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The mechanochemical synthesis of PbTe nanostructures: following the Ostwald ripening effect during milling
摘要： A fundamental understanding of the Ostwald ripening effect (ORE) during the mechanochemical synthesis of PbTe nanostructures is presented. The ripening process involves the coarsening of larger particles from those of smaller size; this phenomenon was systematically evaluated at different stages of milling by microscopy analyses (AFM, TEM, STEM and HRTEM). At the early stage of milling, smaller particles and quantum dots are eventually dissolved to lower the total energy associated with their surfaces. The ripening process – during milling – involves short-range mass transfer among particles. HRTEM analyses allowed us to identify that coarsening occurs by thermo-mechanically activated cooperative mechanisms. The detachment of the atoms from smaller particles to form bigger ones plays a major role in the particle coarsening. It was found that the coarsening process was not limited to crystalline nanostructures; so grain boundaries, edge dislocations and boundaries among crystalline and amorphous phases also play an important role to determine how species migration contributes to generate coarse particles. Those serve as sites for inducing coarsening in an equivalent way as surfaces do. Secondary ion mass spectrometry and elemental chemical mapping (EDX-STEM) revealed that both the purity and the chemical homogeneity of the PbTe nanostructures are prominent features of this material. Additionally, a direct band gap enhancement (780 nm) compared to bulk PbTe (3859 nm) was detected. It occurred due to the quantum confinement effect, lattice imperfections and even surface properties of the nanostructures. It is important to point out that the whole optical behaviour of the PbTe nanostructures was dependent upon the embedded nanoparticles and quantum dots in the clusters and coarse particles ranging from 15 nm to 35 nm.
关键词： PbTe nanostructures,microscopy analyses,quantum confinement effect,mechanochemical synthesis,Ostwald ripening effect,high-energy milling
更新于2025-09-19 17:15:36
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Quasi single-shot two-pulse tilted pulse front autocorrelator coupled with spatial chirp and spectral divergence monitor for ultrashort pulsed laser beams
摘要： Simultaneous single-shot unambiguous detection and measurement of pulse front tilt, spatial chirp, spectral divergence and pulse width has been carried out using two-pulse tilted pulse-front autocorrelator (TP-TPFAC) coupled with spectral interferometry using small part of laser beam intercepted from Mach Zehnder delay unit of TP-TPFAC generating two delayed and spatially inverted pulses. Error in estimation of rotation angle of autocorrelation (AC) trace due to accidental improper positioning of CCD detector is avoided by measuring angle between AC traces corresponding to two delayed and spatially inverted pulses. Likewise, accuracy in estimation of spatial chirp is improved by using spatially resolved spectral trace of two spatially inverted pulses, as errors due to accidental improper positioning of either grating of spectrograph or CCD detector are avoided. Sensitivities and accuracies of the two methods are compared in different experimental situations. Estimated pulse parameters are found in close accordance with respective theoretical values.
关键词： Chirped pulse amplification,Ultrashort laser pulses,High energy high power lasers
更新于2025-09-19 17:13:59
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Binder- and conductive additive-free laser-induced graphene/LiNi1/3Mn1/3Co1/3O2 for advanced hybrid supercapacitors
摘要： Hybrid supercapacitors have recently emerged as next-generation energy storage devices that bridge the gap between supercapacitors and lithium-ion batteries. However, developing high energy cathodes that maintain long-term cycle stability and a high rate capability for real applications remains a significantly challenging issue. Herein, we report a facile synthesis method for a laser-scribed graphene/LiNi1/3Mn1/3Co1/3O2 (LSG/NMC) composite for high energy cathode materials for use in hybrid supercapacitors. LSG/NMC composites exhibit not only a high capacitance of up to 141.5 F/g but also an excellent capacitance retention of 98.1% after 1000 cycles at a high current density of 5.0 A/g. The introduction of an NMC spacer between the LSG layers provides an enlarged interspace that can act as an efficient channel for additional storage sites and rapid access. In addition, we further confirmed that hybrid supercapacitors using LSG/NMC cathodes and H2Ti2O25 anodes with an AlPO4/carbon hybrid coating layer (H-HTO) deliver a remarkable energy density of ~123.5 Wh/kg, power density of ~14074.8 W/kg, and a long-term cycle stability of 94.6% after 20,000 cycles. This work demonstrates that our proposed material can be considered a strong cathode candidate for next-generation hybrid supercapacitors.
