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Old 10-29-2011, 11:37 AM #1
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Default Beam expander

Hello all!

Quick question
Does anyone know where I might find inexpensive beam expanders that would be able to generate a (ca) 45 degree angle? I have looked around for expanders and found a couple of places that sells rather cheap ones, but they usually do not expand to that extent.


Cheers!


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Old 10-29-2011, 12:12 PM #2
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Default Re: Beam expander

Beam expanders don't generate angles, they expand beams.
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Last edited by Bluefan; 10-29-2011 at 12:12 PM.
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Old 10-29-2011, 12:16 PM #3
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Default Re: Beam expander

Hm, okay, I though I saw some expanders that were defined by angle but I might have misunderstood it.

Any clue to where I might find expanders that will do large expansions then?
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Old 10-29-2011, 02:44 PM #4
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Default Re: Beam expander

Quote:
Originally Posted by erik View Post
Hello all!

Quick question
Does anyone know where I might find inexpensive beam expanders that would be able to generate a (ca) 45 degree angle? I have looked around for expanders and found a couple of places that sells rather cheap ones, but they usually do not expand to that extent.


Cheers!
A beam expander used in reverse might do the job.
This app might help. You'll need to know the Beam Size and Divergence of the laser you are using. You'll also need to input a negative focal length lens for example -6 in the box that reads focal length mm then convert the mrad result into degrees.
gausian beam rev 2.0.xls

Even a beam expander that allows you to move the lens beyond the optimum collimation position might work.
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Old 10-29-2011, 03:23 PM #5
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Default Re: Beam expander

Use a plain ol' lens to get 45 degrees. Beam expanders are for making a wide beam, not a cone.
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Old 10-29-2011, 03:34 PM #6
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Default Re: Beam expander

Well, I've done a the math a few times now, and it's telling me it depends on the size of the beam to begin with. I didn't expect that, but an experiment proved it, so...



For 45 degrees (full angle, right?) The focal length would then be

tan θ = D/2ƒ
ƒ = 0.5 D tan θ
ƒ = 0.5 D tan 45/2
ƒ ≈ 0.207 D

where D is the diameter of the beam (in mm) and ƒ is the focal length (in mm) you will need. Divergence is negligible.
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Last edited by Cyparagon; 10-29-2011 at 03:36 PM.
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Old 10-29-2011, 05:48 PM #7
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Default Re: Beam expander

Bionic-Badger:
What kind of lens are you thinking of?

Cyparagon:
Math is not my stronger side hehe
Here is the specs for the laser: DPSS Laser,Green laser,Blue lasers,Red lasers form Lasever
Says beam size is 2x4
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Old 10-29-2011, 09:40 PM #8
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Default Re: Beam expander

So you would need a ~0.5-1mm focal length lens. That is absurdly short, so you'll probably have to use two... perhaps more. Just get 2 of the shortest focal length lenses you can.

For what do you need this?
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Old 10-30-2011, 09:18 AM #9
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Default Re: Beam expander

Yes after searching all morning it seems hard to find focal length under 2mm.

But like you say, will just have to use more lenses.
When browsing for lenses I find a bunch of different types, convex, bi-convex, concave, plano-concave.. All new to me, anything in particular in this case I should look for or, not look for?

Right now I am looking at:
Focal Length Lens-Focal Length Lens Manufacturers, Suppliers and Exporters on Alibaba.com

They have a lot, but hard to know what is what without no real basic knowledge :P

Also noticed that some lenses are plastic, and I am guessing that is not suitable when using like in this case a 500mW laser? Specially if it is supposed to run 18 hours a day?



Posted a couple of inputs on this forum before, I think we talked then to (recognize your image). I am exploring the possibility of growing plants with lasers.
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Old 10-30-2011, 02:10 PM #10
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Default Re: Beam expander

Well, I can promise you that LEDs will be cheaper, and I can almost guarantee they'll grow just as well. In this case, I would try taking all the lenses off so you're left with the bare diode output. If it's not round enough, a single concave cylinder lens can help.
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Old 10-31-2011, 10:52 AM #11
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Default Re: Beam expander

But plants are already being grown with LEDs! Never heard of then being grown with lasers though :P
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