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arXiv2018

An axis symmetric 2D description of the process of the growth of a single crystal Si tube growth from the melt by pulling down method. Part1

This paper is the first part of an axis symmetric description of a single crystal tube growth process by micro-pulling-down method.the description concerns the following aspects:the free surfaces equations and the pressure difference across the free surfaces (section 2) , limits of the pressure differences across the free surfaces (section 3) ;static stability of the capillary free surfaces (section 4). In section 5 the above aspects are numerically investigated in case of a silicon tube growth.This investigation can be helpful in the better understanding the growth process and in the automation of manufacturing.In section 6 some general conclusion are given.Section 7 is an annex which contains the proof of the general statements formulated in sections 3 and 4.

physics.app-ph↗

arXiv2018

Calibration of the oscillation amplitude of electrically excited scanning probe microscopy sensors

Atomic force microscopy (AFM) is an analytical surface characterization tool which can reveal a sample's topography with high spatial resolution while simultaneously probing tip-sample interactions. Local measurement of chemical properties with high-resolution has gained much popularity in recent years with advances in dynamic AFM methodologies. A calibration factor is required to convert the electrical readout to a mechanical oscillation amplitude in order to extract quantitative information about the surface. We propose a new calibration technique for the oscillation amplitude of electrically driven probes, which is based on measuring the electrical energy input to maintain the oscillation amplitude constant. We demonstrate the application of the new technique with quartz tuning fork including the qPlus configuration, while the same principle can be applied to other piezoelectric resonators such as length extension resonators, or piezoelectric cantilevers. The calibration factor obtained by this technique is found to be in agreement with using thermal noise spectrum method for capsulated, decapsulated tuning forks and tuning forks in the qPlus configuration.

physics.app-ph↗

arXiv2018

Fast and direct visualization of piezo-generated charges at the nanoscale using direct piezoelectric force microscopy

The denominated surface charge scraping mechanism was discovered in 2014 by using a new Atomic Force Microscopy (AFM) based mode called Charge Gradient Microscopy. The measurements to probe such mechanism are achieved with the use of a current-to-voltage converter: a transimpedance amplifier (TIA). However, the use of an incorrect approximation, named Gain BandWidth Product (GBWP) to calculate TIAs BandWidth (BW) could mislead to an incorrect data interpretation. By measuring at higher frequencies than permitted, the amplifier is used as a current-to-voltage converter, in conditions where it behaves as a charge-to-voltage converter. In this manuscript, we report the specific conditions in which the transfer function of the same electronic circuit topology is valid, while we spot both ringing and unstable amplifiers artifacts in the published data. We finally perform physical measurements in similar conditions as reported, but fully respecting the BandWidth (BW) of the system. We find that the charge collected is way below the values reported in such publication, diminishing or even nullifying the impact of a possible charge scrapping mechanism. These findings pave the way to employ Direct Piezoelectric Force Microscopy (DPFM) as a fast ferroelectric nanoscale characterization tool.

physics.app-ph↗

arXiv2018

The largest cognitive systems will be optoelectronic

Electrons and photons offer complementary strengths for information processing. Photons are excellent for communication, while electrons are superior for computation and memory. Cognition requires distributed computation to be communicated across the system for information integration. We present reasoning from neuroscience, network theory, and device physics supporting the conjecture that large-scale cognitive systems will benefit from electronic devices performing synaptic, dendritic, and neuronal information processing operating in conjunction with photonic communication. On the chip scale, integrated dielectric waveguides enable fan-out to thousands of connections. On the system scale, fiber and free-space optics can be employed. The largest cognitive systems will be limited by the distance light can travel during the period of a network oscillation. We calculate that optoelectronic networks the area of a large data center ($10^5$\,m$^2$) will be capable of system-wide information integration at $1$\,MHz. At frequencies of cortex-wide integration in the human brain ($4$\,Hz, theta band), optoelectronic systems could integrate information across the surface of the earth.

