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Interested in Beam Expanders ???

Ehgemus

Ehgemus

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So I'm kind of interested in these Beam expanders. I would like to build a few custom beam expanders but I know nothing about what optics I would need. If anybody would like to help with the optics part I would be willing to do the machining on the housing for them. Anyone interested?:wave:
 
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Re: Kind of Interested in Beam Expanders ???

Someone correct me if I am wrong, but would it not just be a set of telescoping lenses? I will look around thorlabs, i know they offer them.

edit: yep, appears so. Heres my results; beam ~2cm after second lens, and a smidge over 2cm a few feet away. Keep in mind this was done with me roughly finding the focal lengths, and using binder clips as lens "mounts." Precision machining would do a much better job for sure.

Mind the craptasticly horrid pictures, this was on the fly and I was using my phone...so yea.

after 2nd lens/"aperture"
HolrWpe.jpg

wall ~few feet away
OIYSvXZ.jpg


This was done with a single mode diode, collimated to the best of my ability. Multimode diodes would have very different results, maybe some sort of correction could be implemented as well. Have a normal sized host that only fits one 16340 cell because the rest is optics :crackup:
 
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I can't give any help, but if you ever come out with these expanders, I'll be a buyer for sure.
 
Me, me, me, me..... arm up.... I love expanders, I have large lenses but unable to machine the fixtures. Also, pretty broke for a few weeks :(

I can send you to edmund optics for some basic info: http://www.edmundoptics.com/technical-resources-center/lasers/beam-expanders

Also, pick just about any telescope you like, they all function as a beam expander in reverse.

There are some folk here who know expanders and I've learned a few things, here's an old thread on what I did learn. I wish some of the senior laser techies would chime in on the subject in this thread, as it is of intense interest to me:

http://laserpointerforums.com/f49/diy-beam-expander-42814-4.html

One of the problems with using a telescope as a beam expander is the curve for the eye piece is rather shallow compared to the diameter of the laser beam hitting it and because of that, they don't always make very good beam expanders. The size of the eye piece, or concave negative focal length lens should be so small so that a significant portion of the lens is filled by the diameter of the laser beam hitting it, close to the entire diameter but even half or a quarter and even less would work to expand the beam. The deeper and more bowl shaped the more negative its focal point will be and when coupled with a positive focal point lens of the right diameter and distance from the expanding concave lens, you have a beam expander.

The correct distance between a negative focal point concave lens and a positive focal point PCX or plano convex lens depends on the focal points of each, the positive or PCX lens sets the majority of the distance. Add the focal lengths of the negative and positive lenses together and you have the approximate distance they need to be separated, if I understand correctly. If you had a 100mm FL PCX lens (flat side towards the laser) and a -10mm FL concave lens, then the beam should be expanded by 10X and the distance between the lenses 110mm center of lens to center of lens, if I understand the principle correctly. Maybe it would just be 100mm between the two? I'm not sure.

My understanding is that the expansion factor or amount of expansion is the negative FL lens divided by the positive FL lens and thus in this example, a 10X beam expander. I believe you could improperly pair negative and positive FL lenses together and still make them work in this example, just that you could either overshoot or undershoot the diameter of the output beam to match the size of the PCX lens on the end of the tube. If you expand too much you waste some light by hitting the side walls of the tube, if too little you have not expanded the beam enough for the available diameter of the PCX lens on the end of the tube, producing less expansion than might otherwise be had. Anyone know if I am correct on this or not? I am thinking this is what happens when you don't have your telescope focused correctly, same with a beam expander except in reverse.
 
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I got some rather large lenses out of a projector today- I will try using one with a small lens like you said. Ill post my results if I remember too.
 
RYDorDIE278 said:
Have a chat to CDBEAM777! he seems to know his stuff when it comes to corrective optics, if you and him work together im sure you's could come up with a very very compact design , heres his last gadget http://laserpointerforums.com/f49/a...any-hand-held-unit-proto-type-done-89122.html
Click to expand...

Except this is regarding beam expanders (as the thread title states), not corrective optics. Although like I mentioned in my post, corrective optics COULD be used before the expansion, but that would make the whole thing quite large.
 
crazyspaz said:
Except this is regarding beam expanders (as the thread title states), not corrective optics. Although like I mentioned in my post, corrective optics COULD be used before the expansion, but that would make the whole thing quite large.
Click to expand...

My bet is that CDBEAM knows about divergence adjusting optics as well though.
 
A simple google search brings up a few really helpful PDF's as well. I am surprised by the amount of info on how to make them. Also, you can use anamorphic prisms too,kinda cool.
 
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ohhh duhh, i was trigger happy on that post! sorry guys
CDBEAM777 will probably still have some good input to this thread if he does chime in,
Well im subscribed to this thread, be interesting to see where this goes!
 
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Anyone that's interested in a large lens from a projector shoot me a PM got half a dozen just gathering dust here.
I love beam expanders own both beam expanders from Dragon Lasers and have plans to build a large one over the winter. Looking for a optical bench first and surplus shed stock magically dissapears whenever they have a sale.
 
I think first we have to decide on a
magnification power, or a range of powers
for an adjustable beam expander and then
make a choice on lenses based on that.
Also the lens supplier and available lenses
will be a factor.
 
Thanks for the help so far guys.
So am rite to say that a basic beam expander would need just two lenes?
 
Yes, two lenses, an expander and a collimation lens for one type, the most common type as below, consisting of a biconcave and a plano convex lens:

36e058f2-5464-46e1-b1b3-53b2c045cbdc_zps72adcbe3.jpg


The above photo ripped from this document: http://assets.newport.com/webDocuments-EN/images/How_to_Build_a_Beam_Expander_5.pdf

To me, the above drawing is a bit misleading because the beam should be expanded enough to cover 80 percent or more of the output lens diameter, to do that, the right expander lens would need to be selected with a shorter negative focal length, the shorter the negative FL the wider the expansion. The following diagram shows the virtual focal length of a negative biconcave lens:

expanderlens_zpsa0d83728.jpg


Optical physics lesson on concave and convex lenses: https://www.youtube.com/watch?v=SqIGBjEB07c&list=PL4jewF29p-5pbOm6WRfBgzfcxW9z34xJq

More on concave lenses: Start at minute 2:45 https://www.youtube.com/watch?v=8gyGfiiC3ms
 
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Let me throw in here ! Well yes, I am an " Optical Guru" WANNA BE !!! Who knows enough to be dangerous !! I have spent all my time trying to get the beam smaller....not larger....but...the approach is basically the same !

Get two (2) pieces of glass in front of the beam. have a way to keep them secure and likely adjustable in the case of Beam Expanders....and there ya go !

I am sure we as a community can do it much less expensive than Edmonds or Thor !!!

I will study up on this and possible mounting options. I have many, many irons in the fire now....so give me a little time....But you can bet we can do something !!! And...
 
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