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Being a new class of materials, transition metal dichalcogenides are paving the way for applications in atomically thin optoelectronics. However, the intrinsically weak light–matter interaction and the lack of manipulation ability has lead to poor light emission and tunable behavior. Here, we investigate the fluorescence characteristic of monolayer molybdenum disulfide on a metal narrow-slit grating, where a highly efficient, 471 times photoluminescence enhancement are realized, based on the hybrid surface plasmon polaritons resonances and the decreased influence of substrate. Moreover, the emitted intensity and polarization are controllable due to the polarization-dependent characteristic and anisotropy of grating. The manipulations of light-matter interactions in this special system provide a new insight into the fluorescent emission process and open a new avenue for high-performance low dimensional materials devices designs. [ABSTRACT FROM AUTHOR]

In a pattern of horizontal lines containing ± 45° zigzagging phase-shifted strips, vivid illusory motion is perceived when the pattern is translated up or down at a moderate speed. Two forms of illusory motion are seen: [i] a motion "racing" along the diagonal interface between the strips and [ii] lateral (sideways) motion of the strip sections. We found the relative salience of these two illusory motions to be strongly influenced by the vertical spacing and length of the line gratings, and the period length of the zigzag strips. Both illusory motions are abolished when the abutting strips are interleaved, separated by a gap or when a real line is superimposed at the interface. Illusory motion is also severely weakened when equiluminant colored grating lines are used. Illusory motion perception is fully restored at < 20% luminance contrast. Using adaptation, we find that line-ends alone are insufficient for illusory motion perception, and that both physical carrier motion and line orientation are required. We finally test a classical spatiotemporal energy model of V1 cells that exhibit direction tuning changes that are consistent with the direction of illusory motion. Taking this data together, we constructed a new visual illusion and surmise its origin to interactions of spatial and temporal energy of the lines and line-ends preferentially driving the magnocellular pathway. [ABSTRACT FROM AUTHOR]

With the continuous development of science and technology, industrial production has higher and higher requirements for precision. Many high-precision measurement technologies emerge as the times require, and nanoscale grating ruler displacement measurement technology is one of them. As a kind of precision sensor, nanoscale grating ruler has important application in displacement measurement system. CPLD has the advantages of high integration and fast programming speed, which is often used to control the displacement measurement system of nanoscale grating ruler. The purpose of this paper is to deeply explore the measurement effect and related application principle of nanoscale grating ruler displacement measurement system based on CPLD technology. A set of nanoscale grating ruler displacement measurement system is designed based on CPLD technology. The output signal of grating ruler is programmed by CPLD. The x-axis displacement of the experimental platform controlled by stepping motor is measured, and the measured data are recorded by carrying out analysis and research. The results show that compared with the traditional phase difference measurement system, the measurement accuracy of the system based on CPLD is improved by 24.7%, the robustness of the measurement system is improved by 18.6%, and the measurement speed is increased by 27.3%. Therefore, this kind of nanoscale measurement precision grating ruler displacement measurement control system based on CPLD has three characteristics: high measurement accuracy, strong anti-interference ability, and high measurement motion efficiency, which can effectively meet the requirements of grating ruler displacement measurement system for high-precision manufacturing technology. [ABSTRACT FROM AUTHOR]

Incompatibility of conventional magneto‐optical (MO) materials with photonic‐system fabrication processes constitutes a major technological roadblock limiting their integration into photonic devices, especially for micro‐ or nano‐patterned films. This paper proposes a photolithography approach toward MO micro‐ and nano‐patterns, based on hybrid photosensitive matrices doped with magnetic nanoparticles to concentrations as high as 20 % vol. The as‐prepared and characterized nanocomposite thin films exhibit excellent MO properties: a high Faraday rotation (3300°/cm), comparable with the best existing materials that nevertheless require much more involved processes. The photosensitive matrices allow patterned gratings with a wide range of periods (100 μm to 500 nm), using a simple procedure at room temperature. The fabricated gratings exhibit well‐defined regular structures and resolutions suitable for optical applications, including those at telecommunications wavelengths. Finally, direct applications of the proposed material and its associated process are demonstrated on two examples: 1) a magneto‐optical grating in free‐space and 2) in combination with a waveguide. The obtained optical and MO results are consistent with simulations. [ABSTRACT FROM AUTHOR]

In the mechanically induced long‐period fiber grating (MLPFG) fabricated by applying the periodical pressure on an optical fiber, the small bending occurs due to the periodical pressure, which influences the losses of the core and cladding modes. We propose the theoretical model of the MLPFG for estimating its transmittance based on the transfer matrix method and investigate the effect of the losses of the core and cladding modes in the MLPFG on the transmittance, theoretically and experimentally. We numerically clarify that the transmitted light spectrum of MLPFG shows only the main attenuation lobe, no side lobe, and the attenuation bandwidth is broadened as the cladding mode loss increases. We also clarify that the coupling coefficient, and the losses of the core and cladding modes in the fabricated MLPFG can be estimated from the measured transmitted spectrum based on our model. Moreover, we measure the transmittance of two types of MLPFGs that fabricated with a screw, weights, and metallic plates, and that fabricated with a screw and a heat‐shrinkable tube. The measured spectra show good agreements with the calculated ones using our model. Our model will be useful for designing MLPFGs applied to the sensors. [ABSTRACT FROM AUTHOR]