cs.ET↗

arXiv2018

Using liner surface modes in ducts to make obstacles reflectionless

Acoustic cloaking for the suppression of backscattering inside ducts is proposed in the audible range where plane waves are curved around the object using the surface modes of the liner. It is numerically shown that a slowly varying resonant liner (e. g. based on an array of tubes) creates a zone of silence in which an object of arbitrary shape can be acoustically hidden for a wide range of frequencies. And then, a resonant liner has deflecting properties without reflection of the wavefront, which are close to an ideal invisibility cloak. This kind of cloaking is effective in a wide frequency band and the cloaking band is a function of the impedance and height of the obstacle relative to the conduit. For smooth shaped obstacles, there is an ability of the object to help hide itself, which increases the cloaking frequency band (self-cloaking). Dispersion effects lead to slow sounds and distortion of the wave phase.

physics.app-ph↗

arXiv2018

0.52 V-mm ITO-based Mach-Zehnder Modulator in Silicon Photonics

Electro-optic modulators transform electronic signals into the optical domain and are critical components in modern telecommunication networks, RF photonics, and emerging applications in quantum photonics and beam steering. All these applications require integrated and voltage-efficient modulator solutions with compact formfactors that are seamlessly integratable with Silicon photonics platforms and feature near-CMOS material processing synergies. However, existing integrated modulators are challenged to meet these requirements. Conversely, emerging electro-optic materials heterogeneously integrated with Si photonics open a new avenue for device engineering. Indium tin oxide (ITO) is one such compelling material for heterogeneous integration in Si exhibiting formidable electro-optic effect characterized by unity order index at telecommunication frequencies. Here we overcome these limitations and demonstrate a monolithically integrated ITO electro- optic modulator based on a Mach Zehnder interferometer (MZI) featuring a high-performance half-wave voltage and active device length product, VpL = 0.52 V-mm. We show, how that the unity-strong index change enables a 30 micrometer-short pi-phase shifter operating ITO in the index-dominated region away from the epsilon-bear-zero ENZ point. This device experimentally confirms electrical phase shifting in ITO enabling its use in multifaceted applications including dense on-chip communication networks, nonlinearity for activation functions in photonic neural networks, and phased array applications for LiDAR.

physics.app-ph↗

arXiv2018

Deep Neural Network Inverse Design of Integrated Nanophotonic Devices

Predicting physical response of an artificially structured material is of particular interest for scientific and engineering applications. Here we use deep learning to predict optical response of artificially engineered nanophotonic devices. In addition to predicting forward approximation of transmission response for any given topology, this approach allows us to inversely approximate designs for a targeted optical response. Our Deep Neural Network (DNN) could design compact (2.6x2.6 μm2) silicon-on-insulator (SOI)-based 1 X 2 power splitters with various target splitting ratios in a fraction of a second. This model is trained to minimize the reflection (smaller than 20 dB) while achieving maximum transmission efficiency (above 90%) and target splitting specifications. This approach paves the way for rapid design of integrated photonic components relying on complex nanostructures.

physics.app-ph↗

arXiv2018

Dissipation engineering in metamaterials by localized structural dynamics

In civil, mechanical, and aerospace engineering, structural dynamics is commonly understood to be a discipline concerned with the analysis and characterization of the vibratory response of structures. Key elements of the response are the amplitude, phase, and damping ratio, which are quantities that vary with the excitation frequency. In this paper, we extend the discipline of structural dynamics to the realm of materials engineering by intrinsically building localized substructures within, or attached to, the material domain itself$-$which is viewed as an extended medium without defined external boundaries. Our system is essentially a locally resonant elastic metamaterial, except here it is viewed from the perspective of unique dissipation characteristics rather than subwavelength effective properties or band gaps, as widely done in the literature. We provide a theory, validated by experiments, for substructurally synthesizing the dissipation under the conditions of free-wave motion, i.e., waves not constrained to a prescribed driving frequency. We use an extended elastic beam with attached pillars as an example of a metamaterial. When compared to an identical infinite beam with no attached substructures, we show that within certain frequency ranges the metamaterial exhibits either enhanced or reduced dissipation$-$which we refer to as positive and negative metadamping, respectively. These regimes are rigorously identified and characterized using the metamaterial's band structure and wavenumber-dependent dissipation diagram. This theory impacts applications that require a combination of high stiffness and high damping or, conversely, applications that benefit from a reduction in loss without the need to change the backbone constituent material.

