Beam me up some power.

• Author: Jean, Grace V.
• Position: INSIDESCIENCE+TECHNOLOGY

Troops on the ground increasingly are relying on small hand-launched aircraft to track enemy fighters in Afghanistan. The problem with those battery-powered systems is that they can only fly for short periods of time before their energy supply becomes depleted.

To give the remotely operated planes better endurance in the skies, scientists are developing battlefield lasers to recharge the batteries in flight.

Transmitting electricity without wires has become feasible thanks to recent advancements in diode lasers, which are widely used in commercial industries, including communications, electronics, manufacturing and medicine. The lasers have become more powerful, more efficient and less expensive on the per watt basis, said Tom Nugent, president of LaserMotive LLC, a Kent, Wash.-based firm that is developing a power beaming system.

The prototype laser acts like a 24-hour sun.

"Just like solar cells taking sunlight and converting it into energy, we use directed, focused laser light onto specialized photovoltaic cells to generate electricity at a remote location," he said.

The near-infrared laser converts power drawn from batteries, generators or an electric grid, into a beam of light that is equivalent to a quarter million laser pointers, or roughly 10 times the intensity of sunlight. When focused on a specialized receiver, photovoltaic cells made from gallium arsenide convert the light's energy back into electricity. The cells have a power density of 1 kilowatt per kilogram, which is higher than or comparable to most batteries, Nugent said.

Small unmanned vehicles, such as the Raven and Puma, can benefit from power beaming, he said. Instead of having to land repeatedly for troops to switch out batteries, the aircraft can fly within one to two kilometers of the laser to recharge and stay aloft for hours.

The receiver could be mounted on the side of the aircraft fuselage. The plane could fly ahead of a Humvee that is transporting the laser. Drawing power from the truck, the laser could recharge the drones.

Nugent and a team of scientists in November demonstrated the concept by powering a small autonomous helicopter for nearly 12.5 hours. The Pelican quadrocopter, made by the German company Ascending Technologies, hovered nonstop overnight in an indoor facility. Its receiver produced about 180 watts of electricity.

"We could have kept on going. It was very stable for the whole time," Nugent recalled.

At one point, engineers turned off the laser...