Stripe Width Research Articles

A novel mid-infrared thermal emitter with ultra-narrow bandwidth and large spectral tunability based on the bound state in the continuum

The development of efficient, compact and low-cost mid-infrared (MIR) sources with easy manufacturing is vital in a variety of applications including gas sensing, thermal photovoltaic power generation, infrared imaging, among others. In this work, we demonstrate that a novel type of MIR thermal emitters with ultra-narrow bandwidth and broad spectral tunability can be realized based on a new operation principle employing the concept of bound state in the continuum (BIC). Using an elaborately designed structure composed of two interdigitated gratings with the same pitch and different stripe width on a slab supported by a conducting substrate, the quasi-BIC mode with both ultra-high Q-factor (>104) and large absorbance/emittance can be achieved, resulting from the destructive interference between the couplings of two guided-mode resonances back to free space. At the operation wavelength of 7.7851 μm, even when the metal dissipation is considered, a near-unity emission at resonance with the full-width at half-maximum less than 0.3 nm is numerically presented, which is three orders of magnitude narrower than conventional metallic metamaterial based thermal emitters. By applying a geometrical scaling of the structure, the operation wavelength can be flexibly extended to other wavelengths of the MIR region. The presented novel thermal emitter with economic advantages and high performances of both ultra-narrow bandwidth and broad wavelength-tunability, will make great impact in practical applications.

Alternating defects and egg and dart textures in de-wetted stripes of discotic liquid crystal

ABSTRACT Isotropic phase de-wetting of discotic liquid crystals on a surface patterned with alternating ~5-10 μm wide wetting and de-wetting stripes results in the formation of long narrow droplets. On slow cooling into the columnar phase, the liquid crystal aligns such that the columns lie either across or along the stripes. However, if the stripes are wider and/or the cooling rate is too fast, defects appear. When there are many such defects, the result is complex zigzag and wavy line optical textures, which are reminiscent of the egg and dart friezes associated with classical architecture. To a first approximation, all of these patterns can be seen as joined up fragments of developable domains in which the columns either circle a defect or propagate in a straight line. They are built up from motifs that involve bend but not splay or twist deformations; deformations that leave the two-dimensional lattice of the columnar phase unchanged. As is shown, these basic circular and straight-line motifs can be combined in a variety of different ways along the stripe but, in all of these, it is found that the defects alternate from side to side.

>25 W pulses from 1.5 μm double‐asymmetric waveguide, 100 μm stripe laser diode with bulk active layer

The experimental characterization of a high-power pulsed semiconductor laser operating in the eye-safe spectral range (wavelength around 1.5 μm), with an asymmetric waveguide structure, a 100 μm wide stripe, and a bulk active layer positioned very close to the p-cladding, is reported. An anti-reflection/high reflection coated laser with a stripe width of 100 μm exhibits a single-facet output power over 25 W at a pumping current amplitude of 100 A.

Universality of stripe domain width change by an in-plane magnetic field

We establish a model for a stripe domain pattern width change under hard-axis magnetic fields in a perpendicularly magnetized system with Dzyaloshinskii–Moriya interaction. With the presence of hard-axis magnetic fields, tilted magnetizations in domains modulate an exchange interaction, a perpendicular magnetic anisotropy and a dipole–dipole interaction into specific forms, which are the main competing interactions to determine the specific form of the stripe domain. In addition, we found that the stripe domain pattern change under a hard-axis perturbation can be analyzed by only considering the amount of magnetization tilting from the initial easy-axis. The proposed model was used to draw a single universal curve for stripe width change as a function of the hard-axis magnetic fields.

6.5: Highly reliable 1W 638nm Laser Diode

We report the reliability test of tensile‐strained GaInP quantum‐well single‐emitter lasers of 638‐nm wavelength for RGB laser projection. P‐side‐down submounted multimode lasers with 110 μm stripe width were subjected to long‐term aging tests at the CW current of 1.5 A and the heat sink temperature of 25 Celsius. Except failures caused by current over‐surging, no devices have failed during the long‐term aging tests. The longest test has accumulated 22297.7 hours and the power degrading coefficient is approximately 3%/10000 hours.

