Search Results (914)

This work aims to achieve both high current emission density and high emission current of carbon nanotube (CNT) cathodes for high-power X-ray generation applications. High-purity small-diameter CNT materials were obtained, and a novel “five-state” electrophoretic deposition method was proposed to fabricate CNT cathodes. For an emission area of 10 mm × 0.45 mm, a high and stable cathode emission current of 350 mA was achieved, corresponding to an emission current density of 7.8 A/cm². An X-ray dose rate of 39.49 mGy/s@50 cm was measured under a tube potential of 120 kV, cathode current of 100 mA, and pulse width of 10 ms. The focal spot size of the X-ray source, measured using a slit camera, was 0.98 mm (width) × 1.05 mm (length) at 15% max intensity, and the pulse width range was 100 µs–100 ms. Through continuous testing at 200 mA emission current, 100 µs pulse width, and 0.3% duty cycle for 400 h, the CNT cathode is estimated to exhibit a lifetime of approximately 5085 h, demonstrating stable and reliable durability. This study, for the first time, simultaneously realizes multi-A/cm²-level emission current density, hundreds-of-milliampere emission current, and hundreds-of-millisecond operating pulse width for CNT cathodes. Full article

We report on a novel approach for the monitoring of tangential laser turning with ultrashort laser pulses. By using an ultra-sonic sensor consisting of a membrane-free optical microphone, the current state of the ablation process can be analyzed, potentially enabling a real-time automated regulation. With its high sensitivity, bandwidth, and sampling rate, it is an ideal tool for process monitoring. The material ablation caused by focused femtosecond laser pulses produces distinct sound waves, which can be detected by the optical microphone. The diameter reduction of a rotating cylindrical workpiece during the laser turning process with ultrashort laser pulses results in a variation in the acoustic emissions. From this, properties like the state of the machining progress can be inferred. Full article

We report on the generation and spectral shaping of ultrabroadband terahertz-to-infrared radiation (>119 THz) from air plasma excited by a conventional tightly focused femtosecond Ti:Sa laser pulse with a duration of 35 fs assisted by its second harmonic (SH). A controllable and large frequency detuning between the SH and blueshifted component of the fundamental spectrum was achieved by utilizing spectral broadening of the fundamental pulse under filamentation and adjusting the longitudinal separation of the two cascaded filaments. For convenience, the resulting ultrabroadband emission is divided into a low-frequency part (<30 THz), an intermediate-frequency part (~50 THz), and a high-frequency part (~100 THz) that can be optimized with the filaments’ longitudinal separation. We attribute such ultrabroadband THz radiation generation to the excitation of photocurrent from the nonlinear interaction of SH with both the field at the fundamental frequency and its blueshifted component acquired during filamentation. Theoretical calculations based on time-dependent Schrödinger equation, as well as the Maxwell–Schrödinger equation for spectral broadening dynamics, reproduced the spectral features as well as the distinct dependence of the low- and high-frequency THz components. Full article

X-band copper resonating cavities are key components of future pulsed GHz normal-conductive multi-TeV accelerators. High electric field gradients are required for emerging applications; however, as gradients increase, components’ lifetime decreases, primarily due to radiofrequency (RF) breakdown. Coating technologies are being investigated in several laboratories to improve RF structure, performance and lifetime. To this end, we investigated the feasibility of fabricating nanometer-periodic Cu/Mo metallic multilayers on three-dimensional (3D) aluminum mandrels designed to replicate X-band copper resonating cavities. These nanometer-period multilayers are proposed to mitigate surface degradation due to electric breakdown at high accelerating gradients by stabilizing inner cavity surfaces against dislocation evolution and roughening caused by thermo-mechanical fatigue. High-Power Impulse Magnetron Sputtering (HiPIMS) in a bias-controlled dual closed-field magnetron configuration was employed to deposit alternating Mo and Cu nano-layers onto the 3D geometries. Given the complexity of HiPIMS technology, plasma pulse evolution was studied by combining time-resolved optical emission spectroscopy with electrical measurements of the pulse discharge. The influence of the process parameters, particularly the applied DC bias, on film growth was studied using non-destructive microprobe α-particle elastic backscattering spectrometry (µEBS) and scanning transmission electron microscopy (STEM). STEM and µEBS analyses confirmed that Mo layers with thicknesses of approximately 5–35 nm were successfully deposited repeatedly on thicker Cu layers (30–150 nm), preserving individual layer properties with minimal interdiffusion and alloying. The layers were deposited inside trenches with an aspect ratio of 5:1 representative of X-band irises. This technology, coupled with the replica process, could be applied to highly engineered nanostructured coatings for X-band cavity treatment in compact particle accelerator prototypes, as it may improve electrical breakdown lifetime under high accelerating fields, at least for degradation processes driven by the high mobility of copper dislocations. Full article

