Diffraction Behavior Research Articles

Diffraction of harmonic generation in metasurfaces of quasi-BICs induced by geometrical perturbations

We report the diffraction behavior of harmonic generation in metasurfaces of quasi-bound states in the continuum (BICs) induced by geometrical perturbations. Conventionally, the geometrical perturbation can transform the symmetry-protected BICs into quasi-BICs in metasurfaces for many important applications. Such geometrical perturbations sometimes lead to the doubled period of metasurfaces, and then dramatically affect the diffraction of light, especially the harmonic generation light of shorter wavelengths. Here, we investigate the efficiency and diffraction angles of different orders of second and third harmonic generation in two typical metasurfaces of quasi-BICs induced by geometrical perturbation, i.e., compound grating waveguide nanostructures and zig-zag nanodisk arrays. The results are important to understand the diffraction behavior of harmonic generation in the period doubled or tripled nanostructures due to geometry perturbations, and to realize the efficient multi-channel nonlinear sources.

Free-volume analysis of the structural and dielectric properties of PMMA/TeO2 composites via positron annihilation lifetime spectroscopy

PMMA (Poly methyl methacrylate) composites have promising potential for applications in optics and dielectric energy storage. To investigate the effects of TeO2 contents in PMMA in this respect, we studied their composites on light absorption in the UVvisible range, structural analysis via X-ray diffraction, dielectric characteristics, and free volume behavior. We added up to approximately 7 % of the weight concentration of the TeO2 micropowder to the PMMA matrix for effective dispersion because of the limitations of ultrasonic agitation. The XRD data demonstrate a widening of the peaks with a filler content of up to 4.8 % and agglomeration at 7 %, indicating TeO2 particle contact. An increase in absorbance was observed in the UVvisible spectrum of the PMMA/TeO2 composites with increasing TeO2 content up to 4.8 %. The dielectric constants exhibit a positive correlation with higher quantities of TeO2, and the polarization mechanism is interpreted by interface polarization and free volume. The free volume measured by positron annihilation lifetime spectroscopy (PALS) increases to 4.8 % but decreases to 7 %. The effect of the free volume within the matrix on the polarization distribution of TeO2 influenced the dielectric constant and the loss factor, which increased to 4.8 % and then decreased to 7 % due to agglomeration.

Microwave assisted Fraunhofer diffraction pattern in a four-level light–matter coupling scheme

The experimental realization of two-dimensional (2D) electromagnetically induced grating is explored by monitoring the Fraunhofer diffraction pattern in a microwave-driven four-level Y-type atomic medium under the action of two orthogonal standing-wave (SW) fields. Due to the position-dependent atom–field interaction, the information about the high diffraction order of the probe light can be obtained via the Fraunhofer diffraction pattern of the probe light. It is found that the diffraction behavior is significantly improved due to the joint quantum interference induced by the SW and microwave-driven cycling fields. Most importantly, the amplitude and phase diagram of the transmission function of the probe light can be modulated at a particular position and the probe energy may transfer to the high orders of the diffraction by properly adjusting the system parameters. The proposed scheme may provide a promising way to achieve highly sensitive diffraction patterns with applications in quantum information processing.

Single-Shot Full Characterization of the Spatial Wavefunction of Light Fields via Stokes Tomography

Since the diffraction behavior of a light field is fully determined by its spatial wavefunction, i.e., its spatial complex amplitude (SCA), full characterization of spatial wavefunction plays a vital role in modern optics from both the fundamental and applied aspects. In this work, we present a novel “complex-amplitude profiler” based on spatial Stokes tomography with the capability to fully determine the SCA of a light field in a single shot with high precision and resolution. The SCA slice observed at any propagation plane provides complete information about the light field, thus allowing us to further retrieve the complete beam structure in the 3D space as well as the exact modal constitution in terms of spatial degrees of freedom. The principle demonstrated here provides an important advancement for the full characterization of light beams with a broad spectrum of potential applications in various areas of optics, especially for the growing field of structured light.

Unveiling the Potential of Diffraction Gratings for Precision Separation of Higher Harmonics in Nonlinear Acoustics.

