Showing papers on "Diffraction published in 2020"

Resolution Analysis in a Lens-Free On-Chip Digital Holographic Microscope

Abstract: Lens-free on-chip digital holographic microscopy (LFOCDHM) is a modern imaging technique whereby the sample is placed directly onto or very close to the digital sensor, and illuminated by a partially coherent source located far above it. The scattered object wave interferes with the reference (unscattered) wave at the plane where a digital sensor is situated, producing a digital hologram that can be processed in several ways to extract and numerically reconstruct an in-focus image using the back propagation algorithm. Without requiring any lenses and other intermediate optical components, the LFOCDHM has unique advantages of offering a large effective numerical aperture (NA) close to unity across the native wide field-of-view (FOV) of the imaging sensor in a cost-effective and compact design. However, unlike conventional coherent diffraction limited imaging systems, where the limiting aperture is used to define the system performance, typical lens-free microscopes only produce compromised imaging resolution that far below the ideal coherent diffraction limit. At least five major factors may contribute to this limitation, namely, the sample-to-sensor distance, spatial and temporal coherence of the illumination, finite size of the equally spaced sensor pixels, and finite extent of the image sub-FOV used for the reconstruction, which have not been systematically and rigorously explored until now. In this article, we derive five transfer function models that account for all these physical effects and interactions of these models on the imaging resolution of LFOCDHM. We also examine how our theoretical models can be utilized to optimize the optical design or predict the theoretical resolution limit of a given LFOCDHM system. We present a series of simulations and experiments to confirm the validity of our theoretical models.

High-Pressure Polymeric Nitrogen Allotrope with the Black Phosphorus Structure.

Abstract: Studies of polynitrogen phases are of great interest for fundamental science and for the design of novel high energy density materials. Laser heating of pure nitrogen at 140 GPa in a diamond anvil cell led to the synthesis of a polymeric nitrogen allotrope with the black phosphorus structure, bp-N. The structure was identified in situ using synchrotron single-crystal x-ray diffraction and further studied by Raman spectroscopy and density functional theory calculations. The discovery of bp-N brings nitrogen in line with heavier pnictogen elements, resolves incongruities regarding polymeric nitrogen phases and provides insights into polynitrogen arrangements at extreme densities.

Managements of scalar and vector rogue waves in a partially nonlocal nonlinear medium with linear and harmonic potentials

Abstract: We consider a ( $$2+1$$ )-dimensional nonautonomous-coupled nonlinear Schrodinger equation, which includes the partially nonlocal nonlinearity under linear and harmonic potentials. Via a projecting expression between nonautonomous and autonomous equations, and utilizing the bilinear method and Darboux transformation method, we find diversified exact solutions. These solutions contain the nonlocal rogue wave and Akhmediev or Ma breather solutions, and the combined solution which describes a rogue wave superposed on an Akhmediev or Ma breather. By adjusting values of diffraction, width and phase chirp parameters of wave, the maximum value of the accumulated time can be modulated. When we compare the maximum value of the accumulated time with that of the excitation position parameters, we study the management of scalar and vector rogue waves, such as the excitations of full shape, early shape and climax shape for rogue waves.

Bessel Beam: Significance and Applications-A Progressive Review.

Abstract: Diffraction is a phenomenon related to the wave nature of light and arises when a propagating wave comes across an obstacle. Consequently, the wave can be transformed in amplitude or phase and diffraction occurs. Those parts of the wavefront avoiding an obstacle form a diffraction pattern after interfering with each other. In this review paper, we have discussed the topic of non-diffractive beams, explicitly Bessel beams. Such beams provide some resistance to diffraction and hence are hypothetically a phenomenal alternate to Gaussian beams in several circumstances. Several outstanding applications are coined to Bessel beams and have been employed in commercial applications. We have discussed several hot applications based on these magnificent beams such as optical trapping, material processing, free-space long-distance self-healing beams, optical coherence tomography, superresolution, sharp focusing, polarization transformation, increased depth of focus, birefringence detection based on astigmatic transformed BB and encryption in optical communication. According to our knowledge, each topic presented in this review is justifiably explained.

