Steep Edge Research Articles

Picosecond pulsed flat-top beam in a mode-locking all-fiber laser.

Ow7ing to the flat center and steep edge, the flat-top beam is widely used in the fields of micromachining and optical image processing. Here, we propose an efficient scheme to generate a picosecond pulsed flat-top beam in a mode-locking all-fiber laser. After utilizing an orthogonal polarization method for complete incoherence and a high-precision all-fiber optical delay line (ODL) for rigorous time synchronization, the pulsed fundamental mode (LP01) and the pulsed vortex beam (VB) are superimposed to generate a pulsed flat-top beam. The pulsed flat-top beam has a duration of 6.10 ps, with a normalized root mean square (NRMS) variation of 0.049 and a steep degree value of 0.876, indicating an excellent beam quality. In addition, the effect of coherence between the two superimposed beams on the quality of the combined beam has also been investigated. This is the first, to the best of our knowledge, demonstration of a picosecond scale pulsed flat-top beam in the mode-locking all-fiber laser, which may greatly promote its application in laser processing and biomedicine.

Merging of quasi-bound states in the continuum and Wood anomalies in terahertz metasurfaces based on complementary periodic cross-shaped resonators

Metasurfaces provide an ideal platform for controlling the merging of multiple modes owing to trimmable periodic meta-atoms. In this work, a terahertz metasurface based on complementary periodic cross-shaped resonators (CPCRs) with mixed modes is demonstrated. The CPCRs support sharp quasi-bound states in the continuum (quasi-BICs) by introducing an offset parameter. The optical response of quasi-BICs such as frequency shift and Q-factor can be optimized by tuning offset parameters. As such parameter increases, a mixed mode originating from quasi-BICs and Wood anomalies appears. The merged resonance has a narrow bandwidth with steep edges and thus can serve as bandpass filters. Simulated electric field distributions reveal the special patterns for these modes. Owing to the effect of quasi-BICs, Wood anomalies exhibit different field patterns in contrast to those of pure modes. These results prove the possibility of multimode merging in metallic metasurfaces, which is beneficial for terahertz applications such as sensing and wave filters.

Bulk acoustic wave—Solidly mounted resonator with a-SiOCN:H as low-Z material

Bulk acoustic wave (BAW) filters have been proven to be of high demand in today's low power RF front-ends for mobile communication devices. Within the launch of 5G applications worldwide, especially in the region of new radio (nr-1) up to 6 GHz, defined frequency bands require filters of wide bandwidths, while simultaneously featuring steep edges and high out-of-band rejection. Due to the coexistence with 4G LTE (long term evolution) wireless standards as well as advanced data transfer concepts such as carrier aggregation, the increasing complexity of antenna systems forces the implementation of highly selective acoustic filters. In contrast to the widely used surface acoustic wave (SAW) technology, BAW filters appear with superior performance for frequencies above 1 GHz. This work describes the fabrication of a BAW-solidly mounted resonator (BAW-SMR) with a tailored material system of a-SiOCN:H as a low impedance (low-Z) material integrated within its acoustic Bragg mirror. A direct comparison to the widely used low-Z material of SiO2 with an acoustic impedance of around 13 MRayl is demonstrated by two equal resonator stacks by replacing only the uppermost low-Z thin film of the acoustic reflector. A single-mask design was chosen with platinum as a bottom electrode to ensure the most equal growth conditions for the piezoelectric aluminum nitride (AlN) layers on both reflectors’ surfaces featuring either the tailored a-SiOCN:H or standard SiO2. The a-SiOCN:H thin films were deposited by plasma-enhanced chemical vapor deposition and the according acoustic impedance was priorly depicted to 7.1 MRayl, which could be exploited to achieve an increase in the effective coupling coefficient beyond 7% as well as a resonator bandwidth of more than 60 MHz.

