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large beam expander?




Alaskan

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Those look very nice, I haven't seen them before. You probably are well aware of this already, but for the guys new to BE's: If you are going to buy a beam expander the things to consider are:

1. Does the input aperture match the beam diameter, not just the size of the input lens, but the size of the beam it will accept as a clear input aperture?
2. Does the Anti Reflective coating, if any, match the wavelength you want to use?
3. At the desired amount of expansion, is the output lens big enough to allow the light to pass through without clipping?

i.e., a 10x beam expander which allows a 2 mm wide input beam (at that expansion factor) will need to have at least 20 mm of clear output aperture, the output lens should usually have a larger diameter than this, perhaps 10 to as much as 20% wider. This is just an example, many of our laser pointers have a larger beam diameter than 2 mm, especially multimode laser diodes.

I love beam expanders, so had to chime in :) I've bought them up to 150 mm diameter output at 20 and 160X. CNI specs are probably very accurate, but some China ebay sellers will flat out lie to you about the amount of expansion and the maximum input diameter beam, I am very disappointed in them, especially Laserlands who either lied to me (or didn't know their product) in three emails before I bought their expander and then received one which clipped 50% of my input beam and would not even focus to infinity, it was meant for stage lighting, not to be used as a laser pointer beam expander at infinity focus.

Some China sellers (Laserlands one) will list these stage lighting "beam expanders" at a specific wavelength alluding they have a AR coating for that wavelength when they have no coating at all, make no assumptions.
 
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ryanlee

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the "BEW Series Beam Expanders" can be used with a "Beam Size of 4-10mm Diameter", that's the biggest i've seen...
 

Alaskan

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That is one of the largest I've seen too, cool.
 

Alaskan

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Thanks, another source for some nice beam expanders, but don't let the input aperture fool you, they show fairly large expansion factors together with large input diameters which at the stated X are greater than the diameter of the output lens will allow. i.e. 17x at 5 mm input with a 25 mm diameter output lens aperture. That won't work, for that to produce 17X the output lens would be more than three inches, probably closer to four inches diameter to have that much expansion, they show 1 inch output aperture diameter.

Most of the output lens diameters don't match the expansion factor at their stated input apertures. What they are showing are probably the input lens diameters, not the input clear aperture at the expansion factor. This is how Laserlands got me bad, I bought a "20x" expander from them which they said could take up to a 2 mm input beam, nope! 1 mm max clear input aperture, it was really a 10x because the output lens wasn't the 40 mm diameter they told me it was, it was closer to 25 mm. Never mind there wasn't enough adjustment thread to reach infinity focus too.
 
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paul1598419

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I noticed that too. They do have some fairly large input apertures, but the output is far too small on many of them. That alone scares me away.
 

ryanlee

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Thanks, another source for some nice beam expanders, but don't let the input aperture fool you, they show fairly large expansion factors together with large input diameters which at the stated X are greater than the diameter of the output lens will allow. i.e. 17x at 5 mm input with a 25 mm diameter output lens aperture. That won't work, for that to produce 17X the output lens would be more than three inches, probably closer to four inches diameter to have that much expansion, they show 1 inch output aperture diameter.

Most of the output lens diameters don't match the expansion factor at their stated input apertures. What they are showing are probably the input lens diameters, not the input clear aperture at the expansion factor. This is how Laserlands got me bad, I bought a "20x" expander from them which they said could take up to a 2 mm input beam, nope! 1 mm max clear input aperture, it was really a 10x because the output lens wasn't the 40 mm diameter they told me it was, it was closer to 25 mm. Never mind there wasn't enough adjustment thread to reach infinity focus too.
i sent them a email asking why their numbers don't add up and this was their response...

Good morning :)

Whether this particular beam expander will be suitable for your needs depends also on the diameter of your beam.

In case you have more questions please let us know.

Have a nice day,

Jonas Kniūkšta
STANDA UAB
for a full 17x the input beam could be no larger than 1.5mm?
 

paul1598419

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Sounds like a politician. Say something, but avoid answering the question. I certainly would not buy from them now.
 

