771 research outputs found

    Spontaneous decay dynamics in atomically doped carbon nanotubes

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    We report a strictly non-exponential spontaneous decay dynamics of an excited two-level atom placed inside or at different distances outside a carbon nanotube (CN). This is the result of strong non-Markovian memory effects arising from the rapid variation of the photonic density of states with frequency near the CN. The system exhibits vacuum-field Rabi oscillations, a principal signature of strong atom-vacuum-field coupling, when the atom is close enough to the nanotube surface and the atomic transition frequency is in the vicinity of the resonance of the photonic density of states. Caused by decreasing the atom-field coupling strength, the non-exponential decay dynamics gives place to the exponential one if the atom moves away from the CN surface. Thus, atom-field coupling and the character of the spontaneous decay dynamics, respectively, may be controlled by changing the distance between the atom and CN surface by means of a proper preparation of atomically doped CNs. This opens routes for new challenging nanophotonics applications of atomically doped CN systems as various sources of coherent light emitted by dopant atoms.Comment: 10 pages, 4 figure

    Annual report / IFW, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden

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    Nanostructured composite materials based on carbon nanotubes and 3-D photonic crystals

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    Carbon nanotubes (CNT) and in particular, single-wall carbon nanotubes (SWCNT) have been extensively studied, in large part, due to their unique one-dimensional crystalline structures and related electronic and optical properties. Various polymeric composite materials, which were based on carbon nanotubes, have been also developed in an attempt to combine the properties of polymer and CNT in a single film. Such composites were mainly formed by mixing carbon nanotubes within the polymer without special emphasis on the structure and thereby, the nanoscopic properties of the resultant material. Photonic crystals belong to a class of man-made structures aimed at manipulating the propagation of electromagnetic waves at sub-wavelength dimensions in the visible range. The objective of this research work was to fabricate optical nano-composites from the bottom up: by incorporating carbon nanotubes within nano-structured templates we attempted to achieve novel composites with unique optical properties. Three-dimensional photonic crystals were made by self-assembly using monodisperse suspension of silicon dioxide colloids. Upon sedimentation, this highly ordered crystal, also known as opal, serves as a template for polymeric and polymer/CNT composites. For example, by infiltrating of the templates voids with a desired polymeric solution followed by etching of the silica template away, a three-dimensional inverse polymeric structure is obtained. Single-wall carbon nanotubes (SWCNT) have been directly grown into the template voids (in the range of 20 - 70 nm) by catalytic Chemical Vapor Deposition (CVD) technique with carbon monoxide as the carbon feedstock. The resultant SWCNTs were mostly semiconductive (p-doped). Control over the growth of SWCNT has been obtained by changing the catalyst concentration and the template\u27s void-size. Various techniques were used to characterize the SWCNT and its composites: Scanning Electron Microscope (SEM) has been used to identify the morphology of structures; interactions between polymer and nanotubes have been characterized by Raman spectroscopy; optical properties were studied by linear and nonlinear optical transmission and optical activity measurements; electrical properties were studied using thermoelectric and photoconductivity measurements. These data suggest that selforganized nano-scale templates are a promising route for realizing novel optical composite materials

    Near-field Electrodynamics of Atomically Doped Carbon Nanotubes

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    We develop a quantum theory of near-field electrodynamical properties of carbon nanotubes and investigate spontaneous decay dynamics of excited states and van der Waals attraction of the ground state of an atomic system close to a single-wall nanotube surface. Atomic spontaneous decay exhibits vacuum-field Rabi oscillations -- a principal signature of strong atom-vacuum-field coupling. The strongly coupled atomic state is nothing but a 'quasi-1D cavity polariton'. Its stability is mainly determined by the atom-nanotube van der Waals interaction. Our calculations of the ground-state atom van der Waals energy performed within a universal quantum mechanical approach valid for both weak and strong atom-field coupling demonstrate the inapplicability of conventional weak-coupling-based van der Waals interaction models in a close vicinity of the nanotube surface.Comment: Book Chapter. 50 pages, 11 figures. To be published in "Nanotubes: New Research", edited by F.Columbus (Nova Science, New York, 2005

    Aperiodic Multilayer Graphene Based Tunable and Switchable Thermal Emitter at Mid-infrared Frequencies