Measurement of pulse current during high voltage tests using Rogowski coil with non-inverting integrator

The work is devoted to the development and modelling of the system of pulse current measurement during high-voltage tests and experiments. The proposed measurement system is based on the application of Rogowski coil with non-inverting integrator. The results of numerical modelling of the developed current measurement system are compared with the results of application of a low-inductance shunt resistor, Rogowski coil with passive RC-integrator and Rogowski coil with inverting active integrator in similar measurement systems. Various standard pulse currents including steep edge pulse (1/20 µs), large amplitude current pulse (4/10 µs), lightning pulse current (8/20 µs), switching pulse current (30/80 µs), and 1-3 ms pulse currents are modelled for the comparative test. From the simulation results, it follows that the developed Rogowski coil with the proposed non-inverting integrator has sufficiently high accuracy in a wide frequency band overlapping the frequency band of standard pulse currents in high-voltage tests.

Structural phase transition and optical properties of zero-dimensional cobalt bromide hybrid material

Zero-Dimensional (0D) metal halide materials have recently emerged as a class of potential optoelectronic materials because of the structural diversity and superior photophysical properties. Here we report a 0D cobalt bromide hybrid material, [Br(CH2)3NH3]2CoBr4 (BPA-CoBr4, BPA=Br(CH2)3NH3, 3-Bromopropylamine), in which the isolated metal halide tetrahedron (CoBr42-) is completely separated each other and surrounded by the organic ligand Br(CH2)3NH3+. Differential scanning calorimetry (DSC) measurements exhibit BPA-CoBr4 undergoes a first-order structural phase transition, as clearly visible to a pair of weak peaks at 340 K (heating) and 317 K (cooling). Single crystal X-ray diffractions were carried out at 293 K and 360 K to explain the phase transformation mechanism, indicating it is an isostructural order–disorder type. The crystal structures which both crystalize in a monoclinic P21/c crystal symmetry and the most distinct difference between room-temperature and high-temperature structures is the order–disorder transition of the 3-Bromopropylamine, which is the driving force of the phase transition. The UV–vis absorption spectra reveal that BPA-CoBr4 has a steep absorption edge at 280 nm corresponding to photo energy of 4.4 eV. The density functional theory (DFT) calculations were performed to study the electronic structure with narrower indirect bandgap 3.9 eV which is lower than the experimental values. PDOS plots show that the electronic states of Co-d and Br-p orbitals are mainly contributed for the VBM and CBM of BPA-CoBr4.

Two-Dimensional Amphibian Diversity along a 3500 m Elevational Gradient at the Eastern Edge of the Qinghai-Xizang Plateau.

Amphibians serve as reliable indicators of ecosystem health and are the most threatened group of vertebrates. Studies on their spatial distribution pattern and threats are crucial to formulate conservation strategies. Gongga Mountains, with a peak at 7509 m a.s.l. and running latitudinally, are in the center of the Hengduan Mountains Range and at the eastern steep edge of the Qinghai-Xizang Plateau, providing heterogeneous habitats and varied niches for amphibians. In this study, we combined 83 days of field work with information from 3894 museum specimens that were collected over the past 80 years, and identified twenty amphibian species belonging to seven families and twelve genera by morphology. Of these species, seven were listed in the threatened categories of the Red List of China's Biodiversity and thirteen were endemic to China. Ten species were found on the plateau side (western slope) and eleven species were found on the other side close to the Sichuan Basin (eastern slope). Only one species was found on both sides, indicating different community structures horizontally. The species richness was unimodal vertically and peaking at mid elevation on both sides, with the maximum number (ten vs. nine) of species occurring at 3300-3700 vs. 1700-1900 m a.s.l. and in different types of vegetation. The elevation span and body length of species distributed on both slopes did not show significant differences. These findings help to understand the horizontal and vertical distribution pattern of amphibian diversity, laying a foundation for future biogeographical and conservation research in this area.

