Negative-index metamaterial at 780 nm wavelength

We further miniaturize a recently established silver-based negative-index metamaterial design. By comparing transmittance, reflectance, and phase-sensitive time-of-flight experiments with theory, we infer a real part of the refractive index of -0.6 at a 780 nm wavelength--which is visible in the laboratory.     

Circular dichroism of planar chiral magnetic metamaterials

We propose, fabricate, and study a double-layer chiral planar metamaterial that exhibits pronounced circular dichroism at near-infrared wavelengths. The antisymmetric oscillation modes of the two coupled layers allow local magnetic-dipole moments and enhanced polarization effects compared with similar single-layer systems where only electric-dipole moments occur. Experiment and rigorous theoretical calculations are in good agreement.     

Three‐dimensional optical laser lithography beyond the diffraction limit

Direct laser writing has become a versatile and routine tool for the mask‐free fabrication of polymer structures with lateral linewidths down to less than 100 nm. In contrast to its planar counterpart, electron‐beam lithography, direct laser writing also allows for the making of three‐dimensional structures. However, its spatial resolution has been restricted by diffraction. Clearly, linewidths and resolutions on the scale of few tens of nanometers and below are highly desirable for various applications in nanotechnology. In visible‐light far‐field fluorescence microscopy, the concept of stimulated emission depletion (STED) introduced in 1994 has led to spectacular record resolutions down to 5.6 nm in 2009. This review addresses approaches aiming at translating this success in optical microscopy to optical lithography. After explaining basic principles and limitations, possible depletion mechanisms and recent lithography experiments by various groups are summarized. Today, Abbe's diffraction barrier as well as the generalized two‐photon Sparrow criterion have been broken in far‐field optical lithography. For further future progress in resolution, the development of novel tailored photoresists in combination with attractive laser sources is of utmost importance.     

Surface-functionalized fluorescent silica nanoparticles for the detection of ATP

The design of two-dyed fluorescent silica nanoparticles for ATP detection is presented. The indicator dye possesses a dipicolyl-amine (DPA) unit complexed with Zn(II) as a receptor function for ATP while a rhodamine derivative is used as the reference dye. The nanoparticles were fully characterized regarding analytical performance, morphology and cytocompatibility.     

DAE-index monitoring for semi-discretized viscous Cosserat rod models

The dynamics of viscous jets due to external forces like gravity and aerodynamics can be described by Cosserat rod models consisting of a system of partial and ordinary differential equations. Depending on the formulation of the equations, in particular the compatibility conditions, the semi-discretization in space yields systems of differential-algebraic equations (DAE) in time of different indices. We present a DAE-index monitoring and discuss the numerical results for the application in a rotational 2d fiber spinning scenario. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the modeling of slender heat sources

Studying the heat exchange of small, slender objects in a surrounding flow, we approximate the impact of extended heat sources by Dirac-distributions (point sources) with appropriate amplitudes in the context of slender-body theory. The proposed model for the source strength functions is deduced from analytical considerations (Green's functions) of the stationary two-dimensional heat equation. Numerical simulations show the L2-approximation quality of the strategy. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On an asymptotic upper-convected Maxwell model for a viscoelastic jet

In this work we present a strict systematic derivation of a one-dimensional upper convected Maxwell model (UCM) for the dynamics of a curved viscoelastic jet using asymptotic analysis in the slenderness ratio of the jet. The model does not pose any restrictions on shape and motion of the center-line or the velocity profile. Numerical results are shown for stationary gravitational fiber spinning. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Detailed optical characterization of three-dimensional visible-frequency polarization-independent carpet invisibility cloak

The invention of the three-dimensional woodpile photonic crystal by Costas M. Soukoulis and coworkers in 1994 has stimulated much further research—excellent research stimulates further research. Here, we report on using spatially inhomogeneous polymer woodpile structures in the long-wavelength limit as artificial graded-index structures. After briefly reviewing previous work on carpet invisibility cloaks designed by transformation optics, we present new experiments for various focus planes of the inspecting microscope as well as for different inspection angles in three-dimensional space. Numerical ray-tracing modeling is also provided. These data confirm our previous assessment that three-dimensional cloaking is quite robust for these structures.