Help!!!!!

This is a forum to share experiences and ideas about holography.
Dutchelm05

Help!!!!!

Post by Dutchelm05 »

Well what I thought was movement on my object may be an issue with mode hopping!! :( :x :sick:
The results look like movement but I noticed last night that they have a slice bread look as well.
I would get these poor results then it would go away, but now it is more often.
I have the Melles Griot 58-BLDR605 Blue laser.

Can anyone tell me how I can verify this this?
Would a Michelson interferometer set up tell me anything?

Thanks in advance,
Tony
Joe Farina

Help!!!!!

Post by Joe Farina »

Holy moley. Not what I want to hear, Tony :oops:

If it's really mode-hopping, then the sliced-bread look will have regularity to it, kind of like zebra stripes. Those bands will appear to run across the surface of the object. Sometimes object movement can be mistaken for mode-hopping, but with object movement, the light/dark patterns tend to be localized in one area of the object, and are often irregular in shape (though they may look banded). With mode-hopping, they run over all parts of the object. If the modes are closely-spaced, you will have wide bands, maybe 1/8 inch per band. If they are widely-spaced, maybe 1 or 2mm.

Even though there are a lot of tests out there for detecting mode-hopping, I would rely on the visual observation of the hologram. The important thing with mode-hopping is that the stripes run over the entire object, and may not be visible right away. But upon close observation of the image, they can be discerned. The dark areas aren't necessarily totally dark, they might appear just a little darker than the light bands.

If worse comes to worse, then the person to talk to might be Sam Goldwasser. Also, Dick Anderson has a technician who knows a lot about these lasers. The Melles-Griot blue lasers are often tuned-up by experienced technicians by using the software, and that may solve the problem.
Dutchelm05

Help!!!!!

Post by Dutchelm05 »

Thanks Joe,
Yes they do look regular and I have tryed some known good object that I have success with.
The rounder the object the closer they are while a more flat object has only one.
I have talked to Sam and Phil who are helping out.
It is heart breaking to be sure.
But I will try to work through it.
I will send some photos tonight for confirmation.

Thanks again,
Tony
Joe Farina

Help!!!!!

Post by Joe Farina »

Yes, please send or post a picture.

I don't know a lot about these lasers, Tony, so it's good that you're in communication with Sam and Phil.

If it's mode-hopping, I wouldn't be despairing about it, though. Something must be causing this erratic behavior to crop up, and it may have something to do with the pump diode. I think there's a good chance that if you send it to Sam, he can use the software to adjust the pump diode, and this might get it out of the danger zone. (The pump diode will age with time.) Have you noticed any unusal power fluctuations when it might be mode-hopping? (But with mine, the power never seemed to be that stable, compared to my 315).

Since your laser includes the letter R, it is a refurbished laser. Do you know what kind of work was done to it? There is a chance that the diode is getting weak. Again, Sam would be the person to ask for advice. But if it turns out that it needs a new diode, definitely talk to Dick Anderson. When I spoke with him last, he said he has access to replacement diodes, and that his technician can install them. The price he quoted me was far, far below what I've heard quoted elsewhere.

If the problem is not with the pump diode, then I'm not sure. There are cases where the contact between some of the of the bonded optical elements begins to fail, but I don't know if this relates to mode-hopping (I don't see how it could, but then again I don't know). I think this kind of event is associated with ghost beams, so have you seen any extra ghost-beams lately? Unfortunately, I don't think there's a cure for that kind of problem, unless Sam or someone else has two units, and the good parts might be swapped to get one good unit. But I think this is a very uncommon event, diode failure is much more likely.

Just thinking out loud, here, Tony. I've just picked up bits of information here and there over the years regarding these lasers. Sam, Phil, or Dick would be the people to ask.
Dutchelm05

Help!!!!!