Exciton intervalley scattering, annihilation, relaxation dynamics, and diffusive transport in monolayer transition metal dichalcogenides are central to the functionality of devices based on them. Here, these properties in a large‐size exfoliated high‐quality monolayer MoSe2 are addressed directly using heterodyned transient grating spectroscopy at room temperature. While the free exciton population is found to be long‐lived (≈230 ps), an extremely fast intervalley scattering (≤170 fs) is observed, leading to a negligible valley polarization, consistent with steady state photoluminescence measurements and theoretical calculation. The exciton population decay shows an appreciable contribution from the exciton–exciton annihilation, with an annihilation rate of ≈0.01 cm2 s−1. The annihilation process also leads to a significant distortion of the transient grating evolution. Taking this distortion into account, consistent exciton diffusion constants D ≈ 1.4 cm2 s−1 are found by a model simulation in the excitation density range of 1011–1012 cm−2. The presented results highlight the importance of correctly considering the many‐body annihilation processes to obtain a pronounced understanding of the excitonic properties of monolayer transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

We introduce a new two-step method to fabricate silver-silicon gratings that can excite surface plasmons efficiently. The grating structure was firstly created on a flat silicon substrate by single-pulse nanosecond laser interference lithography. Next, a silver layer of 50 nm was evaporated on the silicon substrate. With proper laser energy, a silver-silicon grating with a period of 1120 nm and depth of 18 nm was successfully fabricated. This grating can produce high-quality surface plasmon resonance (SPR) peaks at various incident angles. Moreover, a SPR sensor was experimentally demonstrated based on the silver-silicon grating, which had high sensitivity of 961.5 nm/RIU and figure of merit of 60. Our method is an efficient way to fabricate periodically nanostructured metals at high speed and low cost. [ABSTRACT FROM AUTHOR]

In this paper, a dual grating structure for unidirectional transmission is presented. The forward and backward transmission performances have been investigated by finite element method. To enhance the forward transmission and to suppress the backward transmission simultaneously, we suggested to cut grooves on the surfaces of one of the gratings, and the effects of the grooves on the optical transmission have been studied. The numerical simulation results reveal that the transmission contrast ratio and the optical unidirectional transmission of the structure can be improved markedly by properly arranging the size and the position of the grooves. The forward transmission can be more than 90%, while the backward transmission transmittance is less than 5%. [ABSTRACT FROM AUTHOR]

Highly sensitive and selective long-period grating (LPG) fiber-optic sensors modified with molecularly imprinted TiO2 nanothin films were fabricated. The films were deposited onto the surface of the optical fiber via liquid-phase deposition (LPD), using tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) as a template. Three LPG resonance bands were monitored during film deposition, which was of duration 4.5 h. Prior to template removal, heat treatment at 60 °C under high-humidity conditions led to an increase in refractive index of the TiO2 film, evidenced by changes in the central wavelengths of the attenuation bands. After template removal using HCl solution (0.01 M), the TMPyP-imprinted film-modified LPG sensor showed higher sensitivity to the template molecule than to structurally related guest molecules. This was measured at the 1st and 2nd resonance bands, with wavelengths ranging from 690 to 738 nm and 815 to 905 nm, respectively. No selective binding of the template was observed with a non-imprinted TiO2 film prepared in the same manner. Furthermore, the heat-treated imprinted films exhibited a substantial enhancement of photocatalytic activity for template irradiation. In particular, the self-cleaning property of the imprinted film-modified LPG sensor under ultraviolet irradiation led to highly efficient and selective binding to the template. The mechanism of the interaction between the template and the TiO2 matrix was investigated by UV–vis and Fourier-transform infrared (FTIR) spectroscopies. Additionally, morphological studies using scanning electron microscopy (SEM) were conducted. [ABSTRACT FROM AUTHOR]

Gratings enable dispersive spectroscopy from the X-ray to the optical, and feature prominently in proposed flagships and SmallSats alike. The exacting performance requirements of these future missions necessitate assessing whether the present state-of-the-art in grating manufacture will limit spectrometer performance. In this work, we manufacture a 1.5 mm thick, 1000 nm period (1000 gr mm−1) flat grating using electron-beam lithography (EBL), a promising lithographic technique for patterning gratings for future astronomical observatories. We assess the limiting spectral resolution of this grating by interferometrically measuring the diffracted wavefronts produced in ± first order. Our measurements show this grating has a performance of at least R ∼ 14,600, and that our assessment is bounded by the error of our interferometric measurement. The impact of EBL stitching error on grating performance is quantified, and a path to measuring the period error of customized, curved gratings is presented. [ABSTRACT FROM AUTHOR]

