Normal Reflection Research Articles

High-efficiency wide-angle anomalous refraction with acoustic metagrating

Abstract The emergent metagrating, with its unique and flexible beam shaping capabilities, offers new paths to efficient modulation of acoustic waves. In this work, an acoustic metagrating is demonstrated for high-efficiency and wide-angle anomalous refraction. It is shown that the normal reflection and transmission can be totally suppressed by properly modulating the amplitude and phase characteristics of the metagrating supercells for high-efficiency anomalous refraction. The anomalous refraction behavior is achieved in the wide range of incident angles from 28° to 78°, and the efficiency of -1st order diffraction is higher than 90% by finely designing the metagrating structure. The anomalous refraction behaviors are verified experimentally at incidence angle of 28°, 45° and 78°, respectively. The demonstrated metagrating is anticipated to possess efficient wide-angle composite wavefront engineering applications in such fields as communications.

Research on the Quantitative Inversion of Soil Iron Oxide Content Using Hyperspectral Remote Sensing and Machine Learning Algorithms in the Lufeng Annular Structural Area of Yunnan, China.

This study used hyperspectral remote sensing to rapidly, economically, and non-destructively determine the soil iron oxide content of the Dinosaur Valley annular tectonic region of Lufeng, Yunnan Province. The laboratory determined the iron oxide content and original spectral reflectance (OR) in 138 surface soil samples. We first subjected the OR data to Savizky-Golay smoothing, followed by four spectral transformations-continuum removal reflectance, reciprocal logarithm reflectance, standard normal variate reflectance, and first-order differential reflectance-which improved the signal-to-noise ratio of the spectral curves and highlighted the spectral features. Then, we combined the correlation coefficient method (CC), competitive adaptive reweighting algorithm, and Boruta algorithm to screen out the characteristic wavelength. From this, we constructed the linear partial least squares regression model, nonlinear random forest, and XGBoost machine learning algorithms. The results show that the CC-Boruta method can effectively remove any noise and irrelevant information to improve the model's accuracy and stability. The XGBoost nonlinear machine learning algorithm model better captures the complex nonlinear relationship between the spectra and iron oxide content, thus improving its accuracy. This provides a relevant reference for the rapid and accurate inversion of iron oxide content in soil using hyperspectral data.

12571 Ultrasonography Is A Potential Cost-effective Tool To Evaluate Muscle Impairment In Patients With Controlled Cushing’S Disease And Acromegaly

Abstract Disclosure: L. Martel-Duguech: None. H. Bascuñana: None. S. Webb: None. E. Valassi: None. Myopathy is a frequent feature in patients with Cushing’s syndrome (CS) and in patients with acromegaly (ACRO) long-term after biochemical control is achieved. Although ultrasonography (US) is an easy and cost-effective tool to evaluate muscle impairment in the clinical setting, its usefulness in patients with “controlled” ACRO end CS patients has not been established The aim of our study was to evaluate muscle structure using US and assess the correlation between US parameters, muscle function and quality of life (QoL). We included 36 female patients with CS [mean (±SD) age, 50±12 years; mean (±SD) BMI, 26.7±3.8] and 36 age- and BMI-matched healthy women. Mean (±SD) duration of remission was 132±87 months. We also included 36 patients with ACRO [20 females and 16 males, mean (±SD) age, 53±9 years, BMI 27±4 Kg/m2 and duration of control 92±58 months], and 36 age, gender and BMI-matched controls. We obtained transverse ultrasound images of the rectus femoris and assessed muscle intensity at both the midpoint (QmitR) and the distal third (QtercR), between the anterior inferior iliac spine and the proximal end of the patella. We scored muscle intensity using the Heckmatt’s rating scale and classified our findings as follows: 1-normal, 2-mildy increased muscle echoes with normal bone reflection, 3-moderately increased muscle echoes with reduced bone, 4-severely increased muscle echoes with absent bone reflection. We found that mean US intensity score was increased in patients with CS (QmitR p<0.001) and in patients with ACRO (QmitR p<0.05; QtercR p<0.001) vs. the controls, suggesting more impaired muscle architecture in the former, likely due to fibrosis/fatty infiltration. We also measured muscle function using the following tests: gait speed velocity (GS), timed up and go (TUG) and 30-second chair stand. QoL was assessed using both generic (SF-36) and disease-specific (CushingQoL and AcroQoL) questionnaires. US parameters, QoL and muscle function were correlated; in CS patients, higher QtercR was associated with slower GS (r=-0.421, p=0.041) and lower scores in social dimensions on CushingQoL ( friends/family , r=-0.510, p=0.013; and work/study, r=-0.523, p=0.010) . In ACRO patients, higher QmedR was associated with slower GS (r=-0.382, p=0.031) and decreased TUG (r=-0.497, p=0.004) and 30-second chair stand (r=-0.444, p=0.011) in all patients. Higher QmedR was also associated with lower score in physical function (ρ=-0.734, p=0.024), vitality (ρ=-0.728, p=0.026), and AcroQoL total score (ρ=-0.725, p=0.027), in male patients only. Conclusion: muscle US architectural parameters are impaired in “controlled” CS and ACRO patients, and are correlated with muscle function and QoL in both groups of patients. US may be a useful technique to identify, in a clinical setting, those CS and ACRO patients showing residual myopathy. This work was supported by PI17/00749 and PI21/01223 and FEDER funds Presentation: 6/3/2024

