Ultrahigh Peak Power Research Articles

Reliable joining between MgAl2O4 and Ti6Al4V by ultrashort pulse laser

MgAl2O4 and Ti6Al4V, the greatly suitable materials for industrial application, are rarely explored to realize reliable bonding in current research. In this study, the transparent MgAl2O4 and Ti6Al4V were successfully bonded by innovative use of ultrashort pulse laser with ultra-high peak power. The high energy near the laser focus makes MgAl2O4 and Ti6Al4V mix and react with each other after absorbing the laser energy, thus realizing the bridge between them. The homogeneous mixing of all phases was observed in the joint and the newly generated Ti6O phase was identified at the interface. In addition, the effects of laser power and scanning speed on the microstructure and mechanical properties of the joint have been thoroughly clarified. This study creatively used femtosecond laser welding as a new mean to realize ceramic-metal joining, which shows great advantages in superior efficiency and precision compared with other welding methods.

Calculation and measurement of trapping stiffness in femtosecond optical tweezers.

Due to the characteristics of ultra-short pulse width and ultra-high peak power, femtosecond pulse laser can effectively induce nonlinear optical effects in trapped objects. As a result, it holds great value in the fields of micro and nano manipulation, microfluidics, and cell biology. However, the nonlinear optical effects on the stiffness of femtosecond optical traps remain unclear. Calibration of trap stiffness is crucial for accurately measuring forces and manipulating small particles. In this paper, we compare the stiffness between femtosecond optical traps and continuous wave optical traps. Experimental results demonstrate that the stiffness of the femtosecond optical trap in the splitting direction is greater than that in other directions and the stiffness of the continuous wave optical trap under the same laser power condition. Additionally, as the laser power increases, the stiffnesses of both the femtosecond optical trap and the continuous wave optical trap gradually increases. In contrast to a linear increase of the continuous wave optical trap, the stiffness of the femtosecond optical trap exhibits an exponential rise with increasing laser power. This research provides guidance and reference for improving the force measurement accuracy of femtosecond optical tweezer system.

20µm Micro-LEDs Mass Transfer via Laser-Induced In Situ Nanoparticles Resonance Enhancement.

Ultrafast laser is expected as a promising strategy for micro-LEDs (µ-LEDs) transfer due to its inherent property of suppressing thermal effects. However, its ultrahigh peak power and the unclear transfer mechanism make its transfer quality and efficiency unsatisfactory. Here, the study reports the high-precision mass transfer of 20µm fine-pitch µ-LEDs via in situ nanoparticles (NPs) resonance enhancement in burst mode ultraviolet picosecond laser irradiation. This technique suppresses the thermal melting effect and rapid cooling behavior of plasma by temporal modulation of the burst mode, generating NPs-induced resonance enhancement that accurately and controllable drives a single unit up to tens of thousands of µ-LEDs. The transfer of large µ-LED arrays with more than 180 000 chips is also demonstrated, showing a transfer yield close to 99.9%, a transfer speed of 700 pcs s-1, and a transfer error of <±1.2µm. The transferred µ-LEDs perform excellent optoelectronic properties and enable reliable device operation regardless of complex strain environments, providing a reliable strategy for preparing broader classes of 3D integrated photonics devices.

Amorphous MnO2 Lamellae Encapsulated Covalent Triazine Polymer-Derived Multi-Heteroatoms-Doped Carbon for ORR/OER Bifunctional Electrocatalysis.

The intelligent construction of non-noble metal materials that exhibit reversible oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with bifunctional electrocatalytic performance is greatly coveted in the realm of zinc-air batteries (ZABs). Herein, a crafted structure-amorphous MnO2 lamellae encapsulated covalent triazine polymer-derived N, S, P co-doped carbon sphere (A-MnO2/NSPC) is designed using a self-doped pyrolysis coupled with an in situ encapsulation strategy. The customized A-MnO2/NSPC-2 demonstrates a superior bifunctional electrocatalytic performance, confirmed by a small ΔE index of 0.64V for ORR/OER. Experimental investigations, along with density functional theory calculations validate that predesigned amorphous MnO2 surface defects and abundant heteroatom catalytic active sites collectively enhance the oxygen electrocatalytic performance. Impressively, the A-MnO2/NSPC-based rechargeable liquid ZABs show a large open-circuit potential of 1.54V, an ultrahigh peak power density of 181mW cm-2, an enormous capacity of 816 mAh g-1, and a remarkable stability for more than 1720 discharging/charging cycles. Additionally, the assembled flexible all-solid-state ZABs also demonstrate outstanding cycle stability, surpassing 140 discharging/charging cycles. Therefore, this highly operable synthetic strategy offers substantial understanding in the development of magnificent bifunctional electrocatalysts for various sustainable energy conversions and beyond.