Flattop beam shapes are in high demand for various laser applications, including ultra-high-power laser systems and surface processing, which includes interference laser processing and medical treatment. In this study, we report on the improvement of extraction efficiency in a beam shaping method using phase gratings and spatial frequency filtering. By organising the phase grating vector ð'ð'ð'"ð'" unparallel to the normal vectors ð'ð'ð'ð' of the sides of an aimed polygonal beam shapes, which are square and hexagonal in this study, the high-spatial frequency component is maintained in the spatial frequency filtering process, and high-quality beam shaping with good flatness and edge steepness can be obtained. In addition, the extraction efficiency of polygon-shaped beams from a Gaussian beam or flattop circular beam is discussed. [ABSTRACT FROM AUTHOR]

Various diseases are spread by means of contaminated water or food, and the detection of pathogenic bacteria has great significance for securing a proper healthy environment for human beings. In this article, microfiber gratings (MFGs) were fabricated by using a high-frequency CO2 laser. The number of periods is 30, and the length of the period is 600 μm. A type of biosensor is proposed in this study. Results showed that the biosensor was strongly sensitive to the concentration of Escherichia coli and a maximum sensitivity of 1.15 nm/107 CFU was achieved. The mechanism of real-time sensing of prepared MFG was also proposed, which could be due to relationship between dip wavelength shift and the concentration of detected bacteria. The prepared MFGs do not need any coating, and the proposed biosensor has a great potential for application in fields of medical treatment, biology, and farming. [ABSTRACT FROM AUTHOR]

Featured Application: Wavelength-division multiplexing, client-side optical link, mobile backhaul, datacenter network, data-centric communications and computing. This paper reviews receivers that feature low-loss multimode-output arrayed waveguide gratings (MM-AWGs) for wavelength division multiplexing (WDM) as well as hybrid integration techniques with high-speed throughput of up to 100 Gb/s and beyond. A design of optical coupling between higher-order multimode beams and a photodiode for a flat-top spectral shape is described in detail. The WDM photoreceivers were fabricated with different approaches. A 10-Gb/s photoreceiver was developed for a 1.25-Gb/s baud rate and assembled for eight-channel WDM by mechanical alignment. A receiver with 40-Gb/s throughput was built by using visual alignment for a 10-Gb/s baud rate and four-channel WDM. A 100-Gb/s receiver assembled by active alignment with a four-channel by 25-Gb/s baud rate is the basis for beyond-100 Gb/s and future multi-wavelength integrated devices toward data-centric communications and computing. [ABSTRACT FROM AUTHOR]

In this work, a quasi-neutral plasma grating is considered, generated by two counter-propagating identical laser beams. Typical time scales associated with such gratings are given by , where v0 is the electron quiver in the laser field of wavevector k. In most situations, the behavior of the grating can be characterized by a single parameter, µ, which is proportional to the ratio of background electron temperature to the square of the electron quiver velocity. Indeed, even for quasi-neutral gratings, electron pressure might play an important role, via adiabatic electron heating. The influence on grating formation and lifetime of other parameters involving the inclusion of dissipative effects or kinetic effects is also examined in detail. Finally, an approximated analytical solution to the fluid model is found and shows good agreement with first-principle simulations. [ABSTRACT FROM AUTHOR]

The possibility of inducing population gratings in a three-level resonant medium using a pair of unipolar attosecond pulses that do not overlap in the medium has been studied theoretically. It has been shown that the results of the approximate solution of the Schrödinger equation agree with the results of the numerical solution of the system of equations for the density matrix of a three-level medium whose parameters are close to the parameters of atomic vapors of rubidium. [ABSTRACT FROM AUTHOR]

Measurements of pollutant concentrations in the flue gases of a biofuel boiler show that pollutants concentrations fluctuate by 10-100% and more at short time intervals. Large fluctuations in concentrations hinder the effective application of pollution reduction measures. During the research, flue gas composition measurements were performed in 4 MW, 8 MW industrial biofuel boilers and 20 kW experimental model. The results of the research showed that the change of CO, NO, NO2, SO2, H2S, O2 and particulate matter concentrations is related to the periodicity of the boiler grate movement. During the movement of the grate, the surface of the fuel bed is mechanically disrupted. The different composition of the fuel layers is mixed and this affects the changes in the concentration of combustion products. The clarity of the concentration fluctuations depends on the emissions, the type of fuel and the combustion parameters. [ABSTRACT FROM AUTHOR]

