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161 results on '"Broer, D. J."'

1. Circular dichroism of cholesteric polymers and the orbital angular momentum of light

Author

Löffler, W., Broer, D. J., and Woerdman, J. P.

Subjects
Physics - Optics
Abstract

We explore experimentally if the light's orbital angular momentum (OAM) interacts with chiral nematic polymer films. Specifically, we measure the circular dichroism of such a material using light beams with different OAM. We investigate the case of strongly focussed, non-paraxial light beams, where the spatial and polarization degrees of freedom are coupled. Within the experimental accuracy, we cannot find any influence of the OAM on the circular dichroism of the cholesteric polymer., Comment: 3 pages, 4 figures

Published
2011
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2. Fully reversible transition from Wenzel to Cassie-Baxter states on corrugated superhydrophobic surfaces

Author

Vrancken, R. J., Kusumaatmaja, H., Hermans, K., Prenen, A. M., Pierre-Louis, O., Bastiaansen, C. W. M., and Broer, D. J.

Subjects
Condensed Matter - Soft Condensed Matter, Condensed Matter - Materials Science, Physics - Fluid Dynamics
Abstract

Liquid drops on textured surfaces show different dynamical behaviors depending on their wetting states. They are extremely mobile when they are supported by composite solid-liquid-air interfaces (Cassie-Baxter state) and immobile when they fully wet the textured surfaces (Wenzel state). By reversibly switching between these two states, it will be possible to achieve large control over the fluid dynamics. Unfortunately, these wetting transitions are usually prevented by surface energy barriers. We demonstrate here a new and simple design paradigm, consisting of parallel grooves of appropriate aspect ratio, that allows for a controlled, barrierless, and reversible switching of the wetting states upon the application of electrowetting. We report a direct observation of the barrierless dynamical pathway for the reversible transitions between the Wenzel (collapsed) and the Cassie-Baxter (suspended) states and present a theory that accounts for these transitions, including detailed lattice-Boltzmann simulations., Comment: 24 pages, 5 figures, To appear in Langmuir. The supporting movies can be found at: http://www.mpikg-golm.mpg.de/th/people/halim/movies/

Published
2009

3. InP-based two-dimensional photonic crystals filled with polymers

Author

van der Heijden, R., Carlstrom, C. F., Snijders, J. A. P., van der Heijden, R. W., Karouta, F., Notzel, R., Salemink, H. W. M., Kjellander, B. K. C., Bastiaansen, C. W. M., Broer, D. J., and van der Drift, E.

Subjects
Physics - Optics
Abstract

Polymer filling of the air holes of Indium Phosphide based two-dimensional photonic crystals is reported. After infiltration of the holes with a liquid monomer and solidification of the infill in situ by thermal polymerization, complete filling is proven using scanning electron microscopy. Optical transmission measurements of a filled photonic crystal structure exhibit a redshift of the air band, confirming the complete filling., Comment: To be published in Appl. Phys. Lett

Published
2006
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5. Engineering Education on the 'Fuzzy' Front End: A High-Technology Entrepreneurship Model

Author

Crawford, G. P., Broer, D. J., and Bastiaansen, C. W. M.

Abstract

We have developed a university entrepreneurship program, culminating in a prototype and business plan, with five objectives: (1) value for all academic participants' (2) introduction to engineering issues for students; (3) refinement of engineering students' "soft" skills; (4) training for students in creating value out of embryonic ideas; and (5) a genuine entrepreneurship opportunity for students who wish to pursue a start-up company. The framework is disclosed in the context of three case studies. Furthermore, educational outcomes are derived and discussed based on participant evaluations and faculty reflection. Value creation is evaluated in terms of student performance in graduation exams, in external competitions, industrial interest, investment, intellectual property creation, and market intelligence. Finally, factors that add value to or redirect university research are discussed in the context to better serve society. (Contains 2 figures.)

Published
2006
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6. High-Frequency Surface Dynamics at an Electroactive Polymer Producing Underwater Soundwaves

Author

Visschers, F. L. L., Massaad, J., van Neer, P. L. M. J., Verweij, M. D., Liu, D., Broer, D. J., Visschers, F. L. L., Massaad, J., van Neer, P. L. M. J., Verweij, M. D., Liu, D., and Broer, D. J.