Promoting the four electrocatalytic reactions of OER/ORR/HER/MOR using a multi-component metal sulfide heterostructure for zinc-air batteries and water-splitting.

Multi-component metal sulfide heterostructures are promising for multi-functional catalytic activities. In this work, we fabricated a multi-component metal sulfide heterostructure (Co-S-INF, composed of Co3S4 and (Fe, Ni)9S8) with nanoflower morphology clustered with numerous nanosheets by the electrodeposition of cobalt on iron-nickel foam followed by hydrothermal sulfurization treatment. Co-S-INF possesses high multi-functional electrocatalytic properties toward the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and methanol oxidation reaction (MOR). In particular, the ORR potential at 10 mA cm-2 is 0.682 V, and the OER, HER, and MOR potentials at 100 mA cm-2 are 1.478 V, 0.289 V, and 1.417 V, respectively. By using Co-S-INF, the aqueous ZAB with an ultrahigh peak power density of 332.30 mW cm-2 and an overall water splitting (OWS) device with a low splitting voltage of 1.82 V at 100 mA cm-2 can be obtained. In addition, the OWS potential can be further decreased to 1.70 V at a current density of 100 mA cm-2 with the assistance of MOR at the anode accompanying the production of the high value-added formate. Our work opens the way for the application and development of multi-functional electrocatalysts.

Trace Tungsten Microalloying PtCuCo Medium Entropy Alloys: Substructure Reconstruction-Triggered High-Performance for PEMFC.

Refractory metals (W, Nb, or Mo) microalloying Pt-based alloys with unprecedented performance may serve as advanced electrocatalysts for proton exchange membrane fuel cells (PEMFCs). These alloys are endowed with unique stabilizing substructures or lattice defects through the microalloying effect. Herein, trace W microalloying PtCuCo medium entropy alloys (W-PtCuCo) are reported via a stepwise synthesis strategy, starting with home-made Cu nanowires as sacrificial templates by anhydrous solid-phase milling route, and then followed by galvanic replacement-assisted solvothermal in ethylene glycol (EG). In PEMFC tests, the obtained W-PtCuCo exhibits an ultrahigh peak power density and mass power density (relative to cathode) reaching 2.09Wcm-2 and 20.9WmgPt -1 , respectively. During the accelerated degradation test (ADT), the mass activity just lost only 3% after 30k cycles, much better than the above benchmark catalyst. The microalloying-dependent performances shall be attributed to the presence of abundant stepped surfaces, twisted edges, and other lattice defects terminated by W via substructure reconstruction that indeed alters the electronic structure and strain level of the alloys. This work first provides an atomic-level insight into the microalloying-dependent electrocatalytic performance of Pt-based alloys, which is of great significance for developing next-generation efficient catalysts for PEMFC.

Engineering Structurally Ordered High-Entropy Intermetallic Nanoparticles with High-Activity Facets for Oxygen Reduction in Practical Fuel Cells.

High-entropy solid-solution alloys have generated significant interest in energy conversion technologies. However, structurally ordered high-entropy intermetallic (HEI) nanoparticles (NPs) have been rarely reported in electrocatalysis applications. Here, we demonstrate structurally ordered PtIrFeCoCu HEI (PIFCC-HEI) NPs with extremely superior performance for both oxygen reduction reaction (ORR) and H2/O2 fuel cells. The PIFCC-HEI NPs show an average diameter of 6 nm. Atomic structural characterizations including atomic-resolution energy-dispersive spectroscopy (EDS) mapping technology confirm the ordered intermetallic structure of PIFCC-HEI NPs. As an electrocatalyst for ORR, the PIFCC-HEI/C achieves an ultrahigh mass activity of 7.14 A mgnoblemetals-1 at 0.85 V and extraordinary durability over 60 000 potential cycles. Moreover, the fuel cell assembled with PIFCC-HEI/C as the cathode delivers an ultrahigh peak power density of 1.73 W cm-2 at a back pressure of 1.0 bar and almost no working voltage decay after 80 h operation, certifying the top-level performance among reported fuel cells. Theoretical calculations combined with experimental results reveal that the superior performance of PIFCC-HEI/C for ORR and fuel cells is attributed to its ultrahigh-activity facets. Especially, the (001) facet affords the lowest activation barriers for the rate-limiting step, the optimal downshift of the d-band center, and more efficient regulation of electron structures for ORR. This work not only opens up a new avenue for the fabrication of high-activity facets in the catalysts but also highlights structurally ordered HEI NPs as sufficiently effective catalysts in practical fuel cells and other potential energy-related applications.