Plane gratings are widely used as dispersion elements in spectral analysis from the infrared to x-ray regions. This study proposes an optical element, consisting of only a reflection focusing and dispersion plane grating (RFPG) designed for a specific wavelength. A raytracing simulation and a visible light experiment were performed to verify the focusing and wavelength dispersion properties of the proposed RFPG. The raytracing simulation result shows that the designed 635 nm RFPG has a spectral resolution (λ/∆λ) of 423 (linear dispersion = 493.8 eV/m) under specific conditions. Additionally, in the visible light experiment, the spectral resolution of 423 (linear dispersion = 493.8 eV/m) and band range of ±25 nm were obtained at the target wavelength of 635 nm. The experimental results indicate that the proposed optical element, RFPG, exhibits focusing and dispersion properties for a designed wavelength. It is a potential tool for the study of x-ray fluorescence, absorption, and advanced x-ray sources, such as laser wakefield Betatron x-ray sources. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Al-Qadisiya In Arts & Educational Science is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The three-dimensional micro-structure of physical surfaces produces frictional forces that provide sensory cues about properties of felt surfaces such as roughness. This tactile information activates somatosensory cortices, and frontal and temporal brain regions. Recent advances in haptic-feedback technologies allow the simulation of surface micro-structures via electro-static friction to produce touch sensations on otherwise flat screens. These sensations may benefit those with visual impairment or blindness. The primary aim of the current study was to test blind and sighted participants' perceptual sensitivity to simulated tactile gratings. A secondary aim was to explore which brain regions were involved in simulated touch to further understand the somatosensory brain network for touch. We used a haptic-feedback touchscreen which simulated tactile gratings using digitally manipulated electro-static friction. In Experiment 1, we compared blind and sighted participants' ability to detect the gratings by touch alone as a function of their spatial frequency (bar width) and intensity. Both blind and sighted participants showed high sensitivity to detect simulated tactile gratings, and their tactile sensitivity functions showed both linear and quadratic dependency on spatial frequency. In Experiment 2, using functional magnetic resonance imaging, we conducted a preliminary investigation to explore whether brain activation to physical vibrations correlated with blindfolded (but sighted) participants' performance with simulated tactile gratings outside the scanner. At the neural level, blindfolded (but sighted) participants' detection performance correlated with brain activation in bi-lateral supplementary motor cortex, left frontal cortex and right occipital cortex. Taken together with previous studies, these results suggest that there are similar perceptual and neural mechanisms for real and simulated touch sensations. [ABSTRACT FROM AUTHOR]

Over 30 years ago a simple laboratory tool for optical-vortex beams generation was reported as a synthesized 'forked' diffraction grating. We renew the issue, addressing specific properties of such a grating in the sense of geometrical transformation of the grating shape. Stretching or compressing the grating scale results in the astigmatic optical vortex appearance in the first diffraction order. In the case of the induced vortex topological charge higher than unity, the astigmatism forces the optical vortex to separate into a line of unity-charged vortices. The initial splitting occurs along an azimuth angle, depending on the topological charge of the vortex. We show the rotation of the pattern in the free space propagation in simulations and analytical consideration. [ABSTRACT FROM AUTHOR]

In this study, we present and establish a gold surface plasmon polariton (SPP) GaAs photodetector that achieves high internal quantum efficiency (IQE). At a wavelength of 600 nm, the IQE with the SPP was 85%, while the IQE without the SPP was 42%, an enhancement of 43%. Also, at a wavelength of 675 nm, the IQE with SPP was 82%, whereas the IQE without SPP was 45%, which constitutes an increase of 37%. Such excellent performance is ascribed to the subwavelength scope of the optical power in the photoconductive-based gold SPP GaAs that provides high IQE. Moreover, the recombination of the SPP in the photodetector provides greater photocurrent and responsivity. [ABSTRACT FROM AUTHOR]

The need for an easy to fabricate perfect and narrowband light absorber in the visible range of electromagnetic (EM) spectrum has always been in demand for many scientific and device applications. Here, we propose a metal-dielectric-metal (MDM) 1-D grating plasmonic structure as a perfect narrow band light absorber in the visible and its application in glucose detection. The proposed structure consists of a 1- D grating of gold on the top of a dielectric layer on a gold film. Optimization for dielectric grating index (n), grating thickness (t), grating width (W), and grating period (P) has been done to improve the performance of plasmonic structure by calculating its quality factor and figure-of-merit (FOM). The optimized plasmonic structure behaves as a perfect narrowband light absorber. The flexibility to work at a specific wavelength is also offered by the proposed structure through an appropriate selection of the geometrical parameters and refractive index of the dielectric grating. The equivalent RC model is used to understand different components of the proposed structure on the optical response. The absorption response of the structure is invariant to the incident angle. Moreover, the calculated absorbance of the proposed plasmonic structure is ~ 100% with a narrow full-width half maxima (FWHM) of ~ 2.8 nm. We have numerically demonstrated a potential application of the proposed MDM absorber as a plasmonic glucose sensor in the visible range with detection sensitivity in the range of 140 to 195 nm/RIU. [ABSTRACT FROM AUTHOR]

