Unraveling the myths and mysteries of photon avalanching nanoparticles

Photon avalanching (PA) nanomaterials exhibit some of the most nonlinear optical phenomena reported for any material, allowing them to push the frontiers of applications ranging from nanoscale imaging and sensing to optical computing. But PA remains shrouded in mystery, with its underlying physics and limitations misunderstood. Photon avalanching is not, in fact, an avalanche of photons, at least not in the same way that snowballs beget more snowballing in an actual avalanche. In this focus article, we dispel these and other common myths surrounding PA in lanthanide-based nanoparticles and unravel the mysteries of this unique nonlinear optical effect. We hope that removing the misconceptions surrounding avalanching nanoparticles will inspire new interest and applications that harness the giant nonlinearity of PA across a broad range of scientific fields

Modelling RF sheath dynamics for fusion applications

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Case studies on time-dependent Ginzburg-Landau simulations for superconducting applications

The macroscopic electromagnetic properties of type II superconductors are primarily influenced by the behavior of microscopic superconducting flux quantum units. Time-dependent Ginzburg-Landau (TDGL) equations provide an elegant and powerful tool for describing and examining both the statics and dynamics of these superconducting entities. They have been instrumental in replicating and elucidating numerous experimental results over the past decades.This paper provides a comprehensive overview of the progress in TDGL simulations, focusing on three key aspects of superconductor applications. The initial section delves into vortex rectification in superconductors described within the TDGL framework. We specifically highlight the superconducting diode effect achieved through asymmetric pinning landscapes and the reversible manipulation of vortex ratchets with dynamic pinning landscapes. The subsequent section reviews the achievements of TDGL simulations concerning the critical current density of superconductors, emphasizing the optimization of pinning sites, particularly vortex pinning and dynamics in polycrystalline Nb$_3$Sn with grain boundaries. The third part concentrates on numerical modeling of vortex penetration and dynamics in superconducting radio frequency (SRF) cavities, including a discussion of superconductor insulator superconductor multilayer structures. In the last section, we present key findings, insights, and perspectives derived from the discussed simulations.Comment: 20 pages,13 figure

Metamaterial Superconductors

Searching for natural materials exhibiting larger electron-electron interactions constitutes a traditional approach to high temperature superconductivity research. Very recently we pointed out that the newly developed field of electromagnetic metamaterials deals with the somewhat related task of dielectric response engineering on a sub-100 nm scale. Considerable enhancement of the electron-electron interaction may be expected in such metamaterial scenarios as in epsilon near zero (ENZ) and hyperbolic metamaterials. In both cases dielectric function may become small and negative in substantial portions of the relevant four-momentum space, leading to enhancement of the electron pairing interaction. This approach has been verified in experiments with aluminium-based metamaterials. Metamaterial superconductor with Tc = 3.9 K have been fabricated, that is three times that of pure aluminium (Tc = 1.2 K), which opens up new possibilities to considerably improve Tc of other simple superconductors. Taking advantage of the demonstrated success of this approach, the critical temperature of hypothetic niobium, MgB2 and H2S-based metamaterial superconductors is evaluated. The MgB2-based metamaterial superconductors are projected to reach the liquid nitrogen temperature range. In the case of an H2S-based metamaterial projected Tc appears to reach ~250 K.Comment: 78 pages, 24 figures, Invited review article prepared for Nanophotonic

Graphene Nanoscroll Field-Effect Transistor-Based Radiation Sensors

Carbon nanomaterials have excited both academia and industry with their extraordinary electronic, mechanical, optical, thermal, and chemical properties for over forty years, providing opportunities for significant advances in fundamental and applied science and leading to the development of disruptive technologies and applications. While graphene and carbon nanotubes have been at the forefront of research, a relatively new one-dimensional carbon allotrope, graphene nanoscrolls, will likely play significant roles in future technologies. Graphene nanoscrolls have structures similar to carbon nanotubes with a key difference in that they are not seamless – there are exposed edges along their lengths. As such, they share many of the electronic, mechanical, and thermal properties that have brought so much interest to graphene and carbon nanotubes while offering their own unique features.The current body of work on graphene nanoscrolls is sparse, with the majority of presented research either being theoretical in nature or pertaining to the synthesis of these nanostructures. This work provides some of the first experimental work into the application of graphene nanoscrolls. New and promising synthesis techniques were experimentally evaluated for scalability and throughput. Preferred synthesis techniques were employed to create back-gated field-effect transistors that utilize graphene nanoscrolls as the channel material. It was shown that extraordinary current densities and room temperature ballistic transport over long channel lengths are achievable. The field-effect transistors were further extended to the application of radiation sensors by functionalizing the graphene nanoscroll channel material with nanoparticles with high radiation interaction probabilities. The developed radiation sensors are shown to be capable of detecting low levels of X-ray, gamma, and neutron radiation with very small footprints and negligible power consumption. Production of these devices are scalable and inexpensive