7.9 µm Turing Membranes with High Ion Conductivity for High Power Density Zinc‐Based Flow Battery

AbstractIon conductive membranes with rapid and selective ion transport are in high demand for high‐power energy storage devices. Surface periodic Turing microstructures are scientifically compelling for their high specific surface area which can promote ion transport of membranes. Here, high‐conductivity thin Turing membranes prepared by Co2+ coordination with polybenzimidazole (OPBI) are designed and their efficient ion transport in the alkaline zinc‐iron flow battery (AZIFB) is demonstrated. In this design, the Turing structure increases the effective contact area with the electrolyte, and the 7.9 µm thickness shortens the transmembrane pathway for ions. Molecular dynamics simulations further show that Co2+‐coordination enlarges the inner‐chain volume of membranes and forms continuous water channels for rapid ion transport. The boosting effect of membranes with high ion conductivity is proven by the peak power density and energy efficiency of the AZIFB, which shows an ultrahigh peak power density of 1147 mW cm−2 and demonstrates an energy efficiency of 80% even at a high current density of 200 mA cm−2.

Investigation of compression grating misalignment in ultra-high peak power femtosecond laser systems

Investigation of compression grating misalignment in ultra-high peak power femtosecond laser systems

A novel route to produce BaTiO3 glass-ceramics with nanosized cubic BaTiO3 phase precipitating for high energy-storage applications

To meet requirements of miniaturization devices in high pulsed power technology, super dielectric energy storage performance, such as high dielectric breakdown strength (DBS), large energy storage density with high power density, is extremely important in dielectric materials. However, for BaTiO3 based ceramics and glass ceramics, there is still a critical challenge to achieve high DBS and large energy storage density. Herein, a novel route was proposed to precipitate nanocrystals with cubic BaTiO3 phase from glass matrix, which can elevate dielectric constant and meanwhile maintain high DBS compared to parent glass. A high recoverable energy storage density of ∼ 3.66 J cm−3 at 1000 kV cm−1 and high discharge energy density of ∼3.57 J cm−3 with good thermal stability and ultra-high peak power density of ∼ 910 MW cm−3 can be achieved in BaTiO3 glass ceramic, which implies this type of glass ceramics is suitable for high pulsed power technology application.

Generation of High‐Peak‐Power Femtosecond Pulses in Mamyshev Oscillators: Recent Advances and Future Challenges

AbstractMamyshev oscillators (MOs) have attracted significant attention given their potential in yielding ultrafast lasers with high peak power. Based on step‐like saturable absorbers and self‐similar evolution in the gain fiber, MO technology features an advanced system capable of generating ultrastable femtosecond pulses with ultrahigh peak power. In this review, the principle of MO is presented in terms of their transmission function and tolerance to nonlinear phase shift and recent progress is reported in the advanced output performance of MO, manifested through high peak power, few‐cycles, high repetition rate, and supercontinuum generation. MO with various operation wavelengths (1, 1.5, and 2 μm) are examined, and MO starting methods are fully discussed, followed by a detailed account of diverse potential applications in areas such as biomedical imaging and material processing. Based on current progress, the prospective challenges and future directions of MO are highlighted and discussed.

Stability improvement of multi-beam picosecond–petawatt laser system for ultrahigh peak-power applications

Pointing fluctuations of beams reduce the possibility of incoherent or coherent addition for ultrahigh peak power in a multi-beam picosecond–petawatt laser system. Pointing fluctuations on the target were observed on Shenguang Upgrade Petawatt (SGII-UP-Petawatt) beam using a high-speed and high-resolution active pointing stabilization control system. The maximum frequency of the pointing fluctuations was less than 50 Hz, and the amplitude was approximately 2.8 µrad (RMS). An online test of pointing fluctuations with active stabilization control demonstrated that pointing fluctuations could be reduced to 0.63 µrad (RMS), approximately one-quarter of that without active stabilization control. The benefits of reduced pointing fluctuation were estimated using a multi-beamlet petawatt laser system; the results demonstrated that peak power could be increased by 51.7% when active stabilization control was used in an eight-beamlet picosecond–petawatt laser system.

