http://www.newscientist.com/article.ns?id=mg18725146.400

US on course for shrink-to-fit laser

    * 25 August 2005
    * NewScientist.com news service
    * David Cohen
    * Helen Knight

A HIGH-powered, lightweight laser weapon that can be fitted to fighter
aircraft to destroy missiles tens of kilometres away has been designed by
DARPA, the Defence Advanced Research Projects Agency in the US.

Until now, lasers powerful enough to blow up missiles have been so big they
can only be carried by large aircraft such as jumbo jets. For example, the
Airborne Laser being developed by the US's Missile Defense Agency is
designed to fit onto a Boeing 747 freighter aircraft to track and destroy
ballistic missiles during their boost phase, although the weapon has yet to
undergo flight tests.

But now DARPA says it has managed to shrink all the hardware for such a
weapon so that it can fit under the wing of a fighter jet or piggyback on a
vehicle to zap anything from ground-to-air and air-to-air missiles to
rocket-propelled grenades.

The weapon, called the High Energy Liquid Laser Area Defence System
(HELLADS), will weigh just 750 kilograms, including its cooling system, and
will fit into a space of about 2 cubic metres, around the volume of a large
refrigerator. Details of the design were revealed this month at the annual
DARPATech conference in Anaheim, by project leader Donald Woodbury of the
organisation's Tactical Technology Office in Arlington, Virginia.

The team, which is working with General Atomics of San Diego, California,
has already built a prototype scaled model that is capable of producing a
1-kilowatt beam. They hope to have a 15-kW version finished and ready for
testing by the end of the year, and a full-sized prototype capable of
firing a 150-kW beam is due to be completed by 2007. "That's well within
the design cycle of the Joint Strike Fighter," says Woodbury, referring to
the next-generation US-UK fighter jet currently under development.

Precise details of the laser's design are classified, but New Scientist has
learned that it involves a hybrid of two different types of laser, liquid
and solid-state, each with their own advantages and disadvantages. Liquid
lasers can fire a continuous beam, but require large cooling systems.
Solid-state lasers are highly efficient but cannot be cooled in the same
way, so they have to be pulsed to prevent them overheating, and that
consumes more energy.

Woodbury's team claims to have combined the best of each, while shrinking
the cooling system. "We've combined the high energy density of the
solid-state laser with the thermal management of the liquid laser," he
says.

But not everyone is convinced by DARPA's claims. Philip Coyle at the Center
for Defense Information in Washington, says DARPA's goal of developing a
lightweight tactical laser is not yet feasible. "These are still very much
pie-in-the-sky concepts, and so far no high-power laser system has been
developed for the US military with demonstrable military effectiveness
under realistic operational conditions," he says.