Carsten Rockstuhl

Karlsruhe Institute of Technology, Carlsruhe, Baden-Württemberg, Germany

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Publications (312)706.67 Total impact

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    ABSTRACT: The spontaneous emission rate of dipole emitters close to plasmonic dimers are theoretically studied within a nonlocal hydrodynamic model. A nonlocal model has to be used since quantum emitters in the immediate environment of a metallic nanoparticle probe its electronic structure. Compared to local calculations, the emission rate is significantly reduced. The influence is mostly pronounced if the emitter is located close to sharp edges. We suggest to use quantum emitters to test nonlocal effects in experimentally feasible configurations.
    Optics Letters 11/2014; 39(21). · 3.39 Impact Factor
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    ABSTRACT: The standard hydrodynamic Drude model with hard-wall boundary conditions can give accurate quantitative predictions for the optical response of noble-metal nanoparticles. However, it is less accurate for other metallic nanosystems, where surface effects due to electron density spill-out in free space cannot be neglected. Here we address the fundamental question whether the description of surface effects in plasmonics necessarily requires a fully quantum-mechanical approach, such as time-dependent density-functional theory (TD-DFT), that goes beyond an effective Drude-type model. We present a more general formulation of the hydrodynamic model for the inhomogeneous electron gas, which additionally includes gradients of the electron density in the energy functional. In doing so, we arrive at a Self-Consistent Hydrodynamic Model (SC-HDM), where spill-out emerges naturally. We find a redshift for the optical response of Na nanowires, and a blueshift for Ag nanowires, which are both in quantitative agreement with experiments and more advanced quantum methods. The SC-HDM gives accurate results with modest computational effort, and can be applied to arbitrary nanoplasmonic systems of much larger sizes than accessible with TD-DFT methods. Moreover, while the latter typically neglect retardation effects due to time-varying magnetic fields, our SC-HDM takes retardation fully into account.
    08/2014;
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    ABSTRACT: The seeded growth of poly(ethylene imine) – gold nanoparticle clusters enables the formation of particle assemblies with tunable optical properties. Clusters with increasing particle sizes, filling factors and assemblies consisting of PEI–gold–silver core shell particles can be synthesized in this way. Profound structural characterization is carried out via TEM imaging and FIB milling which allows visualizing the cross-section of the clusters. Determination of the optical properties was performed via UV-Vis spectroscopy and spectral dark field microscopy of individual particles. Additionally, numerical calculations were carried out based on the Mie theory. The results are in good agreement with the experimental findings and reveal the contribution of different multipoles to the spectra which cannot be resolved by UV-Vis spectroscopy in solution. The isotropic nature and adjustable properties of these clusters could render them versatile building blocks for metamaterials.
    J. Mater. Chem. C. 07/2014; 2(31).
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    ABSTRACT: In this work, the impact of two different growth modes on the efficiency of an amorphous thin film solar cell comprising randomly textured interfaces is investigated. The two modes are the commonly used conformal growth which assumes identical textured interfaces and the isotropic growth, in which deposited material grows in the direction of the local surface normal. In the latter, the texture's morphology can change significantly. The rivalling impact of these two growth modes on the solar cell absorption is not yet fully understood. Here, we show that the efficiency of a solar cell crucially depends on the growth mode. In different size regimes, they may outperform each other with regard to efficiency by almost 15%. The insights gained by this study will guide experimentalists in the future in selecting the optimised growth mode.
    Applied Physics Letters 06/2014; 104(23):231103-231103-5. · 3.79 Impact Factor
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    Renwen Yu, Rasoul Alaee, Falk Lederer, Carsten Rockstuhl
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    ABSTRACT: The excitation of localized or delocalized surface plasmon polaritons in nanostructured or extended graphene has attracted a steadily increasing attention due to their promising applications in sensors, switches, and filters. These single resonances may couple and intriguing spectral signatures can be achieved by exploiting the entailing hybridization. Whereas thus far only the coupling between localized or delocalized surface plasmon polaritons has been studied in graphene nanostructures, we consider here the interaction between a localized and a delocalized surface plasmon polariton. This interaction can be achieved by two different schemes that reside on either evanescent near- field coupling or far-field interference. All observable phenomena are corroborated by analytical considerations, providing insight into the physics and paving the way for compact and tunable optical components at infrared and terahertz frequencies.
