Diffraction Effects Research Articles

Modulation Instability Induced by Quadratic Nonlinearity in Optically Anisotropic Medium

Abstract In anisotropic crystals, the inherent breakdown of circular symmetry due to anisotropy significantly impacts optical phenomena. This study theoretically investigates the effects of anisotropic diffraction on modulation instability (MI) spectra and subsequent optical filament formation. We model an anisotropic medium with quadratic nonlinearity, exhibiting noncritical phase-matched second-harmonic generation, using coupled nonlinear Schrödinger equations. Through linear stability analysis and numerical simulations, we examine MI in quasi-isotropic and anisotropic quadratic nonlinear media. Our results reveal that anisotropic diffraction induces asymmetry in the MI gain spectrum, leading to the formation of elliptical optical filaments for both fundamental and second harmonics. Notably, this asymmetry in the MI gain spectrum facilitates the generation of multiple filaments in high-gain MI regions.

Enhancement of dual autofocusing ability for ring Pearcey edge dislocation beams

Abstract When the ring with the maximum intensity deviates from the central point, the dual autofocusing performance of the ring Pearcey edge dislocation (RPED) beams in free space is gradually destroyed. To address the degradation in the dual autofocusing ability, we investigate the propagation dynamics of the RPED beams in a system with fractional diffraction effect or parabolic potential. The simulation results show that there exists a critical value for the Lévy index, that results in the RPED beams exhibiting an obvious dual autofocusing phenomenon with equal focusing intensities. When the Lévy index is near the critical value, the RPED beams have dual autofocusing characteristics, and the focusing intensity and focal distance can be controlled by changing the Lévy index. The introducing of the parabolic potential leads to the periodic evolution of the RPED beams, and the dual autofocusing property of the RPED beams with smaller radius can be restored within one evolution cycle by changing the potential depth. Moreover, the positions of the edge dislocation affect the focusing intensity, but have no effect on the number of foci. Our research provides some inspiration for the control of dual autofocusing beams, and has potential applications in optical manipulation and optical trapping.

Design of a tunable microlens based on hybrid single-wall carbon nanotube and liquid crystal

: Tunable liquid crystal (LC) lenses have garnered significant interest in recent years for their lightweight, cost-effectiveness, and versatility in applications like augmented reality, ophthalmic devices, and astronomy. Despite numerous proposed structures to enhance LC lens performance, achieving a minimal focal length while preserving image quality and balancing cost and complexity remains a daunting challenge. Adaptive microlenses encounter these obstacles due to physical constraints and diffraction effects. One promising solution lies in using adaptive LC-carbon nanotubes (CNTs) lenses. By adjusting external stimuli like electric or magnetic fields, it is possible to modify the refractive index distribution of the LC medium, thus changing the focal length of the microlens. When paired with CNTs, the LC molecules' orientation and control of focal length can be even more precise. Our research findings suggest that to achieve the shortest focal length in a microlens with a thickness of 22.5 μm, it is recommended that the diameter of the CNT should not exceed 10 nm, and the height of CNT should fall within the range of 10 to 20 μm considering the presence of screening effect. Conversely, for a microlens with low full width at half maximum (FWHM), narrower light spot, it is advisable to use CNT with a diameter larger than 100 nm and a height greater than 13 μm. Additionally, for a microlens with an efficient Fresnel number in the range of 1 to 10, the microlens should have CNT with widths from 100 to 200 nm. Therefore, based on the importance of each factor (focal length, FWHM, and Fresnel number), the dimensions of the carbon nanotube can be selected to suit the desired application.

Optical and electrical transport properties of α-Ga2O3 thin films with electrical compensation of Sn impurities

Polycrystalline α-Ga2O3 thin films containing secondary phase SnO were grown on BaF2 substrates by magnetron sputtering. The impurity tin concentration, electron concentration, and room temperature mobility of the α-Ga2O3 films are 4.5 × 1020 cm−3, 1.5 × 1015 cm−3, and 26.9 cm2 V−1 s−1, respectively, determined by secondary ion mass spectrometry and Hall effect experiments. The mobility vs temperature dependence confirms that the electrons are mainly subject to polar optical phonon scattering and ionized impurity scattering in the temperature range of 160–400 K. Two ionization energies, 29 and 71 meV, were determined for different temperature ranges by logarithmic resistivity vs the reciprocal of temperature, where the former is the shallow donor SnGa formed by the incorporation of tin into gallium sites. The latter is the shallow acceptor VSn–H associated with secondary phase SnO, and it is the electrical compensation of this shallow acceptor that results in the very low carrier concentration of α-Ga2O3 films. The photoluminescence spectrum exhibits 280 and 320 nm UV radiation, where 280 nm is due to the radiation recombination of electrons trapped by the deep donor state (EC−1.1 eV) with holes trapped by the VSn–H complex. In addition, there are several narrow radiation peaks in the visible region, and the energy levels involved in the radiation transitions are determined one by one after excluding the effects of interference and diffraction.

