This work was supported by the National Science Foundation (NSF) under DMR-1608258 and the Vannevar Bush Faculty Fellowship from DOD under N00014-17-1-3023. The work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. Portions of this research were supported by the Global Research Laboratory Program through the National Research Foundation of Korea funded by the Ministry of Science and ICT (grant no. 2016911815). The work used the Northwestern University Micro/Nano Fabrication Facility, which is partially supported by Soft and Hybrid Nanotechnology Experimental Resource (grant no. NSF ECCS-1542205), the Materials Research Science and Engineering Center (grant no. DMR-1720139), and the State of Illinois and Northwestern University. A.T. was supported by the Weizmann Institute of Science—National Postdoctoral Award Program for Advancing Women in Science. We thank F. Scotognello for assistance with the ultrafast lasing measurements at the Molecular Foundry.