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Keplerian BE to improve focus of NUBM/NUGM diodes after G-ball (stock lens)

Feb 12, 2016
The question what to do with rectangular spot from some of NUBM08 and NUGM03 diodes while keping the original G-ball in place has been mentioned several times here.

I remember that one LPF member managed to decollimate the beam passing through another G-ball lens (removed from elsewhere) and then collimate it again with G-2.

Me and some other members did it years ago with focusabe Sanwu expander installed after the G-ball. In this way the resulted spot was a thin line similar to NUBM44 spot after G-2 lens.

Now I thought about better focusing of 8 beams emitted from the NUBM08 block and from cost and simplicity considerations the easier construction would seem to put 2 DTR G-2 barrels back to back to each other. In this way they would form a kind of Keplerian beam expander with expansion ratio close to 1.

Galilean BE like (I think) Sanwu could of course also work but making it would require different lenses (PCC and PCX) and I am not sure where to find such small lenses to fit 8 of such mini-BE over the N. block with diodes centers only 11mm apart...

So I experimented a little with DTR G-2, Sanwu G-2 and asymmetric collimators I had from Lasertack (these are shorter but more expensive) and found that the idea works.

Inserted in my CNC made multilens holder the BE from 2x DTR G-2 resulted 24mm long in total when the spot from NUBM08 gave a line on the wall similar to what NUBM44 gives. Since these G-2 themselves are 10mm long, the distance bw lenses backs at this point had to be 4mm.
With 2x Sanwu G-2 the total length was 23mm and with 2x LT collis 19mm. So not very much difference. Only issue was that my multilens holder was just 10mm thick and now I want to make a thicker one (15-20mm) to screw barrels deeper in for better parallelness.

However, when the evening came I noticed on the dark wall some glowing around the focused spots which I did not see without these mini-BE. So it means that some light is lost in the way of refocusing and dissipated around the spot... And I thought that with Aspherical lenses this should not happen!!!

Mesured the output with LPM installed 1m away from aperture (just not very far to fit the whole line into sensor) at 2.6-3A current and found 6-7% loss compared to output of NUBM08 as such. So not super savvy but workable...

It also looks to work with NUGM01 and NUGM02 (I do not have NUGM03 to check) but the glowing arount is more bright (maybe just beacuse of high brightness of green to the eye?).

Sorry I do not attach the pictures of the spots because this was done hundreds of times here.


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Jan 29, 2014
We like to see spot pictures hundreds of times plus :) Well, maybe not everyone, but I do! Earlier today I was looking at some of these diodes on ebay and thinking about this same thing to keep the gball intact, but for the 07E.