    05/2014;
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    ABSTRACT: We report on a novel metamaterial structure that sustains extremely sharp resonances in the terahertz domain. This system involves two conductively coupled split ring resonators that together exhibit a novel resonance, in broad analogy to the antiphase mode of the so-called Huygens coupled pendulum. Even though this resonance is in principle forbidden in each individual symmetric split ring, our experiments show that this new coupled mode can sustain quality factors that are more than one order of magnitude larger than those of conventional split ring arrangements. Because of the universality of the metamaterial response, the design principle we present here can be applied across the entire electromagnetic spectrum and to various metamaterial resonators.
    Physical Review Letters 05/2014; 112(18):183903. · 7.73 Impact Factor
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    ABSTRACT: Surface-enhanced Raman spectroscopy takes advantage of plasmonic substrates that sustain resonances at tunable frequencies with a reproducibly extraordinary field enhancement. Low-cost and large-scale fabrication of these substrates is further required. Here, we present stacked large-scale arrays of strongly coupled gold nanoparticles as promising candidates for such substrates. These arrays are fabricated by bottom-up techniques that fulfill the aforementioned requirements. The distance between adjacent arrays in the stack is controlled with high precision using a discrete number of monolayers of molecules that enable the spectral position of the plasmonic resonances to be tuned. Although the nanoparticles are randomly arranged in each array, the spatial proximity of the stacked arrays enables a strong coupling among nanoparticles to be achieved in adjacent arrays. The huge field enhancements due to these strongly coupled gold nanoparticles are shown to enhance the Raman signal. We show that effectively the optical response from these stacked arrays and the Raman signals can be understood in a simplifying picture where only an individual nanoparticle dimer is considered. The possibility to tune the plasmonic resonances of the substrate across the visible spectrum makes our material a plasmonic substrate of choice for many applications where light–matter interactions need to be intensified.
    The Journal of Physical Chemistry C. 05/2014; 118(19):10230–10237.
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    ABSTRACT: We report on the design, simulation, fabrication, and characterization of a novel two layer anti-reflective coating (ARC) based on a plasmonic metamaterial and a dielectric. Promoted by the strong material dispersion of the plasmonic metamaterial, our novel concept (called hybrid ARC) combines two possible arrangements for layers in an anti-reflection coating into a single structure; albeit at two different wavelengths. This, however, causes a broadband reduction of reflection that is less sensitive against oblique incidence when compared to traditional antireflective coatings. Furthermore, we show that the current metamaterial on a metal reflector can be used for the visualization of different coloration such as plasmonic rainbow despite its sub-wavelength thickness.
    Nanoscale 04/2014; · 6.73 Impact Factor
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    ABSTRACT: Within the past several years a tremendous progress regarding optical nano-antennas could be witnessed. It is one purpose of optical nano-antennas to resonantly enhance light-matter interactions at the nanoscale, e.g. the interaction of an external illumination with molecules. In this specific, but in almost all schemes that take advantage of resonantly enhanced electromagnetic fields in the vicinity of nano-antennas, the precise knowledge of the spectral position of resonances is of paramount importance to fully exploit their beneficial effects. Thus far, however, many nano-antennas were only optimized with respect to their far-field characteristics, i.e. in terms of their scattering or extinction cross sections. Although being an emerging feature in many numerical simulations, it was only recently fully appreciated that there exists a subtle but very important difference in the spectral position of resonances in the near-and the far-field. With the purpose to quantify this shift, Zuloaga et al. suggested a Lorentzian model to estimate the resonance shift. Here, we devise on fully analytical grounds a strategy to predict the resonance in the near-field directly from that in the far-field and disclose that the issue is involved and multifaceted, in general. We outline the limitations of our theory if more sophisticated optical nano-antennas are considered where higher order multipolar contributions and higher order antenna resonances become increasingly important. Both aspects are highlighted by numerically studying relevant nano-antennas.
