FOM Institute DIFFER

Nieuwegein, Netherlands

FOM Institute DIFFER

Nieuwegein, Netherlands
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Alpers A.,TU Munich | Gritzmann P.,TU Munich | Moseev D.,FOM Institute DIFFER | Moseev D.,Max Planck Institute for Plasma Physics (Garching) | Salewski M.,Technical University of Denmark
Computer Physics Communications | Year: 2015

Particle tracking velocimetry in 3D is becoming an increasingly important imaging tool in the study of fluid dynamics and combustion as well as plasmas. We introduce a dynamic discrete tomography algorithm for reconstructing particle trajectories from projections. The algorithm is efficient for data from two projection directions and exact in the sense that it finds a solution consistent with the experimental data. Non-uniqueness of solutions can be detected and solutions can be tracked individually. © 2014 Elsevier B.V. All rights reserved.

Yakunin S.N.,RAS Research Center Kurchatov Institute | Makhotkin V.,MESA Institute for Nanotechnology | Makhotkin V.,FOM Institute DIFFER | Nikolaev K.V.,RAS Research Center Kurchatov Institute | And 5 more authors.
Optics Express | Year: 2014

We present a way to analyze the chemical composition of periodical multilayer structures using the simultaneous analysis of grazing incidence hard X-Ray reflectivity (GIXR) and normal incidence extreme ultraviolet reflectance (EUVR). This allows to combine the high sensitivity of GIXR data to layer and interface thicknesses with the sensitivity of EUVR to the layer densities and atomic compositions. This method was applied to the reconstruction of the layered structure of a LaN/B multilayer mirror with 3:5 nm periodicity. We have compared profiles obtained by simultaneous EUVR and GIXR and GIXR-only data analysis, both reconstructed profiles result in a similar description of the layered structure. However, the simultaneous analysis of both EUVR and GIXR by a single algorithm lead to a ∼2x increased accuracy of the reconstructed layered model, or a more narrow range of solutions, as compared to the GIXR analysis only. It also explains the inherent difficulty of accurately predicting EUV reflectivity from a GIXR-only analysis. © 2014 Optical Society of America.

Peeters F.J.J.,TU Eindhoven | Van De Sanden M.C.M.,TU Eindhoven | Van De Sanden M.C.M.,FOM Institute Differ
Plasma Sources Science and Technology | Year: 2015

The determination of internal electrical discharge parameters, such as plasma current and burning voltage, in dielectric barrier discharges (DBDs) relies on an equivalent circuit based on series capacitances for the discharge gap and dielectric material. An effective dielectric capacitance for the discharge can be obtained from Q-V diagrams, also called Lissajous figures, during discharging, which may not be a constant for a given DBD geometry. It has been shown experimentally that microdischarges, which can consist of narrow channels in either diffuse or filamentary form, may not fully cover the available discharge area. Here, we report measurements of the effective dielectric capacitance as a function of applied voltage amplitude in a DBD plasma jet system operating in N2 and derive equations to determine the conductively transferred charge, burning voltage and the proportion of the electrode surface over which discharging occurs when the effective dielectric capacitance is not equal to the dielectric capacitance of the complete electrode area. © 2015 IOP Publishing Ltd.

Boessenkool H.,FOM Institute DIFFER | Boessenkool H.,TU Eindhoven | Abbink D.A.,Technical University of Delft | Heemskerk C.J.M.,Heemskerk Innovative Technology B.V | And 3 more authors.
IEEE Transactions on Haptics | Year: 2013

Telemanipulation allows human to perform operations in a remote environment, but performance and required time of tasks is negatively influenced when (haptic) feedback is limited. Improvement of transparency (reflected forces) is an important focus in literature, but despite significant progress, it is still imperfect, with many unresolved issues. An alternative approach to improve teleoperated tasks is presented in this study: Offering haptic shared control in which the operator is assisted by guiding forces applied at the master device. It is hypothesized that continuous intuitive interaction between operator and support system will improve required time and accuracy with less control effort, even for imperfect transparency. An experimental study was performed in a hard-contact task environment. The subjects were aided by the designed shared control to perform a simple bolt-spanner task using a planar three degree of freedom (DOF) teleoperator. Haptic shared control was compared to normal operation for three levels of transparency. The experimental results showed that haptic shared control improves task performance, control effort and operator cognitive workload for the overall bolt-spanner task, for all three transparency levels. Analyses per subtask showed that free air movement (FAM) benefits most from shared control in terms of time performance, and also shows improved accuracy. © 2013 IEEE.

Peeters F.J.J.,TU Eindhoven | Peeters F.J.J.,FOM Institute DIFFER | Yang R.,CAS Beijing National Laboratory for Molecular | Van De Sanden M.C.M.,TU Eindhoven | Van De Sanden M.C.M.,FOM Institute DIFFER
Plasma Sources Science and Technology | Year: 2015

In a nitrogen plasma jet, atomic nitrogen is the longest lived radical species and, through recombination, gives rise to highly reactive excited nitrogen species. In this paper, the atomic nitrogen concentration in the effluent of a nitrogen-fed dielectric barrier discharge (DBD) is determined by using direct 2D imaging of the visible FPS emission. The relationship between radical production and the electrical characteristics of the discharge is assessed by making use of an electrical model which assumes only a part of the electrode area is discharged every half-cycle. For the pure nitrogen jet used here, the specific energy input per nitrogen atom is found to be 320 ± 20 eV atom-1, comparable to the specific energy for other atomic nitrogen sources in the literature. It is shown that the production efficiency of atomic nitrogen does not depend on the amplitude of the applied voltage of the DBD and any increase in radical production is due to an increase of the electrode area covered by the discharge, i.e. an increase in the number of microdischarges. © 2015 IOP Publishing Ltd.

