ABSTRACT
Pumped Graphene ............................................................................ 101 4.3.2 Population Inversion and Negative Conductivity in Optically
Pumped Graphene ............................................................................ 103 4.3.2.1 Low Electronic Temperature Case..................................... 103 4.3.2.2 High Electronic Temperature Case .................................... 105
4.3.3 Observation of Ampli•ed Stimulated THz Emission from Optically Pumped Graphene ............................................................ 106
4.4 Summary and More ...................................................................................... 111 References .............................................................................................................. 111
Graphene, a monolayer of sp2-bonded carbon atoms in a honeycomb crystal lattice, has attracted considerable attention due to its unique carrier transport and optical properties [1-4]. Figure 4.1 depicts the energy band structures and dispersion relations for graphene. The conduction band and the valence band of graphene take a symmetrical corn shape around the K and K′ points and contact each other at the K and K′ points. Electrons and holes in graphene hold a linear dispersion relation with zero band gap, resulting in peculiar features like massless relativistic Fermions with backscattering-free ultrafast transport [2-8] as well as the negative-dynamic conductivity in the terahertz (THz) spectral range under optical pumping [9-11].
