Normal Reflection Research Articles

Measurement of Reflectance Covering UV to MIR of Solar Selective Coatings by One Fourier Transform Spectrometer

Abstract The reflectance of solar selective coating, covering UV to MIR bands, is measured by only one Fourier Transform (FT) spectroscope. The measurement is done for different wavelength ranges from 0.3 to 20 μm and different surface morphologies of substrate by different optical accessories. For flat smooth substrate, the reflectance of UV and VIS bands is measured by near normal relative reflectance accessory for mirror reflection, and that of NIR and MIR bands is measured by VW absolute reflectance accessory. For rough or curved substrate, the reflectance from UV to VIS is measured by white sphere accessory, and that of NIR and MIR is measured by gold sphere accessory. The sample holder is customized for the measurement of tubular substrate, and data in different bands is carefully calibrated with high reflection reference line and zero baseline approximation. Aluminum and gold coated mirrors are used for calibration in UV-VIS and NIR-MIR bands respectively. The reflectance of sample holder without any samples is considered as zero baseline. Smooth reflectance curves from 0.3 to 20 μm are obtained for solar selective coatings which are deposited on the flat smooth, rough and tubular substrates, respectively.

Association of Retinal Artery and Other Inner Retinal Structures With Distribution of Tapetal-like Reflex in Oguchi's Disease.

To report novel ophthalmoscopic features of patients with Oguchi's disease, and to describe how they may be related to the unusual tapetal-like fundus appearance. Twenty-one eyes of 11 patients who were diagnosed with Oguchi's disease were investigated. Genetic screening of seven cases showed homozygous mutations in the SAG gene (c.926delA). The retinal appearance was retrospectively assessed in the fundus photographs, and the optical coherence tomographic (OCT) and fundus autofluorescence (AF) images. In 11 eyes of 7 patients, clearly demarcated dark regions without tapetal-like reflex were observed in the midperipheral retinal regions. In the dark regions, OCT showed lower reflectances in the photoreceptor layer but the AF images had normal reflectances. In nine eyes of six patients, the dark regions were partially demarcated by retinal arteries but not by veins. In nine eyes of five patients, the extent of the dark regions either increased or decreased during the course of the disease process, and these changes were not due to the state of adaptation or a posterior vitreous detachment. In all eyes, the peripheral retinal arteries but not veins had either high or low reflective regions along one side. Although the alterations of the outer retinal layers are believed to be most responsible for the abnormal tapetal-like reflex in patients with Oguchi's disease, these ophthalmoscopic features cannot be explained solely by the abnormality of the outer retina. Our findings suggest that the appearance of tapetal-like reflex is strongly affected by alterations of structures in the inner retinal layers.

Stratigraphic coordinates: a coordinate system tailored to seismic interpretation

ABSTRACTIn certain seismic data processing and interpretation tasks such as spiking deconvolution, tuning analysis, impedance inversion, and spectral decomposition, it is commonly assumed that the vertical direction is normal to reflectors. This assumption is false in the case of dipping layers and may therefore lead to inaccurate results. To overcome this limitation, we propose a coordinate system in which geometry follows the shape of each reflector and the vertical direction corresponds to normal reflectivity. We call this coordinate system stratigraphic coordinates. We develop a constructive algorithm that transfers seismic images into the stratigraphic coordinate system. The algorithm consists of two steps. First, local slopes of seismic events are estimated by plane‐wave destruction; then structural information is spread along the estimated local slopes, and horizons are picked everywhere in the seismic volume by the predictive‐painting algorithm. These picked horizons represent level sets of the first axis of the stratigraphic coordinate system. Next, an upwind finite‐difference scheme is used to find the two other axes, which are perpendicular to the first axis, by solving the appropriate gradient equations. After seismic data are transformed into stratigraphic coordinates, seismic horizons should appear flat, and seismic traces should represent the direction normal to the reflectors. Immediate applications of the stratigraphic coordinate system are in seismic image flattening and spectral decomposition. Synthetic and real data examples demonstrate the effectiveness of stratigraphic coordinates.