We propose a technique to design highly-efficient and -unidirectional DFB Raman fiber lasers based on the engineering of the grating's coupling coefficient including a π-phase shift position in the fiber. For this purpose, first the ideal intra-cavity signal powers for different pump power levels are determined for given fiber lengths. Then, the sum and difference between the counter-propagating wave intensities at each small segment within fiber lengths are calculated resulting in determining the ideal grating's coupling functions for co- and contra-directional-pumping. The steady-state behavior of the laser using realistic parameters is finally simulated for modified coupling functions considering the Kerr nonlinearity. For a 10 W co-directional-pumped, ∼1 m long single-mode super-efficient DFB, a ∼50% increase in the laser efficiency, more than 44 dB reduction in contra-directional lasing power, ∼15 times drop in the peak power of intra-cavity signal and ∼38% decrease in the unused-pump power are found, compared to those in a standard DFB with the same coupling-length product. Although an enhanced nonlinear refractive index due to thermal gradient reduces the output power of such lasers, it is shown that the super-efficient laser presents a better performance than the standard one, under such conditions. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Diffractive optics play a key role in hard X‐rays imaging for which many scientific, technological, and biomedical applications exist. Herein, high‐aspect‐ratio microfabrication of gratings for X‐ray interferometry is demonstrated using Pt as a catalyst for the metal assisted chemical etching of Si in a solution of HF and H2O2. The Pt layer is thermally treated to realize a porous catalyst layer that stabilizes the etching of a pattern with a pitch size from 4.8 to 20 μm in the direction perpendicular to the <100> Si substrate and an aspect ratio up to 60:1. The superior etching performance of Pt as a catalyst and its stability in a solution with high HF content are reported in direct comparison with the Au catalyst for the same grating parameters. The Si structure is then used as a template for filling with Au, as a high absorbing X‐ray material. The Pt catalyst layer is used as a conductive seed for Au electroplating. The quality of the overall process is assessed by obtaining a visibility map using 30 μm‐thick Au grating in an X‐ray interferometric setup at 20 keV. [ABSTRACT FROM AUTHOR]

We theoretically and numerically demonstrate a tunable and wide-angle terahertz absorber, which is composed of multilayer graphene-dielectric grating and bottom metal substrate. Numerical simulation shows that the proposed absorber has the advantage of dynamically tunable range from 1.015 THz to 1.165 THz when the chemical potential of graphene increases from 10 meV to 150 meV. The absorption efficiency can reach a high value of 99%. To show the working mechanism of absorption, the near field distributions of magnetic components are presented at the absorption wavelength. We also demonstrate that the tunable range of absorption can be engineered by designing the geometry parameters. In addition, it is shown that the designed absorber can maintain the good performance of absorption over a wide incident angle from 0 ∘ to 6 0 ∘ under TM-polarization. [ABSTRACT FROM AUTHOR]

This paper explores resident experiences of life in PLACE/Ladywell, a "pop‐up" social housing scheme in London providing temporary accommodation for homeless families. Specifically, we consider barriers to, and assertions of, homemaking in this temporary setting through fixtures and fittings—a door lock, wall stickers, and a fireplace. The paper utilises assemblage thinking to understand homemaking within these time‐limited and constrained circumstances. Despite their seeming banality, fixtures and fittings offer a material, politicised, and lively means of studying the attempted and thwarted production of home by residents living in PLACE/Ladywell. The absence of door locks reduces parents' ability to maintain privacy and intimate relations; restrictions on hanging pictures and other decorative measures are circumvented by the use of wall stickers; and a defiant decorative fireplace establishes a sense of home in a temporary setting. Together, these objects constitute vital elements in negotiations between fixity and impermanence in temporary accommodation. [ABSTRACT FROM AUTHOR]

A novel slow wave structure (SWS), called the chevron-shaped double-staggered grating waveguide structure, is proposed for traveling wave tube (TWT) amplifier for the terahertz (THz) region. The potential of this SWS is that it provides higher interaction impedance and has low phase velocity; thus, higher output power can be expected at a lower beam voltage. The electromagnetic characteristics and particle-in-cell (PIC) large-signal simulations were performed with CST Microwave Studio software. The SWS was optimized for the central frequency of 200 GHz, which synchronizes with a beam voltage of 18.8 kV in the second spatial harmonic (2π-3π). A sheet electron beam with a current density of 133~A/cm2 was used to excite the structure, which interacts with the longitudinal electric field component to provide gain. The reflection coefficient at the port interface is less than −15 dB over the frequency range 181–220 GHz, and a small-signal gain of 30.98 dB is achieved for a tube length of 60 mm. [ABSTRACT FROM AUTHOR]

