DARPA's HELLADS (High Energy Liquid Laser Area Defense System) will be light enough to fit on a fighter jet or drone aircraft, and yet powerful enough to fire a 150 kilowatt beam of energy. Star Wars laser cannon may be closer than you think.
High energy laser weapons already in development are powerful enough to bring down missiles (see MTHEL - Mobile Tactical High Energy Laser). However, their very large size has precluded placement on any but the largest planes. The main weight problem comes from the cooling systems needed.
HELLADS makes use of a unique cooling technique to save weight. The high-energy laser uses a liquid that has the same angle of refraction as the mirrors inside the blaster. That way, the "ray gun" can fire away, even while it's being cooled. Currently in the third of five phases of development, a 15 kilowatt subscale prototype is being tested in the laboratory. In the next phase, the demonstrator device will be scaled up to 150 kW, and will specifically be targeted to achieve the low specific weight (5 kg/kW) and compact size need to be mounted in a smaller airborne vehicle. The final phase is engineering, fabricating, integrating and demonstrating the complete HELLADS weapon system on a tactical platform. The device will be built by General Atomics and the tracking system will be built by Lockheed.
This kind of compact system is getting very close to what science fiction writers since H.G. Wells have envisioned when writing about the heat ray in War of the Worlds. More recently, Larry Niven and Jerry Pournelle wrote about laser cannon in their 1974 novel Mote in God's Eye:
(This Science Fiction in the News story used with permission from Technovelgy.com - where science meets fiction.)