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ArcticMyst Security by Avery

best way to collimate and focus 5w multimode

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Sep 27, 2009
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Hello, I have purchased a 5w C-mount 808nm IR diode.
I'd like to know what lenses to get to focus it to a pinpoint.
I know what I need, a cylinder lens and then a convex to focus it, but I'd like to get the very best to get the smallest dot for burning for cnc use.

I have a 3,2w O-like laser which only has a focusing lens and the result is not very good, the beam diameter is too big and it wants to set everything on fire, rather then finely etching and cutting.

Please help with specific optics to get.
 





Joined
Aug 15, 2009
Messages
1,443
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I'd try it with the two lenses, focus with the spherical and then insert the cylindrical somewhere to compensate for the fast axis of the laser. Play around with both and it should work quite good if the optics have the right focal lengths. Can't think of better ways right now, unless you build a single mode YAG laser out of it.

Edit: You do have proper safety goggles do you? It's a class IV and you're playing with optics. I'd recommend a trusted brand goggles manufactor like glendale or EN-207 certified with proper ratings: OD >5 at 808nm, D 808nm L5 at least.
 
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Joined
Sep 27, 2009
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Hello, thanks for the advice. Would you know where I can buy gless cylinder lenses at a bargain price?
For goggles I have the O-Like 808nm, they seem to be pretty good because they are completely tight around the eyes and because I can't see the beam AT ALL, the instructions say they are OD-5 at 808, so hopefully it should be alright. I might even wear the goggles and still try to focus the beam through a laptop camera, we'll.
The safer the better.
Question though, I thought the cylinder lens would go before the spheric lens, very close to the diode. You say that it can be done the opposite way as well?
Interesting.
 
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Sep 27, 2009
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oops, I just found out that the diode is 915nm 4 to 6 whatt 5-8A, does it sound right?
Do you think it's safe to run it at 8A? the diode is ebay item 330379953122.

I also bought from the same guy this item 290371521464,

it's 980nm 2W it should be able to go to 490nm blue with KNbO3 CRYSTAL
 
Last edited:
Joined
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915 nm is quite far off 808nm, probably too far! 4-6 watts is so much, you'd need OD 5 for 915nm, the O-like isn't rated for that. It may have an OD much lower!
980nm is even more off, no chance yuo're protected against that. Get some wider rated goggles or stay with 808nm.

Note that the conversion efficiency will probably be a bit low if you directly double a diode because of beamprofile issues, although it can be done very nice with some effort.
 
Joined
Aug 15, 2009
Messages
1,443
Points
48
Hello, thanks for the advice. Would you know where I can buy gless cylinder lenses at a bargain price?
For goggles I have the O-Like 808nm, they seem to be pretty good because they are completely tight around the eyes and because I can't see the beam AT ALL, the instructions say they are OD-5 at 808, so hopefully it should be alright. I might even wear the goggles and still try to focus the beam through a laptop camera, we'll.
The safer the better.
Question though, I thought the cylinder lens would go before the spheric lens, very close to the diode. You say that it can be done the opposite way as well?
Interesting.
I haven't found a nice source for cylindrical lenses yet, but I haven't really been searching. 808 is barely visible, worry if you can see it!
Focusing in a laptop camera? sounds like a bad idea, you'll fry the camera.
The placing of the lenses depends on the focal length of the lenses and which axis you correct with the cylindrical lens.
 




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