Novel multi-spectral short-wave infrared imaging for assessment of human burn wound depth.

Burn depth determination is critical for patient care but is currently lacking accuracy. Recent animal studies showed that Short Wave Infrared (SWIR) imaging can distinguish between superficial and deep burns. This is a first human study correlating reflectance of multiple SWIR bands using a SWIR assessment tool (SWAT) with burn depth classifications by surgeons and histology. Burns and adjacent normal skin in 11 patients with thermal injuries were imaged with visual and narrow bands centred at 1200, 1650, 1940 and 2250 nm and biopsies were taken from select areas. Reflectance intensities for each band in 273 regions of interest (ROI) were divided by the normal skin reflectance and combined into three Reflectance Indices (RIs). In addition, burns in ROIs and biopsies were classified by five surgeons and three pathologists, respectively, as superficial partial, deep partial, or full thickness. Results show that for burn depth increase classified by the surgeons, reflectance increased at 1200 and 2250, decreased at 1940, and didn't change at 1650 nm. In contrast, all three RIs increase with burn depth and predict the deep and full depths ROIs representing operable regions (Area Under Curve >0.6507, p < 0.0001). Pathologists' classification matched surgeons' classification of burn category only in eight of 21 biopsies (38.1%), but reflectance at all bands and one RI for all deep partial and full thickness biopsies were larger than in non-biopsy normal and superficial partial thickness ROIs (p < 0.0118). In conclusion, multi-spectral imaging with a new SWAT is a promising approach for evaluation of burn wound depth.

Foam density mapping via THz imaging

Plastic foams, near-ubiquitous in everyday life and industry, show properties that depend primarily on density. Density measurement, although straightforward in principle, is not always easy. As such, while several methods are available, plastic foam industry is not yet supported with a standard technique that effectively enables to control density maps. To overcome this issue, this paper proposes Terahertz (THz) time-of-flight imaging using normal reflection measurements as a fast, relatively cheap, contactless, non-destructive and non-dangerous way to map plastic foam density, based on the expected relationship between density and refractive index. The approach is demonstrated in the case of polypropylene foams. First, the relationship between the estimated effective refractive index and the polypropylene foam density is derived by characterizing a set of carefully crafted samples having uniform density in the range 70–900 kg/m3. The obtained calibration curve subtends a linear relationship between the density and the refractive index in the range of interest. This relationship is validated against a set of test samples, whose estimated average densities are consistent with the nominal ones, with an absolute error lower than 10 kg/m3 and a percentage error on the estimate of 5%. Exploiting the calibration curve, it is possible to build quantitative images depicting the spatial distribution of the sample density. THz images are able to reveal the non-uniform density distribution of some samples, which cannot be appreciated from visual inspection. Finally, the complex spatial density pattern of a graded foam sample is characterized and quantitatively compared with the density map obtained via X-ray microscopy. The comparison confirms that the proposed THz approach successfully determines the density pattern with an accuracy and a spatial scale variability compliant with those commonly required for plastic foam density estimate.

Temperature-dependent optical constants of vanadium dioxide thin films deposited on polar dielectrics

Coating polar dielectrics with thin film vanadium dioxide (VO2) enables one to exploit the temperature-dependent phase transition within VO2 to actively tune and modulate surface phonon polaritons at mid-infrared. However, controlling the behavior of such systems requires intimate knowledge of the temperature-dependent optical constants of VO2, which depend greatly on the growth conditions and substrate material. Here, we accurately determine the complex optical constants of VO2 on polar dielectrics across the insulator-to-metal phase transition (IMT) using only normal incident reflectance spectra by analyzing the reflectance with Kramers–Kronig relations and thin film Fresnel equations. This non-ellipsometry technique offers an advantage in determining the refractive index using a standard infrared spectrometer.