In this study, an electrochemical sensor based on magnesium zirconate (MgZrO₃) synthesized using a deep eutectic solvent (DES)-assisted approach was developed for the detection of dopamine. The structural and morphological properties of MgZrO₃ were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, energy-dispersive spectroscopy, and elemental mapping. The electrochemical performance of the MgZrO₃-modified glassy carbon electrode (GCE) was evaluated using cyclic voltammetry and differential pulse voltammetry. The MgZrO₃/GCE exhibited an enhanced redox response and a reduced oxidation potential for dopamine in phosphate-buffered solution (PBS, pH 7.0), indicating improved electrocatalytic activity compared to the bare electrode. This improvement is attributed to the material’s increased active surface area and facilitated charge transfer kinetics. Under optimized conditions, the sensor showed a linear response over a concentration range of 0.3–80 µM, with a detection limit of 127 nM and quantification limit of 423 nM. The MgZrO₃/GCE also demonstrated good selectivity in the presence of common interfering species and was successfully applied for dopamine detection in biological samples, with satisfactory recovery results. The findings presented here contribute to the growing body of knowledge in the field and open up new possibilities for the development of advanced electrochemical sensors for neurotransmitter detection in clinical and research settings related to Breast Cancer Treatment. Full article

This study investigates the selective synthesis of α- and γ-alumina nanoparticles using plasma-induced microbubbles. Although plasma-induced bubbles provide an effective reaction environment for the synthesis of nanomaterials, precise phase control remains challenging. Herein, we demonstrate that the modulation of the pulse off time regulates the thermal environment within the bubbles. Optical emission spectroscopy revealed that a shorter off time maintains a high electron temperature, indicating substantial heat accumulation. This high-energy state promotes the atomization of the precursor mist and the subsequent growth of molten droplets, providing sufficient activation energy for the formation of the thermodynamically stable α-phase. In contrast, a longer off time leads to the formation of a metastable γ-phase because of insufficient heating and rapid quenching. These findings prove that alumina nanoparticles with desired crystal phase and size can be synthesized by controlling the thermal energy inside the plasma-induced microbubbles. Full article

Diode-pumped alkali vapor lasers (DPALs) offer high quantum efficiency, low thermal loading, excellent beam quality, and emission wavelengths matched to important application scenarios. Extending DPALs toward pulsed regimes is of particular interest for applications such as lidar, free-space optical communication, and precision material processing, where high peak power and flexible temporal control are required. This review surveys the key technologies underlying DPAL systems and summarizes the progress in pulsed-generation approaches. The pulsed techniques reported to date are systematically reviewed, including pump modulation, intracavity modulation, cavity dumping, and mode-locking, together with a comparison of their performance. The current status indicates that pulsed DPALs remain at an early stage, with limitations in parameter space exploration and performance scaling. Future developments are expected along several directions, including further exploration of mode-locked DPALs, burst-mode pulse generation for structured temporal output, power scaling through MOPA architectures, and spectral extension via nonlinear frequency conversion. These directions collectively define the pathway toward high-performance pulsed DPAL systems. Full article

Vertical-External-Cavity Surface-Emitting Lasers (VECSELs) have gained significant attention over the past two decades due to their versatility in a wide range of photonic applications. This review focuses on VECSEL configurations for dual-wavelength emission, highlighting their use in high-resolution spectroscopy, terahertz (THz) generation, and advanced optical communication. We explore recent developments in VECSEL designs, including systems utilizing birefringent crystals for polarization-based frequency separation and configurations with dual-VECSEL chips or dual-gain regions within a single cavity. These two-wavelength VECSELs enable diverse operation modes, including narrow-linewidth, pulsed, multimode, and frequency-converted emission, with high-brightness output, excellent beam quality, and tunable wavelengths. Additionally, the review discusses advancements in dual-frequency VECSELs, with applications in LIDAR systems for environmental monitoring, highly stable optical clocks, and fiber sensors. We examine improvements in cavity design, semiconductor structures, and power stabilization, which have enhanced frequency stability and spectral purity, making VECSELs suitable for precision metrology and sensing applications. Full article

