Comment Re:Calibration (Score 2) 194
Ablation can in theory remove single atomic layers with thermal damage only a few atoms deep to the underlying surface.
So the damage to the surface is only a few times larger than what was removed?
The damage is only a few atomic layers deep, more or less independent of how much material is removed.
A large limitation to how much you can remove is that you build this huge largely opaque cloud of debris blasting off the surface of the material so you can't get new photons into the surface anymore, but you can peel stuff off a few atoms in a burst or a few dozens of micrometers in a burst, with the same very thin heat affected zone at the surface. (Another is that all the stuff you just blasted off immediately sticks to the front of your objective lens, but they don't last long anyway when you have this many photons going through them: objective mirrors last longer but still get covered in junk. Some interesting stuff being done using liquid waveguides through which the laser moves and which wash off the debris, but then you have to not vaporize/ablate your liquid waveguide. And at least with the UV stuff we were doing, even the atmosphere absorbed giant amounts of the energy, so we had to do it in a vacuum and that made the crap-sticking-to-the-lens problem even worse.) My recollection is that people were trying to use laser ablation to do extremely thin heat-treatment, like surfacing treatment, but couldn't actually get it thick enough to make a measurable difference in wear characteristics, but A: I may misremember and B: people may be better at this now, so that bit could be complete hooey. I got out of high-energy lasers like fifteen years ago, when I realized that fully half my coworkers had pie blindness: they'd managed to damage some part of their eyes so they were missing some of their visual area, and stuff may have progressed a lot since then.