Double-ended output near-single-mode quasi-continuous wave monolithic fiber laser

Quasi-continuous fiber lasers have a broad application prospect in the industrial field. However, in the current research on quasi-continuous wave (QCW) fiber lasers only the single-ended output structure is used. A double-ended output fiber laser oscillator needs only one resonator to realize two laser outputs. Compared with single-ended output laser, it has a low cost, small volume and high work efficiency. It is expected to achieve higher power laser output through double-ended output beam combining. Therefore, the double-ended output QCW fiber laser is proposed and studied in this paper. The steady-state rate equation establishes a theoretical model of a QCW fiber laser oscillator with two ends, considering the stimulated Raman scattering (SRS) and amplified spontaneous emission (ASE). The output power, time domain and nonlinear effects of this type of laser are simulated. The results show that the overshoot effect caused by relaxation oscillation will produce a large amount of thermal deposition and ultra-high peak power in the fiber. It will reduce the nonlinear threshold and limit the increase of power of the QCW fiber laser. Prolonging the rise time of the pump can effectively suppress the relaxation oscillation and obtain a stable pulse output during the pulse duration. In addition, compared with the single-ended QCW laser, the double-ended output structure changes the energy distribution in the fiber and reduces the accumulation of nonlinear effects in the gain fiber, thus inhibiting SRS. Then, the ytterbium-doped fiber with a core/cladding diameter of 20/400 μm is used to achieve the first double-ended QCW laser output with a peak power of 3 kW. The peak power values at both ends are 1218 and 2220 W, respectively. The values of corresponding beam quality factor &lt;i&gt;M&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt; are 1.34 and 1.27. The optical-to-optical conversion efficiency is about 60%. The pulse width is 100 μs, and the repetition frequency is 1 kHz. This research verifies the feasibility of high power and high beam quality output by double-ended output QCW fiber laser, which provides support for small volume, low cost, high power and high brightness QCW fiber laser. Further breakthroughs in the research and application of high-power fiber lasers are expected to be made by continually optimizing experiments, increasing pump power, and improving the laser’s output power and conversion efficiency.

Atomically Dispersed Zn‐Pyrrolic‐N4 Cathode Catalysts for Hydrogen Fuel Cells

AbstractTo achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt‐free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn‐Pyrrolic‐N4 moieties and abundant mesoporous structure. The ZnNC‐based anion‐exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm−2 in H2‐O2 and H2‐air (CO2‐free), and also exhibits long‐term stability with more than 120 and 100 h for H2‐air (CO2‐free) and H2‐O2, respectively. Density functional calculations further unveil that the Zn‐Pyrrolic‐N4 structure is the origin of high activity of as‐synthesized ZnNC catalyst, while the Zn‐Pyridinic‐N4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn‐metal‐organic framework ‐derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn‐Pyridinic‐N4 moieties. This work offers a new route for speeding up development of AEMFCs.

Atomically Dispersed Zn-Pyrrolic-N4 Cathode Catalysts for Hydrogen Fuel Cells.

To achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt-free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn-Pyrrolic-N4 moieties and abundant mesoporous structure. The ZnNC-based anion-exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm-2 in H2 -O2 and H2 -air (CO2 -free), and also exhibits long-term stability with more than 120 and 100 h for H2 -air (CO2 -free) and H2 -O2 , respectively. Density functional calculations further unveil that the Zn-Pyrrolic-N4 structure is the origin of high activity of as-synthesized ZnNC catalyst, while the Zn-Pyridinic-N4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn-metal-organic framework -derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn-Pyridinic-N4 moieties. This work offers a new route for speeding up development of AEMFCs.

Designing oxygen-doped Fe-N-C oxygen reduction catalysts for proton- and anion-exchange-membrane fuel cells

Tailoring the local environment and electronic structure of the active center of M-N-C catalysts is a promising route to improve the performance of catalysts. Herein, we design and controllably synthesize an O-doped O-FeN4C-O catalyst and identify its local structure, which contains two kinds of oxygen doping, i.e., axial-oxygen doping and second-coordination-shell oxygen doping of FeN4 species. Density functional theory calculations reveal that the synergy of the two kinds of oxygen doping optimizes electronic structure and therefore boosts oxygen reaction reduction (ORR) performance. Consequently, the O-FeN4C-O exhibits excellent ORR activities in both acidic and alkaline conditions. Importantly, the O-FeN4C-O-based proton- and anion-exchange membrane fuel cells deliver ultra-high peak power densities of 0.88 and 1.24 W cm−2, which ranked among the top performers of non-precious-metal ORR catalysts-based fuel cells. This work paves a new avenue for designing M-N4-X (X = P, S, etc.) catalysts with tunable electronic structures for different electrocatalysis, including carbon dioxide and nitrogen reduction and oxygen and hydrogen evolution.

