A pair of laser beams can now send electrons through a semiconductor in a chosen direction without any external electrical power. Researchers at the University of Michigan built the device to explore a previously unobserved physical effect and demonstrate that light alone can both generate and steer an electronic current. They could also change the direction of that current by rotating the polarization of the two optical fields, meaning the direction in which the light waves oscillate. Earlier experiments had already shown that light could generate an electron current without an applied electric field. The semiconductor absorbs energy from the light in discrete packets called photons, which set its electrical charge carriers in motion.