Influence of Microstructure and Composition on Optical Properties of Plasma Sprayed Al/Al2O3 Cermets

Normal hemispherical spectral reflectances of plasma sprayed Al2O3/Al cermets were acquired from visible to infrared wavelengths for several metal concentrations. Since optical response of these coatings is highly dependent on volumetric and/or surface light scattering, special attention was paid to characterization of the composition, microstructure, and surface roughness of such coatings. The roles of volumetric and surface effects are highlighted by a comparison between the spectral data measured on as-sprayed coatings and on polished coatings. As expected, reflectance rises with the metal addition, but in the transparent region of alumina, a noteworthy behavior is noticed for low aluminum concentrations. Indeed, the reflectance presents strong composition dependence and remains lower than that of the pure alumina sample. The results show that the optical properties of cermets produced by plasma spraying are controllable and therefore open the door to applications in the areas of solar energy or aerona...

Quantized crossed-Andreev reflection in spin-valley topological insulators

We study a three-terminal spin-valley topological insulator/superconductor/insulator (TI/S/TI) device to realize perfect Cooper-pair splitting in real space. The key point is to construct a single topologically-protected interface state in each TI electrode that is valley helical and spin polarized. It is shown that only the crossed Andreev reflection of electrons is allowed when the opposite topological interface states are engineered in the two TI electrodes, but the normal reflection, local Andreev reflection, as well as the electron cotunneling are entirely prohibited. The quantized and noiseless crossed Andreev reflection is protected by the bulk topological invariants of the TI electrodes and persists in a very long junction $(L>{\ensuremath{\xi}}_{s})$ as well as in moderate disorders.

Superhard, Antireflective Texturized Coatings Based on Hyperbranched Polymer Composite Hybrids for Thin‐Film Solar Cell Encapsulation

AbstractIn this study, we demonstrate by simulation and experiment the antireflective (AR) performance of hyperbranched polymer (HBP) nanocomposites textures replicated from a moth‐eye pattern using ultraviolet (UV) nanoimprint lithography. A UV‐curable acrylated HBP and a hybrid composite of the HBP with silica nanoparticles with an organometal precursor were used. Using effective medium theory (EMT) simulations, optimal patterns were found to be arrays of paraboloids with stable AR performance over a large range of geometries. A good agreement was found between the simulated and measured optical behavior of such AR arrays with a normal reflectance within the visible range of approximately 4 % for the use of a glass substrate. The photocurrent of AR‐coated a‐Si:H solar cells was found to be 2 % higher than the reference value of an uncoated cell whereas, for AR‐coated tandem thin film Si cells, the increase was 3 % for the top a‐Si:H cell and 2 % for the bottom microcrystalline Si cell.

Minimal model of point contact Andreev reflection spectroscopy of multiband superconductors

We formulate a minimal model of point contact Andreev reflection spectroscopy of a normal- metal/multiband superconductor interface. The theory generalizes the Blonder-Tinkham-Klapwijk (BTK) formulation to a multiband superconductor and it is based on the quantum waveguides theory. The proposed approach allows an analytic evaluation of the Andreev and normal reflection coefficients and thus is suitable for a data fitting of point contact experiments. The obtained differential conductance curves present distinctive features similar to the ones measured in the experiments on multiband systems, like the iron-based pnictides and the MgB2.

Two-band conductivity of a FeSeTe film by reflectance measurements in the terahertz and infrared range

We report an infrared spectroscopy study of a 200 nm thick FeSeTe film grown on LaAlO3 with Tc = 13.7 K. We analyze the 20 K normal state absolute reflectance RN measured over a broad infrared range and the reflectance ratio RS/RN, RS being the superconducting state reflectance, measured at 6 K in the terahertz range down to 12 cm−1. We show that the normal state model conductivity is given by two Drude components, one of which much broader and intense than the other. In the superconducting state, we find that a gap Δ = 37 ± 3 cm−1 opens up in the narrow Drude band only, while the broad Drude band results to be ungapped, at least in the explored spectral range. Our results show that only a two-band model can coherently describe both normal and superconducting state data.

