A. Yu. Nikitin

Edge and waveguide terahertz surface plasmon modes in graphene microribbons

The authors acknowledge support from the Spanish MECD under Contract No. MAT2009-06609-C02 and Consolider Project “Nanolight.es.” A.Y.N. acknowledges the Juan de la Cierva Grant No. JCI-2008-3123

Surface plasmon enhanced absorption and suppressed transmission in periodic arrays of graphene ribbons

Resonance diffraction in the periodic array of graphene microribbons is theoretically studied following a recent experiment [L. Ju et al., Nature Nanotech. 6, 630 (2011)]. Systematic studies over a wide range of parameters are presented. It is shown that a much richer resonant picture would be observable for higher relaxation times of charge carriers: More resonances appear and transmission can be totally suppressed. The comparison with the absorption cross-section of a single ribbon shows that the resonant features of the periodic array are associated with leaky plasmonic modes. The longest-wavelength resonance provides the highest visibility of the transmission dip and has the strongest spectral shift and broadening with respect to the single-ribbon resonance, due to collective effects.

Fields radiated by a nanoemitter in a graphene sheet

The authors acknowledge support from the Spanish Ministry of Science and Innovation under Grants No. MAT2009- 06609-C02 and No. CSD2007-046-NanoLight.es. A.Y.N. acknowledges Juan de la Cierva Grant No. JCI-2008-3123

Efficient Coupling of Light to Graphene Plasmons by Compressing Surface Polaritons with Tapered Bulk Materials

Graphene plasmons promise exciting nanophotonic and optoelectronic applications. Owing to their extremely short wavelengths, however, the efficient coupling of photons to propagating graphene plasmons-critical for the development of future devices-can be challenging. Here, we propose and numerically demonstrate coupling between infrared photons and graphene plasmons by the compression of surface polaritons on tapered bulk slabs of both polar and doped semiconductor materials. Propagation of surface phonon polaritons (in SiC) and surface plasmon polaritons (in n-GaAs) along the tapered slabs compresses the polariton wavelengths from several micrometers to around 200 nm, which perfectly matches the wavelengths of graphene plasmons. The proposed coupling device allows for a 25% conversion of the incident energy into graphene plasmons and, therefore, could become an efficient route toward graphene plasmon circuitry.

Resonant plasmonic effects in periodic graphene antidot arrays

We show that a graphene sheet perforated with micro- or nano-size antidots has prominent absorption resonances in the microwave and terahertz regions. These resonances correspond to surface plasmons of a continuous sheet “perturbed” by a lattice. They are excited in different diffraction orders, in contrast to cavity surface plasmon modes existing in disconnected graphene structures. The resonant absorption by the antidot array can essentially exceed the absorption by a continuous graphene sheet, even for high antidot diameter-to-period aspect ratios. Surface plasmon-enhanced absorption and suppressed transmission are more efficient for higher relaxation times of the charge carriers.

Resonantly suppressed transmission and anomalously enhanced light absorption in periodically modulated ultrathin metal films

We study light diffraction in the periodically modulated ultrathin metal films both analytically and numerically. Without modulation these films are almost transparent. The periodicity results in the anomalous effects, such as suppression of the transmittance accompanied by a strong enhancement of the absorptivity and specular reflectivity, due to excitation of the surface plasmon polaritons. These phenomena are opposite to the widely known enhanced transparency of periodically modulated optically thick metal films. Our theoretical analysis can be a starting point for the experimental investigation of these intriguing phenomena.

Scattering of surface plasmon polaritons by one-dimensional inhomogeneities.

The scattering of surface plasmons polaritons by a one-dimensional defect of the surface is theoretically studied by means of both Rayleigh and modal expansions. The defects considered are either relief perturbations or variations in the permittivity of the metal. The dependence of transmission, reflection, and out-of-plane scattering on parameters defining the defect is presented. We find that the radiated energy is forwardly directed with respect to the surface plasmon propagation in the case of an impedance defect. However, for relief defects, the radiated energy may be directed into the backward or forward or both direction, depending on the defect width.

Observation of enhanced transmission for s-polarized light through a subwavelength slit

Enhanced optical transmission (EOT) through a single aperture is usually achieved by exciting surface plasmon polaritons with periodic grooves. Surface plasmon polaritons are only excited by p-polarized incident light, i.e. with the electric field perpendicular to the direction of the grooves. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. A 25 fold increase is measured as compared to the case without the dielectric film. Transmission measurements are compared with a coupled mode method and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.

Extraordinary optical transmission through hole arrays in optically thin metal films

A theoretical study is presented on the optical transmission through square hole arrays drilled in optically thin films, where transmission may occur through both the holes and the metal layer. It is shown that, as the thickness of the metal film decreases, the coupling of light with short-range surface plasmons redshifts the extraordinary optical transmission peak to longer wavelengths. At the same time, the maximum-to-minimum transmittance ratio is kept high even for metal thicknesses as small as one skin depth.

In the diffraction shadow: Norton waves versus surface plasmon polaritons in the optical region

Surface electromagnetic modes supported by metal surfaces have a great potential for use in miniaturized detectors and optical circuits. For many applications, these modes are excited locally. In the optical regime, surface plasmon polaritons (SPPs) have been thought to dominate the fields at the surface, beyond a transition region comprising 3-4 wavelengths from the source. In this work, we demonstrate that at sufficiently long distances SPPs are not the main contribution to the field. Instead, for all metals, a different type of wave prevails, which we term Norton waves (NWs) for their resemblance to those found in the radio-wave regime at the surface of the Earth. Our results show that NWs are stronger at the surface than SPPs at distances larger than 6-9 SPP absorption lengths, the precise value depending on wavelength and metal. Moreover, NWs decay more slowly than SPPs in the direction normal to the surface.