Flexural wave absorption by lossy gradient elastic metasurface

Abstract: A broadband elastic wave absorption by a sub-wavelength and lightweight structure is of considerable significance in vibration suppression, especially for low frequencies in plate-like structure. However, it has always been a great challenge. In this research, we systematically study the flexural wave diffraction in a thin plate. Based on the diffraction mechanism, we propose the concept of sub-wavelength lossy gradient elastic metasurface for flexural wave absorption. We theoretically reveal high-efficiency and quasi-omnidirectional absorption behavior, which stem from maximum multireflection-enhanced absorption of the 0th order diffraction. We experimentally demonstrate a robust high-efficiency absorption in the frequency range from 343 to 1000 Hz (larger than 1.5 octaves). In addition, we propose a general approach which involves new physics of adjusting an arrangement sequence of subunits to suppress the first-order diffraction mode. This allows to further reduce the sub-wavelength thickness of the metasurface while maintaining its high-efficiency absorption. Our designs could provide new routes to broadband vibration suppression and cancelation in low frequency by lossy elastic metamaterials and metasurfaces.

Spatial quantification of dynamic inter and intra particle crystallographic heterogeneities within lithium ion electrodes

Abstract: The performance of lithium ion electrodes is hindered by unfavorable chemical heterogeneities that pre-exist or develop during operation. Time-resolved spatial descriptions are needed to understand the link between such heterogeneities and a cell’s performance. Here, operando high-resolution X-ray diffraction-computed tomography is used to spatially and temporally quantify crystallographic heterogeneities within and between particles throughout both fresh and degraded LixMn2O4 electrodes. This imaging technique facilitates identification of stoichiometric differences between particles and stoichiometric gradients and phase heterogeneities within particles. Through radial quantification of phase fractions, the response of distinct particles to lithiation is found to vary; most particles contain localized regions that transition to rock salt LiMnO2 within the first cycle. Other particles contain monoclinic Li2MnO3 near the surface and almost pure spinel LixMn2O4 near the core. Following 150 cycles, concentrations of LiMnO2 and Li2MnO3 significantly increase and widely vary between particles. Dynamic chemical and structural heterogeneities within electrodes are known to lead to battery degradation and failure. Here, the authors show that X-ray diffraction computed tomography can be used to spatially quantify the dynamic crystallographic states of electrodes as they operate and degrade.

Sound vortex diffraction via topological charge in phase gradient metagratings.

Abstract: Wave fields with orbital angular momentum (OAM) have been widely investigated in metasurfaces. By engineering acoustic metasurfaces with phase gradient elements, phase twisting is commonly used to obtain acoustic OAM. However, it has limited ability to manipulate sound vortices, and a more powerful mechanism for sound vortex manipulation is strongly desired. Here, we propose the diffraction mechanism to manipulate sound vortices in a cylindrical waveguide with phase gradient metagratings (PGMs). A sound vortex diffraction law is theoretically revealed based on the generalized conservation principle of topological charge. This diffraction law can explain and predict the complicated diffraction phenomena of sound vortices, as confirmed by numerical simulations. To exemplify our findings, we designed and experimentally verified a PGM based on Helmholtz resonators that support asymmetric transmission of sound vortices. Our work provides previously unidentified opportunities for manipulating sound vortices, which can advance more versatile design for OAM-based devices.

Serial protein crystallography in an electron microscope.