Helical Andreev bound states in topological insulator f-wave Josephson junction

We study the effect of f-wave triplet superconductivity induced by proximity effect on the surface states of a three-dimensional topological insulator (3DTI). In fact, the gapless surface state for excitation spectrum of a triplet superconductor topological insulator gives rise to formation of helical Andreev bound states (ABSs) and, necessarily, suppression of Andreev reflection at the interface of a superconductor/ferromagnetic structure. By calculating the relevant form of Dirac spinors for two-dimensional time-reversal symmetric Hamiltonian, the normal and Andreev reflection coefficients and ABSs corresponding to tunneling and Josephson junctions, respectively, are obtained. It is shown, that the Andreev process vanishing occurs strongly, so that, the evanescent waves will be permissible in tunneling process. It is found that the dispersion of ABSs is an even function of electron incident angle θ for f1-wave and odd for f2-wave. In f1-order, for module of incident angle, θ>0.167π, the ABSs are independent of superconducting phase difference, ϕ, so that the Josephson current may vanish for this region. Effect of magnetization on flattening of ABSs occurs in f2 order faster than f1.

Beam focalization in reflection from flat dielectric subwavelength gratings.

We experimentally demonstrate the recently predicted effect of near-field focusing for light beams from flat dielectric subwavelength gratings (SWGs). This SWGs were designed for visible light 532 nm and fabricated by direct laser writing in a negative photoresist, with the refractive index n=1.5 and the period d=314 nm. The laterally invariant gratings can focus light beams without any optical axis to achieve the transversal invariance. We show that focal distances can be obtained up to 13 μm at normal reflection for TE polarization.

Mechanisms of normal reflection at metal interfaces studied by Andreev-reflection spectroscopy

Andreev-reflection spectroscopy of elemental superconductors in contact with nonmagnetic normal metals reveals that the strength of normal-reflection varies only slightly. This observation imposes strong constrictions on the three possible normal-reflection mechanisms: tunneling through a dielectric barrier, reflection due to the different electronic properties of the two electrodes, and diffusive transport caused by elastic scattering in the contact region. We discuss in detail the role played by Fermi-surface mismatch, represented by the different Fermi velocities on both sides of the contact interface. We find that it is at least not the dominant mechanism and possibly completely absent in the Andreev-reflection process.

Near bottom self-calibrated measurement of normal reflection coefficients by an integrated deep-towed camera/acoustical system

Normal incidence echo data (bottom reflection) can provide acoustic reflectivity estimates used to predict sediment properties with using seabed sediment models. Accuracy of normal reflection coefficient measurement thus become very significant to the bottom inversion result. A deep-towed camera platform with acoustical recording system, developed by the Institution of Undersea Technology, National Sun Yat-sen University, Taiwan, is capable of photographically surveying the seafloor in near scope and acquiring sound data. The real time data transference, including photography (optics) and reflection measurement (acoustics) can be implemented in the same site simultaneously. The deep-towed camera near the bottom was used in several experiments in the southwestern sea off Taiwan in 2014 to acquire acoustic LFM signal sent by surface shipboard source as incident signal as well as the seafloor reflections at frequency bands within 4–6 kHz. The error produced by compensating the roll-off of altitude of vehicle (propagation loss) can be eliminated, which is considered as near bottom self-calibrated measurement for normal reflection coefficient. The collected reflection coefficients were used to inverting the sediment properties with using the Effective Density Fluid model (EDFM), manifested by the coring and camera images. [This work is sponsored by the Ministry of Science and Technology of Taiwan.]

Optimal Stopping Problems in Diffusion-Type Models with Running Maxima and Drawdowns

We study optimal stopping problems related to the pricing of perpetual American options in an extension of the Black-Merton-Scholes model in which the dividend and volatility rates of the underlying risky asset depend on the running values of its maximum and maximum drawdown. The optimal stopping times of the exercise are shown to be the first times at which the price of the underlying asset exits some regions restricted by certain boundaries depending on the running values of the associated maximum and maximum drawdown processes. We obtain closed-form solutions to the equivalent free-boundary problems for the value functions with smooth fit at the optimal stopping boundaries and normal reflection at the edges of the state space of the resulting three-dimensional Markov process. We derive first-order nonlinear ordinary differential equations for the optimal exercise boundaries of the perpetual American standard options.