Diffraction gratings, with their periodically ordered structures, have been critical components in acoustics, optics, and spectroscopy for over a century. The classical grating equation describes the emergence of diffraction phenomena by gratings, considering the groove periodicity and the characteristics of the incident wave. These gratings find extensive applications in communication, spectroscopy, architectural acoustics, and underwater research, and they are foundational to pioneering investigations in phononic crystals and meta-materials. While much attention has been given to understanding the diffraction behavior of linear acoustics concerning gratings, the literature lacks research regarding the influence of high-amplitude ultrasonic waves, which introduce observable nonlinear effects. This experimental enquiry presents a pioneering methodology for isolating higher harmonics from these nonlinear phenomena. We have developed a spatial filtering apparatus with a single-frequency transducer and a specially designed grating profile, enabling precise frequency selection or rejection.

Facile Coaxial Electrospinning Synthesis of Polyacrylonitrile/Cellulose Acetate Nanofiber Membrane for Oil-Water Separations.

Oil-contaminated water and industrial oily wastewater discharges have adversely affected aquatic ecosystems and human safety. Membrane separation technology offers a promising solution for effective oil-water separation. Thus, a membrane with high surface area, hydrophilic-oleophobic properties, and stability is a promising candidate. Electrospinning, a straightforward and efficient process, produces highly porous polymer-based membranes with a vast surface area and stability. The main objective of this study is to produce hydrophilic-oleophobic polyacrylonitrile (PAN) and cellulose acetate (CA) nanofibers using core-shell electrospinning. Incorporating CA into the shell of the nanofibers enhances the wettability. The core PAN polymer improves the electrospinning process and contributes to the hydrophilicity-oleophobicity of the produced nanofibers. The PAN/CA nanofibers were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction, and surface-wetting behavior. The resulting PAN/cellulose nanofibers exhibited significantly improved surface-wetting properties, demonstrating super-hydrophilicity and underwater superoleophobicity, making them a promising choice for oil-water separation. Various oils, including gasoline, diesel, toluene, xylene, and benzene, were employed in the preparation of oil-water mixture solutions. The utilization of PAN/CA nanofibers as a substrate proved to be highly efficient, confirming exceptional separation efficiency, remarkable stability, and prolonged durability. The current work introduces an innovative single-step fabrication method of composite nanofibers, specially designed for efficient oil-water separation. This technology exhibits significant promise for deployment in challenging situations, offering excellent reusability and a remarkable separation efficiency of nearly 99.9%.

The diffraction and re-initiation behavior of detonation wave in premixed H2–O2–Ar mixture

Previous studies have demonstrated the effective enhancement of initiation stability in the combustor of a rotating detonation engine through the use of a pre-detonator. However, when a stable detonation propagates from a small-diameter pre-detonator into a larger-diameter combustor, a brief failure occurs, followed by the re-initiation of the detonation wave. This failure is attributed to detonation diffraction as the wave passes through a sudden expansion section. This study systematically investigates the phenomenon of detonation diffraction and re-initiation through 2D numerical simulations. The effect of the diameter ratio between the pre-detonator and combustor on detonation propagation is examined by adjusting the diameter ratio D/d in the range of 1.1–2.7, where D and d represent the diameters of the larger (corresponding to the combustor) and smaller (corresponding to the pre-detonator) tubes, respectively. Various modes of detonation propagation and the corresponding evolution of the detonation wave are observed. The results reveal that as the detonation wave propagates through the sudden-expansion section, it diffracts at the corner and then rapidly decouples at the boundary. For D/d less than 1.3, the detonation wave can maintain its propagation by adjusting the structure of the cell distribution, referred to as the supercritical mode. As D/d increases, the detonation wave experiences initial failure followed by re-initiation, corresponding to the critical mode. When D/d exceeds 2.6, complete failure of detonation occurs and cannot be re-initiated, resulting in the sub-critical mode. Notably, under the critical mode, the distance LDDT required for re-initiation linearly increases with D/d (LDDT = 41.48(D/d) + 4.30). Additionally, the pressure of the triple point near the wall, formed by the convergence of the reflected shock wave, transmitted wave, and precursor shock wave, determines the possibility of local detonation initiation, which induces re-initiation in the testing tube. It is proposed that when the pressure of the triple point exceeds the theoretical pressure of post-shock (Ppost-shock), a local overdriven detonation occurs. Furthermore, when the convergent point of the transmitted shock wave propagates along the central line and passes through the flame front, local detonation can be induced as well. This study systematically illustrates the details of diffraction and re-initiation when the detonation wave passes through a sudden-expansion section.

