So the second one I left on the DVD-burner carriage, and just touched the battery wires to the diode terminals on the secondary circuit board, and DAMN! The light was bright, and the primary lens focuses it quite nicely, thankyou. (I took the fine-focusing assembly off -- it's the fancy magnet-suspended thing that no doubt brings the beam down to a fraction-of-micron spot, but it also clearly depends on a bunch of servo loops that won't be operating once the drive has been bodged.)
This is the point at which I am officially just the tiniest bit scared. 250 milliwatts of laser power aren't much in the scheme of things, but certainly enough to put a nasty mark on my finger or fry my retinas if I make a mistake. On the other hand, now that the laser works and I can pretty much leave it in place, the rest is just a matter of wiring up the arduino and the stepper boards and a fan and a 5-volt power supply and loading it up with known-good software. This is pretty cool. I think the final object will be about 5x5x3", which is darn near small enough to fit in a pocket.