On the effect of precession for magnetic differential phase contrast imaging

The separation of diffraction effects from phase contrast is a major challenge for differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM). The application of electron beam precession has previously been proven successful in homogenizing the direct beam and improving the imaging of both long-range electric and magnetic fields. However, magnetic STEM-DPC imaging performed in a low magnification (LM) STEM mode suffers from significant aberrations of the probe forming lens and the consequent impediment of small precession angles. By investigating the application of precession path segmentation to LM-STEM precessed scans for the imaging of LSMO and FeAl thin film samples, the initially reported benefits of precession were discovered to be less substantial than originally assumed. The segmentation methodology reveals that precession induced beam phase shifts account for a large part of the DPC induction profile smoothing, and the precession path is non-circular, leading to streaking artifacts in the reconstructed induction maps.

Patterned dielectric back contact design for GaAs thermophotovoltaic devices

—Patterned-dielectric back contact structures in optoelectronic devices are designed to boost the reflectance of light from the device back surface while retaining a low-resistance pathway for electrical conductance. Their reduced light absorption at near- and sub-bandgap photon energies leads to improved luminescence in light-emitting diodes, greater photon recycling, voltage, and efficiency in photovoltaic cells, and greater recuperation of unabsorbed sub-bandgap light in thermophotovoltaic (TPV) systems. However, diffraction from the patterned features can deflect incident light in propagation directions that lead to light trapping and parasitic absorption in the cell. In this article, we use rigorous coupled-wave analysis (RCWA) to study three-dimensional diffractive scattering of electromagnetic waves by periodic metal point-contact gratings on 1.42-eV GaAs TPV cells, to analyze their effect on unwanted sub-bandgap absorption in order to achieve higher TPV system efficiency. Solutions of Maxwell's equations calculated using RCWA are compared to measured sub-bandgap reflectance in experimental GaAs TPV devices with varying metal point-contact diameters and spacing. Modeling and experiments indicate decreased total reflectance due to these diffractive effects for a small point contact diameter of 1 μm, and this effect is much stronger at higher contact coverage fractions.

Analytical design of fourth and fifth harmonic generations of an elliptically polarized Bessel-Gauss beam by using the concept of guided wave optics and TIR-QPM technique in a biaxial material

This paper demonstrates the analytical design of an Elliptically polarized Bessel-Gauss beam-based frequency converter by using the guided wave optics concept and Total Internal Reflection Quasi phase matching technique. An anisotropic positive biaxial crystal featuring a rectangular structure of Rubidium Titanyle Phosphate has been used to carry out this analysis. The efficiency of the fourth and fifth harmonic conversion in the projected scheme is 7.05% and 4.3%, respectively, which is approximately three times greater than in a crystal length of approximately 1.4[Formula: see text]mm and 3.4[Formula: see text]mm, as provided by the scheme illuminated by a linearly polarized Bessel-Gauss beam at a wavelength of 735[Formula: see text]nm and 588[Formula: see text]nm, respectively. The influence of limiting factors, viz Goos Hänchen Shift, surface roughness, absorption, and the diffraction effect rooted in the basic law of nonlinear reflection, has also been taken care of in this analysis. The dependence of conversion efficiency on the length, thickness and angle of incidence of the slab has also been studied.

PyFaults: a Python tool for stacking fault screening

PyFaults is an open-source Python library designed to model stacking fault disorder in crystalline materials and qualitatively assess the characteristic selective broadening effects in powder X-ray diffraction (PXRD). Here, the main capabilities of PyFaults are presented, including unit cell and supercell model construction, PXRD pattern calculation, assessment against experimental PXRD, and methods for rapid screening of candidate models within a set of possible stacking vectors and fault occurrence probabilities. This program aims to serve as a computationally inexpensive tool for identifying and screening potential stacking fault models in materials with planar disorder. Three diverse case studies, involving GaN, Li2MnO3 and Li3YCl6, are presented to illustrate the program functionality across a range of structure types and stacking fault modalities.

