On: Can a Geothermal Startup Vaporize Rock to Drill the Deepest Holes?

[avsteele]

your beam waist is going to increase (and intensity is going to drop) after a few hundred meters. you'd have to lower the whole laser down the hole

[lightedman → avsteele]

That's what adjustable diopters are for. Also, at certain power levels, the beam is self-focusing.

[bilsbie → avsteele]

Maybe use adjustable lenses?