We theoretically study the population inversion and negative dynamicconductivity in intrinsic graphene in the terahertz (THz) frequency range uponpulse photoexcitation with near-/mid-infrared wavelength. The threshold pulseenergy required for the population inversion and negative dynamic conductivitycan be orders-of-magnitude lower when the pulse photon energy is lower, due tothe inverse proportionality of the photoexcited carrier concentration to thepulse photon energy and to the weaker carrier heating. We also investigate thedependence of the dynamic conductivity on the momentum relaxation time. Thenegative dynamic conductivity takes place either in high- or low-qualitygraphene, where the Drude absorption by carriers in the THz frequency is weak.
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