The Strategic Defense Initiative (SDI) included so-called third-generation, or nuclear directed-energy, weapons. While the long-term goal for SDI was an effective nonnuclear defense, research also continued on promising new nuclear explosive concepts. Design teams began studies of the nuclear-powered x-ray laser as a candidate defense technology and explored the physics of such weapons in underground nuclear tests. In addition, particle beams, the free-electron laser, and other nonnuclear directed-energy weapon concepts were studied on a laboratory scale.
Nuclear Powered X-Ray Laser

The initial centerpiece of the project was to be an X-ray laser curtain that was to be deployed as a satellite and powered by a nuclear warhead built into the satellite -- in theory the energy from the warhead detonation was to pump a series of laser emitters in the satellite and produce an impenetrable barrier to incoming warheads. However, the initial (and only) test done on the design, done in an underground shaft, gave nominally positive results that could easily be dismissed as coming from a faulty detector; due to the use of a nuclear explosion as the power source, the detector device was destroyed during the experiment and could not be examined after fact.
SDI- Wiki

A theory that may one day be viable...