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

Li, T.
; 
Luo, L.
; 
Hupalo, M.
; 
Zhang, J.
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.
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2012-01-01
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Physics
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Physics
DOI
https://doi.org/10.1103/PhysRevLett.108.167401
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https://scholarworks.wm.edu/handle/internal/718
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