Abstract

Coatings with dynamic surface structures are appealing to many applications like haptics and soft robotics. Restrictively, the speed of the surface dynamics in these coatings is often limited to frequencies below 1 kHz, which makes them unsuitable for applications like acoustics and communication optics. This work describes a method to create high-frequency surface dynamics controlled by alternating electric fields on a substrate-contact-modulated coating that consists of an elastic poly(dimethyl siloxane) network supported by SU-8 microstructures. The principle is based on the global application of Maxwell stress that is locally resisted by the supporting SU-8 microstructures. In-between the microstructures the elastic material is stretched, causing a large deformation of the surface topography, which is supported by the authors’ finite element method models. By applying a high-frequency alternating field, they discovered resonance effects at frequencies up to 230 kHz, where the surface of the coating vibrates at high speeds and large amplitudes. At these high frequencies, the coatings can produce and detect ultrasound waves underwater, indicating their potential for ultrasound transducers in the future.

Published
2022

21. Holographic phase gratings in back- and frontlights for LCD's

Author

Bastiaansen, C. W.M., van Heesch, N.C.A., Broer, D. J., and Stimuli-responsive Funct. Materials & Dev.

Subjects
Physics::Optics, SDG 7 - Affordable and Clean Energy
Abstract

The light and energy-efficiency of classical liquid crystal displays is notoriously poor due to the use of absorption-based linear polarisers and colour filters. For instance, the light efficiency of PVAL polarisers is typically between 40 and 45 % and the colour filters have a typical efficiency below 35 % which results in a total light and energy-efficiency of the display below 10%. In the past, a variety of polarizers were developed with an enhanced efficiency in generating linearly polarized light. Typically, these polarizers are based on the polarisation-selective reflection, scattering or refraction of light: i.e. one polarisation direction of light is directly transmitted to the LCD/viewer and the other polarization direction of light is depolarised and recycled which results in a typical efficiency for generating linearly polarized light of 70-85 %. Also, special colour filters have been proposed based on chiral-nematic reactive mesogens which increase the efficiency of generating colour. Despite the enormous progress in this field, a need persists for improved methods for generating polarized light and colour based on low cost optical components with a high efficiency. Here, the use of holographic phase gratings is reported for the generation of polarized light and colour. The phase grating are recorded in a photopolymer which is coated onto a back-or frontlight for LCDs. Typically the recording is performed in the transmisson mode or in the waveguiding mode and slanted phase gratings are generated with their refractive index modulation at an angle between 20° and 45° with the normal of the substrate. It is shown that phase gratings with a high refractive index modulation and a high efficiency can be generated by a proper selection of the photopolymer and illumination conditions. These phase gratings couple-out linearly polarized light with a high contrast (> 100) and the light is directed directly to the LCD/viewer without the need for redirection foils. Dependent on the type of phase grating, the different colours are coupled-out at a slightly different angle which potentially increases the efficiency of classical colour filters. Moreover, the phase gratings are completely transparent in direct view which opens the possibility to use them in frontlights for LCDs. Holographic polarization gratings posses a periodic pattern in the polarization state of light (and not in the intensity of light). A periodic pattern in the polarization direction of linearly polarized light is obtained upon interference of two circularly polarized laser beams. In the second part of the lecture, it is shown that these periodic polarization patterns can be recorded in a linear photo-polymerizable polymer (LPP) and that such an alignment layer induces a period rotation in the director of (reactive and non-reactive) liquid crystals. By a proper design, optical components can be produced with only first order diffraction and with a very high efficiency (> 0.98). It is shown that these diffraction gratings are potentially useful in projection displays with a high brightness and energy efficiency.

Published
2006

22. Search for Hermite-Gauss mode rotation in cholesteric liquid crystals

Author

Löffler, W., Van Exter, M. P., 't Hooft, G. W., Nienhuis, G., Broer, D. J., Woerdman, J. P., Löffler, W., Van Exter, M. P., 't Hooft, G. W., Nienhuis, G., Broer, D. J., and Woerdman, J. P.

Abstract

In theory, there are analogous transformations of light's spin and orbital angular momentum [Allen and Padgett, J. Mod. Opt. 54, 487 (2007)]; however, none have been observed experimentally yet. In particular, it is unknown if there exists for the orbital angular momentum of light an effect analogous to the spin angular momentum-based optical rotation; this would manifest itself as a rotation of the corresponding Hermite-Gauss mode. Here we report an experimental search for this effect in a cholesteric liquid crystal polymer, using strongly focussed, spin-orbit coupled light. We find that the relative phase velocities of the orbital modes constituting the Hermite-Gauss mode agree to within 10 -5.

Published
2011

37. InP-based two-dimensional photonic crystals filled with polymers

Author

van der Heijden, R., primary, Carlström, C. F., additional, Snijders, J. A. P., additional, van der Heijden, R. W., additional, Karouta, F., additional, Nötzel, R., additional, Salemink, H. W. M., additional, Kjellander, B. K. C., additional, Bastiaansen, C. W. M., additional, Broer, D. J., additional, and van der Drift, E., additional

Published
2006
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