Design, Synthesis, and Characterization of a Novel Blue-Green Long Afterglow BaYAl3O7:Eu2+, Nd3+ Phosphor and Its Anti-Counterfeiting Application.

Herein, a series of novel long afterglow nanophosphors BaYAl3O7:Eu2+, Nd3+ was synthesized by the combustion method. The investigation encompassed the characterization of X-ray diffraction, morphology, chemical valence, elemental composition, and photoluminescence behavior of BaYAl3O7:Eu2+ and BaYAl3O7:Eu2+, Nd3+ nanoparticles. Under 365 nm excitation, BaYAl3O7:Eu2+ and BaYAl3O7:Eu2+, Nd3+ show emission bands centered at 497 nm and 492 nm, which are attributed to the 4f65d→4f7 transition of Eu2+ ions. The optimal samples of BaYAl3O7:0.03Eu2+ and BaYAl3O7:0.03Eu2+, 0.02Nd3+ have average fluorescence lifetimes of 850 ns and 1149 ns, respectively. The co-doping of Nd3+ ions as the trap centers produced long afterglow luminescence properties, and the afterglow time could reach up to 8 min. Furthermore, the fluorescent powder can be mixed with polyacrylic acid to prepare anti-counterfeiting inks; a clover pattern and snowflake pattern have been successfully printed using screen printing technology, proving its potential application in the field of anti-counterfeiting.

Making the Most of 3D Electron Diffraction: Best Practices to Handle a New Tool

Along with the adoption of three-dimensional electron diffraction (3D ED/MicroED) as a mainstream tool for structure determination from sub-micron single crystals, questions about best practices regarding each step along the workflow, from data collection to structure solutions, arise. In this paper, we discuss three particular aspects of a 3D ED/MicroED experiment which, after hundreds of structures solved in Rigaku’s laboratories, we have found to be important to consider carefully. First, for a representative model system of a hydrated compound (trehalose dihydrate), we show that cryo-transfer of the sample into the diffractometer is an effective means to prevent dehydration, while cooling of the sample without cryo-transfer yields a marginal improvement only. Next, we demonstrate for a small (tyrosine) and a large (clarithromycin) organic compound, how a simplified and fast workflow for dynamical diffraction calculations can determine absolute crystal structures with high confidence. Finally, we discuss considerations and trade-offs for choosing an optimal effective crystal-to-detector distance; while a long distance is mandatory for a protein (thaumatin) example, even a small molecule with difficult diffraction behavior (cystine) yields superior results at longer distances than the one used by default.

Fracture Characteristics of Super Duplex Stainless Steel after Hot Tensile Testing

This study’s temperature range of hot tensile testing is 1000–1200 °C, which is consistent with ordinary industrial hot working temperatures. The fractography of super duplex stainless steel S32750 after hot tensile testing is investigated with Optical Microscopy and Scanning Electron Microscopy, and Electron Back-scatter Diffraction and Transmission Electron Microscopy study hot deformation behaviors of the necking area. The results reveal that ~1050–1150 °C is the optimal hot working temperature range regarding hot ductility and cracking sensitivity. The micro-voids nucleate at the ferrite-austenite interphase boundaries following the Kurdjumov-Sachs (K-S) or Nishiyama-Wasserman (N-W) orientation relationship at 1000 °C. Therefore, a quasi-cleavage fracture forms along the interphase boundaries. At the temperature range 1050–1150 °C, a uniform distribution of fracture surface is formed, and the highest Reduction in Area appears at 1150 °C. Dynamic phase transformation occurs with the formation of secondary austenite at ferrite grain boundaries at 1200 °C, which results in an intergranular fracture surface morphology.