Performance characteristics of low threshold current 1.25 μm type-II GaInAs/GaAsSb ‘W’-lasers for optical communications

Type-II ‘W’-lasers have made an important contribution to the development of mid-infrared laser diodes. In this paper, we show that a similar approach can yield high performance lasers in the optical communications wavelength range. (GaIn)As/Ga(AsSb) type-II ‘W’ structures emitting at 1255 nm have been realised on a GaAs substrate and exhibit low room temperature threshold current densities of 200–300 A cm−2, pulsed output powers exceeding 1 W for 100 µm wide stripes, and a characteristic temperature T 0 ≈ 90 K around room temperature. Optical gain studies indicate a high modal gain around 15–23 cm−1 at 200–300 A cm−2 and low optical losses of 8 ± 3 cm−1. Analysis of the spontaneous emission indicates that at room temperature, up to 24% of the threshold current is due to radiative recombination, with the remaining current due to other thermally activated non-radiative processes. The observed decrease in differential quantum efficiency with increasing temperature suggests that this is primarily due to a carrier leakage process. The impact of these processes is discussed in terms of the potential for further device optimisation. Our results present strong figures of merit for near-infrared type-II laser diodes and indicate significant potential for their applications in optical communications.

Surface acoustic wave assisted depinning of magnetic domain walls

We investigate the effects of high frequency strain on the depinning of magnetic domain walls in perpendicular anisotropy materials. Micron wide stripes of [Co(0.3 nm)/Pt(0.6 nm)]5 are patterned between a pair of identical inter-digital transducers that generate high frequency (114.8 MHz) standing surface acoustic waves. We use magneto-optical Kerr effect microscopy to characterize the thermally-assisted depinning of domain walls at defect sites within the strips. Our results show that the excitation of the domain walls with surface acoustic waves results in an increase in their depinning probabilities by approximately a factor of 10. Our data are consistent with a model in which the magnetoelastic anisotropies induced by the acoustic waves modulate the energy barriers that pin the domain walls. These results suggest an alternative route to domain wall depinning in thin films and nanostructures and are relevant to the development of racetrack memories, where domain wall pinning can result in reduced velocities and non-deterministic motion.

Phase diagram of the two-dimensional dipolar Heisenberg model with Dzyaloshinskii-Moriya interaction and Ising anisotropy

We study phase transitions in the two-dimensional Heisenberg model with Dzyaloshinskii-Moriya interaction, Ising anisotropy $\ensuremath{\eta}$, and dipolar interaction under zero and finite magnetic fields $H$. For three typical strengths (zero, weak, and strong) of the dipolar interaction, we present the $H\text{\ensuremath{-}}\ensuremath{\eta}$ phase diagrams by estimating order parameters for skyrmion-lattice and helical phases and in-plane magnetization using a Monte Carlo method with an $O(N)$ algorithm. We find in the phase diagrams three types of skyrmion-lattice phases, i.e., two square lattices and a triangular lattice, helical phases with diagonal and vertical (or horizontal) stripes, a canted ferromagnetic phase, and a polarized ferromagnetic phase. The effect of the dipolar interaction varies the types of the skyrmion and helical phases in a complex manner. The dipolar interaction also expands the regions of the ordered phases accompanying shifts of the phase boundaries to the positive $H$ and $\ensuremath{\eta}$ directions and causes an increase of the density of skyrmions and shortening of the pitch length (stripe width) of helical structures. We discuss the details of the features of the phase transitions.

