FAC lens nubm44 correction.

[kecked]

You you necroposter you

[Laser57]

One milliradian at 68 kilometers is 68 meters - if you expand a 3mm beam with one milliradian divergence to one meter diameter at the source your beam would still be on the order of 200mm across at 68 kilometers, and vibration would be a real problem...

Here's how to get a spot beam of about 68 meters or less diameter after 68 km using the setup I used:

Not wanting to be bashed about the head and shoulders for necroposting, but I built a pointer using the NUBM44 diode which had a pair of cylinder lenses for 6X expansion of the higher divergence polarity and then put a 3.3x beam expander made by Sanwu Laser in front of it and although I didn't measure the divergence, it seemed fairly good, then I put a 3.6X camera teleconverter in front of that which is really an inexpensive fixed beam expander, and then the divergence was far lower. I still have not measured it, but with the beam squared up and then expanded further with the Sanwu expander and this camera lens (link below), it was a very good fit with a total of 6 + 3.3 + 3.6 X of expansion for a total of almost 13X expansion, that ought to bring the divergence down to somewhere close to 1 mRad, if not below it, which is outstanding for this laser diode. Sure, lots of elements in front to add to the loss, but not objectionable or too expensive either.

With about 1 mRad of divergence, the spot size should be 68 meters or less at 68 km.

https://www.ebay.com/itm/3-6X-TELEPH...1/161728890763

Note: I don't remember the uncorrected divergence of the NUBM44 using a 6 mm diameter collimation lens, but I believe it was somewhere between 11 and 12 mRad, if so, then 12.9 X correction would make a tighter diameter spot than 68 meters.