An inter-MRSEC collaboration between the University of Chicago and the Pennsylvania State University led to the discovery of a new technique that enables bidirectional control of the chemical potential in a topological insulator (TI). A central challenge with these materials is to reliably tune the chemical potential of their electrons with respect to the Dirac point and the bulk bands, thereby hindering research and potential applications. This all-optical effect is persistent and allows for direct patterning and imaging of p-n junctions . The ability to optically write and erase mesoscopic electronic structures in a TI may aid in the investigation of the unique properties of the topological insulating phase. The gating effect also generalizes to other thin-film materials, implying that these phenomena could provide optical control of chemical potential in a wide range of ultrathin electronic systems. The persistence and bidirectionality of the optical gating effect also suggest its potential relevance as a platform for optically defined reconfigurable electronics. The results were highlighted in the Science section of the New York Times, and discussed on National Public Radio. It recently was selected as a finalist for the NPR Golden Mole Award.