physics.app-ph↗

arXiv2018

Highly-efficient second and third harmonic generation in a monocrystalline lithium niobate microresonator

Nonlinear optics in whispering-gallery-mode (WGM) microresonators have attracted much attention. Owing to strong confinement of the light in a small volume, a WGM microresonator can dramatically boost the strength of light field, giving rise to enhancement of the nonlinear interactions of light with the resonator material. Here, we demonstrate highly efficient second harmonic generation (SHG) and third harmonic generation (THG) in an on-chip monocrystalline lithium niobate (LN) microresonator. Benefitting from a cyclic phase matching scheme for the transverse-electric WGMs, nonlinear wavelength conversion utilizing the largest second-order nonlinear coefficient d33, which has not been demonstrated until now despite of its obvious advantage, is successfully achieved in an X-cut LN microresonator. We obtain high conversion efficiencies in not only the SHG (3.8% mW^-1) but also the THG (0.3% mW^-2) realized through a cascaded sum-frequency process. Our results represent a major step toward the classical and quantum photonic integrated circuits.

physics.app-ph↗

arXiv2018

Thermal Switching of Lasing Regimes in Heavily Doped Er3+ Fiber Lasers

A pulsed regime of short-cavity, heavily erbium-doped fiber lasers is of high interest for its possible applications in telecommunications and sensorics. Here, we demonstrate these lasers in two configurations, distributed feedback laser and compare it with a classic Fabry-Perot type laser. We have managed to create lasers that function stably with cavities as small as 50 mm. Pulse properties such as amplitude, frequency and duration, are in a good agreement with our theoretical analysis, which takes into account spontaneous emission. We report the observation of the thermal switching effect, which consists of the pulsing regime changing to CW upon cooling the laser cavities down to the liq-uid nitrogen temperature. We theoretically show that this effect may be explained by weakening of the up-conversion process responsible for the pulsed regime. The slowing of the up-conversion processes is due to the energy mismatch in this process, which is overcome by interaction with phonons. At low temperatures, the number of phonons decreas-es and pulsing switches off.

cond-mat.mes-hall↗

arXiv2018

Phonon-mediated thermal transport at exponentially mass-graded interfaces: A computational study

We numerically investigate thermal transport at solid-solid interfaces with graded intermediate layers whose masses vary exponentially from one side to the other. Using Non-Equilibrium Green's Function and Non-Equilibrium Molecular Dynamics simulations, we show that an exponentially mass-graded junction with a finite thickness can result in 68\% of enhancement in thermal conductance larger compared to a single bridging layer (29\%) and a linear mass-graded junction (64\%) of similar thickness. We examine how the thermal conductance at such interfaces is influenced by geometric qualities and strength of anharmonicity. For geometric properties, we tested the effects from number of layers and the junction thickness. In the absence of anharmonicity, increasing the number of layers results in better elastic phonon transmission at each individual boundary, countered by the decrease of available conducting channels. Consequently, in the harmonic regime, conductance initially increases with number of layers due to better bridging, but quickly saturates. The presence of slight anharmonic effects (at ultra-low temperature T = 2 K) turns the saturation into a monotonically increasing trend. Anharmonic effects can facilitate interfacial thermal transport through the thermalization of phonons. At high temperature, however, the role of anharmonicity as a facilitator of interfacial thermal transport reverses. Strong anharmonicity introduces significant intrinsic resistance, overruling the enhancement in thermal conduction at the boundaries. Our analysis shows that in our model Lennard-Jones system, the influence of a mass-graded junction on thermal conductance is dominated by the phonon thermalization through anharmonic effects, while elastic phonon transmission plays a secondary role.