Scandate cathodes have garnered significant attention for their exceptional low-temperature, high-current-density emission characteristics. However, their widespread deployment in vacuum electronic devices is currently hindered by stringent vacuum requirements and susceptibility to ion bombardment. To enhance the engineering applicability of scandate cathodes, this study employs first-principles density functional theory (DFT) to model the surface microstructures of strontium (Sr)–scandium (Sc) co-doped systems. Guided by simulation predictions regarding surface elemental ratios, corresponding emission active materials and cathode samples were fabricated. A systematic comparison between theoretical calculations and experimental measurements reveals a critical trade-off: while increasing Sr content enhances structural stability (indicated by lower formation energies), it concurrently increases the work function. Consequently, an optimal Sr doping level of approximately 2 wt% is identified, which significantly improves emission current density without compromising stability. Cathodes fabricated with this optimized composition were tested in a practical electron gun configuration. Results demonstrate that under low-temperature conditions (1000 °C) and wide-pulse operation (2 ms), the cathode achieves an emission current density of 21.57 A/cm². These findings validate the efficacy of simulation-guided material design and highlight the potential of Sr-doped scandate cathodes for high-power microwave applications. Full article

Achieving selective cleavage of specific chemical bonds using ultrafast laser pulses remains a central challenge in ultrafast strong-field molecular physics. Here, we theoretically investigate the coherent control of strong-field dissociation of the heteronuclear molecular ion HD⁺ initially prepared in vibrationally excited states driven by an ultrashort pulse with a quadratic spectral phase. Our results reveal a pronounced sensitivity of both the total dissociation probability and the branching ratio (H⁺ + D vs. H + D⁺) to the chirp rate of the laser pulse. To uncover the underlying physical mechanism, we analyze the population dynamics in the coupled $1s\sigma$ and $2p\sigma$ electronic states and identify pronounced Rabi oscillations arising from the coherent interplay between multiphoton excitation and field-induced stimulated emission. By tuning the laser chirp rate, these oscillations can be suppressed via quantum interference, thereby reshaping the dissociation dynamics and significantly enhancing the dissociation probability of the H + D⁺ channel. These findings demonstrate that spectral-phase engineering provides a robust and versatile strategy for selective control of branching ratios in strong-field molecular dissociation. Full article

Rising temperatures and atmospheric CO₂ exert complex, interacting effects on plant carbon metabolism and volatile organic compound (VOC) emissions. This study investigated the physiological mechanisms underlying acute thermal tolerance in Populus nigra by integrating leaf gas exchange with high-resolution proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). We employed a factorial design (25–40 °C; 400 and 800 ppm CO₂) to examine how metabolic regulation and pulse-induced signalling interact across thermal gradients. Our results identify a critical metabolic tipping point around 40 °C, representing a transition toward a survival-orientated state. Isoprene emission decoupled from net photosynthesis at this threshold; while carbon assimilation collapsed, isoprene was maintained at near-maximal rates to prioritize thylakoid thermal protection. Under moderate temperatures (25–35 °C), emission capacity scaled linearly with the chloroplastic DMADP pool, but this relationship broke down at 40 °C. Notably, elevated CO₂ sustained the magnitude of stress-related “bursts” at the thermal limit, suggesting that increased carbon availability provides the metabolic stamina required to fuel emergency defence and fermentative pathways. These findings demonstrate that acute thermal exposure triggers a metabolic reconfiguration, shifting resources from growth-oriented processes toward survival-based stabilization mechanisms. Full article

Large-sized, room-temperature ultrafast scintillator single crystals are highly demanded for fast timing applications such as time of flight–positron emission tomography, high-speed medical imaging, and pulse heavy-ray detection. Sub-nanosecond scintillation was discovered in 16 mm sized CsPbCl₃Br_x single crystals in our previous research. In this work, the crystal size of CsPbCl₃Br_0.03 was enlarged to 2 inches (50.8 mm). Meanwhile, by precisely optimizing the vertical Bridgman growth process, we further increased the concentration of Br dopant to realize even faster scintillation decay. In this study, we conducted a series of tests on the grown crystals, including temperature-dependent photoluminescence tests, alpha particle excitation tests, X-ray imaging tests, etc. Via the strategy of the incorporation of Br₂, Br dopant introduces highly efficient fast recombination centers in perovskite CsPbCl₃Br_0.03 crystals, resulting in an unprecedently fast scintillation decay time of 303 ps under ²⁴¹Am α-particle excitation, which is significantly shorter than that of the pure CsPbCl₃ and all other perovskites by at least two orders of magnitude. Benefiting from the excellent optical transparency and high crystalline quality of the CsPbCl₃Br_0.03 crystal, an X-ray spatial resolution of up to 20 lp/mm is achieved. These results further demonstrate the great potential of large-sized CsPbCl₃Br_x single crystals for fast timing applications. Full article