Engineering in the morphology of Ni3S2 via doping of Ce with different concentration to improve the capacitive properties

Transition metal oxides (TMOx) have garnered focused for their potential usage in supercapacitors attributed to their high specific capacitance (Cs), safety, economical, and notable electrochemical activity. But their low cycling stability has been increased by doping strategy. In this research, we report the fabrication of Ni3S2 (NS) and Ce doped Ni3S2 (CNS) with different concentration (0.1, 0.3 and 0.5 mmol) via hydrothermal method without the use of surfactants. Structure, morphology, and electrochemical performances of pure and Ce doped Ni3S2 nanostructures have been investigated. The crystalline structure has been investigated by powder X-ray diffraction (PXRD) and morphological behavior with Scanning electron microscopy (SEM). The electrochemical finding suggests that the specific capacitance (Cs) of a Ni3S2 nanomaterial doped with 0.3 Ce is studied by using a three-electrode setup exhibited the maximum capacitance of 2349.10 F g−1 and energy density (Ed) of 72.07 Wh kg−1 at 1 A g−1. The symmetric behavior of 0.3 Ce doped Ni3S2 electrode also determined with a two-electrode device made from 0.3 Ce doped Ni3S2 which display a higher specific capacitance (Cs) of 1139.22 F g−1 at 1 A g−1. This highlights the electrocatalytic potential of an symmetric device based on 0.3-CNS for next-generation supercapacitors.

Fast and rigorous optical simulation of periodically corrugated light-emitting diodes based on a diffraction matrix method.

Increasing the light extraction efficiency has been widely studied for highly efficient organic light-emitting diodes (OLEDs). Among many light-extraction approaches proposed so far, adding a corrugation layer has been considered a promising solution for its simplicity and high effectiveness. While the working principle of periodically corrugated OLEDs can be qualitatively explained by the diffraction theory, dipolar emission inside the OLED structure makes its quantitative analysis challenging, making one rely on finite-element electromagnetic simulations that could require huge computing resources. Here, we demonstrate a new simulation method, named the diffraction matrix method (DMM), that can accurately predict the optical characteristics of periodically corrugated OLEDs while achieving calculation speed that is a few orders of magnitude faster. Our method decomposes the light emitted by a dipolar emitter into plane waves with different wavevectors and tracks the diffraction behavior of waves using diffraction matrices. Calculated optical parameters show a quantitative agreement with those predicted by finite-difference time-domain (FDTD) method. Furthermore, the developed method possesses a unique advantage over the conventional approaches that it naturally evaluates the wavevector-dependent power dissipation of a dipole and is thus capable of identifying the loss channels inside OLEDs in a quantitative manner.

Light Reconfigurable Topological Optical Phase Structure Enabled by a Photoresponsive Chiral System

AbstractThe ability to establish significant phase modulation at low applied field provides a promising route toward polarization control and wavefront shaping for liquid‐crystal‐based devices. Owing to the polarization‐selective reflectivity of chiral liquid crystals (CLCs), reflective wavefront shaping via geometric phase is demonstrated when a circularly polarized light is Bragg reflected by a spatially orientated chiral layer. Nowadays, photoresponsive CLCs have attracted extensive attention due to their exotic feature that endows the CLC devices with the capability of electric‐free remote control. Despite the mature photoresponsive CLC materials and the sophisticated reflective geometric phase devices, a light‐induced topological optical phase modulation for a transmissive wave exiting a CLC cell remains elusive. Here, with the employment of a photosensitive chiral dopant, a hybrid aligned photoresponsive CLC system, demonstrating the simultaneous light modulation of topological geometric phase and dynamic phase via helical pitch manipulation is established. The continuous dual‐phase modulation engenders a smooth optically controllable diffraction efficiency (i.e., from <5% to >90%) of the proposed light‐reconfigurable CLC geometric phase optical element prototypes with multistable diffractive behavior, thus launching a paradigm shift for the application of novel liquid‐crystal photonic devices in the field of all‐optical polarization and spin processing.