Medvedev V.V.,FOM Institute DIFFER | Yakshin A.E.,FOM Institute DIFFER | Van De Kruijs R.W.E.,FOM Institute DIFFER | Krivtsun V.M.,Russian Academy of Sciences | And 4 more authors.
Optics Letters | Year: 2012

An extreme ultraviolet multilayer mirror with an integrated spectral filter for the IR range is presented and experimentally evaluated. The system consists of an IR-transparent B4C/Si multilayer stack which is used both as EUV-reflective coating and as a phase shift layer of the resonant IR antireflective (AR) coating. The AR coating is optimized in our particular case to suppress CO2 laser radiation at a wavelength of 10.6 μm, and a suppression of more than two orders of magnitude is demonstrated. The method allows high suppression over a large angular acceptance range, relevant for application in lithography systems. © 2012 Optical Society of America.

Van Der Meer R.,MESA Institute for Nanotechnology | Kozhevnikov I.V.,Russian Academy of Sciences | Bastiaens H.M.J.,MESA Institute for Nanotechnology | Boller K.-J.,MESA Institute for Nanotechnology | And 2 more authors.
Optics Express | Year: 2013

An extended set of coupled wave equations were derived to describe non-idealized lamellar multilayer grating structures with properties as obtained with state-of-the-Art fabrication techniques. These generalized equations can include all relevant effects describing the influence of passivation and contamination layers, non-rectangular lamel profiles and sidewall scalloping. The calculations showed that passivation and contamination plays an important role in that it may significantly reduce peak reflectivity. However, we also derived a condition for layer thicknesses having negligible effects. Slightly positive tapered lamel profiles are shown to further reduce the bandwidth as compared to a rectangular lamel profile, whereas negative tapers significantly increased the bandwidth. The influence of intriguing effects, such as the sidewall scalloping caused by Bosch Deep Reactive Ion Etching, are also modeled. We identified the signature of such scalloping as additional side peaks in the reflectivity spectrum and present parameters with which these can be effectively suppressed. © 2013 Optical Society of America.

Groot I.M.N.,Leiden University | Groot I.M.N.,FOM Institute DIFFER | Kleyn A.W.,Leiden University | Kleyn A.W.,FOM Institute DIFFER | And 2 more authors.
Journal of Physical Chemistry C | Year: 2013

Heterogeneous catalysis relies to a large extent on the reactivity of metal nanoparticles. The surface of these particles consists of atomically smooth terraces and edges. As local environments of atoms in edges and terraces are different, their catalytic ability varies. This severely complicates accurate predictions of reaction kinetics in heterogeneous catalysis. In this study, we use the reaction dynamics of H2 dissociation on a series of [n(111) × (100)] stepped platinum single-crystal surfaces to resolve how reactivity for atoms in edges and terraces can be separated and quantified individually. A simple reactivity model that only requires input from n = 3 accurately predicts reactivity for any combination of a (100) step with a (111) terrace over the entire energy range of interest for incident molecules. Our results support the assumption in theoretical kinetics studies that the smallest unit cell accurately models the essential features of the catalytic surface, and we discuss limitations to this assumption. Finally, from our model, we quantify for the first time the absolute reaction cross section for a direct dissociative process in a gas-surface collision. © 2013 American Chemical Society.

Lee C.J.,University of Twente | Lee C.J.,FOM Institute DIFFER | Boller K.J.,University of Twente
Optics Express | Year: 2012

With recent developments in microscopy, such as stimulated emission depletion (STED) microscopy, far-field imaging at resolutions better than the diffraction limit is now a commercially available technique. Here, we show that, in the special case of a diffusive regime, the noise-limited resolution of STED imaging is independent of the saturation intensity of the fluorescent label. Thermal motion limits the signal integration time, which, for a given excited-state lifetime, limits the total number of photons available for detection. © 2012 Optical Society of America.

Epping J.P.,University of Twente | Kues M.,University of Munster | Van Der Slot P.J.M.,University of Twente | Lee C.J.,University of Twente | And 3 more authors.
Optics Express | Year: 2013

We present a theoretical investigation of an integrated nonlinear light source for coherent anti-Stokes Raman scattering (CARS) based on silicon nitride waveguides. Wavelength tunable and temporally synchronized signal and idler pulses are obtained by using seeded four-wave mixing. We find that the calculated input pump power needed for nonlinear wavelength generation is more than one order of magnitude lower than in previously reported approaches based on optical fibers. The tuning range of the wavelength conversion was calculated to be 1418 nm to 1518 nm (idler) and 788 nm to 857 nm (signal), which corresponds to a coverage of vibrational transitions from 2350 cm-1 to 2810 cm-1. A maximum conversion efficiency of 19.1% at a peak pump power of 300Wis predicted. ©2013 Optical Society of America. © 2013 Optical Society of America.

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