Weak and strong chirality-anomaly-manipulations in a superconducting Weyl semimetal sandwich structure

We investigate the quantum interference of the electron–hole conversions from the two interfaces in a Weyl semimetal (WSM)-based hybrid structure, in which a superconducting WSM is sandwiched in between two normal ones. The quantum interference is characterized by the chirality-anomaly-manipulation (CAM). It is found that only low energy is in favor for s-wave BCS pairing states. The Andreev reflection (AR) chirality blockade can be tuned by the stagger angle α for the relative orientation of paired Weyl points, accompanied by an AR bipolar chirality diode. Thus, a strong CAM is indicated for the electron–hole conversion. However, the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) pairing states have no energy preference, with the weak and strong CAMs being near and far away from the zero energy, respectively. More interestingly, a perfect AR with the normal reflection suppressed thoroughly can be obtained at any α as a result of the FFLO paring with the same chirality. In addition, the conductance or noise power, which incorporates the contributions of the two paired Weyl nodes, not only, in turn, embodies the respective features of their contributions but also can be experimentally measured to discern between the BCS and FFLO paring states.

Andreev reflections in deformed semi-Dirac material superconducting junctions

Besides the strong anisotropy, another unique feature of the semi-Dirac materials (SDMs) is the evolution of its dispersion with gap parameter from a merging semi-Dirac point to two Dirac points. In this study, we study the superconducting coherent transport at the SDM superconducting junction and focus on the influence of evolution of the SDM dispersion on the Andreev reflection. We found that the coexistence of peculiar quadruple reflections, including double specular normal reflection and double retro Andreev reflection, can occur within a wide range of parameters. We in detail discuss the dependence of reflection probabilities on the incident angle, incident energy, and gap parameter. By modulating these parameters, we also observe rich double reflection scenarios. These results enrich our understanding of the superconducting coherent transport and facilitate the probing of the intrinsic gap parameter in SDMs experimentally.

Rough Differential Equations Containing Path-Dependent Bounded Variation Terms

We consider rough differential equations whose coefficients contain path-dependent bounded variation terms and prove the existence and a priori estimate of solutions. These equations include classical path-dependent stochastic differential equations containing running maximum processes and normal reflection terms. We apply these results to determine the topological support of the solution processes.

Superconducting pump manipulated by non-topologically quasi and topological interface states

We propose an adiabatic superconducting charge pump based on massive Dirac electrons. A superconductor is sandwiched in between two pumping sources, which are formed by introducing the time-dependent and out-of-phase staggered potentials in graphene as pumping parameters. The pump is shown to be characterized by not only the topological interface state (TIS) but also the non-topologically quasi interface state (QIS). Hereafter, our attention is focused on the pumping currents ILNR and ILAR from the normal and Andreev reflections, respectively, which predominate by making the electron energy reside in the effective energy gap. It is found that modulating the energy E, superconductor length L 0, and pumping source length LP results in the considerable variation of competitive behaviors between ILNR and ILAR . In particular, the reversal effect of current direction can be realized by tuning LP . More interestingly, the current-phase relationship exhibits the platform behaviors, which can be manipulated by LP and the pumping strength. All the above pumping properties are attributed to the adiabatic evolution of TIS and non-topologically QIS, particularly the conversion between each other is the crucial origin. We also obtain the quantized pumping current by adjusting LP and L 0, and present the corresponding qualitative explanation through the pumping contour circled by the two parameters. In addition, we discuss the features of pumping current based on the armchair graphene as well.

Andreev and normal reflections in gapped bilayer graphene–superconductor junctions

Andreev and normal reflections in gapped bilayer graphene–superconductor junctions

Effect of Andreev processes on the Goos–Hänchen (GH) shift in the Graphene–Superconductor–Graphene (GSG) junctions

In this article, we study the transport properties of Graphene–Superconductor–Graphene (GSG) heterojunction where the superconducting region is created in the middle of a graphene sheet, as contrasted to widely studied transport properties through a Superconductor–Graphene–Superconductor (SGS) type of Josephson junction. We particularly analyse in detail the Goos–Hänchen shift of the electron and the hole at the GS interface in such a junction, due to normal as well as Andreev reflection, using a transfer matrix-based approach. Additionally, we evaluate the normalised differential conductance as a function of bias voltage that characterises the transport through such junction and point out how they are influenced by Andreev and normal reflection. In the subsequent parts of the article we demonstrate how the GH shift for both electron and hole changes with the width of the superconducting region. The behaviour of the differential conductance in such junctions as a function of the bias voltage in the region, dominated by Andreev and normal reflection, is also presented and analysed.

End-to-end neural network for pBRDF estimation of object to reconstruct polarimetric reflectance.