Co-crystallization of sofosbuvir with sugars for enhanced dissolution rate

Sofosbuvir is one of the direct acting antiviral agents which is approved in the treatment of chronic HCV in combination with other agents. The low aqueous solubility of sofosbuvir resulted in slow dissolution which is supposed to be responsible for its low and variable bioavailability after oral administration. Accordingly, the objective of this work was to investigate the effect of co-crystallization of sofosbuvir with hydrophilic sugars on its crystalline structure and dissolution rate. Mixtures of sofosbuvir with hydrophilic sugars at various molar ratios were prepared by ethanol assisted kneading followed by drying. The dry products were then characterized by attenuated total reflectance fourier transform infrared spectroscopy (ATR FTIR), differential scanning calorimetry (DSC), powder X-ray diffraction (XRD) and in vitro dissolution studies. Combined instrumental analysis reflected development of new crystalline species of co-crystal type. This was evidenced by the existence of hydrogen bonding as shown from FTIR spectra, change in the thermal behaviour and appearance of new diffraction peaks in the diffractograms recorded by XRD. The co-crystallization was associated by weakening of intermolecular bonds which resulted in significant increase in the dissolution rate of sofosbuvir. The study introduced hydrophilic sugars as co-crystal co-formers for enhanced dissolution of sofosbuvir.

VEViD: Vision Enhancement via Virtual diffraction and coherent Detection

The history of computing started with analog computers consisting of physical devices performing specialized functions such as predicting the position of astronomical bodies and the trajectory of cannon balls. In modern times, this idea has been extended, for example, to ultrafast nonlinear optics serving as a surrogate analog computer to probe the behavior of complex phenomena such as rogue waves. Here we discuss a new paradigm where physical phenomena coded as an algorithm perform computational imaging tasks. Specifically, diffraction followed by coherent detection becomes an image enhancement tool. Vision Enhancement via Virtual diffraction and coherent Detection (VEViD) reimagines a digital image as a spatially varying metaphoric “lightfield” and then subjects the field to the physical processes akin to diffraction and coherent detection. The term “Virtual” captures the deviation from the physical world. The light field is pixelated and the propagation imparts a phase with dependence on frequency which is different from the monotonically-increasing behavior of physical diffraction. Temporal frequencies exist in three bands corresponding to the RGB color channels of a digital image. The phase of the output, not the intensity, represents the output image. VEViD is a high-performance low-light-level and color enhancement tool that emerges from this paradigm. The algorithm is extremely fast, interpretable, and reduces to a compact and intuitively-appealing mathematical expression. We demonstrate image enhancement of 4k video at over 200 frames per second and show the utility of this physical algorithm in improving the accuracy of object detection in low-light conditions by neural networks. The application of VEViD to color enhancement is also demonstrated.

Non-paraxial diffraction analysis for developing DMD-based optical systems.

We propose a non-paraxial diffraction model of the digital micromirror device (DMD) by combining the conventional Fraunhofer diffraction and a simple method of coordinative mapping. It is equivalent to adding aberrations of diffracted wave fields to the aberration-free Fraunhofer diffraction instead of complex integral calculations, allowing the simulated diffraction patterns to be consistent with the actual experimental counterparts. Moreover, it is verified by the experiments and literature that the diffraction angles, orders, and efficiency can all be well predicted for arbitrary incident angles and wavelengths. Especially for diffracted zenith angles within 50°, the predicted values reveal ∼1% error, and in a broader range, the predicted errors of diffracted azimuth angles are less than 4%. To the best of our knowledge, it is the first model capable of describing the non-paraxial diffraction behavior of the DMD. The proposed model with universality and effectiveness will help users to optimally construct DMD-based optical systems by guiding optical layouts, selection of light sources, and utilization and suppression of diffraction effects.

Integrated acoustic multilayer metasurfaces for high degree of diffractive functionality