Combinatorial sputtering synthesis of TbCu7-type Sm-Fe based compounds: A study on phase, composition, and extrinsic magnetic properties

We investigated the effect of composition on the phase and extrinsic magnetic properties of TbCu7-type SmFe-based compounds using a combinatorial sputtering technique. Composition-spread thin films of SmFex (x=6.4–12.7) and SmFexN (x=6.8–12.8) were synthesized using a linear shutter-assisted combinatorial sputtering technique. A high-throughput composition, phase, and magnetic characterization were performed on 18 different locations along the film using X-ray diffraction (XRD), X-ray fluorescence (XRF), and magneto-optical Kerr effect (MOKE) magnetometry. The optimal composition with the highest fraction of the main phase was found to be in SmFe9.8 and SmFe9.5N and beyond this composition, the α-Fe secondary ferromagnetic phase emerges. The coercive field and remanence of the SmFe9.5N are estimated to be ∼0.8 T and ∼1.2 T, respectively. Further, scanning transmission electron microscopy (STEM) was performed at SmFe9.5N to correlate the microstructure with their extrinsic magnetic properties. Overall, this study demonstrates the impact of composition variation on the phase and extrinsic magnetic properties of TbCu7-type SmFe-based compounds, which can be utilized to tailor magnetic properties for targeted advanced magnet applications.

High-temperature stability and decoding of large field-of-view observable color codes prepared by femtosecond laser on titanium alloy

This study reported on the large field-of-view observable color code obtained by femtosecond laser-induced oxidation on titanium alloy. The simulation results showed that simultaneous roughening of the oxide layer and metal layer could effectively increase the color rendering range of the structural colors. Based on the diffraction effect of the diaphragm, the laser energy was periodically distributed. In addition, the simultaneous formation of the oxide layer and the micro/nano structures was attributed to the periodic distribution of laser energy. Compared to the substrate, the increase in oxygen content of the colored area ranged from 5 % to 11 %, indicating that the infiltration of oxygen inside the material was increased. Additionally, the surface chemical composition of the upper oxide layer of the colored areas was TiO2. XRD analysis showed that laser-induced surface coloring did not affect the phase composition of the alloy except for the generation of a small amount of carbon. Moreover, different scanning numbers affected the color difference ΔE∗ ab of adjacent scanning speeds. High-temperature experiments showed that the color code prepared by femtosecond laser-induced oxidization of titanium alloy was reliable in use at less than 100 °C. Since the color code could still be clearly obtained at a field angle of 77.3°, the angle insensitivity of the color code could be effectively improved by selective roughening of the oxide layer prepared by femtosecond laser. Furthermore, the decoding of color code was the inverse encoding process. Therefore, the angle insensitivity of the color code was improved and the temperature range of the structural color was clarified.

Contribution to the Statistical Mechanics of Static Triplet Correlations and Structures in Fluids with Quantum Spinless Behavior

The current developments in the theory of quantum static triplet correlations and their associated structures (real r-space and Fourier k-space) in monatomic fluids are reviewed. The main framework utilized is Feynman’s path integral formalism (PI), and the issues addressed cover quantum diffraction effects and zero-spin bosonic exchange. The structures are associated with the external weak fields that reveal their nature, and due attention is paid to the underlying pair-level structures. Without the pair, level one cannot fully grasp the triplet extensions in the hierarchical ladder of structures, as both the pair and the triplet structures are essential ingredients in the triplet response functions. Three general classes of PI structures do arise: centroid, total continuous linear response, and instantaneous. Use of functional differentiation techniques is widely made, and, as a bonus, this leads to the identification of an exact extension of the “classical isomorphism” when the centroid structures are considered. In this connection, the direct correlation functions, as borrowed from classical statistical mechanics, play a key role (either exact or approximate) in the corresponding quantum applications. Additionally, as an auxiliary framework, the traditional closure schemes for triplets are also discussed, owing to their potential usefulness for rationalizing PI triplet results. To illustrate some basic concepts, new numerical calculations (path integral Monte Carlo PIMC and closures) are reported. They are focused on the purely diffraction regime and deal with supercritical helium-3 and the quantum hard-sphere fluid.