Optimal Stopping Problems in Diffusion-Type Models with Running Maxima and Drawdowns

We study optimal stopping problems related to the pricing of perpetual American options in an extension of the Black-Merton-Scholes model in which the dividend and volatility rates of the underlying risky asset depend on the running values of its maximum and maximum drawdown. The optimal stopping times of the exercise are shown to be the first times at which the price of the underlying asset exits some regions restricted by certain boundaries depending on the running values of the associated maximum and maximum drawdown processes. We obtain closed-form solutions to the equivalent free-boundary problems for the value functions with smooth fit at the optimal stopping boundaries and normal reflection at the edges of the state space of the resulting three-dimensional Markov process. We derive first-order nonlinear ordinary differential equations for the optimal exercise boundaries of the perpetual American standard options.

Optimal Stopping Problems in Diffusion-Type Models with Running Maxima and Drawdowns

We study optimal stopping problems related to the pricing of perpetual American options in an extension of the Black-Merton-Scholes model in which the dividend and volatility rates of the underlying risky asset depend on the running values of its maximum and maximum drawdown. The optimal stopping times of the exercise are shown to be the first times at which the price of the underlying asset exits some regions restricted by certain boundaries depending on the running values of the associated maximum and maximum drawdown processes. We obtain closed-form solutions to the equivalent free-boundary problems for the value functions with smooth fit at the optimal stopping boundaries and normal reflection at the edges of the state space of the resulting three-dimensional Markov process. We derive first-order nonlinear ordinary differential equations for the optimal exercise boundaries of the perpetual American standard options.

Coherent control of Snell's law at metasurfaces.

It was recently demonstrated that the well-known Snell's law must be corrected for phase gradient metasurfaces to account for their spatially varying phase, leading to normal and anomalous transmission and reflection of light on such metasurfaces. Here we show that the efficiency of normal and anomalous transmission and reflection of light can be controlled by the intensity or phase of a second coherent wave. The phenomenon is illustrated using gradient metasurfaces based on V-shaped and rectangular apertures in a metal film. This coherent control effect can be exploited for wave front shaping and signal routing.

Combined EUV reflectance and X-ray reflectivity data analysis of periodic multilayer structures.

We present a way to analyze the chemical composition of periodical multilayer structures using the simultaneous analysis of grazing incidence hard X-Ray reflectivity (GIXR) and normal incidence extreme ultraviolet reflectance (EUVR). This allows to combine the high sensitivity of GIXR data to layer and interface thicknesses with the sensitivity of EUVR to the layer densities and atomic compositions. This method was applied to the reconstruction of the layered structure of a LaN/B multilayer mirror with 3.5 nm periodicity. We have compared profiles obtained by simultaneous EUVR and GIXR and GIXR-only data analysis, both reconstructed profiles result in a similar description of the layered structure. However, the simultaneous analysis of both EUVR and GIXR by a single algorithm lead to a ∼ 2x increased accuracy of the reconstructed layered model, or a more narrow range of solutions, as compared to the GIXR analysis only. It also explains the inherent difficulty of accurately predicting EUV reflectivity from a GIXR-only analysis.

On seismic monitoring of $$\hbox {CO}_{2}$$ CO 2 leakage from geological storages and its primary detection

Geological storage of $$\hbox {CO}_{2}$$ in mature sedimentary basins and deep saline water aquifer requires special considerations on the potential leakage pathways. Early detection of $$\hbox {CO}_{2}$$ leakage from geological storage is one of the primary objectives of any carbon capture and storage technique. Thermodynamic properties of injected $$\hbox {CO}_{2}$$ and formation fluid, and change in in-situ conditions may act as driving agent to $$\hbox {CO}_{2}$$ leakage. Therefore, it is important to monitor the saturation of $$\hbox {CO}_{2}$$ and identify the phase of $$\hbox {CO}_{2}$$ during the injection, storage and after storage stages in order to monitor its possible migration and leakage risks. Seismic monitoring of sequestrated $$\hbox {CO}_{2}$$ in subsurface is in practice in which Gassmann fluid substitution model is used to estimate porous rock and pore fluid properties. The seismic properties of $$\hbox {CO}_{2}$$ contaminated fluids are predicted by Wood’s volume average formula. The analysis reveals that Wood’s approach is unable to account properly the properties of fluid mixture especially near bubble point pressure of $$\hbox {CO}_{2}$$ /water mixture, thus unable to monitor primary leakage of $$\hbox {CO}_{2}$$ . A modified approach based on thermodynamics is adopted for the detection of primary leakage of $$\hbox {CO}_{2}$$ . The analysis shows that for a minute amount of free $$\hbox {CO}_{2}$$ , the P-wave velocity is much lower than the values predicted by the Gassmann-Wood approach. The resulting normal reflectivity and AVO anomalies are much stronger than attained by conventional Gassmann-Wood approaches.

