Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene

Journal Article · Mon Apr 16 00:00:00 EDT 2012 · Physical Review Letters

DOI:https://doi.org/10.1103/PhysRevLett.108.167401· OSTI ID:1045010

Li, Tianqi; Luo, Liang; Hupalo, Myron; Zhang, Jian; Tringides, Michael; Schmalian, Joerg; Wang, Jigang

We show that strongly photoexcited graphene monolayers with 35 fs pulses quasi-instantaneously build up a broadband, inverted Dirac fermion population. Optical gain emerges and directly manifests itself via a negative conductivity at the near-infrared region for the first 200 fs, where stimulated emission completely compensates absorption loss in the graphene layer. Our experiment-theory comparison with two distinct electron and hole chemical potentials reproduce absorption saturation and gain at 40 fs, revealing, particularly, the evolution of the transient state from a hot classical gas to a dense quantum fluid with increasing the photoexcitation.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC02-07CH11358
• OSTI ID: 1045010
• Report Number(s): IS-J 7688
• Journal Information: Physical Review Letters, Vol. 108
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE