High Laser Fluence Research Articles

In-situ laser ablation of mineral fluid inclusions: Evaluating the effects of solid and liquid matrices, laser repetition rate and fluence on data quality

Fluids play an important role in many geological/ore genetic processes. The composition of the hydrothermal fluid is a critical but often unknown parameter that controls the mobilization of elements and their concentration into mineralized zones. In-situ analyses of fluid inclusions trapped in minerals using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is a powerful tool to constrain the composition of the mineralizing fluid. The LA-analysis of fluid inclusions is analytically challenging due to potential mismatch of matrix between fluid inclusions and solid NIST reference glasses commonly used as calibrating standards. We conducted experiments to evaluate the effects of using solid and liquid as calibrating standard on data quality during ablation of liquid/mineral fluid inclusions, as well as the effects of variable energy fluence and repetition rate on the time-dependent elemental fractionation. The LA-analyses of liquids (with NaCl matrix) when standardized against another solution has lower precision and accuracy compared to standardization with NIST reference glasses. The 193 nm laser has little matrix effect and causes negligible elemental fractionation. The trace element concentrations of liquids retrieved by external standardization with NIST reference glass has better accuracy and precision. Higher laser fluence (8.5 J/cm2) produces better sensitivity, lesser time-dependent elemental fractionation, lower detection limits, and better accuracy/precision and is recommended for ablation of natural fluid inclusions or liquids. We tested our preferred analytical protocol by analyzing the composition of quartz-hosted fluid inclusions from the Malanjkhand copper deposit in central India. The LA-ICPMS measurements of the fluid inclusions help to establish that the mineralizing fluid had high concentrations of K, Rb, and Cs. Fluid inclusions from the Malanjkhand copper deposit are trapped from fluids that are dominantly of magmatic origin, sourced from highly differentiated granitic magmas. The NIST glasses are appropriate calibrating standards for ablation of synthetic liquids as well as natural fluid inclusions.

Multiphysics modeling of femtosecond laser–copper interaction: From electron dynamics to plasma eruption

The femtosecond laser ablation of metals is a complex and violent nonequilibrium process, and numerous studies have sought to reveal the evolution of a single physical phenomenon, such as laser-induced periodic surface micro-nanostructures or plasma eruptions. By considering the multiphysics scenarios of energy and heat transfer, structural mechanics, hydrodynamics, and nucleation dynamics, a femto-nanosecond and nano-micrometer multiscale framework combining electron–phonon-coupled heat transfer, lattice deformation, phase transition, and plasma eruption was constructed to describe the heat and mass transfer mechanism of femtosecond laser–copper interaction. A multiphysics model was proposed in this study to simulate the ablation process with different laser fluences. Ablation occurs at low near-threshold fluences primarily via a combination of the thermal phase transition process of melting and thermoplastic deformation coupled with the nonthermal phase transition process of hot electron explosion. Marangoni convection and non-uniform nucleation at the solid–liquid interface create micro-nano structures on the surface of the ablation crater. At a high laser fluence, plasma plumes are emitted via gasification and eruption, and as the material is heated to decrease its density, the surface is broken into a micro-column structure, and then the micro-columns fracture and erupt to form micro-nano structures and plasma plumes. Numerical results offer a better understanding of surface topography modifications and plasma plume evolution and promote the application of femtosecond laser precision fabrication in the fields of aviation, mechanics, electronics, and materials engineering.