AgNPs@Fe-N-C oxygen reduction catalysts for anion exchange membrane fuel cells

Anion exchange membrane fuel cells (AEMFCs) are hopeful clean energy equipment due to the mild reaction condition and the possibility of using Pt-free catalysts for cathodic oxygen reduction reaction (ORR). Developing excellent Pt-free ORR catalysts for AEMFC is still of great significance. Here, we construct a composite catalyst (AgNPs@Fe-N-C) of Ag nanoparticles (NPs) surrounded by the atomically dispersed Fe-N-C porous carbon. The AgNPs@Fe-N-C demonstrates outstanding ORR performance and enhanced durability, and its half-wave potential obviously exceeds AgNPs-N-C and Fe-N-C counterparts in alkaline condition. Impressively, the AgNPs@Fe-N-C-based AEMFC exhibits not only the ultrahigh peak power density of 0.848 W cm−2, but also long-term device durability of 200 h in H2/air (CO2-free) system, which is obviously better than that of the Fe-N-C-based AEMFC. Density functional theory (DFT) calculations further reveal the synergistic effect of Ag NPs and Fe-N-C for ORR. In short, this work provides a new route to develop high activity and robust Pt-free ORR catalysts for AEMFCs.

Concave Pt-Zn Nanocubes with High-Index Faceted Pt Skin as Highly Efficient Oxygen Reduction Catalyst.

High dosage of expensive Pt to catalyze the sluggish oxygen reduction reaction (ORR) on the cathode severely impedes the commercialization of proton exchange membrane fuel cells. Therefore, it is urgent to cut down the Pt catalyst by efficiently improving the ORR activity while maintaining high durability. Herein, magic concave Pt–Zn nanocubes with high‐index faceted Pt skin (Pt78Zn22) are proposed for high‐efficiency catalysis toward proton exchange membrane fuel cells. These unique structural features endow the Pt‐skin Pt78Zn22/KB with a mass activity of 1.18 mA μgPt –1 and a specific activity of 3.64 mA cm–2 for the ORR at 0.9 V (vs RHE). Meanwhile, the H2–O2 fuel cell assembled by this catalyst delivers an ultrahigh peak power density of ≈1449 mW cm–2. Both experiments and theoretical calculations show that the electronic structure of the surface is adjusted, thereby shortening the length of the Pt–Pt bond and reducing the adsorption energy of OH*/O* on the Pt surface. This work demonstrates the synergistic effect of the oxidation‐resistant metal Zn and the construction of Pt‐rich surface engineering. Also, it guides the future development of catalysts for their practical applications in energy conversion technologies and beyond.

Single-frame measurement of complete spatiotemporal field of ultrashort laser pulses using frequency domain separate spectral interferometry

The spatiotemporal coupling distortion of large aperture ultra-high peak power laser will degrade the pulsed beam in both near-field and far-field. To accurately predict the light field distribution at the focus and compensate for the spatiotemporal coupling distortion, a single-frame measurement of full three-dimensional spatiotemporal coupling distortion is proposed based on the frequency domain separate spatial-spectral interference. The setup requires only a slit array attached to the front of an Imaging spectroradiometer. The whole procedure of carrier frequency distinguished spectral interference measurement is simulated in this study. The simulation results prove that the presented measuring method is correct and effective. The effectiveness of this method will be further verified experimentally in next step.

A parametric study of sub-picosecond laser ablation of thin metal foils

With the properties of ultrashort pulse width and ultrahigh peak power, femtosecond lasers excel at processing materials whose thickness is less than 500 μm. Numerous experiments and theoretical analyses have testified to the fact that there are solid grounds for the future applications of femtosecond laser micromachining [1, 2]. However, with the high costs and complexity of these devices, it is the sub-picosecond laser that might be an alternative when it comes to micromachining of thin metal foils. Furthermore, investigating the sub-picosecond laser interactions with matter could provide a better understanding of the ablation mechanisms and experimental verification of existing models concerning the ultrashort pulse regime. We present research on sub-picosecond laser interaction with metal foils with a thickness of less than 250 μm under various laser pulse parameters. The research was conducted by two types of ultrafast lasers: a lab-designed sub-picosecond Yb:KYW laser (650 fs) and a commercial femtosecond Ti:S laser (35 fs). The results show how variables, such as pulse duration, energy, repetition rate, wavelength and irradiation time, affect the micromachining process.