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    Over the past few decades, there have been tremendous innovations in electronics and photonics. The development of these ultra-fast growing technologies mostly relies on fundamental understanding of novel materials with unique properties as well as new designs of device architectures with more diverse and better functionalities. In this regard, the promising approach for next-generation nanoscale electronics and photonics is to exploit the extraordinary characteristics of novel nanomaterials. There has been an explosion of interest in graphene for photonic applications as it provides a degree of freedom to manipulate electromagnetic waves. In this thesis, to tailor the broadband blackbody radiation, new aperiodic multilayer structures composed of multiple layers of graphene and hexagonal boron nitride (hBN) are proposed as selective, tunable and switchable thermal emitters. To obtain the layer thicknesses of these aperiodic multilayer structures for maximum emittance/absorptance, a hybrid optimization algorithm coupled to a transfer matrix code is employed. The device simulation indicates that perfect absorption efficiency of unity can be achieved at very narrow frequency bands in the infrared under normal incidence. It has been shown that the chemical potential in graphene enables a promising way to design electrically controllable absorption/emission, resulting in selective, tunable and switchable thermal emitters at infrared frequencies. By simulating different aperiodic thermal emitters with different numbers of graphene layers, the effect of the number of graphene layers on selectivity, tunability, and switchability of thermal emittance is investigated. This study may contribute towards the realization of wavelength selective detectors with switchable intensity for sensing applications

    Bio-Inspired Nanomembranes as Building Blocks for Nanophotonics, Plasmonics and Metamaterials

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    Nanomembranes are the most widespread building block of life, as they encompass cell and organelle walls. Their synthetic counterparts can be described as freestanding or free-floating structures thinner than 100 nm, down to monatomic/monomolecular thickness and with giant lateral aspect ratios. The structural confinement to quasi-2D sheets causes a multitude of unexpected and often counterintuitive properties. This has resulted in synthetic nanomembranes transiting from a mere scientific curiosity to a position where novel applications are emerging at an ever-accelerating pace. Among wide fields where their use has proven itself most fruitful are nano-optics and nanophotonics. However, the authors are unaware of a review covering the nanomembrane use in these important fields. Here, we present an attempt to survey the state of the art of nanomembranes in nanophotonics, including photonic crystals, plasmonics, metasurfaces, and nanoantennas, with an accent on some advancements that appeared within the last few years. Unlimited by the Nature toolbox, we can utilize a practically infinite number of available materials and methods and reach numerous properties not met in biological membranes. Thus, nanomembranes in nano-optics can be described as real metastructures, exceeding the known materials and opening pathways to a wide variety of novel functionalities

    Unconventional van der Waals heterostructures beyond stacking

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    Two-dimensional crystals provide exceptional opportunities for integrating dissimilar materials and forming interfaces where distinct properties and phenomena emerge. To date, research has focused on two basic heterostructure types: vertical van der Waals stacks and laterally joined monolayer crystals with in-plane line interfaces. Much more diverse architectures and interface configurations can be realized in the few-layer and multilayer regime, and if mechanical stacking and single-layer growth are replaced by processes taking advantage of self-organization, conversions between polymorphs, phase separation, strain effects, and shaping into the third dimension. Here, we highlight such opportunities for engineering heterostructures, focusing on group IV chalcogenides, a class of layered semiconductors that lend themselves exceptionally well for exploring novel van der Waals architectures, as well as advanced methods including in situ microscopy during growth and nanometer-scale probes of light-matter interactions. The chosen examples point to fruitful future directions and inspire innovative developments to create unconventional van der Waals heterostructures beyond stacking

    Investigations of Optical Coherence Properties in an Erbium-doped Silicate Fiber for Quantum State Storage

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    We studied optical coherence properties of the 1.53 μ\mum telecommunication transition in an Er3+^{3+}-doped silicate optical fiber through spectral holeburning and photon echoes. We find decoherence times of up to 3.8 μ\mus at a magnetic field of 2.2 Tesla and a temperature of 150 mK. A strong magnetic-field dependent optical dephasing was observed and is believed to arise from an interaction between the electronic Er3+^{3+} spin and the magnetic moment of tunneling modes in the glass. Furthermore, we observed fine-structure in the Erbium holeburning spectrum originating from superhyperfine interaction with 27^{27}Al host nuclei. Our results show that Er3+^{3+}-doped silicate fibers are promising material candidates for quantum state storage

    Annual report / IFW, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden

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