Improvement of fundamental frequency performance of SGII-UP laser facility

The SGII-UP laser facility is one of the most important high power laser systems in China, and it is also one of a few inertial confinement fusion laser devices that operate all year round in the world. In order to further improve its output capacity to meet higher physical requirements, measures such as increasing the number of neodymium glasses, adopting new N41 neodymium glasses, and improving the energy configuration of xenon lamps are taken to improve the gain capacity of the main amplifier. Calculation of the new main amplifier construction model predicts that the small gain coefficient will reach 4.9%. And further modulation of the laser device shows that when the output of 10 kJ fundamental frequency energy is needed, the injection energy decreases from 5 J to 1.26 J, which supports a higher output energy and a stronger basic frequency output capability. Furthermore, it is analyzed that under different laser pulse injection conditions of 1, 5, 10 ns, the <i>B</i> integral is obviously reduced, which means that the near-filed quality of the beams is better. According a small-size modulation suppression is induced by nonlinear phase shift, and high-fluence laser is expected to pass before and after the improvement, which is a key prerequisite for a higher output energy. Based on these analyses, fundamental frequency output energy values with different pulse injections are calculated and an improvement from 8 kJ to 12.5 kJ output is expected under 10 ns square pulse condition. Tests show that the small signal gain coefficient of the device increases from 4.15% cm to 4.94% cm, which is consistent with simulation results, and the average gain multiple of a single beam increases from 9000 to 118000, which is an order of magnitude higher. The output verifies the fundamental frequency output capacity exceeding 12.5 kJ under 10 ns square pulse as well as a small-size modulation suppression around 0.16 mm<sup>–1</sup> as a result of joint action of non-linear phase shift and spatial filtering. After the significant improvement, the SGII-UP laser facility will strongly support more ambitious physical experiment targets.

Design of an ultrafast pulsed ponderomotive phase plate for cryo-electron tomography

Ponderomotive phase plates have shown that temporally consistent phase contrast is possible within electron microscopes via high-fluence static laser modes resonating in Fabry-Perot cavities. Here, we explore using pulsed laser beams as an alternative method of generating high fluences. We find through forward-stepping finite element models that picosecond or shorter interactions are required for meaningful fluences and phase shifts, with higher pulse energies and smaller beam waists leading to predicted higher fluences. An additional model based on quasi-classical assumptions is used to discover the shape of the phase plate by incorporating the oscillatory nature of the electric field. From these results, we find the transient nature of the laser pulses removes the influence of Kapitza-Dirac diffraction patterns that appear in the static resonator cases. We conclude by predicting that a total laser pulse energy of 8.7μJ is enough to induce the required π/2 phase shift for Zernike-like phase microscopy.

Enhanced and Selective Absorption of Molybdenum Nanostructured Surfaces for Concentrated Solar Energy Applications

Surfaces of commercial molybdenum (Mo) plates have been textured by fs-laser treatments with the aim to form low-cost and efficient solar absorbers and substrates for thermionic cathodes in Concentrated Solar Power conversion devices. Morphological (SEM and AFM), optical (spectrophotometry), and structural (Raman spectroscopy) properties of the samples treated at different laser fluences (from 1.8 to 14 J/cm2) have been characterized after the laser treatments and also following long thermal annealing for simulating the operating conditions of thermionic converters. A significant improvement of the solar absorptance and selectivity, with a maximum value of about four times higher than the pristine sample at a temperature of 800 K, has been detected for sample surfaces treated at intermediate fluences. The effects observed have been related to the light trapping capability of the laser-induced nanotexturing, whereas a low selectivity, together with a high absorptance, could be revealed when the highest laser fluence was employed due to a significant presence of oxide species. The ageing process confirms the performance improvement shown when treated samples are used as solar absorbers, even though, due to chemical modification occurring at the surface, a decrease of the solar absorptance takes place. Interestingly, the sample showing the highest quantity of oxides preserves more efficiently the laser texturing. The observation of this behaviour allows to extend the applicability of the laser treatments since, by further nanostructuring of the Mo oxides, it could be beneficial also for sensing applications.

Self-recoverable near-infrared mechanoluminescence from ZnS:Mn by controlling manganese clusterization

Near-infrared (NIR)-emitting mechanoluminescence (ML) materials are highly desirable since they are biological transparency and suitable for deep-imaging inside biological tissues. So far, NIR emission can be found in very limited number ML materials. Moreover, reported NIR ML materials suffer from limitations associated with the incompetence in self-reproducibility. Herein, we observe sustainable and self-recoverable NIR ML emission in pulsed laser deposition (PLD) method grown ZnS:Mn film, for the first time. ML emission in ZnS:Mn can be explained by the piezoelectricity-induced detrapping model. Broad ML emission covering both red and NIR ranges arises from the presence of (Mn)n clusters, which facilitates the energy transfer from excited Mn2+ ions to them. During the PLD growth, high laser fluence and deposition rate contribute to the formation of (Mn)n clusters, which was verified by electron paramagnetic resonance EPR and X-ray photoelectron spectroscopy XPS analysis. The device exhibits durable NIR ML over 105 repeated mechanical stresses, suggesting new possibilities aiming for constructing self-recoverable NIR ML materials.