Seasonal regulation of tidal creek burrow distribution: Unveiling the dynamic interplay of biotic and abiotic factors

Intertidal creek ecosystems in saltmarsh wetlands provide crucial ecological services, with burrows facilitating material exchange between these environments. Investigating burrow distribution in tidal creeks is essential, yet the underlying mechanisms remain poorly understood. Our study conducted field observations during two seasons, dividing the typical creek section into microhabitats: flat (F), gentle edge (GE), gentle slope (GS), steep slope (SS), and steep edge (SE). Comprehensive analysis of sediment samples encompassed assessments of water content, organic matter, particle size, and salinity. Burrow parameters were extracted using a deep learning method applied to sample images. Benthic biodiversity and community compositions were characterized through eDNA analysis. Our findings revealed significant variations in burrow distribution, sediment properties, and community compositions, both between and within creek sections. Temporal heterogeneity emerged as a substantial influencer of burrow characteristics, while the propensity of benthic communities to respond to topography and sediment properties constituted a chief determinant of burrow distribution. Utilizing a structural equation model based on field data, we illuminated four response pathways governing burrow distribution. Abiotic factors, especially under temporal heterogeneity, had a paramount impact, highlighting the need to explore relative biotic and abiotic influences, considering seasonal regulation. These findings establish a foundational understanding of burrow distribution and its driving mechanisms in creek ecosystems. They offer valuable insights for future field observations and research directions in this field.

Partial discharge diagnostics on inverter-fed drives of electric vehicles

In this paper, the possibilities of partial discharge measurement at square-wave voltages are discussed. The focus is on low-voltage machines, such as those used in electric vehicles. An insight into common measurement methods is given. In this work, high-frequency current transformers and near-field probes are used as sensors. The generation of a realistic steep-edged test voltage according to IEC/TS 61934 is also discussed and demonstrated on an inverter with silicon carbide semiconductors.Experiments are conducted to compare the sensors used. A direct comparison between cable-based sensors (HFCT) and antennas (near-field probes) is provided. Resonance points to open motor windings according to IEC/TS 60034-27‑5 and their significance for partial discharge measurement are also investigated. The results show that the high-frequency current transformers and the ball probe are able to detect PD even at steep voltage edges. Excitation with a fast voltage edge results in non-negligible overshoots in the overall system due to resonances. It can be shown that the partial discharges occur during these overvoltages.

Core-Shaped Tools from the Early Pleistocene Deposits at Bairaki, Moldova

This a rticle deals with a series of core-shaped tools from Early Pleistocene deposits (layers 5 and 6) of the stratifi ed site of Bairaki, located on high above-fl oodplain terrace VII of the Dniester, in the outskirts of Dubăsari, Moldova. The site was discovered in 2010 by the joint Russian-Moldovan archaeological expedition and excavated in 2011– 2014. The interdisciplinary studies revealed six layers with Early Paleolithic artifacts. Two lowest layers (5 and 6) are associated with the channel alluvium of terrace VII. The paleomagnetic studies have shown that these deposits correspond to the Jaramillo episode of the Matuyama epoch. The lithic industry of layers 5 and 6 are comparable to the Late Oldowan. Most artifacts are made of poor quality fl int; there are also pebble tools made of non-silicic rocks. Most lithics are small. A distinct series of core-shaped end-scrapers and side-scrapers made on residual cores (9 spec.), fragments (1 spec.), and fl akes (5 spec.) is identifi ed. All these tools are robust and had been processed in a similar way. They are made of pebbles no larger than 6 сm. The steep working edges of all implements in this series are heavily retouched. Similar items have been recorded from the Early Paleolithic materials of the region. Such tools were widespread in the Early Paleolithic of Africa and Eurasia. The earliest pieces were found in the Bed I assemblage of the Olduvai Gorge.

