The high average power infrared FreeElectron Laser (FEL) provides intense beams of laser light that can be tuned to atmosphere-penetrating wavelengths.
While some of these weapon and sensor systems like the Electromagnetic Railgun or the FreeElectron Laser are at least a decade away, the Laser Weapon System and Air and Missile Defense Radar systems are almost ready for prime time deployment today.
The US Navy's free-electron laser has broken a few records already, but it's just plowed through another fairly big one -- one that its creators say could put it on the fast track to actually being used to shoot down missiles.
Normally, an incoming electron would have a good chance of displacing one of these low-energy incumbents, but unlike the free electrons in metals, which are usually singletons, those in a superconductor tend to wander around in pairs.