Laser‐Induced Transient Anisotropy and Large Amplitude Magnetization Dynamics in a Gd/FeCo Multilayer

AbstractUltrafast laser‐induced dynamics in a ferrimagnetic gadolinium iron cobalt (Gd/FeCo) multilayer with a magnetization compensation temperature of TM = 320 K is studied at room temperature as a function of laser‐fluence and strength of the applied magnetic field. The dynamics is found to be substantially different from that in archetypical GdFeCo alloys, and depending on the laser fluence one can distinguish two different regimes. At low laser fluence (⩽1.6 mJ cm‐2), ultrafast laser excitation of the medium triggers spin precession of an extraordinary large amplitude reaching over 30°. At high laser fluence (⩾2.2 mJ cm‐2), the pump heats the medium over the magnetization compensation point, spin precession reduces significantly in amplitude and the process of field‐assisted reversal of magnetization of Gd and FeCo is launched. It is argued that such a distinctly different laser‐induced magnetization dynamics in the multilayers compared to the alloys is due to the symmetry breaking at the numerous interfaces, giving rise to additional surface anisotropy. The temperature dependence of the latter is found to be the key ingredient in the mechanism of ultrafast laser‐induced magnetization dynamics in ferrimagnetic multilayers. Controlling the amount and properties of interfaces in multilayers can thus serve as a mean to achieve efficient ultrafast all‐optical control of magnetism.

(Digital Presentation) Preparation of Metal Halide Perovskite Thin Films Via Laser Deposition

We have been preparing metal halide perovskite (hereinafter referred to as perovskite) thin films by laser deposition. In this study, we report the results of our investigation of the effects of laser wavelength and fluence on the deposition process. One of the most important features of perovskites, which have been rapidly developed in recent years as materials for high-efficiency and low-cost thin-film solar cells, is the applicability of a simple process using solution coating under atmospheric pressure [1]. Crystal growth of perovskite by the solution method occurs through equilibrium chemical reactions, enabling the formation of thin films on the order of μm thickness in less than a few seconds; however, it is difficult to systematically control the crystal growth process at the molecular layer level by the solution method. On the other hand, in the physical vapor deposition (PVD) method, although the deposition rate is relatively low, ranging from sub-nanometer to several nm/s, the deposition can be controlled at the molecular layer level, as well as allowing different atoms to be readily introduced into the film. Therefore, the PVD method allows the addition of elements that are difficult to achieve with solution reactions and is suitable for studies that investigate the effects of such elements on physical properties.In laser deposition (LD), one of the PVD methods, materials are irradiated with an infrared (IR) or an ultraviolet (UV) laser beam, and thin films are formed by evaporation through IR heating or ablation with plasma formation through UV electron excitation. The advantage of LD is that it can cause instantaneous heating or ablation by switching on and off laser irradiation only on the material surface, thus enabling the deposition of molecular layers of organic materials with high vapor pressure or high melting point materials such as inorganic oxides with minimal cross-contamination caused by evaporation. We have prepared perovskite thin films by alternate deposition of PbI2 and CH3NH3I (MAI) using an IR laser and solid-phase reaction at room temperature aiming at the detailed investigation of the crystal growth process and introduction of various dopants in perovskite materials. [2, 3]. In this study, we have also performed perovskite film deposition by UV pulsed laser and investigated the difference in the physical properties of the perovskite films compared to those deposited by IR laser.Fig. 1 shows a schematic structure and appearance of the laser deposition system used in this experiment. The experimental method is described below. A synthetic quartz substrate was introduced into an ultra-high vacuum chamber with a base vacuum of 2×10-5 Pa., Then a semiconductor continuous IR laser (wavelength: 808 nm) or a UV pulse laser beam generated by the fourth harmonic of an Nd:YAG Q-Switch laser (wavelength: 266 nm, 10 Hz) was irradiated alternately onto PbI2 and MAI targets to form CH3NH3PbI3.The optical band gap of the thin films deposited by continuous infrared laser deposition shows a change in optical band gap depending on the thickness of the alternately deposited PbI2 and MAI, which can be attributed to the different content ratios of the tetragonal and orthorhombic phases. Interestingly, in UV pulsed laser deposition, the deposition rate was about 0.35 nm/s under the high laser fluence condition with lens focusing, while a high deposition rate of 20 nm/s was obtained under the low laser fluence condition without lens focusing. This result suggests that the excess kinetic energy of the deposition precursor in the case of lens-focused deposition causes re-sputtering on the surface of the already deposited film, resulting in a reduction of the effective deposition rate.In the presentation, we will demonstrate and discuss the results of crystallinity and optical absorption properties.[1] T. Miyasaka, A. Kulkarni, G. M. Kim, S. Öz and A. K. Jena, Adv. Energy Mater. 2020, 11902500 (2020).[2] K. Kawashima, Y. Okamoto, O. Annayev, N. Toyokura, R. Takahashi, M. Lippmaa, K. Itaka, Y. Suzuki, N. Matsuki and H. Koinuma, Science and Technology of Advanced Materials 18, 307 (2017).[3] N. Matsuki, Y. Iida, T. Shimada, Yuta Abeand T. Sato, ECS Meeting abst. MA2020-02, 1860 (2020). Figure 1