Phase-gradient metasurfaces exhibit diverse extraordinary diffractive behaviors. These range from reflective or transmissive scattering of an incident wave toward any targeted direction to temporal trapping of waves inside structures. The behaviors are determined by the design parameters, phase gradient and number of discrete unit cells within a supercell. In this study, we propose a higher-level design scheme by integrating a stack of multiple metasurfaces. We focus on a case with negligible separation in which the constituent metasurfaces perfectly interact with each other. A significantly higher degree of diffractive behavior compared with that of a conventional single layer is observed for multilayer metasurfaces specifically in the regime above the critical angle. The scattering angular characteristics can be enriched remarkably in multilayers because, unlike in a single layer, the transformation of the incident tangential wavenumber is not restricted by the number of integer multiples of the phase gradient. The wavenumber transform is available for the entire range of incident angles in multilayers, whereas it is available only for half of this range in a single layer. The temporal duration of internal wave trapping can also be enhanced dramatically in multilayers because the supercell periodicity can be effectively lengthened from those of the constituents by combining different phase gradients. To our knowledge, this is the first report of the distinctive diffractive behaviors of multilayer metasurfaces, particularly for an incident angle above the critical angle. To fully describe the underlying physics, we derive a generalized diffraction law that robustly addresses the multilayers by proposing a novel physical concept to straightforwardly connect repetitive phase accumulations inside metasurface unit cells to diffraction. The reciprocal lattice of a unit cell, rather than that of a supercell, is observed to play an important role in determining dominant scattering. The proposed theories are thoroughly verified by analytical and numerical simulations.

Engineered refractive and diffractive optical composites via photo-thermal processes

Oxide and non-oxide glass with tailored morphology or microstructure induced by photo-exposure and subsequent heat treatment can result in new materials with unique optical functions. Spatial control of where this local modification occurs can result in optical materials with refractive or diffractive behavior different from those found in homogeneous optical materials. We review the use of such strategies to introduce such unique optical function to commercially developed oxide and prototype chalcogenide glass ceramic media that have yielded a range of performance attributes that make them unique in applications requiring reduced size, weight, power and cost (SWAP-C). We summarize how these materials have been designed and created to yield components that combine multiple functions in a single optical element, resulting in unique performance solutions for a variety of optical systems, highlighting the future potential these materials offer.

Decomposition mechanism, sintering process and properties of zircon ceramics: Role of CaO, MnO and Cr2O3

In this paper, the influence of the CaO, MnO and Cr2O3 on the decomposition mechanism, sintering process and properties of zircon ceramics were studied. The X-ray diffraction (XRD), microstructure, pore characteristics and densification behaviour were used to evaluate the decomposition mechanism and the properties of the zircon ceramics. The results indicated that the addition of CaO could accelerate the decomposition rate of zircon by the formation of the solid solution, which caused the appearance of the large pores to weaken the properties. Cr2O3 could limit the sintering process, decomposition reaction and grain growth of zircon to degrade the performance of the zircon ceramics. The addition of MnO promoted the grains growth and had no effect on the decomposition of zircon by the formation of solid solution. Thus, the zircon ceramics with MnO rendered an optimal bulk density and an apparent porosity of 3.53 g/cm3 and 22.5%, a high compressive strength of 212.6 MPa sintered at 1550 °C.

Trace amounts of mercaptans with key roles in forming an efficient three-component photoinitiation system for holography

Investigating the photoinitiation mechanisms will help to find new directions for high-efficiency photoinitiation systems (PS). This article aimed to explore other possible roles of mercaptans in a PS where mercaptans were widely regarded as chain transfer agents. A bis-chalcone dye (BDEA) and a biimidazole (HABI) were employed as photosensitizer and co-initiator, and 2-mercaptobenzoxazole (MBO) was chosen as a representative of mercaptans. Trace amounts of mercaptans have been shown a negligible chain transfer effect in previous research studies, but in this work, they were found a miraculous ability to significantly promote the diffraction efficiency. Besides, the diffraction efficiency showed an interesting trend of first increasing and then decreasing with the increase of MBO content. The diffraction behavior was subsequently confirmed to be closely correlated with photoinitiation efficiency by monomer polymerization kinetics. Therefore, we made many efforts to detect the photoinitiation mechanism of PS and the roles of mercaptans. Combining the thermodynamic feasibility analysis with the spin trapping of free radicals, the presence of mercaptans could make the PS evolve a double-cycle photoreaction, which was considered to be an important contribution to the obvious promotion of photoinitiation efficiency. Meanwhile, considering the results of the fluorescence and absorption spectra, the static quenching between BDEA and MBO was presumed to be the factor of the decline in photoinitiation efficiency. Finally, the optimized photopolymers exhibited good performance in recording and reproducing reflection holograms.