher]

This seems like it should be a more active topic than it has been. Isn't anyone experimenting with the now-cheap 405 nm laser diodes?

[holomaker]

heres another older forum post about the 405nm diodes, as i remember these diodes had plenty of coherent depth ..............

http://holoforum.org/oldforum/viewtopic ... dc6#p51485

[Joe Farina]

The real problem with 405nm diodes may be diode-to-diode variation. One works, while the other one does not. This is what Ahmet told me about. The original diode that he used for that spectacular DCG hologram stopped working (or maybe he fried it). He tried other 405nm diodes after that, and could not get good results.

If you are really interested in 405nm diodes for DCG, then I would suggests buying an assortment of cheap ones, and try them. If you find one that works, don't blow it!

[jsfisher]

The real problem with 405nm diodes may be diode-to-diode variation. One works, while the other one does not. This is what Ahmet told me about. The original diode that he used for that spectacular DCG hologram stopped working (or maybe he fried it). He tried other 405nm diodes after that, and could not get good results.

If I recall correctly, the diodes used were the higher power units, 100mW and above. I am curious if anyone has experimented at the low end, say 20mW and below. My uninformed guess is that there'd be better luck finding usable diodes in the 5 to 20mw range.

If you are really interested in 405nm diodes for DCG, then I would suggests buying an assortment of cheap ones, and try them. If you find one that works, don't blow it!

Yes, indeed. I already had on order a 20mw module. If things prove favorable with it, I may be inspired to play with a variety of low power diodes.

[holomaker]

just to answer the original question, the coherent 405nm was i think putting out 25mw and was only temp controlled with no feedback window...

[jsfisher]

just to answer the original question, the coherent 405nm was i think putting out 25mw and was only temp controlled with no feedback window...

Coherent Radius, right? Did you use if for display DCG work? I'm interested in what sort of sensitivity you got versus 532nm. Also, was color shift towards the ultraviolet a problem?

[jsfisher]

I bought a low-power 405nm laser from this seller on eBay: http://www.ebay.com/itm/Sony-405nm-20mw ... 1191944643. $19.99, postage included.

Then it came time to try it out. Here is my simple setup.

I used a 3-30-300 recipe for the dichromated gelatin with potassium instead of ammonium dichromate and veil-coated it onto 2x3" microscope slides. I then tried a sequence of test exposures ranging from 30 seconds to 5 minutes and got...nothing. Absolutely nothing. Had I not been able to scrape some of the gelatin off the post-development plate, I'd have convinced myself the gelatin had all been dissolved in the water bath.

Then again, my basement has something of a moisture problem. Add to that a storm moving through, and I started to suspect the water content of my plates was higher than optimal.

So, I microwaved a few in the hopes of lowering the water content.

Bad idea. The gelatin turned a solid white in the final alcohol bath. But, despite the damage the microwave must have inflicted, there was still a glimmer of color around the edges of the white masses. I decided to try a minute or two under a hair dryer instead of nuking to reduce water content in the plates. Here's how that worked:

Milky, colorful, and hiding one little detail. You cannot tell from the picture, but buried in the upper middle of all that mush is one, very distinct golden image of a 1/4" socket head bolt. I looked for evidence of mode-hopping and any other laser diode misbehavior, but did not see any.

This thing might actually work! Now, if I can solve my moisture problem....

Oh, by the way, it was a 45 second exposure, and probably should have been much shorter.

[Joe Farina]

Now that's the way to make progress

When exposing at 457nm, I had good luck with 3-30-200, especially after it aged for several weeks in the refrigerator.

[jsfisher]

One more. This was the last of my high-humidity batch of plates. I warmed this one more gently than before. About a minute on the lower setting of my trusty hair dryer. Most of the hologram came out either deep, deep, deep, deep blue or clear. I will assume the clear parts are where the images is shifted into the ultraviolet. One area, one small area, though, came out slightly more identifiable. The photograph sort of shows what's there.

This was a 30 second exposure, by the way, and it is likely an over-exposure.

At any rate, I am ready to declare to things as universal truths: (1) My skills with dichromated gelatin are crap. (2) The 20mW 405nm diode laser I acquired is suitable for holography.

Anyone else willing to invest the $20.00 to confirm my findings? (Well, the second one, anyway. The first needs no additional confirmation.)