ABSTRACT
In this chapter, the authors report, within a picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons and holes in an exfoliated graphene under infrared pulse excitation. They conduct time-domain spectroscopic studies using an optical pump and terahertz probe with an optical probe technique and shows that graphene sheet amplifies an incoming terahertz field. The authors report on the fast relaxation and relatively slow recombination dynamics in optically pumped graphene. The graphene emission spectrum also shows a threshold behavior versus the optical pumping intensity, providing proof of the negative dynamic conductivity in the terahertz spectral range. The authors observe amplification of an incoming terahertz pulse during the relaxation-recombination process in graphene. They conclude that the terahertz emission from graphene is stimulated by the coherent terahertz probe radiation and that the terahertz emission is amplified via electron-hole recombination in the range of the negative dynamic conductivity.