Modelling the influence of process parameters on precipitate formation in powder-bed fusion additive manufacturing of IN718

In this work, we have developed a two-scale (finite element + phase field) model for simulating the precipitate evolution in IN718 in powder-bed fusion additive manufacturing. The thermal simulations at the scale of the component are resolved at the level of a single stripe of the scan path. This resolution allows to model various process parameters (or scan strategies) in complex geometry domains, here demonstrated by an impeller, and predicts the complete thermal history within each finite element layer. The predicted thermal history is in-full passed to multiple phase-field simulation representative volume elements (RVEs) that explicitly model the evolution of the γ′ and γ″ precipitates in various locations of the impeller. We simulate the precipitate microstructures in different regions of the impeller and demonstrate the influence of process parameters on the volume fraction, size, and shape of the precipitates. Although no precipitates are found to form during the standard printing conditions (for instance EOS M290), we show that changing the process parameters such as stripe width or chamber temperature may induce significant precipitation in the as-built component.

A Framework in Calibration Process for Line Structured Light System Using Image Analysis

Line structured light systems have been widely applied in the measurement of various fields. Calibration has been a hot research topic as a vitally important process of the line structured light system. The accurate calibration directly affects the measurement result of the line structured light system. However, the external environment factors, such as uneven illumination and uncertain light stripe width, can easily lead to an inaccurate extraction of light stripe center, which will affect the accuracy of the calibration. An image analysis-based framework in the calibration process was proposed for the line structure light system in this paper. A three-dimensional (3D) vision model of line structure light system was constructed. An image filtering model was established to equalize the uneven illumination of light stripe image. After segmenting the stripe image, an adaptive window was developed, and the width of the light stripe was estimated by sliding the window over the light stripe image. The light stripe center was calculated using the gray centroid method. The light plane was fitted based on the calibration points coordinates acquired by the camera system. In the measurement experiment of standard gauge block width, the maximum and minimum average deviations of 0.021 pixels and 0.008 pixels and the maximum and minimum absolute deviations of 0.023 pixels and 0.009 pixels could be obtained by using the proposed method, which implies the accuracy of the proposed method.

Effects of spatial heterogeneity of leaf density and crown spacing of canopy patches on dry deposition rates

Trees have a large role in improving urban air quality, among other mechanisms, through dry deposition of scalars and aerosols on leaf surfaces. We tested the role of leaf density and canopy structure in modulating the rate of dry deposition. We simulated the interactions between a virtual forest patch and deposition rate of an arbitrary scalar using the Parallelized Large Eddy Simulation Model (PALM). Two canopy structures were considered: a homogenous canopy and canopy stripes. For each canopy stripe scenario, we considered thin, intermediate, and wide stripes, while the space between stripes equals the stripes’ width. Four leaf area densities were considered for each case (LAI = 0.5, 1, 1.5, and 2). The results showed that denser canopies and canopy stripes experienced more total deposition, noting that stripes had a larger per leaf area deposition than homogeneous canopies. Our results can be explained by canopy-induced turbulence structures that couple the air within and above the canopy and lead to more effective leaf area where this coupling is stronger. We aggregate our results to the whole-patch scale and suggest a canopy-structure and leaf-area dependent correction to the canopy resistance parameter so to be used in coarse models that resolve dry deposition.

Nanoscale magnonic Fabry-P\xe9rot resonator for low-loss spin-wave manipulation

Active control of propagating spin waves on the nanoscale is essential for beyond-CMOS magnonic computing. Here, we experimentally demonstrate reconfigurable spin-wave transport in a hybrid YIG-based material structure that operates as a Fabry-Pérot nanoresonator. The magnonic resonator is formed by a local frequency downshift of the spin-wave dispersion relation in a continuous YIG film caused by dynamic dipolar coupling to a ferromagnetic metal nanostripe. Drastic downscaling of the spin-wave wavelength within the bilayer region enables programmable control of propagating spin waves on a length scale that is only a fraction of their wavelength. Depending on the stripe width, the device structure offers full nonreciprocity, tunable spin-wave filtering, and nearly zero transmission loss at allowed frequencies. Our results provide a practical route for the implementation of low-loss YIG-based magnonic devices with controllable transport properties.

