I want to build an IR laser someday too, been thinking about it for two years now, already have the 808nm C-Mount with FAC lens laser diode too but a bit higher power. The thing which is holding me back is the beam expander I want to put on it, has to be big for a decent divergence due to the 400um wide emitter on mine, much larger than many IR laser diodes. Another thing holding me back is finding a machinist who will build a host to hold the large 6+ inch diameter PCX lens I want to put on it. Mine couldn't be used for burning, not with that much expansion, but would make one heck of a nightlight for night vision etc, if the focus adjustable, the light could make a tight spot or a wide beam output. Not posting to discuss that, but wanted to let you know my interest in this kind of build too and share some of my findings to help others who might also be interested in IR.
If you have a camera which can pick up the beam at night I'd love to see what the beam looks like going out into a dark sky. I bought a cheap camera on ebay and took out the IR filter to be able to do so with one of my other IR projects, you can see it scan by in my avatar as a pink-purplish looking beam color. That beam was produced by a Coherent FA800 laser diode module with a small 20mm diameter SMA coupled PCX collimator on it, the divergence was terrible, but still tight enough to make a decent beam into the night sky, as viewed with my modified camera. That wasn't a pointer though, had a 2 VDC 25 AH Gates Clyclon battery hooked directly to the diode using just a couple of inches of 6 gauge copper wire hanging off the back, well, holding the battery with one hand, the FAP800 with another. The voltage from the single cell lead acid battery was low enough that with a large enough heat sink the diode would not overcurrent, so it didn't have a driver on it for that test. Even after 10 minutes of run time the diode did not go into current runaway because the battery was beginning to be drained by then and loosing power due to voltage sag. Later took everything apart though, need a host built for it using a larger lens.
If someone is interested in building a C-Mount 850nm laser diode pointer, Junktronix on ebay is selling 1.5 watt C-Mount diodes for under 20 dollars each:
http://www.ebay.com/itm/850nm-C-Mou...d-SDL-2365-Burning-Illumination-/252501958250
For burning, I'd get a much higher power one unless using a fairly large diameter PCX lens at least 2 inches diameter to allow the beam to be focused down to a tight spot several feet away, do that and this 1.5 watt IR diode will burn well enough, especially black colored objects. Easiest way to know the diameter and focal length needed is to put a spot on a wall without a lens, see how wide it is at different distances from the wall (using a camera). Then you can know the approximate PCX lens diameter needed at what focal length for infinity focus, then the lens can be moved in or out to widen the beam, or focus to a small spot. Get a lens at least 20% larger diameter than you think you need to allow room for error as well as to keep from using the whole diameter of the lens, you can do that, but having the beam diameter 20 percent smaller than the lens used to collimate it is a good rule of thumb to use. To reduce or possibly eliminate astigmatism wing artifacts I like to use PCX lenses twice as large as the beam diameter.