Ring/vortex-like extreme wave in the partially nonlocal medium with different diffraction characteristics in both directions under influence of external potential and gain/loss

In this study, we analyze a (3+1)-dimensional partially nonlocal nonlinear Schrödinger (NLS) model, which incorporates various diffraction effects, gain or loss mechanisms, and confinement within linear and parabolic potentials. By reducing this complex model to a (2+1)-dimensional framework, we uncover analytical solutions that exhibit high-dimensional extreme wave structures with Hermite-Gaussian envelopes, illustrating the model's nonautonomous characteristics. Our investigation focuses on ring-like and vortex-like extreme waves, examining how different parameters—such as radius, Hermite parameter, gain, and thickness—affect these wave structures. Specifically, we find that, for fixed thickness, Hermite, and gain parameters, the radius influences the size of the wave structures. Conversely, with a fixed radius, Hermite, and thickness parameters, the gain parameter modifies the wave properties. The introduction of the Hermite parameter p increases the number of concentric layers in the ring-like extreme waves by p+1. Additionally, incorporating gain and loss effects enhances the model's applicability to real-world scenarios.

Enhancing Mineral Exploration Programs Through Quantitative XRD: A Case Study from the Gumsberg Polymetallic Sulphide Deposits, Sweden

As challenges in precious and base metal exploration intensify due to the diminishing availability of high-grade ore deposits, rising demand, energy costs, and stricter regulations towards net-zero carbon activities, advanced techniques to enhance exploration efficiency are becoming increasingly critical. This study demonstrates the effectiveness of quantitative X-ray diffraction (QXRD) with Rietveld refinement, coupled with multivariate statistical analysis (including agglomerative hierarchical clustering, principal component analysis, and fuzzy analysis), in characterizing the complex mineralogy of strata-bound volcanic-associated limestone-skarn Zn-Pb-Ag-(Cu-Au)-type sulphide deposits (SVALS). Focusing on 113 coarse rejects from the Gumsberg project located in the Bergslagen mining district in central Sweden, the research identified five distinct mineralogical clusters corresponding to polymetallic base metal sulphide mineralization, its proximal alteration zones, and variably metamorphosed host rocks. The results reveal significant sulphide mineralization, ranging from disseminated to massive occurrences of sphalerite, pyrrhotite, pyrite, and galena, with trace amounts of secondary minerals like anglesite in certain samples indicating weathering processes. The study also identifies rare minerals such as armenite, often overlooked in traditional geological logging. These findings underscore the potential of QXRD to enhance resource estimation, optimize exploration strategies, and contribute to more efficient and sustainable mineral exploration programs. The accuracy of QXRD was cross-validated with geological logs and geochemical data, confirming its reliability as a mineralogical discrimination tool.

Correlated tunneling in high-order above threshold dissociative ionization of H2

Comprehension of photon-triggered molecular processes is essential in the study of various important topics in physics, chemistry, and biology. Here we propose a correlated tunneling picture to understand the dissociative ionization process of molecules in intense laser fields based on a quantum model developed in the framework of many-body S-matrix theory including nuclear vibrational motion. In this quantum correlation picture, the single ionization of H2 and the subsequent electron-ion recollision-induced dissociation are considered as an entangled correlated process. It enables us to attribute the interference pattern in the joint-energy spectra to combined effects of single-slit diffraction and multi-slit interference of correlated electron-nuclear wave packets in the time domain. Our work opens a new avenue to understanding molecular dissociative ionization processes in external fields.

Ionospheric plasma irregularities over Dronning Maud Land in Antarctica and associated space weather effects

Ionospheric plasma irregularities and associated space weather effects over Dronning Maud Land in Antarctica are studied with a multi-instrument approach. It is demonstrated during a substorm event that auroral particle precipitation associated with the edges of auroral arcs can lead to irregularities in the ionospheric plasma density that can have significant impact on trans-ionospheric radio waves. Both refractive and diffractive effects are observed on signals from the GNSS satellites, where the latter are identified by the ionospheric free linear combination approach and amplitude scintillation. Thus, intense auroral particle precipitation can lead to plasma irregularities at scales from several kilometers down to and below the Fresnel radius, and they can result in space weather effects which can lead to losing the integrity of the GNSS signals.

Numerical estimation of wave breaking forces on seawalls

ABSTRACT This paper presents a computationally efficient numerical scheme to estimate wave forces from plunging breakers on vertical rigid seawalls. The approximated velocity equation, an asymptotical solution of the Green-Naghdi equation in the Camassa-Holm scaling, is utilized to obtain the evolution of the free surface and the depth-averaged horizontal velocity over time, leading to the formation of a plunging breaker. The uniform dynamic pressure along the depth is obtained by utilizing the unsteady Bernoulli equation. The wave forces on seawalls are then determined using Froude-Krylov theory, with adjustments for diffraction effects. The results, while being comparable to some existing formulations, notably differ with some others. This highlights the limitations imposed by the inherent assumptions in the existing empirical formulations and underlines the importance of the proposed methodology that is founded on an accurate modelling of the wave breaking process to estimate wave breaking forces on seawalls.

