Photons Crash Into Each Other—on a Time Mirror

Usually, electromagnetic waves pass through each other unseen and undisturbed. Getting light beams to notice each other is no easy task. Typically, scientists must coax them into interacting via complex materials. Now, physicists at the City University of New York (CUNY) Advanced Science Research Center have designed a fundamentally new way to make light beams collide with each other—by reflecting them both on the same mirror in time. By controlling light with light, the team also showed off the beam-shaping capabilities of their technique, with possible applications in telecommunications and scientific measurement.