Coherent pulse generation based on noise-like-pulse pumped Raman amplification

The coherent Raman pulse generation based on the noise-like-pulse (NLP) pumped Raman amplification is numerically investigated in the cases with weak and strong walk-off effects between the pump and Stokes pulses. In the former case, the amplified Stokes pulse suffers from the temporal and spectral distortions because the random time-varying intensity profile of the NLP can be transferred to the Stokes pulse through combined effects of cross-phase modulation (XPM), stimulated Raman scattering (SRS), and spontaneous Raman scattering. In the latter case, the heavily germanium-doped fiber with large normal dispersion is firstly used as the Raman gain medium to improve the walk-off effect and Raman gain. As a result, the Stokes pulse can be amplified undistorted and possess linear frequency chirp and conversion efficiency of up to 82.4 %. Further, it is important to note that the NLP-pumped Raman fiber laser based on the large normal dispersion fiber can generate the Stokes pulse with linear frequency chirp, narrow temporal duration, and dissipative-soliton-like spectrum with steep edges, even though the saturable absorber is not introduced into the Raman fiber cavity.

Characterization and assessment of projection probability density function and enhanced sampling in self-collimation SPECT.

We have recently reported a self-collimation SPECT (SC-SPECT) design concept that constructs sensitive detectors in a multi-ring interspaced mosaic architecture to simultaneously improve system spatial resolution and sensitivity. In this work, through numerical and Monte-Carlo simulation studies, we investigate this new design concept by analyzing its projection probability density functions (PPDF) and the effects of enhanced sampling, i.e. having rotational and translational object movements during imaging. We first quantitatively characterize PPDFs by their widths and edge slopes. Then we compare the PPDFs of an SC-SPECT and a series of multiple-pinhole SPECT (MPH-SPECT) systems and assess the impact of PPDFs - combined with enhanced sampling - on image contrast recovery coefficient and variance through phantom studies. We show the PPDFs of SC-SPECT have steeper edges and a wider range of width, and these attributes enable SC-SPECT to achieve better performance.

Металлургический «завод» раннего железного века в Уральских горах

The authors describe the westernmost metallurgical center of the 5th—2nd centuries BC left by the aboriginal Itkul’ culture of the forest Trans-Urals in 8th/7th—3rd/2 nd centuries BC. It was founded in the upper reaches of the Ufa river, in Serny Klyuch tract, on top of a high (20—25 m) limestone rock with three steep edges, on the ruins of sites and settlements of the Eneolithic and Bronze Age. After the construction of the first copper-smelting complexes, the site of the settlement from the floor side was fenced with a log defensive wall with an external moat 40—42 m long. The ancient settlement is miniature, with an area of about 1,000 sq. m. Two excavations (502 sq. m) explored half of the site and 26 m of the fortification line. The remains of 19 adobe blast furnaces, three adobe platforms for metal processing, several pits and fireplaces for melting metal, three industrial and residential buildings of a frame-and-pillar structure were uncovered. In addition to the clan of metallurgists of the aboriginal Itkul’ culture, the population of the settlement included small groups of newcomers: initially, the descendants of the taiga communities of the Gamayun culture, who migrated from the north, from the upper reaches of the Iset’ river, later — the bearers of the Gorokhovo culture, who fled from the Tobol region and the lower reaches of the Iset’ river under the pressure of the warlike Sargat tribes, the ancient ancestors of the Hungarians who came from the east, from the Ishim-Irtysh forest-steppe. Traces of full cycle metallurgical production were revealed on the site — from copper smelting to casting and forging of finished products. The main part of non-ferrous metal produced by metallurgists of the mountain-forestry Trans-Urals was intended for export to neighboring and more distant territories. A blank of an iron knife-dagger found in one of the furnaces, and a series of Itkul’ iron products found in other places, confirm the hypothesis of the emergence of its own ferrous metallurgy in the forests of the Middle Urals around the 5 th—4 th centuries BC.

