If I remember right (which is unlikely :-) the US DoD did some experiments
with xray lasers for the "Star Wars" (SDI) program. These invloved a nuke
as the trigger, surrounded by rods of lasing material. This was probably
a "single pass" type of laser (ie no bouncing back & forth to get really
good amplification) and relied on the fact that the xrays went faster than
the heat/shock wave which destroyed the laser rods.
I think one was tested in an underground detonation test but I don't think
the results were very good. Any one remember anything more about this one ?
Dave (going back to lurking :-) Sansom