    Optics Express 04/2014; 22(8):9971-9982. · 3.55 Impact Factor
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    ABSTRACT: Genuinely homogeneous metamaterials, which may be characterized by local effective constitutive relations, are required for many spectacular metamaterial applications. Such metamaterials have to be made of meta-atoms, i.e., subwavelength resonators, which exhibit only electric and or magnetic dipole and negligible higher-order multipolar polarizabilities in the spectral range of interest. Here, we show that these desired meta-atoms can be designed by exploiting the extreme coupling regime. Appropriate meta-atoms are identified by performing a multipole analysis of the field scattered from the respective meta-atom. To design those particular meta-atoms it is important to disclose the frequency and angular-dependent polarizability of both dipole moments. We demonstrate the applicability of a purely analytical model to accurately calculate for a normally incident plane wave reflection and transmission from meta-surfaces made of periodically arranged meta-atoms. With our work we identify a possible route towards the engineering of artificial materials while only considering the response from its constituents. Our approach is generally applicable to all spectral domains and can be used to evaluate and design metamaterials made from different constituting materials, e.g., metals, dielectrics, or semiconductors.
    Physical Review B 04/2014; 89(15):155125. · 3.66 Impact Factor
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    ABSTRACT: We investigate the optical properties of a hybrid system consisting of a quantum emitter that is strongly coupled to a pair of metallic nanoparticles. Emphasis is put on the exploitation of such a hybrid system as a highly efficient source for nonclassical light. The properties of the emitted light are analyzed in detail for a system that was designed to maximize the single-photon emission rates. Such sources may represent important constituents for the future architecture of fully integrated quantum circuits and may soon drastically improve the performance of quantum information protocols.
    Physica Scripta 03/2014; T160. · 1.03 Impact Factor
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    ABSTRACT: Within the past several years a tremendous progress regarding optical nano-antennas could be witnessed. It is one purpose of optical nano-antennas to resonantly enhance light-matter interactions at the nanoscale, e.g. the interaction of an external illumination with molecules. In this specific, but in almost all schemes that take advantage of resonantly enhanced electromagnetic fields in the vicinity of nano-antennas, the precise knowledge of the spectral position of resonances is of paramount importance to fully exploit their beneficial effects. Thus far, however, many nano-antennas were only optimized with respect to their far-field characteristics, i.e. in terms of their scattering or extinction cross sections. Although being an emerging feature in many numerical simulations, it was only recently fully appreciated that there exists a subtle but very important difference in the spectral position of resonances in the near-and the far-field. With the purpose to quantify this shift, Zuloaga et al. suggested a Lorentzian model to estimate the resonance shift. Here, we devise on fully analytical grounds a strategy to predict the resonance in the near-field directly from that in the far-field and disclose that the issue is involved and multifaceted, in general. We outline the limitations of our theory if more sophisticated optical nano-antennas are considered where higher order multipolar contributions and higher order antenna resonances become increasingly important. Both aspects are highlighted by numerically studying relevant nano-antennas.
    Optics Express 03/2014; 22(8). · 3.55 Impact Factor
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    [Show abstract] [Hide abstract]
    ABSTRACT: We report on the design, simulation, fabrication, and characterization of a novel two layer anti-reflective coating (ARC) based on a plasmonic metamaterial and a dielectric. Promoted by the strong material dispersion of the plasmonic metamaterial, our novel concept (called hybrid ARC) combines two possible arrangements for layers in an anti-reflection coating into a single structure; albeit at two different wavelengths. This, however, causes a broadband reduction of reflection that is less sensitive against oblique incidence when compared to traditional antireflective coatings. Furthermore, we show that the current metamaterial on a metal reflector can be used for the visualization of different coloration such as plasmonic rainbow despite its sub-wavelength thickness.