Dynamic Wavelength-Selective Diffraction and Absorption with Direct-Patterned Hydrogel Metagrating.

Hydrogel nanophotonic devices exhibit attractive tunable capabilities in structural coloration and optical display. However, current hydrogel-based tunable strategies are mostly based on a single physical mechanism, and it remains a challenge to merge multiple mechanisms for active devices with integrated functionalities. Here, a hydrogel metagrating combining Fabry-Pérot (FP) resonance and diffraction effects is proposed for achieving tunable absorption and dynamic wavelength-selective beam steering. Through exploiting hydrogel shrinkage under electron-beam exposure, a hydrogel nanocavity composed of Ag/Hydrogel/Ag three-layer films can be directly printed with arbitrary patterns, enabling the direct-pattering technique of metagrating. The hydrogel nanocavity performs as an FP-type absorber, and its absorption peak rapidly shifts with humidity variation due to the hydrogel layer scaling. The response speed is <320ms, and the absorption peak shift range is >150nm. It is further demonstrated that the hydrogel metagrating exclusively deflects light at the resonance wavelength, and its operating wavelength can be actively switched by regulating ambient humidity. The proposed tunable hydrogel metagrating can promote new technologies of tunable metasurfaces for optical filtering, gas sensing, and optical imaging.

Physical coherent cancellation of optical addressing crosstalk in a trapped-ion experiment

Abstract We present an experimental investigation of coherent crosstalk cancellation methods for light delivered to a linear ion chain cryogenic quantum register. The ions are individually addressed using focused laser beams oriented perpendicular to the crystal axis, which are created by imaging each output of a multi-core photonic-crystal fibre waveguide array onto a single ion. The measured nearest-neighbor native crosstalk intensity of this device for ions spaced by 5 µm is found to be ∼ 10 − 2 . We show that we can suppress this intensity crosstalk from waveguide channel coupling and optical diffraction effects by a factor &gt; 10 3 using cancellation light supplied to neighboring channels which destructively interferes with the crosstalk. We measure a rotation error per gate on the order of ϵ x ∼ 10 − 5 on spectator qubits, demonstrating a suppression of crosstalk error by a factor of &gt; 10 2 . We compare the performance to composite pulse methods for crosstalk cancellation, and describe the appropriate calibration methods and procedures to mitigate phase drifts between these different optical paths, including accounting for problems arising due to pulsing of optical modulators.

Effect of background noise and diffraction on localization of sound sources using distributed acoustic measurement equipment

This study is focused on the development of a system designed to pinpoint the positions of sound sources within a plane through the analysis of cross-correlated signals obtained from distributed microphones. Our investigation delved into assessing the impact of physical barriers and background noise on the accuracy of the proposed method for localizing sound sources. Prior research has demonstrated that measurements conducted within an anechoic chamber yield estimations accurate to within ±20 mm. When the signal-to-noise ratio of the target sound source is reduced by the background noise, the estimation is performed at the point of background noise generation. Furthermore, the introduction of physical barriers between the sound source and the microphones resulted in sound diffraction, thereby leading to estimation errors attributable to the varying lengths of diffraction paths. These findings underscore the importance of considering environmental factors in sound source localization endeavors. The estimation at Mic, where the sound-receiving level drops below -10 dB due to physical barriers, confirmed that the background noise source point is estimated as well as the background noise estimation error.

Metal-mesh-integrated lateral nanowire array solar cells for ultra-thin photovoltaic antennas.

An integrated photovoltaic antenna based on a lateral nanowire array solar cell and metal mesh is proposed and studied by three-dimensional electromagnetic simulation. The results show that the integration of the metal meshed antenna significantly enhances the absorption of the nanowire array due to the diffraction effects of the two-dimensional grating and the excitation of localized surface plasmons. By optimizing the nanowire diameter, antenna linewidth, and gap between them, the integrated solar cell achieves a maximum conversion efficiency of 11.1%, 38% higher than that before integration. The antenna exhibits an operational frequency range of 5.88-6.16 THz (S11 < 10 dB) and radiation efficiency of 59.617%, which are almost unaffected by the underlying solar cell due to the ultra-small thickness of nanowires. This study may pave the way for the development of ultra-thin flexible high-performance integrated photovoltaic antennas.