Frequency and Clinical Pattern of Vitelliform Macular Dystrophy Caused by Mutations of Interphotoreceptor Matrix IMPG1 and IMPG2 Genes

To assess the frequency of and to characterize the clinical spectrum and optical coherence tomography findings of vitelliform macular dystrophy linked to IMPG1 and IMPG2, 2 new causal genes expressed in the interphotoreceptor matrix. Retrospective epidemiologic, clinical, electrophysiologic, and molecular genetic study. The database of a national referral center specialized in genetic sensory diseases was screened for patients with a macular vitelliform dystrophy without identified mutation or small deletion or large rearrangement in BEST1 and PRPH2 genes. Forty-nine families were included. Clinical, imaging, and electro-oculogram findings were reviewed. Mutation screening of IMPG1 and IMPG2 genes were performed systematically. Frequency, inheritance, and clinical pattern of vitelliform dystrophy associated with IMPG1 and IMPG2 mutations were characterized. IMPG1 was the causal gene in 3 families (IMPG1 1-3, 11 patients) and IMPG2 in a fourth family (2 patients). With an autosomal dominant transmission, families 1 and 2 had the c.713T→G (p.Leu238Arg) mutation in IMPG1 and family 4 had the c.3230G→T (p.Cys1077Phe) mutation in IMPG2. Patients with IMPG1 or IMPG2 mutations had a late onset and moderate visual impairment (mean visual acuity, 20/40; mean age of onset, 42 years), even in the sporadic case of family 3 with a presumed recessive transmission (age at onset, 38 years; mean visual acuity, 20/50). Drusen-like lesions adjacent to the vitelliform deposits were observed in 9 of 13 patients. The vitelliform material was above the retinal pigment epithelium (RPE) at any stage of the macular dystrophy, and this epithelium was well preserved and maintained its classical reflectivity on spectral-domain optical coherence tomography (SD-OCT). Electro-oculogram results were normal or borderline in 9 cases. IMPG1 and IMPG2 are new causal genes in 8% of families negative for BEST1 and PRPH2 mutations. These genes should be screened in adult-onset vitelliform dystrophy with (1) moderate visual impairment, (2) drusen-like lesions, (3) normal reflectivity of the RPE line on SD-OCT, and (4) vitelliform deposits located between ellipsoid and interdigitation lines on SD-OCT. These clinical characteristics are not observed in the classical forms of BEST1 or PRPH2 vitelliform dystrophies.

Zero-energy bound state at the interface between ans-wave superconductor and a disordered normal metal with repulsive electron-electron interactions

In recent years, there has been a renewed interest in the proximity effect due to its role in the realization of topological superconductivity. Here, we study a superconductor--normal metal proximity system with repulsive electron-electron interactions in the normal layer. It is known that in the absence of disorder or normal reflection at the superconductor--normal metal interface, a zero-energy bound state forms and is localized to the interface [Fauch\`ere et al., Phys. Rev. Lett. 82, 3336 (1999).]. Using the quasiclassical theory of superconductivity, we investigate the low-energy behavior of the density of states in the presence of finite disorder and an interfacial barrier. We find that as the mean free path is decreased, the zero-energy peak in the density of states is broadened and reduced. In the quasiballistic limit, the bound state eliminates the minigap pertinent to a noninteracting normal layer and a distinct peak is observed. When the mean free path becomes comparable to the normal layer width, the zero-energy peak is strongly suppressed and the minigap begins to develop. In the diffusive limit, the minigap is fully restored and all signatures of the bound state are eliminated. We find that an interfacial potential barrier does not change the functional form of the density of states peak but does shift this peak away from zero energy.