    Nanoscale 03/2014; 6:6037-6045. · 6.73 Impact Factor
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    ABSTRACT: A novel scheme is proposed to generate a maximally entangled state between two qubits by means of a dissipation-driven process. To this end, we entangle the quantum states of qubits that are mutually coupled by a plasmonic nanoantenna. Upon enforcing a weak spectral asymmetry in the properties of the qubits, the steady-state probability to obtain a maximally entangled, subradiant state approaches unity. This occurs despite the high losses associated to the plasmonic nanoantenna that are usually considered as being detrimental. The entanglement scheme is shown to be quite robust against variations in the transition frequencies of the quantum dots and deviations in their prescribed position with respect to the nanoantenna. Our work paves the way for novel applications in the field of quantum computation in highly integrated optical circuits.
    03/2014;
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    ABSTRACT: We propose to use nanoantennas (NAs) coupled to incoherently pumped quantum dots for ultrabright single photon emission. Besides fully quantum calculations, we analyze an analytical expression for the emitted photon rate. From these analytical considerations, it turns out that the Purcell factor and the pumping rate are the main quantities of interest. We also disclose a trade-off between the emitted photon rate and the nonclassical nature of the emitted light. This trade-off has to be considered while designing suitable NAs, which we also discuss in depth.
    Optics Letters 03/2014; 39(5):1246-9. · 3.39 Impact Factor
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    ABSTRACT: The unique properties of plasmonic nanostructures have fuelled research based on the tremendous amount of potential applications. Their tailor-made assemblies in combination with the tunable size and morphology of the initial building blocks allow for the creation of materials with a desired optical response. In this respect, it is crucial to synthesize nanoparticles with a defined shape that are at the core of such developments. Moreover, the interaction of individual nanoparticles with an incident electromagnetic field cannot only be influenced by their structure, but in fact, also by their spatial arrangement to each other. To harvest such opportunities, a profound theoretical understanding of these interactions is required as well as concise strategies to create such ordered assemblies. A quantitative evaluation of their optical properties can only be conducted when discrete structures of high uniformity can be achieved. As a consequence, separation steps have to be applied in order to obtain materials of high purity and uniformity. This also allows for an easier structural characterization of the nanoparticles and their assembled superstructures. In this progress report, an overview about the current development in this field of research is provided.
    Particle and Particle Systems Characterization 03/2014; · 0.86 Impact Factor
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    ABSTRACT: Plasmonic nanoantennas permit many functional components for future generations of nanoscale optical devices. They have been intensively studied and means were devised to engineer their optical response. However, as a metal-based resonator, the low quality factor of a plasmonic antenna hinders its further applications. Here, we propose a novel design to improve the quality factor of a dipolar nanoantenna by combining it with plasmonic Bragg gratings. This specific antenna design can support extraordinary sharp resonances and highly directional emissivity. Therefore, it promises to achieve many novel applications, e.g., in the field of cavity quantum electrodynamics where the strong coupling regime for light and matter comes in reach.
    Journal of the Optical Society of America A 02/2014; 31(2):388-93. · 1.67 Impact Factor
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    ABSTRACT: We investigate the magnetic response of meta-atoms that can be fabricated by a bottom-up technique. Usually such meta-atoms consist of a dielectric core surrounded by a large number of solid metallic nanoparticles. In contrast to those meta-atoms considered thus far, here we study hollow metallic nanoparticles (shells). In doing so, we solve one of the most pertinent problems of current self-assembled metamaterials, namely, implementing meta-atoms with sufficiently large resonance strength and small absorption. Both conditions have to be met for deep subwavelength meta-atoms to obtain effectively homogeneous metamaterials which may be meaningfully described by negative material parameters. Eventually we show that by using these findings, self-assembled negative index materials come within reach.
