Abstract

Linear dispersion relations for the electron and hole energy spectra with zero energy band gap in graphene [1] provide nontrivial features like negative-dynamic conductivity in far infrared and terahertz (THz) spectral ranges [2]. Due to a very short time of the optical phonon emission τ₀ ≈ 10⁻¹²s, the photogeneration of electrons and holes leads to the emission of a cascade of optical phonons, so that the photoelectrons and photoholes occupy the states with the energies close to ε_N = ħ(Ω/2-Nω₀)< ħω₀ , where ħΩ the pumping photon energy. ħω₀ the optical phonon energy, and N the number of emitted optical phonons. As a consequence, photoelectrons/holes recombine to radiate THz photons with the energy ħω = 2 ε_N (inset in Fig. 1(a)) [1]. The incident photon spectra will reflect on the THz photoemission spectra as a proof of occurrence of such a process.

© 2009 IEEE