Annealing duration dependent optical, nonlinear optical, and optical limiting properties of rare-earth doped glasses embedded with gold nanoparticles

In this work, the Eu2O3 doped B2O3 glass specimen embedded with gold nanoparticles (NPs) was designed by the process of melt-quenching and subjected for thermal treatment to understanding the efficacy of thermal dependency on the optical and nonlinear optical (NLO) characteristics. Linear optical studies have revealed a decrease trend in the energy band gap as the function of annealing duration, indicating the increase of non-bridging oxygen concentration in the glass host. The NLO properties were assessed in near-infrared region utilizing 150 fs laser pulses delivered at the rate of 80 MHz. The aperture free Z-scan measurements exhibited an increased nonlinear absorption coefficient with annealing duration. Further, the closed aperture Z-scan data depicted an increase trend in the positive nonlinear refraction with annealing duration and eventually reduced at the greater duration of annealing. The optical limiting studies demonstrated similar behaviour to the nonlinear absorption characteristics of studied glass samples. These results are related to the local field stimulated by surface plasmons of gold NPs near the Eu3+ ions during the exposure of glass to high fluence laser beam. Our results indicate that B2O3 glasses embedded with Au NPs heat-treated for 30 h at 450 °C are good candidates for nonlinear photonic, optoelectronic, and optical power limiting applications in photonics.

Photo-engineered optoelectronic properties of indium tin oxide via reactive laser annealing

Transparent conductive oxides are appealing materials for optoelectronic and plasmonic applications as, amongst other advantages, their properties can be modulated by engineering their defects. Optimisation of this adjustment is, however, a complex design problem. This work examined the modification of the carrier transport properties of sputtered tin-doped indium oxide (ITO) via laser annealing in reactive environments. We relate the optical modifications to the structural, compositional, and electronic properties to elucidate the precise mechanisms behind the reactive laser annealing (ReLA) process. For sufficiently high laser fluence, we reveal an ambient-dependent and purely compositional modulation of the carrier concentration of ITO thin films. Hereby, we demonstrate that ReLA utilises the precise energy delivery of photonic processing to enhance the carrier mobility and finely tune the carrier concentration without significantly affecting the crystal structure. Exploitation of this phenomena may enable one to selectively engineer the optoelectronic properties of ITO, promising an alternative to the exploration of new materials for optoelectronic and photonic applications.