关键词： laser-scribed graphene,high energy density,hybrid supercapacitors,LiNi1/3Mn1/3Co1/3O2,long-term cycle stability
更新于2025-09-19 17:13:59
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Maximizing magnetic field generation in high power laser–solid interactions
摘要： In order to understand the transport of fast electrons within solid density targets driven by an optical high power laser, we have numerically investigated the dynamics and structure of strong self-generated magnetic fields in such experiments. Here we present a systematic study of the bulk magnetic field generation due to the ponderomotive current, Weibel-like instability and resistivity gradient between two solid layers. Using particle-in-cell simulations, we observe the effect of varying the laser and target parameters, including laser intensity, focal size, incident angle, preplasma scale length, target thickness and material and experimental geometry. The simulation results suggest that the strongest magnetic field is generated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency. The recent commissioning of experimental platforms equipped with both optical high power laser and X-ray free electron laser (XFEL), such as European XFEL-HED, LCLS-MEC and SACLA beamlines, provides unprecedented opportunities to probe the self-generated bulk magnetic field by X-ray polarimetry via Faraday rotation with simultaneous high spatial and temporal resolution. We expect that this systematic numerical investigation will pave the way to design and optimize near future experimental setups to probe the magnetic fields in such experimental platforms.
关键词： laser–plasmas interaction,X-ray free electron laser probing,high energy density physics
更新于2025-09-19 17:13:59
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Experimental observation of stress formation during selective laser melting using in situ X-ray diffraction
摘要： Despite the ongoing success of metal additive manufacturing and especially the selective laser melting (SLM) technology, process-related defects, distortions and residual stresses impede its usability for fracture-critical applications. In this paper, results of in situ X-ray diffraction experiments are presented that offer insights into the strain and stress formation during the manufacturing of multi-layer thin walls made from Inconel 625. Using different measuring modes and laser scanning parameters, several experimental observations are discussed to validate and extend theoretical models and simulations from the literature. As a sample is built-up layer by layer, the stress state changes continuously up until the last exposure. The localized energy input leads to a complex stress field around the heat source that involves alternating tensile and compressive stresses. The correlation of temperature and yield strength results in a stress maximum at a certain distance to the top layer. The present study demonstrates the potential of high-energy synchrotron radiation diffraction for in situ SLM research.
关键词： Inconel 625,Selective laser melting,Stress formation,In situ,High energy synchrotron radiation diffraction
更新于2025-09-16 10:30:52
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[Laser Institute of America ILSC? 2019: Proceedings of the International Laser Safety Conference - South Kissimmee, Florida, USA (March 18–21, 2019)] International Laser Safety Conference - Construction and utilization of probabilistic dynamic bidirectional reflectance distribution functions
摘要： Reflections of high energy lasers from surfaces can present hazards to persons and instruments at significant distances. Heating from these lasers causes changes in the reflection characteristics of surfaces they illuminate. As such, reflections from these surfaces cannot be properly modeled with static bidirectional reflectance distribution functions (BRDFs), but require time-dynamic BRDFs. Moreover, the time-evolution of the surface reflections is not deterministic, but can vary even when the materials and illumination conditions are nearly identical, such that only probabilistic characterization is realistic. Due to the swiftly changing nature of the reflections, traditional BRDF measurements with goniometric instruments are impossible, so BRDFs must be deduced from images of the reflected light incident on a screen intercepting a portion of the reflection solid angle. A new BRDF model describes these complex probabilistic dynamic BRDFs with only four intuitive parameters for a given laser wavelength, irradiance, and duration, where these parameters have central values and statistical variances over discrete regimes corresponding to surface conditions. An automated procedure determines appropriate parameter values and variances from captured screen images, requiring only a single angle of laser incidence. Parameters from sample tests illustrate the model.
关键词： high energy lasers,probabilistic modeling,dynamic BRDFs,bidirectional reflectance distribution functions,laser safety
更新于2025-09-16 10:30:52
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High energy proton micro-bunches from a laser plasma accelerator
摘要： Recent advances on laser-driven ion accelerators have sparked an increased interest in such energetic particle sources, particularly towards the viability of their usage in a breadth of applications, such as high energy physics and medical applications. Here, we identify a new ion acceleration mechanism and we demonstrate, via particle-in-cell simulations, for the first time the generation of high energy, monochromatic proton micro-bunches while witnessing the acceleration and self-modulation of the accelerated proton beam in a dual-gas target, consisting of mixed ion species. in the proposed ion acceleration mechanism due to the interaction of an ultra-short, ultra-intense (2 PW, 20 fs) laser pulses with near-critical-density partially ionized plasmas (C & H species), we numerically observed high energy monochromatic proton microbunches of high quality (peak proton energy 350 MeV, laser to proton conversion efficiency ~10?4 and angular divergence <10 degree), which can be of high relevance for medical applications. We envisage that through this scheme, the range of attained energies and the monochromaticity of the accelerated protons can be increased with existing laser facilities or allow for laser-driven ion acceleration investigations to be pursued at moderate energies in smaller scale laser laboratories, hence reducing the size of the accelerators. the use of mixed-gas targets will enable high repetition rate operation of these accelerators, free of plasma debris and electromagnetic pulse disruptions.