This paper designed a novel three-port reflective surface-covered grating with a connecting layer. The grating can be used as a splitter, and the polarized light can be divided into zero order, first order and second order. Through rigorous coupled-wave analysis, the efficiency of the three orders of diffraction light is close to 33% under the condition that the incident light at 1550 nm is incident at the second Bragg angle and the given duty cycle is 0.5. The efficiency and bandwidth of the surface-covered grating are improved compared with that of the surface-relief grating reported in the past. Especially for transverse magnetic polarized light, the beam splitting effect is more uniform, the efficiency ratio of the zeroth order to first order can reach 1.01, and the efficiency ratio of the first order to second order can reach 1. [ABSTRACT FROM AUTHOR]

We design structures with switchable, narrowband thermal absorption peaks, based on metallic gratings incorporating phase-change materials. An insulator-to-metal phase transition in vanadium dioxide is used to turn the coupling between a surface plasmon mode and a normally incident electromagnetic wave on and off. We analyze the limits on absorptive switching within the framework of coupled-mode theory, in order to evaluate the optimality of specific designs. [ABSTRACT FROM AUTHOR]

Reflection phase gratings based on write-once optical discs are proposed. Their morphology and backward diffraction characteristics are investigated. Home-made phase gratings with well-defined spacing about 1 524, 751, 335 nm are readily produced by pulling off ordinary optical discs. The backward diffraction characteristics of three phase gratings are compared. The research results show that diffraction phenomena of CD-R, DVD-R and BD-R gratings are observed in visible, visible-NIR and ultraviolet regions, respectively; successive spectra overlap are observed in diffraction spectra of the CD-R grating and angular dispersion of diffraction spectra increases as the diffraction order increases; diffraction angle of the three gratings is linearly proportional to the diffraction peak, angular dispersion increases as the grating constants decreases and the maximum angular dispersion is 0.333(°)/nm. In addition, when wavelength of incident light is more than the grating period, there is only zero-order diffraction wave in diffraction spectra of the DVD-R and BD-R subwavelength gratings. [ABSTRACT FROM AUTHOR]

Laser-driven non-local electron dynamics in ultrathin magnetic samples on a sub-10 nm length scale is a key process in ultrafast magnetism. However, the experimental access has been challenging due to the nanoscopic and femtosecond nature of such transport processes. Here, we present a scattering-based experiment relying on a laser-induced electro- and magneto-optical grating in a Co/Pd ferromagnetic multilayer as a new technique to investigate non-local magnetization dynamics on nanometer length and femtosecond timescales. We induce a spatially modulated excitation pattern using tailored Al near-field masks with varying periodicities on a nanometer length scale and measure the first four diffraction orders in an x-ray scattering experiment with magnetic circular dichroism contrast at the free-electron laser facility FERMI, Trieste. The design of the periodic excitation mask leads to a strongly enhanced and characteristic transient scattering response allowing for sub-wavelength in-plane sensitivity for magnetic structures. In conjunction with scattering simulations, the experiment allows us to infer that a potential ultrafast lateral expansion of the initially excited regions of the magnetic film mediated by hot-electron transport and spin transport remains confined to below three nanometers. [ABSTRACT FROM AUTHOR]

Purpose: To study interobserver variability for measurement of grating acuity in preverbal and nonverbal children with developmental delay using Lea Grating Paddles (Lea Hyvärinen). Methods: In this prospective study, preverbal patients younger than 3 years and older nonverbal patients (with developmental delay) were included. Those with poor neck holding were excluded. Binocular and monocular visual acuity assessment was done simultaneously using Lea Grating Paddles by two examiners who were blinded from each other's results. Results: Thirty-one children were tested (19 [61.29%] males and 12 [38.71%] females). The mean age was 28.5 months (range: 4 to 44 months). A total of 92% of the observations showed interobserver agreement of 0.5 octave or better in binocular testing. Results for monocular testing showed interobserver agreement (0.5 octaves or better) in 95.65% and 95.23% of right and left eyes, respectively. Combined results showed agreement better than 0.5 octaves in 94.20%. The mean binocular visual acuity was 2.07 and 2.14 cycles per degree (cpd) for the first and second observer, respectively (Thirty-one children were tested (19 [61.29%] males and 12 [38.71%] females). The mean age was 28.5 months (range: 4 to 44 months). A total of 92% of the observations showed interobserver agreement of 0.5 octave or better in binocular testing. Results for monocular testing showed interobserver agreement (0.5 octaves or better) in 95.65% and 95.23% of right and left eyes, respectively. Combined results showed agreement better than 0.5 octaves in 94.20%. The mean binocular visual acuity was 2.07 and 2.14 cycles per degree (cpd) for the first and second observer, respectively (P =.59). Similarly, the mean monocular visual acuity for the right and left eyes was 0.98 and 0.97 cpd for observer 1 and 0.89 and 0.79 cpd for observer 2, respectively (P =.91 and.14, for the right and left eyes, respectively). Conclusions: Interobserver variability for grating acuity measurement using Lea Grating Paddles is minimal, signifying it to be a reliable and reproducible alternative to conventional preferential looking testing procedures. [[J Pediatr Ophthalmol Strabismus. 2020;57(5):305–308.] [ABSTRACT FROM AUTHOR]

