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High optical gain in InP-based quantum-dot material monolithically grown on silicon emitting at telecom wavelengths
(2022-04-01)
We describe the fabrication process and properties of an InP based quantum dot (QD) laser structure grown on a 5° off-cut silicon substrate. Several layers of QD-based dislocation filters embedded in GaAs and InP were used to minimize the defect density in the QD active region which comprised eight emitting dot layers. The structure was analyzed using high resolution transmission electron microscopy, atomic force microscopy and photoluminescence. The epitaxial stack was used to fabricate optical amplifiers which ...
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Multichannel single center method
(2022-08-10)
A multichannel single center (MCSC) method for the theoretical description of the electron continuum spectrum in molecules is reported. The method includes coupling between different continuum channels via electron correlations and describes, thereby, photoelectron continuum in the Tamm–Dancoff (configuration interaction singles) approximation. Basic equations of the non-iterative one-channel single center (SC) method and their extension to the MCSC method are presented, and an efficient scheme for their numerical ...
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3D Arrangement of Magnetic Particles in Thin Polymer Films Assisted by Magnetically Patterned Exchange Bias Layer Systems
(2021-10-31)
The possibility to arrange and embed magnetic micro- and nanoparticles in thin polymer film systems using flat magnetically patterned substrate templates is investigated. In contrast to self-organized particle rows forming by applying a homogeneous magnetic field, particles adapt to the magnetic field landscape of the substrate's magnetic pattern prior to polymer crosslinking. Crosslinking then fixes the particle positions in the polymer. The process is tested for composites of hydrophobic polydimethylsiloxane (PDMS) ...
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Temperature resistant fast InxGa1−xAs / GaAs quantum dot saturable absorber for the epitaxial integration into semiconductor surface emitting lasers
(2020-06-30)
Quantum-dot-based semiconductor saturable absorber mirrors (SESAMs) with fast response times were developed by molecular beam epitaxy (MBE). Using quantum dots (QDs) in the absorber region of the SESAMs instead of quantum wells, enables additional degrees of freedom in the design, the control of saturation parameters and the recovery dynamics. However, if one wants to integrate such a SESAM element into semiconductor surface emitting lasers such as a mode-locked integrated external-cavity surface-emitting laser ...
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Modelling stress‐state dependent nonlocal damage and failure of ductile metals
(2021-01-25)
Damage and failure of ductile metals is highly influenced by the stress state. In fact, void growth takes place under hydrostatic tensile loading and void coalescence leads eventually to ductile failure. A completely different damage mechanism occurs for shear dominated loading that results in void elongation within a narrow shear band. In order to account for both failure mechanisms, a stress state dependent damage model is proposed. The model is based on a continuum damage mechanics approach, whereby nonlinear ...
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Influence of Accelerated Aging on the Fiber-Matrix Adhesion of Regenerated Cellulose Fiber-Reinforced Bio-Polyamide
(2023-03-23)
With regard to the sustainability and biological origin of plastic components, regenerated cellulose fiber (RCF)-reinforced polymers are expected to replace other composites in the future. For use under severe conditions, for example, as a housing in the engine compartment, the resistance of the composites and the impact on the fiber and fiber-matrix adhesion must be investigated. Composites of bio-polyamide with a reinforcement of 20 wt.% RCF were compounded using a twinscrew extruder. The test specimens were ...
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Artificial intelligence for online characterization of ultrashort X-ray free-electron laser pulses
(2022-10-24)
X-ray free-electron lasers (XFELs) as the world’s brightest light sources provide ultrashort X-ray pulses with a duration typically in the order of femtoseconds. Recently, they have approached and entered the attosecond regime, which holds new promises for single-molecule imaging and studying nonlinear and ultrafast phenomena such as localized electron dynamics. The technological evolution of XFELs toward well-controllable light sources for precise metrology of ultrafast processes has been, however, hampered by the ...
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Modification of Polyamide 66 for a Media-Tight Hybrid Composite with Aluminum
(2023-04-06)
Metal–plastic composites are becoming increasingly important in lightweight construction. As a combination, e.g., for transmission housings in automobiles, composites made of die-cast aluminum housings and Polyamide 66 are a promising material. The interface between metal and plastic and the properties of the plastic component play an important role with regard to media tightness against transmission oil. The mechanical properties of the plastic can be matched to aluminum by glass fibers and additives. In the case ...
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Mechanisms of one-photon two-site double ionization after resonant inner-valence excitation in Ne clusters
(2023-01-30)
The role of interatomic and intermolecular energy and charge-transfer processes in weakly bound matter is currently lively debated due to emerging destructive low-energy electrons and radicals. Here, we discuss two mechanisms of single-photon two-site double ionization occurring competitively or subsequently to resonant interatomic Coulombic decay (rICD) in inner-valence (2s→np) excited Ne dimers and clusters. The first mechanism is photoelectron-impact ionization which is, in general, not related to resonant excitation, ...
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Miniaturized interferometric confocal distance sensor for surface profiling with data rates at ultrasonic frequencies
(2023-01-12)
Point-wise measuring profilometers like the tactile stylus instruments or optical sensors are established measurement tools in science and industry to measure and characterize surface textures. We present a fiber-coupled laser interferometric confocal distance sensor for surface profiling. The sensor is characterized by small geometric dimensions and by its high lateral
scanning speed. The ability to measure specularly reflecting and rough surface textures are demonstrated by performing several measurements on a ...