Abstract: Serial X-ray crystallography at free-electron lasers allows to solve biomolecular structures from sub-micron-sized crystals. However, beam time at these facilities is scarce, and involved sample delivery techniques are required. On the other hand, rotation electron diffraction (MicroED) has shown great potential as an alternative means for protein nano-crystallography. Here, we present a method for serial electron diffraction of protein nanocrystals combining the benefits of both approaches. In a scanning transmission electron microscope, crystals randomly dispersed on a sample grid are automatically mapped, and a diffraction pattern at fixed orientation is recorded from each at a high acquisition rate. Dose fractionation ensures minimal radiation damage effects. We demonstrate the method by solving the structure of granulovirus occlusion bodies and lysozyme to resolutions of 1.55 A and 1.80 A, respectively. Our method promises to provide rapid structure determination for many classes of materials with minimal sample consumption, using readily available instrumentation. For conventional three-dimensional microcrystal electron diffraction (3D ED/MicroED), a crystal is slowly rotated under an electron beam, leading to inevitable accumulation of radiation damage during data collection. In this work, the authors present a serial electron diffraction method, where still diffraction patterns from many protein nanocrystals are rapidly recorded and merged, which minimises radiation damage and only requires a slightly modified standard scanning transmission electron microscope.

Reflective Polarization Volume Lens with Small f-Number and Large Diffraction Angle

Abstract: DOI: 10.1002/adom.202000170 then it could function as a converging or diverging lens, depending on the incident circular polarization.[3] Based on these attractive optical properties, many novel CLC devices have been developed and widely utilized in band pass filter,[4] laser beam steering,[5] optical combiners for augmented reality displays,[6] optical vortex generators,[7] beam shaper,[8] and many broadband devices.[9–11] Previously, transmissive planar lenses, such as LC lens and metalens, along the optical axis of a symmetric structure have been developed.[12–19] However, these lenses either have a small f/# but small size, or have a large aperture but large f/#. As the demand for compact device structure keeps increasing, such a transmissive planar lens becomes too bulky and the reflective planar lens is urgently needed to provide foldable optical structure. In this paper, we demonstrate a reflective polarization volume lens (rPVL) based on patterning slanted CLCs, exhibiting a large aperture and a small f/# (=0.825). In an rPVL, ideally the incident light is primarily reflected and focused onto a specific off-angle. To obtain these functions, such a device requires both asymmetric subwavelength alignment and lens phase for achieving reflective off-axis imaging and an ultralow f/#. In comparison with conventional transmissive planar lenses, our new rPVL with an f/# < 1 and 45° off-axis diffraction angle is a critical enabler for future compact optical systems.[20,21] PVL is a combination of a slanted polarization volume grating (PVG) and a lens. In the past studies, the LC director distribution in a CLC device was often assumed planar without slanted helical axis. Because the bottom photoalignment is planar, which produces cholesterics with nearly zero pretilt angle; this means that the helical axis is perpendicular to the substrate. Until recently, some experimental evidences and rigorous analyses prove that the actual LC director configuration in a PVG is not planar; instead, it possesses slanted structure.[22,23] Due to the trend of the lowest volume free energy, the helical axis of CLC bulk analyzed by the optimized Frank–Oseen model exhibits slanted rather than perpendicular to the substrate.[23] Therefore, the helical axis of rPVL is also slanted, which differs from conventional CLC devices. Figure 1a illustrates the schematic of the proposed rPVL. The substrate is treated to provide a rotation of LC optical axis in xy-plane, and the rotating angle changes continuously and Planar optics based on patterned cholesteric liquid crystals (CLCs) has attracted increasing attention owing to the self-organized helical structure and the ability to create arbitrary reflected wavefront through spatial orientation control. However, because of the subwavelength-orientation requirement, it is challenging for liquid crystal lens to achieve a low f-number (f/#) and large deflection angle simultaneously. Furthermore, with the increasing demand for compact size in novel optical systems, reflective lens has advantage over the transmissive one because it can fold the optical path. Here, a new off-axis reflective polarization volume lens (PVL) with f/# = 0.825, large aperture size, simple fabrication process, thin profile, circular polarization selectivity, and large diffraction angle is proposed. In contrast to traditional vertical spiral structure, PVL is based on patterned CLCs with a slanted helical axis. In this paper, the PVL is theoretically evaluated and then three reflective PVLs at red, green, and blue wavelengths (R = 605 nm, G = 532 nm, and B = 450 nm) are fabricated. Meanwhile, a simple approach is utilized to achieve 20 mm diameter and 16.5 mm focal length. The low scattering and good image quality of reflective PVL enrich these functional devices and provide promising applications to novel foldable optical systems and waveguide-based wearable near-eye displays.

