Laser induced plasma channels (LIPC) combine three of the most awesome things modern science can produce: lasers, plasma, and giant electrical sparks. It's a method of controlling electrical discharges so that they actually hit a specified target, rather than jumping to whatever grounded object happens to be closest.
The idea of using Tesla coils as a weapon has been around for a long time, most famously in the RTS series Command & Conquer. Unfortunately the silly things can't be aimed. But if they could! They could destroy sensitive electronics, ignite flammable materials, and kill or, at less-than-lethal settings, stun human targets. Giant bolts of man-made lightning are pretty versatile.
The trick to aiming an electric discharge is creating a conductive path between the weapon and the target. This is the idea behind the Taser gun, which fires a pair of metal hooks trailing a pair of wires. The electricity travels down the wires to the victim to deliver its tetanizing dose of high voltage. The problem here is that the hooks are a one-shot weapon. They need to be reeled back in and recharged with compressed air to be fired again. If you miss, the victim will not likely wait while you reload. They also don't penetrate well into body armor, or leather jackets for that matter.
The idea behind a laser induced plasma channel is to create a conductive path without the need to provide wires as a physical medium. Instead, powerful ultraviolet lasers can ionize a thin channel of air between the weapon and its target. Hey, you ask, why not cut out the middle man and just shoot the dude with your ultraviolet laser? Because it takes a lot more power to build a laser strong enough to damage a target directly. In fact the technology does not yet exist to do this in a man-portable size (military HMMWVs exist, however, with lasers capable of destroying IEDs from a safe distance). The power requirements to simply ionize a thin channel of air are much, much lower, although stil pretty significant over long distances.
filoraene adds: The reason they use UV is because it can do single-photon ionization of nitrogen, argon and oxygen. Using straightforward thermal emission works too, but requires thousands of times more power.
Plasma, the high-energy fourth state of matter consisting of positive ions and a cloud of free electrons, is a better conductor of electricity than ordinary air. All those free electrons floating around, you see. This laser-induced channel of plasma takes the place of the wires in a traditional Taser, allowing the weapon to be re-aimed and fired numerous times quickly. Furthermore, it can be aimed at any grounded target, without the need to find vulnerable fleshy targets which will accept the hooks. It will not, however, work in a vacuum, because there is no air to ionize. But if your target is in a vacuum he probably has other problems.
Aside from the obvious use as a directed-energy weapon, the military is investigating this technology as a means of designing a portal denial system, which is army speak for "We've booby-trapped the door so you can't get in." A series of LIPCs across a doorway can guide a fence-like series of high-voltage sparks across it, shocking or even killing anyone who attempts to enter. It's the closest thing we've got to a force field right now.
On a more peaceful note, this can also be used as a lightning rod. Standard lightning rods use a tall metal spike to attract bolts of lightning and guide them safely to the ground without setting anything on fire on the way down. You can thank Benjamin Franklin for this one, it almost makes up for him getting the direction of electric current backwards. The LIPC could work in a similar manner. If the ultraviolet laser is fired up into a stormcloud, it could guide the lightning harmlessly to the ground without the need to install a metal spike on the tallest building you can find.
Peaceful intentions or not, any time you're talking about harnessing massive amounts of power, somebody can figure out a way to weaponize it. I'm looking in your general direction, Alfred Nobel. Airplanes equipped with powerful (very powerful) ultraviolet lasers could just as easily fly above stormclouds and intentionally direct lightning strikes on targets on the ground. It would be awfully difficult to prove this wasn't a natural occurrence, despite the fact that natural lightning rarely strikes targets on the CIA's assassination list with such regular convenience.