Infrared high-speed thermography of combustion chamber wall impinged by diesel spray flame

As a demonstration of a new method to examine the extremely unsteady and spatially varying wall heat transfer phenomena on diesel engine combustion chamber wall, high-speed imaging of infrared thermal radiation from the wall surface impinged by a diesel spray flame was attempted using a high-speed infrared camera. A 35 mm-diameter chromium-coated quartz window surface was impinged by a diesel spray flame with an impinging distance of 27 mm from the nozzle orifice in a constant volume combustion chamber. The infrared thermal radiation from the back surface of the 0.6 µm thick chromium layer was successfully visualized at 10 kHz frame rate and 128 × 128 pixel resolution through the quartz window. The infrared radiation exhibited coherent and streaky structure with radial stripes extending and waving from the stagnation point. The width of the radial stripes, spatial amplitude and the period of the waving movement were comparable to the ones for turbulent heat transfer on the engine cylinder wall previously measured with a heat flux sensor, suggesting that they are resulting from the turbulent structure in the wall-impinging diesel flame. The radiation intensity was calibrated to temperature and converted to heat flux via 3-D numerical analysis of transient thermal conduction in the quartz window. The peak-to-peak variation amplitudes of temperature and heat flux among the radial stripes during the diesel spray flame impingement were about 20 K and 2.3 MW/m2, corresponding to 13% of 150 K maximum temperature swing amplitude and 18 MW/m2 maximum heat flux, respectively.

Universal method for magnetic skyrmion bubble generation by controlling the stripe domain instability

Magnetic skyrmions, which are topological swirling spin textures, have drawn much attention in spintronics because of their use as an information carrier with distinct robustness rooted in their topological nature. Real-time generation of skyrmions is therefore imperative for realizing skyrmion-based spintronic devices. However, to date, experimental demonstration has been limited to exquisite works with well-tuned samples. Here, we report a method to generate skyrmions by driving the stripe instability via an in-plane magnetic field. We have demonstrated that the key parameter determining the stripe domain instability is the stripe width, regardless of other material parameters. This skyrmion generation method can be applicable to generic magnetic films with perpendicular magnetic anisotropy. Our work will facilitate the development of skyrmion-based devices by offering a general method for controlling a large skyrmion population.

Resonant subwavelength control of the phase of spin waves reflected from a Gires\u2013Tournois interferometer

Subwavelength resonant elements are essential building blocks of metamaterials and metasurfaces, which have revolutionized photonics. Despite similarities between different wave phenomena, other types of interactions can make subwavelength coupling significantly distinct; its investigation in their context is therefore of interest both from the physics and applications perspective. In this work, we demonstrate a fully magnonic Gires–Tournois interferometer based on a subwavelength resonator made of a narrow ferromagnetic stripe lying above the edge of a ferromagnetic film. The bilayer formed by the stripe and the film underneath supports two propagative spin-wave modes, one strongly coupled with spin waves propagating in the rest of the film and another almost completely reflected at the ends of the bilayer. When the Fabry–Perot resonance conditions for this mode are satisfied, the weak coupling between both modes is sufficient to achieve high sensitivity of the phase of waves reflected from the resonator to the stripe width and, more interestingly, also to the stripe-film separation. Such spin-wave phase manipulation capabilities are a prerequisite for the design of spin-wave metasurfaces and may stimulate development of magnonic logic devices and sensors detecting magnetic nanoparticles.