关键词： proton micro-bunches,laser-driven ion accelerators,medical applications,particle-in-cell simulations,high energy physics
更新于2025-09-16 10:30:52
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Modeling the Impact of High Energy Laser Weapon on the Mission Effectiveness of Unmanned Combat Aerial Vehicles
摘要： With the rapid development of high energy laser weapons (HELWs), the integration of HELW on unmanned combat aerial vehicles (UCAVs) has become a hot research topic. To study the impact of HELW on UCAV mission effectiveness, this paper proposes a 4-level design framework based on the system-of-system (SoS) oriented design. To validate the framework, the impact of HELW is analyzed in four aspects: the strike capability, the stealth performance, the vulnerability, and the defense capability, where the UCAV design constrains are noted. Simulation experiments of penetration scenario are carried out using agent-based modeling and simulation. The simulation results show that the integration of HELW can increase the survivability and mission effectiveness rate (MER) of the UCAV, especially for UCAVs with high speed and stealth performance. But the MER of the UCAV does not increase with the increase of HELW output power in most cases, indicating the importance of balancing the HELW and UCAV performances in concept design.
关键词： mission effectiveness evaluation,system-of-systems oriented design,agent-based modeling and simulation,High energy laser,unmanned combat aerial vehicle
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Towards a kW-Class Picosecond Laser at 1 kHz
摘要： Secondary sources development such as X-rays for medical applications demand diode-pumped high-energy, high-power and high repetition rate picosecond lasers leading to a race to the kW milestone. Year after year, the pulse energy increased to few hundreds of millijoules at 1 kHz [1], but all the kW systems are based on the Yb:YAG thin disk technology which until now, to the best of our knowledge, has come short to deliver the full kilowatt level at 1 kHz. On the other side, cryogenically cooled bulk Yb:YAG amplifiers has shown its capabilities to reach 1 J at 500 Hz with 3.8 ps pulses [2]. Since two years, CELIA has launched new technology developments for a new system (HORIZON) aiming to reach 1 J, 1 kHz, 1 ps. We selected Yb:YAG crystal as laser gain medium since its thermal properties and its low quantum defect are suitable for high power laser generation. However, its narrow spectral bandwidth and its high saturation fluence impose large constraints on both the amplifier and compressor architectures. Cutting-edge technologies such as hypercompressor [3], divided pulse amplification [4], thin-disk and liquid-cooled disks are explored to address these limitations.
关键词： thin disk technology,cryogenically cooled bulk Yb:YAG amplifiers,high repetition rate,high-power,divided pulse amplification,hypercompressor,picosecond lasers,Yb:YAG,high-energy
更新于2025-09-12 10:27:22
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High energy and high frequency electro-optic Q-switching laser with alternating output of energy amplitude
摘要： The high energy and high frequency electro-optic Q-switching laser with alternating output of energy amplitude was the first reported by the temporal delay of pulse energy in 1064 nm laser. The experimental schematic of the output 1064 nm laser with different trigger time were obtained when turn on the Q-switch on the 60 μs. When turn on the Q-switch on the 71 μs, the pulse energy of 1064 nm is distributed in a “high-low” pulse sequence: the pulse energy of the 1st was higher than 2nd, and the 2nd pulse energy was lower than the 3rd is formed repeatedly, when turn on the Q-switch on the 48 μs, the output process of the pulse laser is reversed. To the best of our knowledge, it is the first time to report the high energy and high frequency electro-optic Q-switching laser with alternating output of energy amplitude. In experiment a repetition rate of 100 kHz with a pulse width of 13 ns was achieved when the pump power was 24 J and the charging voltage is 650 V, the total output power of 0.8 J was obtained and the conversion efficiency is 0.3%. And the result of the photon density distributions and the inverse population by numerical calculations are basically agree with the experiment result.
关键词： Alternating output of energy amplitude,Temporal delay,Rate equation model,High energy and High frequency
更新于2025-09-12 10:27:22