Estimating the polarization properties of objects from polarization images is still an important but extremely undefined problem. Currently, there are two types of methods to probe the polarization properties of complex materials: one is about the equipment acquisition, which makes the collection of polarization information unsatisfactory due to the cumbersome equipment and intensive sampling, and the other is to use polarized imaging model for probing. Therefore, the accuracy of the polarized imaging model will be crucial. From an imaging perspective, we propose an end-to-end learning method that can predict accurate, physically based model parameters of polarimetric BRDF from a limited number of captured photographs of the object. In this work, we first design a novel pBRDF model as a powerful prior knowledge. This hybrid pBRDF model completely defines specular reflection, body scattering and directional diffuse reflection in imaging. Then, an end-to-end inverse rendering is performed to connect the multi-view measurements of the object with the geometry and pBRDF parameter estimation, and a reflectance gradient consistency loss is introduced to iteratively estimate the per-pixel normal, roughness, and polarimetric reflectance. Real-world measurement and rendering experiments show that the results obtained by applying our method are in strong agreement with ground truth, validating that we can reproduce the polarization properties of real-world objects using the estimated polarimetric reflectance.

Light-trapping structures fabricated in situ for ultrathin III-V solar cells

Here, we describe a fully in situ method of fabricating light-scattering structures on III-V materials that generates a rough morphology via vapor phase etching and redeposition. Fully in situ methods support higher industrial throughput by utilizing the growth reactor to generate the light-trapping structures after device growth without removal from the reactor. We use HCl and PH3 to etch and redeposit scattering morphologies on Ga0.5In0.5P in a dynamic hydride vapor phase epitaxy (D-HVPE) reactor. We show that the addition of PH3 leads to redeposition during the vapor phase HCl etching of Ga0.5In0.5P and that HCl flow rate and time exposed to HCl-PH3 each independently cause a linear increase in the redeposited feature size, indicating that redeposition proceeds by island growth in a III-Cl-limited, hydride-enhanced HVPE regime. Auger electron spectroscopy and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS) reveal redeposition to be highly Ga-rich GaInP, i.e., Ga(In)P. The Ga-rich nature of the redeposition results from the higher thermodynamic driving force for Ga incorporation than for In during HVPE growth and the difference in the volatility of the III-Cl etch products. The resulting morphologies have high broadband scattering, as determined by normal specular reflectance and integrating sphere measurements, indicating effectiveness as light-scattering structures. In a 270-nm-thick GaAs photovoltaic device with a textured back surface, we achieve a 4.9% increase in short circuit current density (JSC) without any loss in open-circuit voltage (VOC) relative to a planar control using only a 60 s in situ texturing treatment.

Prediction of Potassium Content in Rice Leaves Based on Spectral Features and Random Forests

The information acquisition about potassium, which affects the quality and yield of crops, is of great significance for crop nutrient management and intelligent decision making in smart agriculture. This article proposes a method for predicting the rice leaf potassium content (LKC) using spectral characteristics and random forests (RF). The method screens spectral characteristic variables based on the linear correlation analysis results of rice LKC and four transformed spectra (original reflectance (R), first derivative reflectance (FDR), continuum-removed reflectance (CRR), and normalized reflectance (NR)) of leaves and the PCA dimensionality reduction results of vegetation indices. Following a second screening of the correlated single band and vegetation index variables of the four transformed spectra, the RF is used to obtain the mixed variable (MV), and regression models are developed to achieve an accurate prediction of rice LKC. Additionally, the effect of potassium spectral sensitivity bands, indices, spectral transformation form, and different modeling methods on rice LKC prediction accuracy is assessed. The results showed that the mixed variable obtained with the second screening using the random forest feature selection method could effectively improve the prediction accuracy of rice LKC. The regression models based on the single band variables (BV) and the vegetation index variables (IV), FDR–RF and IV–RF, with R2 values of 0.62301 and 0.7387 and RMSE values of 0.24174 and 0.15045, respectively, are the best models. In comparison to the previous two models, the MV–RF validation had a higher R2 and a lower RMSE, reaching 0.77817 and 0.14913, respectively. It can be seen that the RF has a better processing ability for the MV that contains vegetation indices and IV than for the BV. Furthermore, the results of different variable screening and regression analyses also revealed that the single band’s range of 1402–1428 nm and 1871–1907 nm, as well as the vegetation indices constituted of reflectance 1799–1881 nm and 2276–2350 nm, are of great significance for predicting rice LKC. This conclusion can provide a reference for establishing a universal vegetation index related to potassium.

