Researchers find new properties of the carbon material graphene May 30, 2012 Researchers find new properties of the carbon material graphene Enlarge Iowa State physicist Jigang Wang, right, examines graphene monolayers grown on a substrate mounted in a cooper adapter as graduate students Tianq Li, far left, and Liang Luo look on in Wang's laboratory. Credit: Steve Jones/College of Liberal Arts and Science, Iowa State University Graphene has caused a lot of excitement among scientists since the extremely strong and thin carbon material was discovered in 2004. Just one atom thick, the honeycomb-shaped material has several remarkable properties combining mechanical toughness with superior electrical and thermal conductivity. Now a group of scientists at Iowa State University, led by physicist Jigang Wang, has shown that graphene has two other properties that could have applications in high-speed telecommunications devices and laser technology population inversion of electrons and broadband optical gain. Wang is an assistant professor in the Department of Physics and Astronomy in the College of Liberal Arts and Sciences at Iowa State University. He also is an associate scientist with the Department of Energy's Ames Laboratory. Wang's team flashed extremely short laser pulses on graphene. The researchers immediately discovered a new photo-excited graphene state characterized by a broadband population inversion of electrons. Under normal conditions, most electrons would occupy low-energy states and just a few would populate higher-energy states. In population-inverted states, this situation is reversed: more electrons populate higher, rather than lower, energy states. Such population inversions are very rare in nature and can have highly unusual properties. In graphene, the new state produces an optical gain from the infrared to the visible. Simply stated, optical gain means more visible light comes out than goes in. This can only happen when the gain medium is externally pumped and then stimulated with light (stimulated emission). Wang's discovery could open doors for efficient amplifiers in the telecommunication industry and extremely fast opto-electronics devices. Graphene as a gain medium for light amplification "It's very exciting," Wang said. "It opens the possibility of using graphene as a gain medium for light amplification. It could be used in making broadband optical amplifiers or high-speed modulators for telecommunications. It even provides implications for development of graphene-based lasers." Wang's team unveiled its findings in the journal Physical Review Letters on April 16. In addition to Wang, the paper's other authors are Tianq Li, Liang Luo and Junhua Zhang, Iowa State physics graduate students; Miron Hupalo, Ames Laboratory scientist; and Michael Tringides and Jörg Schmalian, Iowa State physics professors and Ames Laboratory scientists.