Statistical imaging of transport in complex fluids: a journey from entangled polymers to living cells

Combining advanced fluorescence imaging, single particle tracking, and quantitative analysis in the framework of statistical mechanics, we studied several transport phenomena in complex fluids with nanometer and millisecond resolution. On the list are diffusion of nanoparticles and vesicles in crowded environments, reptational motion of polymers in entangled semidilute solutions, and active endosome transport along microtubules in living cells. We started from individual trajectories, and then converged statistically to aggregate properties of interests, with special emphasis on the fluctuations buried under the classic mean-field descriptions. The unified scientific theme behind these diversified subjects is to examine, with experiments designed as direct as possible, the commonly believed fundamental assumptions in those fields, such as Gaussian displacements in Fickian diffusion, harmonic confining potential of virtual tubes in polymer entanglements, and bidirectional motion of active intra-cellular transport. This series of efforts led us to discoveries of new phenomena, mechanisms, and concepts. This route, we termed as ???statistical imaging???, is expected to be widely useful at studying dynamic processes, especially in those emerging fields at the overlap of physics and biology

All-optical modulation with single-photons using electron avalanche

The distinctive characteristics of light such as high-speed propagation, low-loss, low cross-talk and power consumption as well as quantum properties, make it uniquely suitable for various critical applications in communication, high-resolution imaging, optical computing, and emerging quantum information technologies. One limiting factor though is the weak optical nonlinearity of conventional media that poses challenges for the control and manipulation of light, especially with ultra-low, few-photon-level intensities. Notably, creating a photonic transistor working at single-photon intensities remains an outstanding challenge. In this work, we demonstrate all-optical modulation using a beam with single-photon intensity. Such low-energy control is enabled by the electron avalanche process in a semiconductor triggered by the impact ionization of charge carriers. This corresponds to achieving a nonlinear refractive index of n2~7*10^-3m^2/W, which is two orders of magnitude higher than in the best nonlinear optical media (Table S1). Our approach opens up the possibility of terahertz-speed optical switching at the single-photon level, which could enable novel photonic devices and future quantum photonic information processing and computing, fast logic gates, and beyond. Importantly, this approach could lead to industry-ready CMOS-compatible and chip-integrated optical modulation platforms operating with single photons

Miniaturized Silicon Photodetectors

Silicon (Si) technologies provide an excellent platform for the design of microsystems where photonic and microelectronic functionalities are monolithically integrated on the same substrate. In recent years, a variety of passive and active Si photonic devices have been developed, and among them, photodetectors have attracted particular interest from the scientific community. Si photodiodes are typically designed to operate at visible wavelengths, but, unfortunately, their employment in the infrared (IR) range is limited due to the neglectable Si absorption over 1100 nm, even though the use of germanium (Ge) grown on Si has historically allowed operations to be extended up to 1550 nm. In recent years, significant progress has been achieved both by improving the performance of Si-based photodetectors in the visible range and by extending their operation to infrared wavelengths. Near-infrared (NIR) SiGe photodetectors have been demonstrated to have a “zero change” CMOS process flow, while the investigation of new effects and structures has shown that an all-Si approach could be a viable option to construct devices comparable with Ge technology. In addition, the capability to integrate new emerging 2D and 3D materials with Si, together with the capability of manufacturing devices at the nanometric scale, has led to the development of new device families with unexpected performance. Accordingly, this Special Issue of Micromachines seeks to showcase research papers, short communications, and review articles that show the most recent advances in the field of silicon photodetectors and their respective applications

Astrophysics in 2006

The fastest pulsar and the slowest nova; the oldest galaxies and the youngest stars; the weirdest life forms and the commonest dwarfs; the highest energy particles and the lowest energy photons. These were some of the extremes of Astrophysics 2006. We attempt also to bring you updates on things of which there is currently only one (habitable planets, the Sun, and the universe) and others of which there are always many, like meteors and molecules, black holes and binaries.Comment: 244 pages, no figure