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

TitleFemtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene
Publication TypeJournal Article
Year of Publication2012
AuthorsLi T, Luo L, Hupalo M, Zhang J, Tringides MC, Schmalian J, Wang J
Journal TitlePhysical Review Letters
Volume108
Pages167401
Date Published04
Type of ArticleArticle
ISBN Number0031-9007
Accession NumberWOS:000302854500007
Keywordsepitaxial graphene, ultrafast
Abstract

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.

URL<Go to ISI>://WOS:000302854500007
DOI10.1103/PhysRevLett.108.167401
Alternate JournalPhys. Rev. Lett.