The increasing demand for civil infrastructure has contributed significantly to CO₂ emissions and global warming potential (GWP), largely due to concrete production, cement manufacturing, and natural aggregate extraction. Automotive shredder residue (AutoSR) offers a sustainable alternative; however, its effects on concrete performance remain poorly understood. This study evaluates AutoSR fines, termed eco-friendly aggregates (EFAs), used at 10% volumetric replacement for natural fine aggregate in eight concrete mixtures. Fresh and hardened properties were assessed for EFAs with varying particle characteristics. Microstructural features, including the interfacial transition zone (ITZ), and maturity indicators based on the temperature–time factor (TTF) and ultrasonic pulse velocity (UPV) were examined. All EFA mixtures showed reduced workability compared to the control mix, while hydration behavior and UPV responses remained comparable, allowing the development of maturity master curves. Mechanical performance was strongly influenced by EFAs’ characteristics, with an increased ITZ thickness identified as the primary driver of strength reduction. The study establishes a clear mechanistic link between EFA absorption, ITZ development, and strength loss, supporting a practical 10% replacement level for structural applications and providing guidance for future optimization. The potential economic benefits are also briefly discussed. Full article

Increasing data rates in optical networks require ultra-fast all-optical logic gates to avoid electro-optic conversion bottlenecks. This work presents a numerical simulation and performance analysis of an all-optical XNOR logic gate operating at 250 Gb/s, implemented using a single quantum-dot semiconductor optical amplifier (QD-SOA) embedded in a Mach–Zehnder interferometer (MZI). Using the QD-SOA’s ultrafast carrier dynamics and high nonlinearity, the gate achieves a quality factor (QF) of 26.30 at 250 Gb/s, corresponding to a theoretical bit-error rate below 10⁻⁹. A systematic numerical investigation examines performance dependence on six critical parameters. Data rate analysis shows that the gate maintains QF > 6 up to 700 Gb/s, with QF = 10.47 at this maximum reliable speed, providing a safety margin of approximately 1.8× above the QF = 6 threshold. Performance degrades progressively thereafter, with QF falling to 5.18 at 800 Gb/s and 0.73 at 1 Tb/s due to finite carrier recovery dynamics. Pulse energy optimization identifies an optimum at 0.20 pJ, beyond which gain saturation and nonlinear effects degrade performance below QF = 6 at 0.40 pJ. Continuous-wave probe power exhibits optimal operation at 0.40 mW, with failure above 0.80 mW. Injection current density analysis establishes an optimal bias at 4 kA/cm², where balanced gain and nonlinearity yield peak performance. Noise tolerance assessment demonstrates operation up to a spontaneous emission factor of 6 and phase noise below 6 × 10⁻¹⁴ rad²/Hz, beyond which signal integrity collapses. This parameter sweep delineates the operational envelope and optimization guidelines for QD-SOA-MZI-based all-optical logic, confirming its potential as a compact core component for future ultra-high-speed optical communication and signal processing systems. Full article

Improving the quality of welded joints, as well as the advancement of equipment and materials, inevitably requires deep theoretical knowledge of the physical phenomena occurring in the arc column and in the cathode and anode regions. Achievements in the field of controlling metal transfer at the micro- and nanoscale through the regulation of current and voltage in welding power sources have encountered the problem of the formation of cathode and anode spots, which affect the stability of welding arcs and the quality of the weld. Under short current pulses and pauses, the stability of the arc discharge depends on the ability to form a cathode spot, melt the wire metal, and transfer it through the arc column. In this article, based on the generalization of known experimental facts and studies performed using a high-speed camera, it is shown that the current-carrying channel of the electric arc has a discrete structure consisting of a multitude of thin channels through which the main discharge current flows. The cathode spot of the arc discharge represents a highly heated and brightly luminous region on the cathode surface. Electron emission sustaining the discharge and the removal of cathode material occur from this region. A new method is proposed for investigating the reverse side of the cathode spot, which makes it possible to identify a structure consisting of individual cells or fragments of the cathode spot. For the first time, anode spots recorded with a high-speed camera are presented. An analysis of the spot structure is carried out. The parameters influencing the mobility of cathode and anode spots are determined. Based on the obtained experimental facts, a hypothesis is proposed regarding the non-uniform structure of cathode and anode spots in the arc discharge. Full article