A self-calibration method, in which the wavefronts of zeroth and first-order diffracted beams from a scale grating measured by a Fizeau interferometer are employed, is applied for the evaluation of the pitch deviation of a reflective-type linear scale with a grating pitch of 2.048 μm used in a commercial interferential scanning-type optical linear encoder. One of the advantages of the self-calibration method is that the pitch deviation of a scale grating can be evaluated while measuring the out-of-flatness of the scale grating under inspection and the Z-directional out-of-flatness (surface profile) of the reference optical flat in the Fizeau interferometer. Meanwhile, in a practical case, the self-calibration method is valid under the condition where the out-of-flatness of the scale grating is on the same order or less than that of the reference optical flat in the Fizeau interferometer. In this paper, theoretical analysis and numerical calculations are thus carried out to investigate the influence of the out-of-flatness of the scale grating on measurement of the pitch deviation and the out-of-flatness of the reference optical flat. Some experiments with a linear scale from a commercial interferential scanning-type linear encoder are also carried out to verify the feasibility of the self-calibration method for the evaluation of the pitch deviation of the scale having an out-of-flatness of approximately 600 nm over the analyzed area. [ABSTRACT FROM AUTHOR]

Plasmonic metasurfaces have attracted much attention for use in device applications over the past decade. Dynamic color tuning (DCT), where the displacement of periodic nanostructures is controlled to generate different colors in real time, is one of the great possibilities of plasmonic metasurfaces for optical strain sensors or display devices. In this study, an Al metasurface embedded in an elastomer nanosheet with film thickness 400 nm is fabricated by means of sacrificial release using a polyvinyl alcohol sacrificial layer. This plasmonic metasheet shows not only the seven colors produced by surface plasmons, but also DCT by stretching the elastomer nanosheet. Each pixel, designed with a grating period of 300–600 nm, emits the bright colors expected in electromagnetic simulation. Moreover, stretching the plasmonic metasheet demonstrates DCT from 495 to 660 nm in the visible light range. The freestanding metasheet with maximum thickness 400 nm may be easily integrated into any active device by post‐processing transfer. Stretching the metasheet requires an estimated × 10−3 lower force than previously reported for plasmonic metasurfaces, owing to a film thickness of only several hundreds of nanometers. These results facilitate the realization of microdevices with novel capabilities based on plasmonic metamaterials. [ABSTRACT FROM AUTHOR]

We study the near-field radiative heat transfer between two twisted finite-size polar dielectric nanoparticle gratings. Different from previous studies of the same configuration, we do not rely on any approximated effective medium theory to describe the gratings. By the full many-body radiative heat transfer theory, we are able to investigate how the size, distance, and relative orientation between the gratings influence the radiative heat flux. By changing the twisting angle θ, we show a significant oscillation of the thermal conductance G (θ) , due to the size effect for gratings of both square and circular shapes. The distance- and twisting-dependent coupling between the gratings accounts for a strong and characteristic modulation of radiative thermal conductance with implications for the energy management, sensing, and the micro-electromechanical system (MEMS) and nano-electromechanical system (NEMS) devices. [ABSTRACT FROM AUTHOR]

We report on the use of ultra-high frequency photoacoustics to detect gratings with linewidths as narrow as 75 nm, buried underneath optically opaque metal layers. Our results show that buried gratings can be detected by observing diffraction from the spatially periodic acoustic replica of the buried grating at the glass/metal interface and from replicas of the acoustic wave inside the glass substrate. The measured diffraction signals show a linear dependence on grating duty cycle rather than the expected quadratic one. We find that this is due to the presence of a coherent background optical field, which interferes with and coherently amplifies the weaker fields diffracted off the grating-shaped acoustic waves. Our measurements show that ultra-high frequency photoacoustics is a promising technique for detection of sub-wavelength periodic nanostructures. [ABSTRACT FROM AUTHOR]

Experimental results on effective two-wave mixing (TWM) via dynamic population gratings in saturable erbium doped fibers (EDFs) at liquid nitrogen temperature (77 K) are reported. It is shown that formation of the spectral holes (SHs) by the recording coherent waves in the wavelength region 1500–1540 nm results in a complex dynamics of the transient TWM response. In addition to conventional slow, even-type response due to amplitude grating formation via spectrally uniform EDF absorption saturation we also observed a dominating contribution due to SH formation. In particular, at the recording wavelength 1527 nm the relaxation time of the SH contribution to the TWM process was significantly shorter (< 4.7 ms) and with the effective recording power ∼4 times lower than that for conventional EDF population grating. [ABSTRACT FROM AUTHOR]

