Jesper Jung

Scaling for gap plasmon based waveguides

Using the effective-index approach and an explicit expression for the propagation constant of gap surface plasmon polaritons (G-SPPs) obtained for moderate gap widths, we introduce a normalized waveguide parameter characterizing the mode field confinement and obtain the corresponding expressions for various (gap, trench and V-groove) G-SPP based waveguides. Usage of the obtained relations is investigated with a finite-element method, demonstrating that waveguides with different dimensions and operating at different wavelengths, but having the same normalized parameter, exhibit very similar field confinement. These relations allow one to design G-SPP waveguides for single-mode operation supporting a well-confined fundamental mode.

Theoretical analysis of gold nano-strip gap plasmon resonators

Gold gap plasmon resonators consisting of two nm-thin and sub-micron-wide gold strips separated by a nm-thin air or quartz gap are considered. Scattering resonances and resonant fields are related to a model of resonances being due to counter-propagating gap plasmon polaritons forming standing waves. A small gap (~10 nm) is found to result in small resonance peaks in scattering spectra but large electric field magnitude enhancement (~20), whereas a large gap (~100 nm) is found to result in more pronounced scattering peaks but smaller field enhancement. Design curves are presented that allow construction of gap plasmon resonators with any desired resonance wavelength in the range from the visible to the infrared, including telecom wavelengths. The relation between resonance wavelength and resonator width is close to being linear. The field magnitude enhancement mid between the gold strips is systematically investigated versus gap size and wavelength.

Analysis of plasmonic properties of heavily doped semiconductors using full band structure calculations

Surface plasmon polaritons (SPPs) and localized surface plasmon (LSP) resonances are not limited to noble metals. Any material with a substantial amount of free carriers will support surface plasma oscillations which, when coupled to an electromagnetic field, will result in surface plasmon polaritons and localized surface plasmon resonances in confined systems. Utilizing a full band structure approach, we analyze the plasmonic properties of several heavily doped semiconductors. We present rigorous quantum mechanical calculations of the plasma frequency, and study in detail its dependence on impurity doping concentration. Results are presented for silicon, germanium, gallium arsenide, zinc oxide, and gallium nitride. For silicon and zinc oxide, the surface plasmon resonance frequency is calculated for a large range of doping concentrations and we study the dispersion of surface plasmon polaritons on thin films. The investigated properties of heavily doped semiconductors hold promises for several interestin...

Polarizability of supported metal nanoparticles: Mehler-Fock approach

Using toroidal coordinates and the Mehler-Fock transform, we present an analysis of the polarizability of a complex structure allowing for the study of arbitrarily truncated metal spheres including a dielectric substrate. Our analysis is based on an electrostatic approach, i.e., we are in the quasi-static limit, where we solve the Laplace equation for the potential. The derived method is used to analyze the behavior of localized surface plasmon resonances of truncated metal nanospheres including substrate effects. The method is fast, simple, easy to implement, and useful for analysis of experimental work on supported metal nanoparticles, e.g., within the area of plasmonic photovoltaics.

Light transmission properties of holey metal films in the metamaterial limit: effective medium theory and subwavelength imaging

The light transmission properties of holey metal films in the metamaterial limit, where the unit length of the periodic structures is much smaller than the operating wavelength, are analyzed theoretically utilizing the modal expansion formalism. A detailed derivation of the transmission coefficients of both one-dimensional (1D) slit and 2D hole arrays is presented. We show that under certain assumptions the transmission coefficient becomes unity independent of the parallel momentum of the incident field. This result indicates that holey metal films can be used as endoscopes; i.e. they are capable of transforming an image with subwavelength resolution from the input to the output surface of the film. We also demonstrate how such films can effectively be mapped into homogenous anisotropic films with optical properties controlled by the geometrical parameters of the holes. Lastly, the subwavelength imaging properties of an endoscope based on a 1D slit array is demonstrated for p-polarized light using numerical simulations.

Diffractive coupling and plasmon-enhanced photocurrent generation in silicon

Arrays of metal nanoparticles are considered candidates for improved light-coupling into silicon. In periodic arrays the coherent diffractive coupling of particles can have a large impact on the resonant properties of the particles. We have investigated the photocurrent enhancement properties of Al nanoparticles placed on top of a silicon diode in periodic as well as in random arrays. The photocurrent of the periodic array sample is enhanced relative to that of the random array due to the presence of a Fano-like resonance not observed for the random array. Measurements of the photocurrent as a function of angle, reveal that the Fano-like enhancement is caused by diffractive coupling in the periodic array, which is accordingly identified as an important design parameter for plasmon-enhanced light-coupling into silicon.

Nanoparticle plasmon resonances in the near-static limit

Localized surface plasmon resonances of metal nanoparticles of arbitrary shape are analyzed in the near-static limit with retardation included to the second order. Starting from the electrostatic approximation, the second-order correction to the resonant dielectric constant is expressed by means of a triple surface integral. For arbitrary nanoparticles with cylindrical symmetry we show how the triple surface integral can be significantly simplified, resulting in a computationally efficient scheme for evaluation of nanoparticle plasmon eigenresonances in the near-static limit. The approach allows for calculation of both dipolar and higher-order resonances.

Theoretical analysis and experimental demonstration of resonant light scattering from metal nanostrips on quartz

Using the Greens tensor area integral equation method and reflection spectroscopy, resonant light scattering from rectangular gold nanostrips on quartz substrates fabricated with electron-beam lithography is analyzed theoretically and demonstrated experimentally. Theory and experiments are compared and found in a good agreement. Design curves presenting the scattering resonance wavelength as a function of the nanostrip width allow one, by carefully choosing the strip width and thickness, to realize the resonance at a given wavelength in a broad wavelength spectrum ranging from the visible (~600 nm) to the near infrared including telecommunication wavelengths (~1600 nm).

A mixed C-vine copula model for hedging price and volumetric risk in wind power trading

Abstract When energy trading companies enter into long-term agreements with wind power producers, where a fixed price is paid for the fluctuating production, they are facing a joint price and volumetric risk. Since the pay-off of such agreements is non-linear, a hedging portfolio would ideally consist of not only forwards, but also a basket of e.g. call and put options. Illiquidity and an almost non-existent market for options challenge however the optimal hedging of joint price and volumetric risk in many market places. Here, we consider the case of the Danish power market, and exploit its strong positive correlation with the much more liquid German market to construct a proxy hedge. We propose a three-dimensional mixed vine copula to model the evolution of the Danish and German spot electricity prices and the Danish wind power production. We construct a realistic hedging portfolio by identifying various instruments available in the market, such as real options in the form of the right to transfer electricity across the border and the right to convert electricity to heat. Using the proposed vine copula to determine optimal hedging decisions, we show that significant benefits are to be drawn by extending the hedging portfolio with the proposed instruments.

Polarizability of nanowires at surfaces: exact solution for general geometry

The polarizability of a nanostructure is an important parameter that determines the optical properties. An exact semi-analytical solution of the electrostatic polarizability of a general geometry consisting of two segments forming a cylinder that can be arbitrarily buried in a substrate is derived using bipolar coordinates, cosine-, and sine-transformations. Based on the presented expressions, we analyze the polarizability of several metal nanowire geometries that are important within plasmonics. Our results provide physical insight into the interplay between the multiple resonances found in the polarizability of metal nanowires at surfaces.