RedCowboy

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I made offers on this one but did not get it, his best counter offer was 130.00 plus 12 dollars shipping, I was willing to pay 100.00 in total, but there will be others.

We need AR coated for our diodes wavelength and lenses wide enough to accept our beam and allow it to exit without clipping and that means our entry width x the magnification factor plus a 20% margin would be nice. ( My beam will be corrected before the expander ) if yours is highly divergent even with your primary lens ( G2 ) then don't cut your lens diameter short or you can get clipping.

I would avoid any that use a center relay lens, I have made that mistake.

https://www.ebay.com/itm/Thorlabs-BE05M-Optical-Laser-AR-Coated-400-650nm-Variable-5X-Beam-Expander-KS1/132370300399?_trkparms=aid=888007&algo=DISC.MBE&ao=1&asc=41375&meid=ffe8336911604b079a930f0aa549a4cd&pid=100009&rk=1&rkt=1&sd=272621552402&_trksid=p2047675.c100009.m1982


I have been looking at these : https://www.ebay.com/itm/The-laser-beam-expander-lens/261521056220?_trkparms=aid=222007&algo=SIM.MBE&ao=1&asc=49476&meid=89ded6bcaf7f42b5b42dab7c085c78bf&pid=100011&rk=6&rkt=12&sd=132370300399&_trksid=p2047675.c100011.m1850
 
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Encap

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RedCowboy

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Yes but many have a very small relay lens in the center and many are AR coated outside of the range we need so read carefully, we could possibly use just the relay and final output without the original input because they are typically positive, negative, positive.

This one is AR coated for 1064 and I did test it with a 650nm and a 445nm, the 650 works ok but the 445 clips even at 2X, it's a 2-8x but even at 2x it clips because of the small relay lens, I could possibly use the relay as an input and the final output/objective but the coating would rob power and likely burn over time.








----edit-----

If it wasn't for the aggressive and uneven divergence of our multi mode diodes we could simply use our positive primary (G2) and adjust it to work with a larger lens at longer length, I have done this but it's better to correct the divergence first.

If you have not tried a 7A75 or 44 diode with a G2 primary followed by cylindrical correction and then a 3X BE that's readily available it is pretty impressive.

---edit----

This beautiful build commissioned by minimoto and built by 777 if Im not mistaken uses a different Linos than those relay lens units for sale on ebay.

 

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lazeristasUVISIR

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Thanks, another source for some nice beam expanders, but don't let the input aperture fool you, they show fairly large expansion factors together with large input diameters which at the stated X are greater than the diameter of the output lens will allow. i.e. 17x at 5 mm input with a 25 mm diameter output lens aperture. That won't work, for that to produce 17X the output lens would be more than three inches, probably closer to four inches diameter to have that much expansion, they show 1 inch output aperture diameter.

Most of the output lens diameters don't match the expansion factor at their stated input apertures. What they are showing are probably the input lens diameters, not the input clear aperture at the expansion factor. This is how Laserlands got me bad, I bought a "20x" expander from them which they said could take up to a 2 mm input beam, nope! 1 mm max clear input aperture, it was really a 10x because the output lens wasn't the 40 mm diameter they told me it was, it was closer to 25 mm. Never mind there wasn't enough adjustment thread to reach infinity focus too.
The input aperture is not the same as the input beam. :wave:

For 5 mm input beam you would need a larger aperture than 5 mm.

imho, for 5 mm aperture the 1 mm beam is good. With 17x you would have a ~17mm beam and that would pass through 25 mm exit easily.
A 2 mm beam will enter well but at the exit it will be cut. Maybe you don't mind that and it will be suitable for the application.
 

lazeristasUVISIR

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RedCowboy

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Larger lenses are fun to experiment with, this 25mm is actually 2 lenses with a spacer and when used with the raw output of this de-canned 05 it will light a lunch bag at 20 feet and it makes a good looking far field point, there is some clipping because I use it as a primary by sliding it to focus.







 

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Cyparagon

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Rather than use a Newtonian or Keplerian expander, why not just change the collimating lens to something larger with a shorter focal length? It is cheaper, simpler, and smaller.

I found an old mspaint sketch I used to illustrate this a few years ago:



My proof of concept:

 
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