laser divergence and machine size

Discussions on optics for laser cutter/engravers

Re: laser divergence and machine size

Postby educa » Fri Jul 13, 2012 6:36 pm

TLHarrel, I guess thats something I will have to do IF the beam would not fit inside it. If it does fit, then I don't see why not.

The whole reason of asking this thread anyway was to see if there are reasonable doubts as to if the beam would fit or not. I still find it very strange that RECI lasers doesn't mention beam diameter and divergence on their website, because these params are important. On the other hand I see quite some machines with a path size likt mine and the same pro laser head, so I guess I'm worried for nothing.

Better worry then sorry I always say, these tubes are not cheap!
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Re: laser divergence and machine size

Postby macona » Fri Jul 13, 2012 9:18 pm

Why not just install a beam expander. Limits divergence while giving a larger beam which is better on the optics with less power density on the optics. Less divergence means your spot size will not change as the beam distance gets longer.

Pretty cheap on ebay:

http://www.ebay.com/itm/CO2-10600nm-10- ... 1c277a61a5
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Re: laser divergence and machine size

Postby educa » Fri Jul 13, 2012 9:27 pm

Well, the one you show there allready makes the beam 16mm, so I guess thats just what I don't want to happen
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Re: laser divergence and machine size

Postby macona » Sat Jul 14, 2012 4:57 am

That was just ann example. They make them in various sizes, here is a 2x:

http://www.ebay.com/itm/CO2-10600nm-10- ... 1c277a61b5
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Re: laser divergence and machine size

Postby educa » Sat Jul 14, 2012 8:36 am

ok thanks, good to know.

I still hope that the beam will fit without this, but in case I need it its nice to know
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Re: laser divergence and machine size

Postby educa » Thu Jul 19, 2012 5:48 pm

Just a little extra question about these beam expanders.

Is the laser beam just after the laser tube is 5mm, then I know that it will get bigger based on the divergence value.
If it gets bigger then 14mm then I'm scrued and even if it becomes 12mm it will require precision(which such a machine requieres anyway)

But suppose I put a X2 beam expander directly between the laser tube and my first mirror.since its a 2x expander I'll get a 10mm diameter beam, but will this maybe not get bigger anymore then? Will it stay 10mm behind the expander or will it also become wider again?

If it gets wider again, then I don't really see how it'll solve my problem, so I hope it doesn'tgetany wider after the expander?

Kind regards,

Bart
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Re: laser divergence and machine size

Postby macona » Fri Jul 20, 2012 6:24 am

I beam expander, also known as a collimator, has two functions. First it makes the beam larger in diameter. This decreases the power density on the optics which increases their life. It also has the effect of creating a smaller spot size when focused down which means higher power density and better cutting and finer engraving.

The second thing it does is it keep the beam at a constant diameter. It is basically a telescope and the focus is set to infinity. Ideally you get a nice fat beam with no divergence. Since the beam diameter is constant over the extents of the table the spot size will stay the same and you will get more consistent kerf for cuts and detail for engraving.

So, 5mm beam in, 10mm out and it stays that way all the way to the lens. Most beam expanders have adjustment to fine tune the focus.
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Re: laser divergence and machine size

Postby Techgraphix » Sat Jul 21, 2012 9:49 am

macona wrote: and better cutting

I have my thoughts on this better cutting ... Ok, your spotsize will become smaller, giving you a higher density. But also you Depth of Field gets very small.. For cutting you need quite a big DOF, though?
I do not have any experience with beamexpanders yet, but this came up to me..
someone does??

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Re: laser divergence and machine size

Postby 3DTOPO » Sat Sep 15, 2012 9:04 pm

I just got my 150W Reci and I am planning to add it to my 5x10 foot CNC machine, so I am very interested in this topic.

Does the beam expander shorten the depth of field?
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Re: laser divergence and machine size

Postby Techgraphix » Sat Sep 15, 2012 10:21 pm

yes, in the same ratio as the expansion..roughly
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