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Beam expander to focus laser beam

The trick is matching up the diameter of the spot the laser diode produces on the lens at it's focal length, if using just one lens. A bi-convex lens will collimate a laser diode output, so will a Plano-convex and an aspherical, but the latter is the best for the job due to reduced spherical aberration. I haven't tried using a bi-convex lens to collimate with yet, usually using PCX/plano-convex lenses.
 





Yea, you would need a primary to match that projection lens, I have not had any luck with those projection TV lens, they are nice big lens and I saw Ehgemus build a M-140 HH with one of those lenses, but I don't remember what primary he used, typically a PCX is a better choice for MM.
 
Ha! That' Alaskan's YouTube video. I'd recognize that BE and the place it was shot in my sleep. Chris does do a lot of BE work as he hates not being able to see the spot of a cloud bank. I still think the 6X cyl lens correction first is the best way to go with the NUBM44 diodes.
 
paul1598419 said:
Ha! That' Alaskan's YouTube video. I'd recognize that BE and the place it was shot in my sleep. Chris does do a lot of BE work as he hates not being able to see the spot of a cloud bank. I still think the 6X cyl lens correction first is the best way to go with the NUBM44 diodes.
Click to expand...

Funny. I thought that big lens looked familiar.
 
Ghetto Monster, proof of concept which was never machined into something nice, but still does the job.
 
What lens is at your output? Is it an aspheric? Bi convex? PCX?
 
It’s just an uncoated PCX lens from an old photographic enlarger I found on ebay searching under the term of condensor lens.
 
Yes a large PCX is a good choice for use with high divergence MM beams, the lens in those projection TV housings are aspheric and make huge wings when I have tested them.

They could be made to work, but I don't think there the optimum shape......I have seen beam expanders with a double output lens arrangement, but the more uncoated glass the more parasitic loss.

microscopelasersfigure3.jpg
 
I know you have seen me write this several times over the last two years in a few posts, but if using a large diameter relatively long focal length PCX lens and the diameter of the beam shooting into it covers 50%, perhaps less (for some lenses) of the diameter, then no wings are produced! This may seem to be a huge waste of diameter, but I will take it. I'm imagining the reason for this is due to the lens being flatter, due to less curvature from being a long FL, and from this produces less astigmatism with our rectangle shaped MM laser diode emitters.

This probably has nothing to do with how much percentage of the lens diameter is used, just that the curvature is so much slighter when a long focal length, I just happened to have large lenses which have long FL's.
 
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Yes, that's why I am thinking a long FL very " thin in the middle " PCX because it's the more aggressive curve near the edges that throws the wings, or so it seems, granted I have not worked with all the lenses I have, but I have seen what you are describing.....maybe a thick edged PCX such as a larger lens with the outer circumference reduced so the edge is thick........there's experimenting yet to be done. :beer:


This 350mm FL would need 14 inches from your G2 that would be focused so that it's beam crossed over and printed to cover 80% of this 3 inch wide lens around 14 inches away, but that's positive/positive. Really correcting the MM beam 1st is the best way, then expanding with a concave to print on a PCX. That's what seems to be the best way from what I have read.

https://www.ebay.com/itm/NEWPORT-OR...m=222873847295&_trksid=p2047675.c100005.m1851
 
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Took me a couple of readings and pondering to catch on to what you are saying, but I understand now, a lens which is overall thicker from center to edge with a longer FL might do well to keep the wings from showing up.
 
I expect the problem is more the amount of curvature, even if thick, if the curvature is the same as my larger long FL lenses, not sure what the result will be. The ratio of thickness from center to edge might be the problem with our long emitter MM diodes, but looking at the photograph for that lens, it does appear to have a much smaller ratio, but I am not sure that is an illusion or not, from the camera angle.
 
The longer the FL the shallower the curve, that is longer FL lenses should be flatter ( but not flat of course ) just a less aggressive curve/bulge such as a binocular objective lens is shallow and thick edged.

It makes sense because a shorter FL lens that bends light in faster to bring it to a point closer would have a more aggressive bulge, where as a longer FL lens would be flatter looking as it bends light in more slowly to bring it to a point further away.

This lens is a doublet ( double convex ) but they are shallow and the edge is thick, if it were tapered all the way at this shallow angle to a thin edge the lens would be very wide. The thick edge gives the user the sweet center without all the wasted edge that tapers down to thin.


This lens might be better after 6X C lens correction and a concave expanding lens.

https://www.ebay.com/itm/1pc-72mm-O...519685?hash=item3ad985ad45:g:OqEAAOSwA3dYmBh4
 
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I think I wrote that wrong, I meant, I am not sure what that thick lens will produce with a mere 75 mm of focal length, that is fairly short compared to the results I was able to get with a large 300 mm FL PCX lens with the relatively shallow curve, I just can't see at that camera angle if that thick lens has a relatively shallow curve, it may not need as much curve though, it makes sense, with a given refractive index, a thicker lens will require less curve.
 
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