Post by Dutchelm05 »

I really appreciate it Joe, I never knew how emotionally attached I was to this thing, quite embarrassing actually. It was like a scene from Ole Yeller. :boohoo:

I know before I bought it Sam looked at it. I know Sam and Phil are honest guys and had no problem forking over the money for it. It could be as you suggested.
I know power has not change much. And seems pretty stable, however, Sam and Phil mentioned it was running on the upper limit of the current and it should be turned down a bit. I thought it could be a TEC issue but who knows.
Phil had a good idea and check the mode with a lenses and see if it mode hops, I use to do that on argon lasers back in the old days.
I will post the results so everyone can benifit.

I guess I will use my green laser for a while until this is resolved.

Tony
Joe Farina

Help!!!!!

Post by Joe Farina »

Tony, I would just send it to Sam and ask him to do his best, and don't be in hurry.

Since you will be switching to green, I would suggest using this opportunity to try something new. It might open up some new horizons. Try dye-sensitized DCG. (For me, I'm planning to use dye-sensitized DCG from now on.)

For one thing, that's how 2 or 3-color DCG can be made. I know you had some disappointing results with 2-color holography using straight DCG, but that was just a speculative technique. The tried-and-true method uses dye-sensitized DCG. Not to suggest that you should get into 2-color holography right now, but it's worth keeping on mind.

What I would recommend is that you green-sensitize your DCG with a dye. This would also require TMG, and you would need to monitor the pH, but that's no big deal. That way, you won't have to load your DCG with heavy amounts of dichromate. In fact, you can use extremely tiny amounts of chromate. I would expect the sensitivity to be comparable to heavily-loaded straight DCG, perhaps much better. I don't know of any side-by-side tests at 532nm for heavily-loaded straight DCG vs. dye-sensitized (green sensitive) DCG, and it would be interesting to see how they compare. Besides the environmental benefit of using tiny amounts of chromate, I have the feeling (unsubstantiated) that dye-sensitized DCG will give you better results. If it doesn't, then you can always go back to the old method.

I would take a look at Jeff Blyth's paper in Applied Optics (let me know if you don't have it, and I will send it). In particular, note the simple procedure noted on page 1601. He recommends the dye eosin Y for 514nm, but he may have something better for 532.
Dutchelm05

Help!!!!!

Post by Dutchelm05 »

Many thanks Joe.
Last night I changed my set up so that I had a 6-8 inch beam size verses something like 20 inches. The energy on my plate and object was like 20x then normal. I was able to make much shorter exposures and got good results. I guess it is a lot like walking around with a large flock of seagulls above you, you have to stay in beween the you know what.
So my plan is to keep this set until the end of the year and finish some experiements I am doing, then send it in.

I know a lot more now than I did before regarding two color DCG and look forward to returning to it. However my frist priorty is to strive on consistancy and a degree of repeatability. Like Dave always say, that looks good, now repeat it.
Joe Farina wrote:I would take a look at Jeff Blyth's paper in Applied Optics (let me know if you don't have it, and I will send it). In particular, note the simple procedure noted on page 1601. He recommends the dye eosin Y for 514nm, but he may have something better for 532.
Yes I would be very interested in this paper, if it is not too much trouble.
Tony
Dutchelm05

Help!!!!!

Post by Dutchelm05 »

I was getting around my possible mode hopping by using smaller plates and lower exposures.
I have been trying a 5x7 plate resently and I am getting them again.
I still don't know if it is movement or mode hopping.
Is the result always multible slices at even intervals or can it be one ring???
I get what seems to be one ring or line across.

Let me know if you can help :wall:
dave battin

Help!!!!!

Post by dave battin »

Hi tony! as a suggestion try some forced air on your heatsink to see if this changes things, my old coherent radius laser (35MW RED) would mode hop when the weather got warmer in the lab, i then discovered the additonal forced cooling worked as a band-aid (telling me the TEC controler was shot)........... :wall:
Dutchelm05

Help!!!!!

Post by Dutchelm05 »

Thanks Dave,
I actually did do that, a fan with a freezer pack behind it.
I also ran a portable AC unit in there an cooled down my lab as much as possible (like 75F)
I will have to try something to verify it
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