The Sonnets: Including the Erotic Sonnets, the Crimean Sonnets, and Uncollected Sonnets [Sonety

The Sonnets: Including the Erotic Sonnets, the Crimean Sonnets, and Uncollected Sonnets [Sonety

High order coupled microring resonator filters for on-chip optical interconnects with steep edge response

ABSTRACT In this paper, high-order microring resonator filters coupled serially up to the 7th order are proposed for on-chip optical interconnects. This work mainly focuses on achieving a flat-top, higher out-of-band rejection ratio, and enhanced group delay value than previously demonstrated microring filters. Further, the effect of varying inter-resonator coupling coefficients on the filtering operation of wavelength 1552 nm is investigated, using the continued fraction method, and optimum conditions for coupling coefficients between ring-ring waveguides are realized to obtain steep edge response. The proposed design exhibits a minimum group delay of 7.457 ps at a coupling value of 0.04.

Morphological Characteristics and Printing Mechanisms of Grid Lines by Laser-Induced Forward Transfer

Laser-induced forward transfer (LIFT) is an innovative metallization technique used in the processing of grid lines of solar cells for the photovoltaics industry. A study on the morphology and transfer mechanisms of formed lines with high-viscosity silver paste and small gap was performed in this paper. There were three different transfer states under different laser fluences: non-transferred lines or transferred but no continuous lines, continuous transferred lines, and explosive transferred lines. There was a critical transfer threshold for the continuous line transfer under different processing speeds. Higher processing speed required a larger critical transfer threshold. The line width increased as the laser fluence increased. For all continuous formed lines, the cross-sectional morphologies with single and double peaks were shown at critical and above transfer threshold, respectively. Two symmetrical protrusions with steep edges were observed for the formed line with double peaks. By comparing the silver paste remaining on the donor and transferred to the acceptor under different laser fluences, it can be found the transferred silver paste exhibited a retracting characteristic under the critical and above transfer threshold. While a stretching characteristic was obvious when the laser fluence was much higher than the transfer threshold. Morphological characteristics with single or double peaks were determined by the distance between the rupture position of the bridge and the bottom of the bubble, under the action of the axial combined forces. This work can provide insights for improving fine-line metallization and understanding transfer mechanisms in the photovoltaic application and flexible electronics devices.

Simulation for generation of several kinds of solitons in anomalous dispersion erbium-doped fiber lasers

We numerically demonstrated seven types of solitons in an anomalous dispersion erbium-doped fiber laser, including conventional soliton (CS), dissipative soliton (DS), dissipative soliton resonance (DSR), two- and triple-soliton bound states, and period doubling and period tripling solitons. We found that DSR is achieved when the net cavity dispersion is large. CS with a narrow pulse width is obtained in the near-zero dispersion region, and period doubling and period tripling solitons are achieved around CS by properly adjusting the polarization state. The large net cavity dispersion and high gain saturation energy contribute to the generation of DS. Furthermore, further increasing the gain saturation energy under specific dispersion condition enables DS to transform into two- and triple-soliton bound states, and bound states have smooth spectral profiles and steep edges similar to DS. Furthermore, the influence of the net cavity dispersion and gain saturation energy on pulse type is diagrammed intuitively.

Myeloma bone disease imaging on a 1st-generation clinical photon-counting detector CT vs. 2nd-generation dual-source dual-energy CT

