We discuss the properties of surface plasmons-polaritons in graphene and describe three possible ways of coupling electromagnetic radiation in the terahertz (THz) spectral range to this type of surface waves. (i) the attenuated total reflection (ATR) method using a prism in the Otto configuration, (ii) graphene micro-ribbon arrays or monolayers with modulated conductivity, (iii) a metal stripe on top of the graphene layer, and (iv) graphene-based gratings. The text provides a number of original results along with their detailed derivation and discussion.

This paper gives an overview of theoretical and experimental results on Raman-active optical phonon modes confined in nearly spherical nanocrystals (NCs) of polar semiconductor materials with cubic crystal structure. A systematic consideration of the effect of reduced dimensionality on both electrons and phonons is presented. The theoretical approach is based on a continuum lattice dynamics model and the effective mass approximation for electronic states in the NCs. Calculated resonant and non-resonant Raman scattering spectra are compared to experimental data stressing the effects of phonon confinement, type of excitation, polaron correction to the exciton spectrum enhanced because of the reduced dimensionality, and individual features of the NC material.

We use an exact solution of the relaxation-time Boltzmann equation in a uniform ac electric field to describe the nonlinear optical response of graphene in the terahertz (THz) range. The cases of monolayer, bilayer, and ABA-stacked trilayer graphene are considered, and the monolayer species is shown to be the most appropriate one to exploit the nonlinear free electron response. We find that a single layer of graphene shows optical bistability in the THz range, within the electromagnetic power range attainable in practice. The current associated with the third harmonic generation is also computed.

Multiphonon processes in a model quantum dot (QD) containing two electronic states and several optical phonon modes are considered taking into account both intra-and inter-level terms. The Hamiltonian is exactly diagonalized including a finite number of multi-phonon processes, large enough as to guarantee that the result can be considered exact in the physically important region of energies. The physical properties are studied by calculating the electronic Green's function and the QD dielectric function. When both the intra-and inter-level interactions are included, the calculated spectra allow for explanation of several previously published experimental results obtained for spherical and self-assembled QDs, such as enhanced 2LO phonon replica in absorption spectra and up-converted photoluminescence. An explicit calculation of the spectral line shape due to intra-level interaction with a continuum of acoustic phonons is presented, where the multi-phonon processes also are shown to be important. It is pointed out that such an interaction, under certain conditions, can lead to relaxation in the otherwise stationary polaron system. PACS numbers: 78.67.De; 63.22.+m; 63.20.Kr Keywords: quantum dot, phonon, exciton, absorption, emission Rule, the broadening could be a lifetime effect owing to the electron (or exciton) transition to another state with emission or absorption of an optical phonon. However, it would require strict energy conservation in the electronphonon scattering, i.e. exact resonance between the optical phonon energy and level spacing, which should be rather accidental. This kind of argument also justified the theoretical concept of "phonon bottleneck", a very slow carrier relaxation which should be inherent to small QDs 2 . Nevertheless, an efficient phonon-mediated carrier relaxation has been reported in a number of works 21,28,30 . All these experimental results imply that multiphonon processes are important and that the e-ph interaction in QDs must be treated in a non-perturbative way, even for the moderate values of the coupling constants coming out from the calculations 31 . An important ingredient to be included is the non-adiabaticity of this interaction 2,7,22 leading to a phonon-mediated coupling of different electronic levels, even if they are separated by an energy quite different from the optical phonon energy. This is essential for understanding those experimental results which are in clear disagreement with the single level-generated Franck-Condon progression.Polaron effects in QDs have been studied theoretically in several recent papers 32,33,34,35 . The model considered in these works included two electronic levels and several Einstein phonon modes. The one-electron spectral function was obtained applying either self-consistent perturbation theory approximations 32,33 or exactly, using a combined analytical and numerical approach 34 . The results calculated using the perturbation theory approaches show shift and broadening of the levels, even for a sufficiently large detuning (defined ...

Abstract. -It is shown that one can explore the optical conductivity of graphene, together with the ability of controlling its electronic density by an applied gate voltage, in order to achieve resonant coupling between an external electromagnetic radiation and surface plasmon-polaritons in the graphene layer. This opens the possibility of electrical control of the intensity of light reflected inside a prism placed on top of the graphene layer, by switching between the regimes of total reflection and total absorption. The predicted effect can be used to build graphene-based opto-electronic switches.Among the many promised graphene dreams [1-3], the possibility of exploring the electronic, thermal, and mechanical properties of graphene, having in view a new generation of optoelectronic devices, is one of the most exciting of those dreams. Understanding the fundamental physics of the interaction of electrons (in graphene) with an electromagnetic field is a key step toward the realization of such devices.The optical response of graphene has been an active field of research, both experimental [4][5][6][7] and theoretical [8][9][10], and much is already understood. From the theoretical point of view, the independent electron approximation predicts that the real part of optical conductivity of graphene, at zero temperature, has the form σ = σ 0 θ( ω − 2µ), where σ 0 = πe 2 /(2 ) is the AC universal conductivity of graphene, ω is the photon energy, µ is the chemical potential, and θ(x) is the Heaviside step function. The imaginary part of the conductivity is finite everywhere, as long as µ is also finite [11]. For zero chemical potential, the experiments [4,5,7] confirm the independent electron model predictions. On the other hand, for finite chemical potential and ω < 2µ, the experiments show a substantial absorption in this energy range, at odds with the theoretical prediction. In simple terms, the real part of the conductivity, as measured experimentally, follows roughly the formula, where E D is the energy at which the Drude peak starts developing. Below E D , the optical response increases dramatically. The difference between experiment and theory can be explained by both interband and intra-band scattering, due to impurities and electronelectron interactions. In what concerns our present study, the deviations seen in the experimental data are actually vital for the effect we discuss below, and therefore the calculations we present below use the experimentally measured conductivity of graphene. The exact form of σ(ω) below the 2µ threshold is essential for the particular type of interaction of the electrons in graphene with an electromagnetic field leading to the formation of surface plasmon-polaritons [12].Surface plasmon-polariton (SPP) is an evanescent electromagnetic wave induced by the coupling of the electromagnetic field to the electrons near the surface of a metal or a semiconductor. Its amplitude decays exponentially at both sides of the interface. The SPP properties are determined by the dielectric funct...