annoying fringes in hologram

[blue_electric_71]

Very cool hologram! The fringes are so symmetrical on the objects they cover.

haha..yeah, it looks quite psychedelic doesnt it...

I did another attempt with a bronze cat figure with the sparkly background.

http://vimeo.com/12526174

The plate was on top of the rather flat cat figure. I let it settle for a couple of minutes, took all the stability precautions I could think of, but there's still fringing going on but more faint, bigger and blurrier on the flat sparkle background and on the cat as well but acceptable... I made another one yesterday with a copper souvenir castle. with the laser attached to a bench vice for more stability...but even that doesn't seem to help...I really don't think it's vibration because they do turn out very bright and crisp. I only got 10 plates left for now and don't want to waste any of them. So I really need a new laser..if it's really a mode hopping problem. :think:

But I'm really lost as to which laser to purchase..and I'm really eager to continue making some nice holograms..
cheers,
Gibert

[bernardb]

That cat one is the best so far...really nice, clear, bight, just cool!

[Colin Kaminski]

go back to batteries and see if the fringes go away, the power supply needs to be good and stable !.................. this could be your problem

It is amazing how stable it needs to be. Run it off of some D-Cells. They last forever.

[blue_electric_71]

go back to batteries and see if the fringes go away, the power supply needs to be good and stable !.................. this could be your problem

It is amazing how stable it needs to be. Run it off of some D-Cells. They last forever.

Yes, I already switched back to batteries..but no difference in the result. I read somewhere to better not use alkaline batteries. How important is this? ..since I can't seem to find any non-alkaline D batteries where I live..

So far, this forum and the people on it have been very helpful thanks

[Cristiano_Perrucci]

Hi, i've been doing some tests and every one of them turned out like this one:

http://vimeo.com/12493171

I just use a simple overhead single beam setup. The video show some clay scarabs and pretty little shiny things..I put them in a black painted metal cup about 1 inch deep. But as you can see the black fringes seem to emanate from each object's center/pivot point..

The is also quite some dust on the concrete floor in the basement where I shoot. Could dust particles be responsible for this effect?

Thanx in advance

Gilbert

A few year ago I tried to stabilize some red LD using TECs and a very accurate driving system. Most of diodes shown the same problem you are talking about. My diodes were free of mode hops because working in stable region and the black fringes were due to lack of spatial coherence (~3cm Coherence Lenght = 1.5cm Depth for Denysiuk configuration).

[jnhong]

Yes, I already switched back to batteries..but no difference in the result. I read somewhere to better not use alkaline batteries. How important is this? ..since I can't seem to find any non-alkaline D batteries where I live..

So far, this forum and the people on it have been very helpful thanks

It is critically important to have a STABLE laser diode so that mode hops are eliminated. This requires (a) a very stable power supply, and (b) a very stable output power. Alkaline cells have terrible voltage-vs-discharge curves. They start dropping in voltage for every microamp you take. Rechargeable NiMH cells have very stable voltage-discharge curves. They will be very steady around 1.2v for a long time until it gets close to empty. E.g. a 2000 mA-hr cell will go for at least 50-75 hours at a discharge rate of 20 mA. Voltage will start around 1.25v and will drop very gradually to 1.20v during that period. You can find AA rechargeables with 2000-2500 mAH easy on the internet, should be just as easy at your local electronics supplier.

That said, in your original case you were already getting very good results with the mains power supply. Your diode is already at 90%.

Stable output is maintained when you have stable power supply, stable operating temperature, and minimum backreflections. When your laser beam hits the plate and the objects, a small portion of laser light reflects back towards the diode's aperture. It doesn't take much reflection for the diode to get confused and produce fluctuations in output power. If your plate/object setup is fairly close to the diode, a good amount of reflection will occur. If the beam is pointed straight on to the plate, a LOT of reflection will feed back into the diode. You need to angle the plate and the laser diode so that reflections are steered away from the diode's aperture. It also helps to have a deep and dark background behind your setup, so that the diode doesn't see itself.

If you need to test the diode for stability, you will have to construct a Michelson interferometer. Watch the fringes over time and maybe you'll see if the diode is good or not.

Joe

[Jeffrey]

Look for what DID work. There are no fringes on the shell. ?? I might have assumed mode hopping, or that your plate moved, but for that.
Check mountings, what holds these objects?

[blue_electric_71]

...so I bought some rechargeable NiMH batteries yesterday and I 'll be doing some testing with the laser distance and angle to the object. I will also try 56 deg angle...

That said, in your original case you were already getting very good results with the mains power supply. Your diode is already at 90%.

does that mean the power adapter would be just as good as the rechargeable batteries..better stick with he batteries right?

An interferometer would be a good idea to rule out stability as a problem....I haven't got any optics to set one up yet..And I don't really know where to start..Edmund optics? and what type and size for laser diode work in general? ..need some optics anyway..and some mounts..Still have a long way to go...but it's all great fun

Look for what DID work. There are no fringes on the shell. ?? I might have assumed mode hopping, or that your plate moved, but for that.
Check mountings, what holds these objects?

You are right Jeffrey about the shell being seemingly unaffected by the fringing, that would suggest vibration on the other objects. ..maybe I could do a test with more stacked coins for a deeper hologram to ensure some stability..

anyway, I will post some results after the weekend
thanx

[Colin Kaminski]

Thanks for the quick reply, I use integraf's 5 mw laser diode...rather odd they would sell you a laser diode that does mode hopping...or could that be different on every single one of them..

I have had three that work. If you look at the board there is a pot. Turn the power down slightly. I have not had to do this but it would be my first idea.

[Viking]

I use the Integraf laser diode too. I have made two holograms that show the same fringes as yours. In between I made holos of other objects without problems.
It only happened with that one object (round shiny metal lighter). So I believe it is the object that somehow is not stable. I would surgest you try other objects.
Untill you are sure about your laser, better use one object only or objects next to each other and not stacked. It is more stable that way.
I tried to video my holo so that you can compare, but I can not upload it.