physics.app-ph↗

arXiv2018

Stimulated Raman with Broadband LED Stokes Source for Analysis of Glucose

We demonstrate stimulated Raman gain using a broadband LED Stokes source to measure vibrational spectra of aqueous glucose solutions. This versatile and cost-effective method increases Raman signal for a variety of applications. We measured both stimulated Raman and spontaneous Raman spectra of glucose solutions with concentrations up to 10 mM with a photon counter and lock-in amplifier. We built partial least squares regression models based on both stimulated Raman and spontaneous Raman spectral data measured with each instrument for predicting concentrations of the glucose solutions. The stimulated Raman spectra measured with the lock-in amplifier based model had the strongest predictive power and predicted the concentrations of the test set of glucose solutions with a mean squared error value an order of magnitude lower than those of the spontaneous Raman based model.

physics.app-ph↗

arXiv2018

Microscope for X-ray orbital angular momentum imaging

Orbital angular momentum (OAM) of photons is carried upon the wave front of an optical vortex and is important in physics research due to its fundamental degree of freedom. As for the interaction with materials, the optical OAM was shown to be transferred to the valence electron based on modified selection rules where a single ion is carefully aligned to the center of a vortex [Schmiegelow et al.(2016)]. We here demonstrate an elaborate way of extracting the distributed OAMs in the two-dimensional x-ray wave field at the exit-face of the specimen by a vorticity-sensitive microscopy, which detects vorticity in the reciprocal-space wave field downstream of the optical vortices. This method enables us to measure the distributed topological charges and OAMs by a single image with the wide field of view over 300 $μ$m. Among various wavelength, the research of x-ray OAM is especially interesting since it could be closely related to the predicted OAM-induced x-ray dichroism [Veenendaal et al.(2007)].

physics.app-ph↗

arXiv2018

Interfering Coherent Lightsheets Assisted Structure Synthesis (iCLASS) Technique for Nanofabrication

We propose a light-sheet based plane-selective fabrication technique that enables fabrication of nano-electronic/nano-fluidic components (nano-wires, nano-waveguides, nano-gratings and nano-channels) with specificity, selectivity on a user-defined patterning area. The technique is termed as, interfering coherent lightsheet assisted structure synthesis (iCLASS). iCLASS use specialized $2π$-geometry (consists of two opposing cylindrical lenses) that facilitates interference of counter-propagating light-sheets at a common geometrical focus. This gives rise to 1D interference pattern with a feature size of less than diffraction limit. A commercially available S1813 photoresist coated on a cleaned glass substrate is subsequently exposed to the light-sheets pattern (visible light). This is followed by the development of photoresist film to imprint the 1D nano-pattern. Experimental study and analysis shows an inter-feature spacing and feature-size of approximately, $λ/2$. Investigation show that the light-dose interaction-time ($τ_{exp} +τ_{dev}$) play crucial role in determining the feature-size and quality of fabricated nano-pattern array. The proposed iCLASS technique may find applications in nanoscience and nanotechnology.

physics.app-ph↗

arXiv2018

Toroidal Plasmonic Meta-Biosensors: Benchmarking against Classical Plasmonic Biosensors and Transducers

