Those clever chaps at the Pentagon's Defense Advanced Research Projects Agency (DARPA) have apparently overcome the traditional impediment to a useful airborne laser weapon - it's so big you need an airliner to carry it.

The spawn of DARPA's High Energy Laser Area Defense System (HELLADS) programme, on the other hand, come in a handy fridge-sized format, weighing in at just 750 kg (1,650 lb). Although the prototype - inevitably dubbed the "HEL weapon" by its chuckling developers - generates just one kilowatt, they're looking to ramp up the power to 150kW by the end of the year, and have an operational prototype in the air by 2007.

The DARPA secret behind the relatively diminuitive HEL is, according to New Scientist, to take the best of liquid lasers (continuous beam but plenty of cooling), and solid-state lasers (plenty of output but short bursts only to prevent meltdown).

DARPA explains:

The Air Laser program will investigate the potential for a high energy laser (HEL) concept based on direct diode pumping of liquid oxygen. If successful, the Air Laser could provide a safe, efficient kilowatt-class HEL which combines the advantages of chemical and solid state lasers and minimizes the disadvantages: it operates in the eye-safe wavelength regime; it uses liquid air as the gain medium and as the diode array coolant, resulting in the reduction or elimination of a separate thermal control system; the use of efficient, high energy density diode pump sources, results in a compact device much smaller than either chemical or solid state lasers; and its pulse length is variable from continuous to sub-picosecond, allowing flexibility in weapons effects.

And if you like the sound of the HEL weapon, try DARPA's MAgneto Hydrodynamic Explosive Munition, or as the highly inventive DARPA acronyms department has it, MAHEM. Boom boom!:

The MAgnetoHydrodynamic Explosive Munition (MAHEM) program will demonstrate compressed magnetic flux generator (CMFG)-driven magnetohydrodynamically formed metal jets and self forging penetrators with significantly improved performance over explosively formed jets and fragments. Explosively formed jets (EFJ) and self forging penetrators (SFP) are used for precision strike against targets such as armored vehicles and reinforced structures. Current technology uses chemical explosive energy to form the jets and fragments.

Nice one. We look forward to seeing both HEL and MAHEM let loose in Iraq in the near future. ®