    01/2014; 89(7).
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    ABSTRACT: Plasmonic nanocomposites find many applications, such as nanometric coatings in emerging fields, such as optotronics, photovoltaics or integrated optics. To make use of their ability to affect light propagation in an unprecedented manner, plasmonic nanocomposites should consist of densely packed metallic nanoparticles. This causes a major challenge for their theoretical description, since the reliable assignment of effective optical properties with established effective medium theories is no longer possible. Established theories, e.g., the Maxwell-Garnett formalism, are only applicable for strongly diluted nanocomposites. This effective description, however, is a prerequisite to consider plasmonic nanocomposites in the design of optical devices. Here, we mitigate this problem and use full wave optical simulations to assign effective properties to plasmonic nanocomposites with filling fractions close to the percolation threshold. We show that these effective properties can be used to properly predict the optical action of functional devices that contain nanocomposites in their design. With this contribution we pave the way to consider plasmonic nanocomposites comparably to ordinary materials in the design of optical elements.
    Materials 01/2014; 7:727-741. · 1.88 Impact Factor
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    ABSTRACT: The combination of modern nanofabrication techniques and advanced computational tools has opened unprecedented opportunities to mold the flow of light. In particular, discrete photonic structures can be designed such that the resulting light dynamics mimics quantum mechanical condensed matter phenomena. By mapping the time-dependent probability distribution of an electronic wave packet to the spatial light intensity distribution in the corresponding photonic structure, the quantum mechanical evolution can be visualized directly in a coherent, yet classical wave environment. On the basis of this approach, several groups have recently observed discrete diffraction, Bloch oscillations and Zener tunnelling in different dielectric structures. Here we report the experimental observation of discrete diffraction and Bloch oscillations of surface plasmon polaritons in evanescently coupled plasmonic waveguide arrays. The effective external potential is tailored by introducing an appropriate transverse index gradient during nanofabrication of the arrays. Our experimental results are in excellent agreement with numerical calculations.
    Nature Communications 01/2014; 5:3843. · 10.74 Impact Factor

Publication Stats

2k Citations
706.67 Total Impact Points

Institutions

  • 2014
    • Karlsruhe Institute of Technology
      • Institute for Theoretical Solid State Physics
      Carlsruhe, Baden-Württemberg, Germany
  • 2005–2014
    • Friedrich-Schiller-University Jena
      • • Institute of Organic Chemistry and Macromolecular Chemistry
      • • Department of Condensed Matter and Optics
      • • Department of Applied Physics
      Jena, Thuringia, Germany
  • 2011–2013
    • École Polytechnique Fédérale de Lausanne
      • Laboratoire d'optique appliquée
      Lausanne, VD, Switzerland
    • The Optical Society
      Society Hill, New Jersey, United States
    • California College San Diego
      San Diego, California, United States
    • Max Planck Institute for Solid State Research
      Stuttgart, Baden-Württemberg, Germany
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2009–2012
    • Oklahoma State University - Stillwater
      • School of Electrical and Computer Engineering
      Stillwater, OK, United States
  • 2008–2011
    • Universität Stuttgart
      • Institute of Physics
      Stuttgart, Baden-Wuerttemberg, Germany
    • Universitätsklinikum Jena
      Jena, Thuringia, Germany
  • 2009–2010
    • Max Planck Society
      München, Bavaria, Germany
  • 2005–2007
    • National Institute of Advanced Industrial Science and Technology
      • Electronics and Photonics Research Institute
      Tsukuba, Ibaraki, Japan
  • 2006
    • Imperial College London
      • Department of Physics
      London, ENG, United Kingdom
  • 2001–2005
    • Université de Neuchâtel
      Neuenburg, Neuchâtel, Switzerland