Period tunability of gratings is extremely desirable for reconfigurable optics. In this study, we report a period-tunable metagrating featuring a bi-layered structure of silicon subwavelength gratings to form a Moiré pattern. Our design is based on the near field Moiré effect and employs the leaky mode resonance to enhance the far-field diffraction. The period of the metagrating can be continuously tuned to its double with the in-plane rotation of the silicon subwavelength gratings. Our simulations indicate that the metagrating exhibits efficient polarization-sensitive diffraction during period-tuning near 1550 nm. Potentially, this metagrating with a wide range of period tunability can be instrumental in developing versatile active optical applications. [ABSTRACT FROM AUTHOR]

In nanolithographic metallic gratings we investigate the dependence of photonic band gaps on geometrical parameters. Finite element modeling was used to develop a model for an optoelectronic device with periodicity of 470 nm and concomitantly the electronic response of a nanofabricated metal-semiconductor-metal photodetector grating was experimentally studied under a sweeping monochromatic light source. The grating spectral response increased in the region between 470 nm and 520 nm, corroborating the computational results. This increase is understood to occur because photons with wavelength shorter than approximately 520 nm are energetic enough to excite interband transitions in the Au, but the period of the structure acts as a cutoff where incident photons with wavelength shorter than the period are less likely to form surface plasmon polaritons. This cutoff originates from a photonic band gap. Magnetic field intensity profiles at the 3 dB cutoff indicate that a surface plasmon wave exists where each finger interacts with the next through overlapping magnetic fields, suggesting that the cutoff is a surface plasmon wave effect. Localized surface plasmon effects were observed at longer wavelengths in the modeled absorbance. The effects of three geometrical parameters on the spectral dependence of modeled absorbance were investigated. [ABSTRACT FROM AUTHOR]

We analyse, using integral equations and a previously developed in-house numerical algorithm, the scattering and absorption of the H-polarized plane wave by a metasurface consisting of a double-layer grating of flat graphene strips placed into a lossless dielectric slab. The algorithm is meshless and its convergence is guaranteed mathematically. It is a version of the method of analytical preconditioning; namely, it uses the set of weighted Chebyshev polynomials as expansion functions in the discretization of a hypersingular electric field integral equation for the on-strip current. Then the computational error is controlled by the matrix size and can be reduced to machine precision. Using this advanced tool, we plot the frequency dependences, in a huge range from 1 GHz to 10 THz, of the transmittance, reflectance and absorbance of such a metasurface. This accurate analysis reveals resonances on several types of natural modes, best understood via visualization of in-resonance near-fields. In addition to plasmon-mode resonances, special attention is paid to the ultra-high-Q resonances on the lattice modes, which are absent on the free-standing graphene strip gratings. [ABSTRACT FROM AUTHOR]

In this study, volume-phase gratings (VPGs) were fabricated inside Ge–As–S chalcogenide glasses (ChG) with femtosecond-laser writing technology. VPGs with high thicknesses were obtained through single-step writing by exploiting the self-focusing effect of highly nonlinear ChGs. The clear diffraction patterns and high diffraction efficiency of the prepared gratings indicated their high optical performance. Testing results showed that the diffraction efficiency of VPGs first increased with laser pulse energies and then decreased when the laser damage threshold of the glass reached 9.42 nJ. Grating thickness also exhibited the same trend as laser pulse energies and reached the maximum value of 28 μm at 9.42 nJ. The changes in the refractive indexes of volume gratings fabricated under different laser pulse energies were carefully investigated. The changes in the refractive indexes of the gratings remained at the same level while laser pulse energy was increased. Meanwhile, grating thickness played a key role in diffraction efficiency. The maximum diffraction efficiency of the prepared VPGs reached 50% at 808 nm under optimized laser parameters. [ABSTRACT FROM AUTHOR]

To realize a surface plasmon resonance-enhanced zinc oxide (ZnO) ultraviolet photodetector based on a sub-wavelength metal grating, we take advantage of the sensitivity of the resonance condition of a sub-wavelength metal grating to the refractive index of the surrounding medium. We theoretically design a sub-wavelength Ag grating covered with a high-refractive-index medium layer and apply it to a ZnO ultraviolet photodetector. By optimizing the parameters (angle of incidence, grating period, grating spacing, grating thickness, high-refractive-index medium layer thickness, refractive index of the covering), the optical field is localized at the interface of the sub-wavelength Ag grating and the ZnO thin film; that is, surface plasmon resonance is realized within the device. Compared with the device without a high-refractive-index medium layer, the maximum absorption enhancement factor of the designed device can reach up to 108. This work will provide theoretical guidance to realize a surface plasmon resonance-enhanced ZnO ultraviolet photodetector with a sub-wavelength metal grating. [ABSTRACT FROM AUTHOR]