How short of a pulse can we get?

I would recommend an Othermill for quick PCB prototyping. Copper is a great mirror at 10600nm. For cutting it, you want a YAG, fiber, diode, or other laser.

That said, you can (I’m told) get some fantastic, super detailed etching by putting a resist on the material, engraving it off with the laser, then chemical engraving. That doesn’t get you holes though.