Nils Feth

Second-harmonic generation from complementary split-ring resonators

We present experiments on second-harmonic generation from arrays of magnetic split-ring resonators and arrays of complementary split-ring resonators. In both cases, the fundamental resonance is excited by the incident femtosecond laser pulses under normal incidence, leading to comparably strong second-harmonic signals. These findings are discussed in terms of Babinets principle and in terms of a recently developed microscopic classical theory that leads to good agreement regarding the relative and the absolute nonlinear signal strengths. The hydrodynamic convective contribution is found to be the dominant source of second-harmonic generation--in contrast to a previous assignment [Science 313, 502 (2006)].

Second-harmonic generation from split-ring resonators on a GaAs substrate

We study second-harmonic generation from gold split-ring resonators on a crystalline GaAs substrate. By systematically varying the relative orientation of the split-ring resonators with respect to the incident linear polarization of light and the GaAs crystallographic axes, we unambiguously identify a nonlinear contribution that originates specifically from the interplay of the local fields of the split-ring resonators and the bulk GaAs second-order nonlinear-susceptibility tensor. The experimental results are in good agreement with theoretical modeling.

Large-area magnetic metamaterials via compact interference lithography

Magnetic metamaterials with magnetic-dipole resonances around 1.2-mum wavelength are fabricated using an extremely compact and robust version of two- or three-beam interference lithography for 1D and 2D structures, respectively. Our approach employs a single laser beam at 532- nm wavelength impinging onto a suitably shaped dielectric object (roof-top prism or pyramid) - bringing the complexity of fabricating magnetic metamaterials down to that of evaporating usual dielectric/metallic coatings.The measured optical spectra agree well with theory; the retrieval reveals a negative magnetic permeability. Importantly, the large-scale sample homogeneity is explicitly demonstrated by optical experiments.

Electromagnetic interaction of split-ring resonators: The role of separation and relative orientation

Extinction cross-section spectra of split-ring-resonator dimers have been measured at near-infrared frequencies with a sensitive spatial modulation technique. The resonance frequency of the dimers coupled mode as well as its extinction cross-section and its quality factor depend on the relative orientation and separation of the two split-ring resonators. The findings can be interpreted in terms of electric and magnetic dipole-dipole interaction. Numerical calculations based on a Discontinuous Galerkin Time-Domain approach are in good agreement with the experiments and support our physical interpretation.

Second-harmonic optical spectroscopy on split-ring-resonator arrays.

Previous second-harmonic-generation experiments on metallic split-ring-resonator arrays have been performed at fixed fundamental laser center frequency. Here, we perform nonlinear optical spectroscopy on a first set of samples, revealing pronounced resonances. Furthermore, to clarify the role of higher-order split-ring resonances, we perform additional experiments on a second set of samples in which the fundamental split-ring-resonator resonance frequencies are lithographically tuned, whereas the higher-order resonances are fixed. We find that the higher-order resonances merely reabsorb the second-harmonic generation, revealing the fundamental split-ring resonance as the nonlinear source.

Photonic metamaterials new opportunities for nanoimprint

This article presents a short discussion on the fabrication of photonic metamaterials. The method of choice for fabricating metamaterials is still electron beam lithography despite its intrinsic drawbacks like long writing time and high operation costs. Thus only small areas can be structured within reasonable time and at reasonable costs. Another way to fabricate high-quality photonic metamaterials on a macroscopic scale is provided by interference lithography which allows structuring huge areas. Another promising technique to achieve large-scale, high-quality metamaterials is nanoimprint lithography, which was recently applied to fabricate photonic metamaterials.

Large-area magnetic metamaterials for photonics by interference lithography

We present a novel approach for fabricating large-area (16 times 22 mm2) magnetic metamaterials with a negative magnetic permeability at telecom wavelengths. Our approach brings the complexity of fabricating magnetic layers down to that of dielectric layers.

Spectroscopy of Individual “Artificial Atoms”

Metamaterials exhibiting a magnetic response at optical wavelengths have recently attracted much attention [1]. The magnetic response depends on both the design of the individual building blocks (“artificial atoms”) and on electromagnetic coupling effects between them. Thus for future developments, investigation of the individual “artificial atoms” is crucial.

Nano-optic of metamaterials by spatially resolved Electron Energy Loss Spectroscopy

We present an Electron Energy Loss Spectroscopy (EELS) study in a Scanning Transmission Electron Microscope (STEM) of individual Split-Ring Resonator (SRR). We show the possibility to map each plasmonic modes with a nanometric spatial resolution in the Near IR to UV spectral range.

Spectroscopy of individual V-shaped silver nanoantennas

Following the theoretical suggestion of Stockman et al., we have fabricated individual V-shaped silver nanoantennas with 20-nm minimum feature size. Measured attenuated total internal reflection spectra are compared with numerical solutions of the vector Maxwell equations.