The team placed pieces of graphene sponge in a vacuum and shot them with lasers of different wavelength and intensity. They were able to push sponge pieces upwards by as much as 40 centimetres. They even got the graphene to move by focusing ordinary sunlight on it with a lens.
Logically, the team had no idea why this was happening. They think the graphene absorbs laser energy and builds up a charge of electrons. Eventually it can’t hold any more, and extra electrons are released, pushing the sponge in the opposite direction. Eventually the team was able to confirm a current flowing away from the graphene as it was exposed to a laser, suggesting this hypothesis is correct.
Graphene sponge could be used to make a light-powered propulsion system for spacecraft that would beat solar sails. “While the propulsion force is still smaller than conventional chemical rockets, it is already several orders larger than that from light pressure,” they write.