Self-Adaptive Multistage Infrared Radiative Thermo-Optic Modulators Based on Phase-Change Materials

Phase-Change Materials (PCMs) are widely applied in dynamic optical modulation due to the dramatic changes in their complex refractive index caused by temperature variation. As the functionality varies, the application of a single PCM cannot meet the compact, efficient and broadband needs of optical modulators. In this work, we combine vanadium dioxide (VO2) and a chalcogenide (Ge2Sb2Te5 (GST) or In3SbTe2 (IST)) to obtain a VO2–GST/IST multiple-stack film that is optimized by a genetic algorithm. This film has a wide spectrum and high modulation properties with three self-switchable modes varied by temperature, including transmission, absorption and reflection. The optimal results are an average normal transmittance, absorbance, and reflectance of 0.76, 0.91, 0.86 in 3–5 μm and 0.72, 0.90, 0.90 in 8–14 μm under different temperature ranges. The film enhances the transmission and absorption properties due to the formation of anti-reflective coating and Fabry–Perot resonance. Compared with GST, the film maintains high reflectance due to the metal-like interface reflection of crystalline IST, which exhibits metallic properties. For different polarization states, the film demonstrates great directional insensitivity when the incidence angles vary from 0° to 60°. The designed self-adaptive multistage infrared radiative thermo-optic modulator has promising implications for optical fuse, fiber-optic communication and energy storage fields.

A generalized Drude–Smith model for ultrafast pump-and-probe experiments and its application for studying of electronic dynamic properties of polycrystalline diamond

In this work, we generalize the Drude–Smith model (DSM) proposed for optical conductivity in frequency-domain to the case of ultrafast pump-and-probe experiments, where the results are measured in time-domain. The generalized DSM (GDSM) considers the optically induced electronic backscattering or localization effect, and can be utilized for studying the electronic dynamics induced by pulsed radiation field in time-domain. By applying the optical-pump and terahertz-probe (OPTP) technique via normal reflection measurement, we study the electronic dynamic properties of polycrystalline diamond (PCD) on Si substrate and examine the validity of the proposed GDSM. We find that this model can lead to a better fitting between the experimental and theoretical results and can reasonably reflect the information about time resolution of the measurement system and the energy relaxation time for free carriers in PCD. For PCD subjected to 800 nm wavelength fs laser irradiation, the effect of carrier backscattering decreases and the electronic energy relaxation time increases with increasing pump radiation fluence. We hope that the GDSM from this work can be helpful for understanding the electronic dynamics in electronic and optoelectronic materials measured by, e.g., ultrafast pump-and-probe experiments.

Multiple Andreev reflections in topological Josephson junctions with chiral Majorana modes

Andreev bound states (ABS) occur in Josephson junctions when the total phase of the Andreev and normal reflections is a multiple of $2\pi$. In ballistic junctions with an applied voltage bias, a quasi-particle undergoes multiple Andreev reflections before entering the leads, resulting in peaks in the current-voltage $I(V)$ curve. Here we present a general model for Josephson junctions with spin-active interlayers i.e., magnetic or topological materials with broken time-reversal symmetry. We investigate how ABS change the peak positions and shape of $I(V)$, which becomes asymmetric for a single incident angle. We show how the angle-resolved $I(V)$ curve becomes a spectroscopic tool for the chirality and degeneracy of ABS.

Competitive spin-flipped normal reflection and equal-spin Andreev reflection in heterojunctions of nodal-line superconductors

The superconducting phase of topological semimetals has become a promising route for the implementation of topological superconductivity and non-Abelian Majorana fermions. Here, we investigate quantum transport in the junctions composed of a nodal-line superconductor, i.e., a topological nodal-line semimetal with superconducting pairing. It is shown that two topologically nontrivial regions exist in the surface Brillouin zone of the nodal-line superconductor labeled by the transverse momentum. Specifically, topological regions with topological invariants $\mathcal{N}=1$ and $\mathcal{N}=2$ host a single and a pair of Majorana zero modes at the surface, respectively. We show that the single Majorana zero mode in the $\mathcal{N}=1$ region can induce resonant equal-spin Andreev reflection, while the Majorana pair in the $\mathcal{N}=2$ region can lead to resonant spin-flipped normal reflection. Both reflection processes can give rise to spin currents but with different polarization directions, whose proportions can be adjusted by a Zeeman field. We also study the transport properties of the device with a sandwich structure and predict that strong crossed Andreev reflection can be implemented with a finite bias. Detection schemes for all these novel transport properties, which can be revealed by spin-resolved transport signatures, are proposed. Our work paves the way for the implementation and detection of Majorana fermions in nodal-line superconductors.

Analysis of shock wave acceleration from normal detonation reflection

Analysis of shock wave acceleration from normal detonation reflection