This laser-powered helicopter can fly for hours, thanks to its ground-based power supply. Of course, this little model weighs only 22 grams, flying on just a few watts of power.
(Laser-powered helicopter video)
LaserMotive says that ground-based lasers can deliver the required power. At last week's AUVSI Unmanned Systems Conference in Denver, Colorado, the firm focused light from an array of semiconductor-diode near-infrared lasers down to a 7-centimetre beam, which automatically tracked a modified radio-controlled helicopter. The aircraft carried photovoltaic cells optimised for the laser wavelength, which converted about half the laser power reaching them to generate a few watts of electricity – enough to power the rotors of the little copter.
SF fans recall that, in their 1974 novel Mote in God's Eye, Larry Niven and Jerry Pournelle wrote about laser cannon that were powerful enough to provide reliable propulsion to space craft.
The basic idea for the laser cannon/light sail propulsion system belongs to Robert L. Forward, who published a short paper Ground-Based Lasers For Propulsion In Space in 1961.