32 research outputs found
Decomposing the scattered field of two-dimensional metaatoms into multipole contributions
We introduce a technique to decompose the scattered near field of
two-dimensional arbitrary metaatoms into its multipole contributions. To this
end we expand the scattered field upon plane wave illumination into cylindrical
harmonics as known from Mie theory. By relating these cylin- drical harmonics
to the field radiated by Cartesian multipoles, the contribution of the lowest
order electric and magnetic multipoles can be identified. Revealing these
multipoles is essential for the design of metamaterials because they largely
determine the character of light propagation. In par- ticular, having this
information at hand it is straightforward to distinguish between effects that
result either from the arrangement of the metaatoms or from their particular
design
Electromagnetic multipole theory for optical nanomaterials
Optical properties of natural or designed materials are determined by the
electromagnetic multipole moments that light can excite in the constituent
particles. In this work we present an approach to calculate the multipole
excitations in arbitrary arrays of nanoscatterers in a dielectric host medium.
We introduce a simple and illustrative multipole decomposition of the electric
currents excited in the scatterers and link this decomposition to the classical
multipole expansion of the scattered field. In particular, we find that
completely different multipoles can produce identical scattered fields. The
presented multipole theory can be used as a basis for the design and
characterization of optical nanomaterials
Doubly resonant optical nanoantenna arrays for polarization resolved measurements of surface-enhanced Raman scattering
We report that rhomb-shaped metal nanoantenna arrays support multiple
plasmonic resonances, making them favorable bio-sensing substrates. Besides the
two localized plasmonic dipole modes associated with the two principle axes of
the rhombi, the sample supports an additional grating-induced surface plasmon
polariton resonance. The plasmonic properties of all modes are carefully
studied by far-field measurements together with numerical and analytical
calculations. The sample is then applied to surface-enhanced Raman scattering
measurements. It is shown to be highly efficient since two plasmonic resonances
of the structure were simultaneously tuned to coincide with the excitation and
the emission wave- length in the SERS experiment. The analysis is completed by
measuring the impact of the polarization angle on the SERS signal.Comment: 13 pages, 5 figure
Multipole nonlinearity of metamaterials
We report on the linear and nonlinear optical response of metamaterials
evoked by first and second order multipoles. The analytical ground on which our
approach bases permits for new insights into the functionality of
metamaterials. For the sake of clarity we focus here on a key geometry, namely
the split-ring resonator, although the introduced formalism can be applied to
arbitrary structures. We derive the equations that describe linear and
nonlinear light propagation where special emphasis is put on second harmonic
generation. This contribution basically aims at stretching versatile and
existing concepts to describe light propagation in nonlinear media towards the
realm of metamaterials.Comment: 7 pages, 3 figure
Identifying diamagnetic interactions in scattering and nonlinear optics
In the generic formulation of optical interactions there is, beyond the familiar electric and magnetic multipolar forms of coupling, an additional diamagnetization term that rarely receives attention. In fact it can give rise to effects that should be observable in the general context of nonlinear optical spectroscopy, as well as scattering. A quantum electrodynamical analysis reveals features of special interest in two specific cases: two-photon absorption and Rayleigh scattering. Diamagnetic contributions are seen to be dispersion free with regards to the frequency of input radiation, and can represent unique interactions within optical absorption and emission processes. There is also a configuration in which diamagnetic couplings, which are quadratic in the magnetic field, can supersede those that are dependent linearly on the electric field strength, such as the electric dipole. In this connection the influence of retroreflected circularly polarized light, which leads to a local distance dependence in magnitude of the electromagnetic fields, produces conditions in which the diamagnetization response can become a prominent feature in two-photon absorption
Evaluation of Colloids and Activation Agents for Determination of Melamine Using UV-SERS
UV-SERS measurements offer a great potential for environmental or food (detection of food contaminats) analytics. Here, the UV-SERS enhancement potential of various kinds of metal colloids, such as Pd, Pt, Au, Ag, Au-Ag core-shell, and Ag-Au core-shell with different shapes and sizes, were studied using melamine as a test molecule. The influence of different activation (KF, KCl, KBr, K 2SO 4) agents onto the SERS activity of the nanomaterials was investigated, showing that the combination of a particular nanoparticle with a special activation agent is extremely crucial for the observed SERS enhancement. In particular, the size dependence of spherical nanoparticles of one particular metal on the activator has been exploited. By doing so, it could be shown that the SERS enhancement increases or decreases for increasing or decreasing size of a nanoparticle, respectively. Overall, the presented results demonstrate the necessity to adjust the nanoparticle size and the activation agent for different experiments in order to achieve the best possible UV-SERS results
Extension of the Multipole Approach to Random Metamaterials
Influence of the short-range lateral disorder in the meta-atoms positioning on the effective parameters of the metamaterials is investigated theoretically using the multipole approach. Random variation of the near field quasi-static interaction between metaatoms in form of double wires is shown to be the reason for the effective permittivity and permeability changes. The obtained analytical results are compared with the known experimental ones
Holographic progressive lenses
Progressive addition lenses (PALs) are realized as optical freeform surfaces by complex manufacturing and inspection processes. In turn, holographic optical elements (HOEs) enable fast and easy fabrication in other applications. Here we present a design method for the combination of both; HOEs that are designed to fulfill the optical function of PALs. We describe how inherent limitations of HOEs, such as angular and wavelength selectivity as well as grating dispersion can be overcome. We show that holographic PALs can be optimized to have a distribution of spherical power and astigmatism, which is a qualitative replication of the performance of their refractive counterparts. The design rules we identify are shown for PALs but have the potential to improve other applications of HOEs as well