Achieving superhydrophobic surfaces with tunable roughness on building materials via nanosecond laser texturing of silane/siloxane coatings

In this work, we employ a versatile laser-based top-down approach that allows to create superhydrophobic and hydrophobic surfaces, with controlled roughness and wetting properties, on marble and potentially other building materials. The process involves two stages: (1) application of an organically modified silica coating to reduce surface energy. (2) Controlled texturing of the coating by ablation using a nanosecond-pulse laser. In general terms, at higher laser fluence (energy per unity of area), the contact angles increased from 110° of the non-textured surface to values around 155°, following a nearly linear correlation with the measured roughness values. Starting from fluence values of 154 J cm−2, the surfaces displayed water repellence (hysteresis ≤10°) and the micrographs showed the formation of sub-micrometric structures on top of the micro-roughness by melting and re-deposition of the coating material, suggesting the formation of a Cassie-Baxter wetting regime. Ablation at lower fluences created a random micro-roughness, leading to static contact angles of 135–145° but no water repellence, which is indicative of a Wenzel wetting regime. At the highest fluence values tested, the increasing trends respect roughness and hydrophobic/water repellent properties are inverted due to the damages suffered by the coating. In terms of durability, the coating demonstrated a good adhesion to the stone surface, maintaining its superhydrophobic properties after repeated cycles of an “adhesive tape test”. The sand falling test showed that water repellence is relatively sensitive to abrasion, although the hydrophobic character of the coating is maintained.

Laser fluence dependence of stoichiometry and superconductivity of iron chalcogenide superconducting films on metal tapes

Iron chalcogenide Fe(Se,Te) films with thicknesses of 150 nm were deposited on CeO2-buffered metal tapes via pulsed laser deposition using various laser fluences. The film crystallinity and stoichiometry improved upon increasing the laser fluence. This was explained by the ablation threshold that the superconducting performance was better at higher laser fluences and was attributed to the joint contribution of higher Te contents, better texture, and strengthened in-plane strain. In addition, the pinning mechanism was studied by analyzing the in-field performance characteristics of the Fe(Se,Te) films. The dominant pinning center remained point pinning and was independent of the magnetic field direction and temperature. A collective pinning theory-based analysis showed that the vortex pinning behavior in the Fe(Se,Te) film varied from δl pinning to δTc pinning as the temperature approached the critical temperature. This was related to film superconductivity inhomogeneity, which was driven by unreacted Se and Te atoms.

Research on the Nonlinear Absorption Coefficient of 98% Deuterated DKDP Crystal at Fourth-Harmonic-Generation Wavelength

A series of 98% deuterated DKDP crystals were grown in solutions with different pD values (2.9, 3.3, 3.8, and 4.3) using the rapid growth method. Samples were cut along the z-direction and fourth-harmonic-generation (FHG) direction which contained both pyramidal and prismatic regions. The nonlinear absorption (NLA) coefficient β of 98% deuterated DKDP crystals was obtained using the Z-scan method operated at the FHG wavelength (266 nm) of a picosecond Nd:YAG laser. According to the results, the nonlinear absorption at 266 nm could be identified as two-photon absorption. The β values of crystal grown in the solution with 3.3 pD value were higher than those of crystals grown in solutions with other pD values under higher laser fluence. The results also indicated that FHG device samples should be prepared from the pyramidal region due to its lower β value. This work will help optimizing the application of 98% DKDP crystals as FHG elements in high-power laser systems.

Numerical and experimental investigation on pulsed nanosecond laser ablation processing of aluminum alloy