Rapid progress in plasmonics biosensors and immunosensors brings many methodologies to employ resonant subwavelength structures associated with the physics of multipoles, Fano resonances, and analogous moments. Here, we review a broad range of traditional and novel techniques that have been utilized for developing advanced biosensing tools including colloidal nanoparticles (NPs)-based systems to well-engineered arrays of meta-atoms and metamolecules. By describing some of the important and practical label-free biosensing methods based on subwavelength plasmonic technology, we discuss the emerging and excitation of toroidal multipoles concept, as a third family of multipolar modes, has made a revolution in enhancing the sensing performance of ultra-low weight diseases proteins and viruses as biological targets. Taking the exquisite and untraditional advantages of toroidal plasmonic metasurfaces, we comprehensively evaluated the detection properties and high-quality of toroidal immunosensors for the sensing of signature of bioproteins at picomolar (pM) concentrations with excellent limit of detection (LOD). This understanding clearly shows how toroidal metasensors have emerged as promising clinical and pharmacology tools, can be considered as alternatives and big competitors for conventional plasmonic sensors and transducers.

physics.app-ph↗

arXiv2018

Experimental evidence of auxetic features in seismic metamaterials: Ellipticity of seismic Rayleigh waves for subsurface architectured ground with holes

Structured soils with regular meshes of metric size holes implemented in first ten meters of the ground have been theoretically and experimentally tested under seismic disturbance this last decade. Structured soils with rigid inclusions embedded in a substratum have been also recently developed. The influence of these inclusions in the ground can be characterized in different ways: redistribution of energy within the network with focusing effects for seismic metamaterials, wave reflection, frequency filtering, reduction of the amplitude of seismic signal energy, etc. Here we first provide some time-domain analysis of the flat lens effect in conjunction with some form of external cloaking of Rayleigh waves and then we experimentally show the effect of a finite mesh of cylindrical holes on the ellipticity of the surface Rayleigh waves at the level of the Earth's surface. Orbital diagrams in time domain are drawn for the surface particle's velocity in vertical (x,z) and horizontal (x,y) planes. These results enable us to observe that the mesh of holes locally creates a tilt of the axes of the ellipse and changes the direction of particle movement. Interestingly, changes of Rayleigh waves ellipticity can be interpreted as changes of an effective Poisson ratio. However, the proximity of the source is also important to explain the shape of the ellipses. We analyze these observations in terms of wave mode conversions inside the mesh and we propose to broaden the discussion on the complexity of seismic wave phenomena in structured soils such as soils foundations and on the coupling effects specific to the soil-structure interaction.

physics.geo-ph↗

arXiv2018

Natural vs. blocked ventilation in naturally ventilated buildings - the effect of finite and decoupled sources

Naturally ventilated buildings harness freely-available resources such as internal buoyancy gains and wind forcing in achieving comfortable interior conditions. Although these resources are free, they are time-variable and can be difficult to control. As a result of this the nonlinear interplay between sometimes competing resources may lead to sub-optimal ventilation states. This problem has been explored by a number of previous researches e.g. Flynn & Caufield (Building and Environment, 44, 216-226, 2009) who, in studying these ventilations states, demonstrated complicated transitions characterized by hysteresis even for the simple case of a one-zone building. The objectives of this research are to extend the previous (theoretical) analysis by conducting complementary numerical experiments using sophisticated algorithms capable of describing turbulent, buoyancy driven flow. A further objective of this study is to specifically decouple the source, which was previously assumed to supply both heat and mass to the interior space. Rather, the flow dynamics in a case where heat and mass are supplied independently are examined.

physics.flu-dyn↗

arXiv2018

All-passive, transformable optical mapping (ATOM) near-eye display

We present an all-passive, transformable optical mapping (ATOM) near-eye display based on the "human-centric design" principle. By employing a diffractive optical element, a distorted grating, the ATOM display can project different portions of a 2D display screen to various depths, rendering a real 3D image with correct focus cues. Thanks to its all-passive optical mapping architecture, the ATOM display features a reduced form factor and low power consumption. Moreover, the system can readily switch between a real-3D and a high-resolution 2D display mode, providing task-tailored viewing experience for a variety of VR/AR applications.

physics.app-ph↗