Omnidirectional iridescence via cylindrically-polarized femtosecond laser processing

Abstract: We report the femtosecond (fs) laser fabrication of biomimetic omnidirectional iridescent metallic surfaces exhibiting efficient diffraction for practically any angle of light incidence. Such diffractive behavior is realized by means of mul-ti-directional low-spatial-frequency, laser-induced periodic surface structures (LSFL) formed upon exploiting the cylindrical symmetry of a cylindrical vector (CV) fs field. We particularly demonstrate that the multi-directional gratings formed on stainless steel surface by a radially polarized fs beam, could mimic the omnidirectional structural coloration properties found in some natural species. Accordingly, the fabricated grating structures can spatially disperse the incident light into individual wavelength with high efficiency, exhibiting structural iridescence at all viewing angles. Analytical calculations using the grating equation reproduced the characteristic variation of the vivid colors observed as a function of incident angle. We envisage that our results will significantly contribute to the development of new photonic and light sensing devices.

Efficient full-path optical calculation of scalar and vector diffraction using the Bluestein method

Abstract: Efficient calculation of the light diffraction in free space is of great significance for tracing electromagnetic field propagation and predicting the performance of optical systems such as microscopy, photolithography, and manipulation. However, existing calculation methods suffer from low computational efficiency and poor flexibility. Here, we present a fast and flexible calculation method for computing scalar and vector diffraction in the corresponding optical regimes using the Bluestein method. The computation time can be substantially reduced to the sub-second level, which is 105 faster than that achieved by the direct integration approach (~hours level) and 102 faster than that achieved by the fast Fourier transform method (~minutes level). The high efficiency facilitates the ultrafast evaluation of light propagation in diverse optical systems. Furthermore, the region of interest and the sampling numbers can be arbitrarily chosen, endowing the proposed method with superior flexibility. Based on these results, full-path calculation of a complex optical system is readily demonstrated and verified by experimental results, laying a foundation for real-time light field analysis for realistic optical implementation such as imaging, laser processing, and optical manipulation. A fast and flexible procedure for evaluating the propagation of light in optical systems is achieved by calculating the diffraction of the light using a computational process called the Bluestein method. It yields information along the entire optical path length on both ‘scalar’ variations in the general magnitude of light waves and ‘vector’ – directional – variations. Researchers led by Jiawen Li and Dong Wu at the University of Science and Technology of China, developed the process and demonstrated that it can deliver results between 100 and 100,000 times faster than two existing alternative methods. Understanding the influence of diffraction in prevailing conditions is important for predicting the fine behaviuor of light waves. The new procedure should lead to greatly improved real-time analyses that will assist in microscopy, laser-based fabrication and optical manipulation technologies.

Wood Anomalies and Surface-Wave Excitation with a Time Grating

Abstract: In order to confine waves beyond the diffraction limit, advances in fabrication techniques have enabled subwavelength structuring of matter, achieving near-field control of light and other types of waves. The price is often expensive fabrication needs and the irreversibility of device functionality, as well as the introduction of impurities, a major contributor to losses. In this Letter, we propose temporal inhomogeneities, such as a periodic drive in the electromagnetic properties of a surface which supports guided modes, as an alternative route for the coupling of propagating waves to evanescent modes across the light line, thus circumventing the need for subwavelength fabrication, and achieving the temporal counterpart of the classical Wood anomaly. We show analytically and numerically how this concept is valid for any material platform and at any frequency, and propose and model a realistic experiment in graphene to couple terahertz radiation to plasmons with unit efficiency, demonstrating that time modulation of material properties could be a tunable, lower-loss and fast-switchable alternative to the subwavelength structuring of matter for near-field wave control.

High-Energy X-Ray Diffraction Microscopy in Materials Science

Abstract: High-energy diffraction microscopy (HEDM) is an implementation of three-dimensional X-ray diffraction microscopy. HEDM yields maps of internal crystal orientation fields, strain states, grain shape...

