Holographyforum.org / holowiki.org

One more think.
Dave or Joe.
If you have a DCG master you made at 445nm at 50mw then you do a an H1 to H2 can you crank the unit to say 500mw?
The point being is that the coherrents length needed is almost nothing since the image plane is just the surface of the glass.
Thanks,
Tony

It stands for external cavity diode laser. These use feedback from a grating to create an extended caity with better coherence. If things work out for Wolfgang and Ahmet, they will have people lined up to buy their lasers, I'm sure.

Excellent!, quite dramatic achievement and good for ALL sensitive materials.

My first DCG test is in and i am seeing micro-bandin on the first shot, this may be due to the current being turned up a bit too high, i was getting greedy and was pushing the output a bit. I'll put it back into the interferometer and check/tune it again ...............

(one hour later)


ok now second time around is much better with the current turned as low as possibe to still allow for lasing. The image now shows no banding again.

pictures later

So it is mode hopping huh, bummer
At what energy were you finally able to shoot at?
Good luck Dave, could be an exciting day

Oh Dave a thought came over me.
When your checking for mode hops play with temperture a bit i.e a hair dryer set on low. Mode hopping can occur with temperature flucuations. Perhaps it will require better heat sinking with a temperature reg. With longer exposures I think it could be a delta T thing.

Good luck my friend!

Thanks a lot for doing those tests Dave. The fact that you got a hologram without banding is very encouraging, even if the current going to the diode was very low. Mirco-banding suggests micro-coherence. I just hope your non-banded hologram did not have even lower coherence (sub-millimeter). In that case, I *think* the hologram would be quite dim (i.e., at 50% brightness). Did that seem to be the case, or was the hologram of "typical" brightness according to your judgement?

Another question I wanted to ask is whether or not you were using feedback. Thieu seemed to be getting excellent results by just using a microscope slide about 2mm in front of the diode. But of course, the only holographic tests done so far have been yours, so we will have to wait and see how Thieu's tests go. Also, how do you determine "single mode" regions for making exposures? Wolfgang has a very interesting noise detection circuit shown on his website, for monitoring stable zones, with an audible indicator. It might be a simple matter to split off part of the beam for monitoring, raise the shutter manually when things are quiet, then lower it when things get noisy.

ok ,there has been a lot going on, and its been difficult to answers all the questions ....

observations to get these diodes to work for holography.

observer fringe structure in an interferometer set up, find the edges of the coherent fringes and note there location, by adjusting current,
dramatic changes can be seen, and only thru trial and error you will begin "tune in" the best structure to make hologram.

my laser is only passive cooled as the diode runs cold at these low mw settings, the trick is to keep the diode temp as stable as possible.
surprisingly the wall transformer from Radio Shack works nicely to drive the unit, Another test i need to do will be to see if the pulsed PS will allow me to turn up output.


it is possible the aspheric optics im using (non coated), are providing some back reflections, helping w/ coherents. A test i need to do is check the diode in the interferometer with no optics ...................

ok so we all had a few days off, as the forum was down over the weekend and is now back! (thanks colin), i did a minor adjustment on raising the output and immediately had banding, so again returning the output power to @ 25mw (after optics), and all the banding ceased. here’s another quick shot at 15 seconds exposure .....

It's good to have the forum up and running again.

Nice holograms, Dave. I like seeing so many DCG holograms, I have a feeling we will be seeing a lot more. By the way, were you using any kind of feedback to the diode?