Books about speculative or actual advances in nuclear or other advanced weaponry since the hydrogen bomb

Talking non-fiction. I'm looking for books that go over actual or speculative advances in nuclear and other advanced weaponry post the development of the hydrogen bomb and MIRVs. Obviously a lot of it is top secret but clearly some things, like advances in directed energy weapons, are "known" to the public. I've heard things about other types of weapons, like nuclear powered plasma jets, but lack the keywords to Google them.

Thanks!