Reversible luminescent humidity chromism of organic–inorganic hybrid PEA2MnBr4 single crystals

Abstract: Organic–inorganic hybrids have drawn great attention for gas sensors due to their high sensitivity, good selectivity and acceptable stability at room temperature. There are two main approaches by which organic–inorganic hybrids convert gas information to electric or optical signals (vapochromism). Here, we have reported a new organic–inorganic hybrid PEA2MnBr4 for humidity detection by luminescent visible chromism. PEA2MnBr4 single crystals were grown by the solution method and determined by single-crystal X-ray diffraction. Luminescent humidity chromism was found on PEA2MnBr4 from green emission at the water-desorption state to pink emission at the water-adsorption state within 18 s at a relative humidity of 38% RH. This obviously visible chromism was further used to check the water content in toluene with a low detection limit between 0.02 and 0.05 vol%.

X-ray diffraction at the National Ignition Facility.

Abstract: We report details of an experimental platform implemented at the National Ignition Facility to obtain in situ powder diffraction data from solids dynamically compressed to extreme pressures. Thin samples are sandwiched between tamper layers and ramp compressed using a gradual increase in the drive-laser irradiance. Pressure history in the sample is determined using high-precision velocimetry measurements. Up to two independently timed pulses of x rays are produced at or near the time of peak pressure by laser illumination of thin metal foils. The quasi-monochromatic x-ray pulses have a mean wavelength selectable between 0.6 A and 1.9 A depending on the foil material. The diffracted signal is recorded on image plates with a typical 2θ x-ray scattering angle uncertainty of about 0.2° and resolution of about 1°. Analytic expressions are reported for systematic corrections to 2θ due to finite pinhole size and sample offset. A new variant of a nonlinear background subtraction algorithm is described, which has been used to observe diffraction lines at signal-to-background ratios as low as a few percent. Variations in system response over the detector area are compensated in order to obtain accurate line intensities; this system response calculation includes a new analytic approximation for image-plate sensitivity as a function of photon energy and incident angle. This experimental platform has been used up to 2 TPa (20 Mbar) to determine the crystal structure, measure the density, and evaluate the strain-induced texturing of a variety of compressed samples spanning periods 2–7 on the periodic table.

Controllably asymmetric beam splitting via gap-induced diffraction channel transition in dual-layer binary metagratings

Abstract: In this work, we designed and studied a feasible dual-layer binary metagrating, which can realize controllable asymmetric transmission and beam splitting with nearly perfect performance. Owing to ingenious geometry configuration, only one meta-atom is required to design for the metagrating system. By simply controlling air gap between dual-layer metagratings, high-efficiency beam splitting can be well switched from asymmetric transmission to symmetric transmission. The working principle lies on gap-induced diffraction channel transition for incident waves from opposite directions. The asymmetric/symmetric transmission can work in a certain frequency band and a wide incident range. Compared with previous methods using acoustic metasurfaces, our approach has the advantages of simple design and tunable property and shows promise for applications in wavefront manipulation, noise control and one-way propagation.

Tunable Beam Steering at Terahertz Frequencies Using Reconfigurable Metasurfaces Coupled With Liquid Crystals

Abstract: Metasurfaces with a spatially varying phase profile enable the design of planar and compact devices for manipulating the radiation pattern of electromagnetic fields. Aiming to achieve tunable beam steering at terahertz frequencies, we numerically investigate metasurfaces consisting of one dimensional arrays of metal-insulator-metal (MIM) cavities infiltrated with liquid crystals (LCs). The spatial phase profile is defined by a periodic voltage pattern applied on properly selected supercells of the MIM-cavity array. By means of the electro-optic effect, the voltage controls the orientation of LC molecules and, thus, the resulting effective LC refractive index. Using this approach, the spatial phase profiles can be dynamically switched among a flat, binary, and gradient profile, where the corresponding metasurfaces function as mirrors, beam splitters or blazed gratings, respectively. Tunable beam steering is achieved by changing the diffraction angle of the first diffraction order, through the reconfiguration of the metasurface period via the proper adjustment of the applied voltage pattern.

