Far out physics, but not a far out question. I can recall seeing an article on advanced nuclear weapons, including pure fusion weapons, in Scientific America a few years ago. Besides getting a fusion reaction to go without a fission trigger, other subjects included issues of efficiency to use less fissionable material in such a way that there would be less fallout, and the use of nuclear pumped x-ray and other wavelenght lasers as a hard target weapon that would have little "collateral" effects. I've read of using either solid state lasers and even conventional explosives as possible triggers. One use for the 3rd generation nuclear weapon, the neutron bomb, that has been discussed is to use one or more against possible asteroid collisions. The object, if intercepted out far enough, would be deflected by the force of the neutrons hitting its surface, thus not breaking it up as would an intercept involving heat and shock might create.

For some more information on this, on the Nuclear Weapons Archive webpage, under Other Archived Material, are excerpts from Weapons of Tomorrow, by Brian Brethut, Plenum Press 1983.

It is related to directed energy thermonuclear device like shaped conventional charge are directed charge.France, US and Russia are working on.

That was interesting reading indeed. It appears that question of feasibility is still unresovled and will remain so for some time.