We've known it was possible for quite some time now — but now there's photographic proof. You can use a laser beam to aim a lightning bolt at a target, with devastating results.
This photo comes via the U.S. Army, which posted it last week but it's been popping up everywhere today. The Laser-Induced Plasma Channel (LIPC) uses a very short laser burst with a modest amount of energy — but because it's so brief, the power mustered is tremendous. The output of the "optical amplifier" is 50 billion watts, according to George Fischer, the lead scientist on the Army's LIPC project.
As Fischer explains in the Army's article/press release:
Light travels more slowly in gases and solids than it does in a vacuum... We typically think of the speed of light in each material as constant. There is, however, a very small additional intensity-dependent factor to its speed. In air, this factor is positive, so light slows down by a tiny fraction when the light is more intense.
If a laser puts out a pulse with modest energy, but the time is incredibly tiny, the power can be huge. During the duration of the laser pulse, it can be putting out more power than a large city needs, but the pulse only lasts for two-trillionths of a second...
For very powerful and high intensity laser pulses, the air can act like a lens, keeping the light in a small-diameter filament. We use an ultra-short-pulse laser of modest energy to make a laser beam so intense that it focuses on itself in air and stays focused in a filament.
If a laser beam is intense enough, its electro-magnetic field is strong enough to rip electrons off of air molecules, creating plasma. This plasma is located along the path of the laser beam, so we can direct it wherever we want by moving a mirror. Air is composed of neutral molecules and is an insulator... [But] the plasma channel conducts electricity way better than un-ionized air, so if we set up the laser so that the filament comes near a high voltage source, the electrical energy will travel down the filament.
See more details at the link. [U.S. Army]