ObjectiveSubjective and objective image quality comparison of bone microstructure and disease-related abnormalities in multiple myeloma patients using a 1st-generation dual-source photon-counting detector CT(DS-PCD-CT) and a 2nd-generation dual-source dual-energy (energy-integrating detector) CT (DS-EID-CT).MethodsFifty multiple myeloma patients (mean age 67.7 ± 10.9 years,16 females) were prospectively enrolled. Unenhanced whole-body CTs were clinically indicated and performed on DS-EID-CT and DS-PCD-CT (median time difference: 12 months). DS-PCD-CT was performed in Quantumplus UHR mode and DS-EID-CT was performed using dual-energy mode. DS-PCD-CT kernel was set at Br64 with Quantum iterative reconstruction strength Q1; for DS-EID-CT a comparable I70f kernel with SAFIRE iterative reconstruction strength 1 was used. Two independent radiologists assessed image quality subjectively using a 5-point Likert scale considering delineation and sharpness of trabecular bone and lytic bone lesions in the spine and pelvic bones. Additionally, ImageJ was used for quantification of bony septa inside the cancellous bone and through or the edges of osteolysis.ResultsOverall quality as well as detectability and sharpness in the delineation of lytic bone lesions were superior for DS-PCD-CT compared with DS-EID-CT (p < 0.0001). The inter-reader agreement for subjective image quality readings showed excellent consistency(α = 94.2–98.8). CTDI and DLP mean values for DS-PCD-CT and DS-EID-CT were 1107.4 ± 247.6 mGy*cm and 8.2 ± 1.8 mGy vs. 1344.3 ± 204.6 mGy*cm and 10.1 ± 1.9 mGy. The quantitative metric for bone microstructure in the femoral head showed significantly better visualization of trabeculae in DS-PCD-CT compared with DS-EID-CT (p < 0.0001). Quantitative analyses of edge sharpness of osteolysis showed significant steeper edges for DS-PCD-CT (p < 0.0001).ConclusionDS-PCD-CT significantly improves spatial resolution of bony microstructure and lytic bone lesions compared to DS-EID-CT.Key Points• Application of photon-counting detector CT is superior to dual-source dual-energy integrating detector in clinical workup of multiple myeloma patients.• Compared to energy integrating detectors, photon-counting detectors significantly increase the spatial resolution of bone microstructure including disease-related lytic bone lesions in patients with multiple myeloma.

Nearly degenerate two-color impulsive coherent Raman hyperspectral imaging.

Impulsive stimulated Raman scattering (ISRS) is a robust technique for studying low frequency (<300cm-1) Raman vibrational modes, but ISRS has faced difficulty in translation to an imaging modality. A primary challenge is the separation of the pump and probe pulses. Here we introduce and demonstrate a simple strategy for ISRS spectroscopy and hyperspectral imaging that uses complementary steep edge spectral filters to separate the probe beam detection from the pump and enables simple ISRS microscopy with a single-color ultrafast laser source. ISRS spectra are obtained that span from the fingerprint region down to <50cm-1 vibrational modes. Hyperspectral imaging and polarization-dependent Raman spectra are also demonstrated.

Influence of growth rate on homoepitaxial growth of AlN at 1450 °C by hydride vapor phase epitaxy

The influence of growth rate on the homoepitaxial growth of AlN at 1450 °C by hydride vapor phase epitaxy on bulk AlN(0001) substrates was studied. X-ray diffraction and Raman spectroscopy revealed that high structural quality comparable to that of the initial substrate can be achieved even when the growth rate is increased to over 150 μm h−1. Although the concentration of Si impurities increased with increasing growth rate, a freestanding AlN substrate prepared from a homoepitaxial layer grown at 155.6 μm h−1 showed a steep optical absorption edge at 207 nm and high optical transmittance at longer wavelengths.

A DFT+U approach to doped SrTiO3 for solar harvesting applications

We present a Hubbard U optimized density functional theory based study of band gap engineered doped SrTiO3 suitable for light sensitive applications. We tune the Hubbard U parameter Uopt to match the experimental direct band gap of SrTiO3. We benchmarked the DFT+Uopt derived density of states, band structure and optical properties with that of sophisticated Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional simulations. The reliability of the DFT+U method is further tested in simulating stability of the cubic SrTiO3 from elastic tensor and density functional perturbation theory based phonon band structure calculations. Moreover, the DFT+Uopt simulated SrTiO3 Raman peaks are identified against the experimental observations found in existing literature. We red shift the energy band gap of SrTiO3 within the DFT+Uopt formalism from ultraviolet to visible range by incorporating different dopants such as Pt, S and Se which is consistent with recent HSE06 hybrid functional based simulations found elsewhere. The optical absorption simulations revealed steep absorption edges of doped SrTiO3 in the visible spectrum. Overall, the DFT+U approach successfully probed the potential of doped SrTiO3 in solar harvesting applications.