Ptychographic characterization of a coherent nanofocused X-ray beam

Abstract: The NanoMAX hard X-ray nanoprobe is the first beamline to take full advantage of the diffraction-limited storage ring at the MAX IV synchrotron and delivers a high coherent photon flux for applications in diffraction and imaging. Here, we characterize its coherent and focused beam using ptychographic analysis. We derive beam profiles in the energy range 6-22 keV and estimate the coherent flux based on a probe mode decomposition approach.

Solution of inverse non-stationary boundary value problems of diffraction of plane pressure wave on convex surfaces based on analytical solution

Abstract: Research in the field of unsteady interaction of shock waves propagating in continuous media with various deformable barriers are of considerable scientific interest, since so far there are only a few scientific works dealing with solving problems of this class only for the simplest special cases. In this work, on the basis of analytical solution, we study the inverse non-stationary boundary-value problem of diffraction of plain pressure wave on convex surface in form of parabolic cylinder immersed in liquid and exposed to plane acoustic pressure wave. The purpose of the work is to construct approximate models for the interaction of an acoustic wave in an ideal fluid with an undeformable obstacle, which may allow obtaining fundamental solutions in a closed form, formulating initial-boundary value problems of the motion of elastic shells taking into account the influence of external environment in form of integral relationships based on the constructed fundamental solutions, and developing methods for their solutions. The inverse boundary problem for determining the pressure jump (amplitude pressure) was also solved. In the inverse problem, the amplitude pressure is determined from the measured pressure in reflected and incident waves on the surface of the body using the least squares method. The experimental technique described in this work can be used to study diffraction by complex obstacles. Such measurements can be beneficial, for example, for monitoring the results of numerical simulations.

Octupolar versus Néel Order in Cubic 5 d 2 Double Perovskites

Abstract: We report time-of-flight neutron spectroscopy and neutron and x-ray diffraction studies of the $5{d}^{2}$ double perovskite magnets, ${\mathrm{Ba}}_{2}M{\mathrm{OsO}}_{6}$ ($M=\text{Zn},\text{Mg},\text{Ca}$). These materials host antiferromagnetically coupled $5{d}^{2}$ ${\mathrm{Os}}^{6+}$ ions decorating a face-centered cubic (fcc) lattice and are found to remain cubic down to the lowest temperatures. They all exhibit thermodynamic anomalies consistent with a single phase transition at a temperature ${T}^{*}$, and a gapped magnetic excitation spectrum with spectral weight concentrated at wave vectors typical of type-I antiferromagnetic orders. However, while muon spin resonance experiments show clear evidence for time-reversal symmetry breaking below ${T}^{*}$, we observe no corresponding magnetic Bragg scattering signal. These results are shown to be consistent with ferro-octupolar symmetry breaking below ${T}^{*}$, and are discussed in the context of other $5d$ double perovskite magnets and theories of exotic orders driven by multipolar interactions.

Epitaxial stabilization of ultra thin films of high entropy perovskite

Abstract: High entropy oxides (HEOs) are a class of materials, containing equimolar portions of five or more transition metal and/or rare-earth elements. We report here about the layer-by-layer growth of HEO [( La 0.2 Pr 0.2 Nd 0.2 Sm 0.2 Eu 0.2)NiO3] thin films on NdGaO3 substrates by pulsed laser deposition. The combined characterizations with in situ reflection high energy electron diffraction, atomic force microscopy, and x-ray diffraction affirm the single crystalline nature of the film with smooth surface morphology. The desired +3 oxidation of Ni has been confirmed by an element sensitive x-ray absorption spectroscopy measurement. Temperature dependent electrical transport measurements revealed a first order metal-insulator transition with the transition temperature very similar to the undoped NdNiO3. Since both these systems have a comparable tolerance factor, this work demonstrates that the electronic behaviors of A-site disordered perovskite-HEOs are primarily controlled by the average tolerance factor.