441 research outputs found
Hydrodynamic interactions in active colloidal crystal microrheology
In dense colloids it is commonly assumed that hydrodynamic interactions do
not play a role. However, a found theoretical quantification is often missing.
We present computer simulations that are motivated by experiments where a large
colloidal particle is dragged through a colloidal crystal. To qualify the
influence of long-ranged hydrodynamics, we model the setup by conventional
Langevin dynamics simulations and by an improved scheme with limited
hydrodynamic interactions. This scheme significantly improves our results and
allows to show that hydrodynamics strongly impacts on the development of
defects, the crystal regeneration as well as on the jamming behavior.Comment: 5 pages, 4 figure
Numerical modeling of fluid flow in porous media and in driven colloidal suspensions
This article summarizes some of our main efforts performed on the computing facilities provided by the high performance computing centers in Stuttgart and Karlsruhe. At first, large scale lattice Boltzmann simulations are utilized to support resolution dependent analysis of geometrical and transport properties of a porous sandstone model. The second part of this report focuses on Brownian dynamics simulations of optical tweezer experiments where a large colloidal particle is dragged through a polymer solution and a colloidal crystal. The aim of these simulations is to improve our understanding of structuring effects, jamming behavior and defect formation in such colloidal systems
Polarization state of the optical near-field
The polarization state of the optical electromagnetic field lying several
nanometers above complex dielectric structures reveals the intricate
light-matter interaction that occurs in this near-field zone. This information
can only be extracted from an analysis of the polarization state of the
detected light in the near-field. These polarization states can be calculated
by different numerical methods well-suited to near--field optics. In this
paper, we apply two different techniques (Localized Green Function Method and
Differential Theory of Gratings) to separate each polarisation component
associated with both electric and magnetic optical near-fields produced by
nanometer sized objects. The analysis is carried out in two stages: in the
first stage, we use a simple dipolar model to achieve insight into the physical
origin of the near-field polarization state. In the second stage, we calculate
accurate numerical field maps, simulating experimental near-field light
detection, to supplement the data produced by analytical models. We conclude
this study by demonstrating the role played by the near-field polarization in
the formation of the local density of states.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.
Surface Plasmon Polariton microscope with Parabolic Reflectors
We report the realization of a two--dimensional optical microscope for
surface plasmons polaritons (SPPs) based on parabolic Bragg mirrors. These
mirrors are built from lithographically fabricated gold nanostructures on gold
thin films. We show by direct imaging by leakage radiation microscopy that the
magnification power of the SPP microscope follows basic predictions of
geometrical optics. Spatial resolution down to the value set by the diffraction
limit is demonstrated.Comment: Opt.Lett.32, 2414 (2007
Extracting the lowest-frequency words: Pitfalls and possibilities
Contains fulltext :
173398.pdf (publisher's version ) (Open Access
Low-Power consumption Franz-Keldysh effect plasmonic modulator
In this paper we report on a low energy consumption CMOS-compatible plasmonic modulator based on Franz-Keldysh effect in germanium on silicon. We performed integrated electro-optical simulations in order to optimize the main characteristics of the modulator. A 3.3 dB extinction ratio for a 30 µm long modulator is demonstrated under 3 V bias voltage at an operation wavelength of 1647 nm. The estimated energy consumption is as low as 20 fJ/bit
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