An effective and efficient model for temperature and molding appearance analyses for selective laser melting process

The selective laser melting (SLM) process is an additive manufacturing technique that can fabricate three-dimensional workpiece by laser scanning and sintering of designated material in powder form on a preset scanning route along a bed of powders. This process involves a moving laser heating source which causes local transient mass and heat transfer with phase change, i.e., melting and solidifying, in a pool of melted powders. To fully investigate such a complicated transport process with reasonable computation cost, a novel quasi-transient numerical model (hopping model) was proposed and validated experimentally in this study. This approach includes a volumetric heat source defined as an elliptical Gaussian laser spot which hops along the scan path. Inconel 718 (IN718) superalloy powder is selected as the material for demonstration. Thermal analysis was carried out using a number of laser power and scan speeds in the range from 80 W to 120 W and from 80 mm/s to 140 mm/s, respectively. The comparison of molding appearance of the work pieces from the developed hopping model, full transient model, effective-transient model, and experiments illustrates the accuracy and the efficiency of the proposed hopping model. Molding appearance obtained from the quasi-transient model was consistent with experimental results with a relative error of less than 1.71% on the width of the IN718 stripes fabricated by SLM. For the cases analyzed in the current study, the quasi-transient model showed a 99% and a 60% reduction in both the computation time and the amount of computer memory needed compared to the full transient model and the effective-transient model, respectively. This novel quasi-transient simulation technique can be used to rapidly and effectively optimize process parameters for intelligent additive manufacturing.

Study of magnetization reversal in Néel and Bloch regime of nickel and permalloy stripes using Kerr microscopy

We present a systematic study of the magnetization reversal of nickel and permalloy micro-stripes with Néel and Bloch domain walls using Kerr microscopy. Magnetic field driven domain propagation was observed from higher width to lower width stripes for magnetic fields applied along the length of micro-stripes. Stripe like domains were observed with nucleation starting in lower width region followed by their propagation to higher width regions for magnetic fields applied along the width of micro-stripes. The comparison of magnetization reversal in Bloch and Néel domain wall regime showed higher domain wall density in Bloch regime for both nickel and permalloy stripes.

Research on laser stripe characteristics and center extraction algorithm for desktop laser scanner

This study presents laser stripe center extraction algorithm for desktop-level 3D laser scanners. The laser stripe center extraction accuracy is an important factor affecting 3D scanning result. Desktop-level devices should have adaptability of a wide range of scanning objects. In this paper, laser stripe energy distribution characteristics with different laser stripe width, ambient light, materials and colors are obtained by experiments. Experiment results show that waveforms of bright spot, low brightness stripe and stripe with large width are complex or easily disturbed, so the center extraction algorithm of them are studied. The extraction effects of extremum method, gradient method and gray centroid method under different conditions are compared. Based on traditional grayscale value, a weighted grayscale value is proposed to extract laser stripe center. Standard deviations of extracted pixel position and fitting pixel position are calculated by different method with different weighted grayscale value. For different conditions, especially for different ambient light intensity, weight matrix plays an important role to extraction result.

Speckle contrast evaluation of multi-emitter broad area 638-nm red laser diodes

Speckle contrast of single, dual, and triple emitter broad area laser diodes (BA-LDs) with a wavelength of 638 nm was experimentally investigated. Speckle noise was relatively small near the threshold current probably due to the longitudinal mode competition. Higher output power led to smaller speckle noise owing to the spectrum widening. A wide stripe presented an advantage in terms of speckle reduction in the single emitter LDs. It is also found that wider emitter width leads to the smaller the speckle noise. A larger number of emitters decreased speckle noise due to the beam superposition effect, even for multi-emitter LDs in which the emitters are built into one chipa.

18.2: Invited Paper: Single‐emitter 638nm laser diode with 4W continuous wave power

High‐power red laser diodes are essential light sources for display applications. In this paper, we report the design, fabrication and characterization of single‐emitter 638nm laser diode with 4 W continuous wave power. The saturation and COD power of this 110um stripe width LD exceeds 4.0 W and 6.3 W at heatsink temperature of 20°C, respectively. At the operation power of 1 W, the Wall‐Plug efficiency can reach 38.3% and 41.8% for the continuous and pulsed wave with duty of 33.3%. The characteristics temperature T0 and T1 for this device is 62 K and 114K.