The laser ablation of aluminum alloy 6061 was studied both experimentally and by computational modeling in this work. Six variations of the number of pulses of irradiation (1, 5, 10, 20, 50, and 100 pulses) combined with four different laser fluence (2.0 J/cm2, 1.5 J/cm2, 1.0 J/cm2, and 0.5 J/cm2) were chosen to study the effect of heat input and laser action time on microstructural changes and the generation of particulate pollutants. Laser fluence and the number of pulses of laser irradiation were found to have a direct influence on thermal diffusion and the ablation depth of aluminum alloy 6061. At a relatively high laser fluence (2 J/cm2) and with the application of 10 pulses of irradiation, ablation cracks were observed on the surface of aluminum alloy 6061 and the production of pollutant particles increased according to a particle counter. Maintaining the laser fluence at 0.5 J/cm2 while increasing the number of pulses of irradiation to 50 also enhanced the depth of thermal diffusion while laser ablation continued to occur. The occurrence of vaporization in the surface region was influenced largely by laser fluence and the number of pulses of irradiation, as evident from the simulation and from experimental results. The single laser pulse duration was 6 ns and the repetition rate was 1 s−1. This article provides a novelty numerical model which could reveal the metal alloys' evapotation at a high-fluence nanosecond laser ablation. A 3D computational model was used to predict the temperature variation upon laser irradiation in a solid material over time. The results of the model (thermal diffusion versus laser ablation) agreed well with the experimental results.

Ultraviolet nanosecond laser ablation of polyimide with thermal and nonthermal effects near threshold fluence

Typically, a 355 nm laser is not sufficient for inducing photochemical ablation and leads to photothermal effects such as melting and recasting. Consequently, most previous studies on the irradiation of polyimide (PI) with such lasers have focused on temperature distribution on the surface and variations in the absorption properties of PI depending on the temperature and time. Herein, the authors demonstrate ablation without thermal effects on the surface of PI using a 355 nm pulse nanosecond laser near the threshold fluence. For ablation without thermal effects, the ablated and nonablated areas can be clearly distinguished in the area exposed to the laser. The interface between these areas, that is, the ablation shape, became wider with increasing laser fluence, even when the spot size remained unchanged; also, the shape of the ablated area was related to the laser intensity distribution. Ablation with thermal effects began to appear in the nonablated areas at higher laser fluence. This study shows that PI, which is physically stable and relatively inexpensive, can be used to develop cation exchange membranes, which can be applied to organic flow cells as well as microbial fuel cells.

Modelling the initial plasma dynamics in a laser triggered vacuum switch

The numerical simulations of the initial plasma dynamics induced by 1064 nm laser irradiation on a KCl-Ti mixture target in a laser-triggered vacuum switch are performed. The simulation results showed that laser irradiance strongly affects the dynamics of the initial plasma. With higher laser fluence, the plasma plume will have higher temperatures and densities, and the shock front will also move faster. During the laser ablation, the plasma shielding is a non-negligible process. As the degree of ionization increases, the absorption coefficient of the plume increases and the it begins to absorb the laser energy. The temperature and velocity of the plume increase dramatically as it absorbs laser energy. When laser fluence gets higher, the plasma shielding starts with a shorter time and a larger proportion of the laser energy is absorbed by the plume.

Absence of isotope effects in the photo-induced desorption of CO from saturated Pd(111) at high laser fluence

Neural network-based potential energy surfaces are currently gaining relevance in the context of gas-solid dynamics. In this work, we use this methodology to theoretically explore femtosecond laser pulse induced desorption of CO from the Pd(111) surface with a coverage of 0.75 ML. We performed molecular dynamics simulations in the high laser fluence regime on two different CO isotopes, 12C16O and 13C18O, in order to search for possible isotope effects affecting the photo-induced desorption. According to our findings, isotope effects of relevance do not appear in desorption probabilities once the whole process has finished after 50 ps. However, for those molecules desorbed with the highest translational kinetic energies, we obtain that 12C16O molecules are more vibrationally excited than 13C18O. This mostly happens as a consequence of the interaction of adsorbed CO with the laser-excited electrons in the substrate.

Determination of sub-ps lattice dynamics in FeRh thin films

Understanding the ultrashort time scale structural dynamics of the FeRh metamagnetic phase transition is a key element in developing a complete explanation of the mechanism driving the evolution from an antiferromagnetic to ferromagnetic state. Using an X-ray free electron laser we determine, with sub-ps time resolution, the time evolution of the (–101) lattice diffraction peak following excitation using a 35 fs laser pulse. The dynamics at higher laser fluence indicates the existence of a transient lattice state distinct from the high temperature ferromagnetic phase. By extracting the lattice temperature and comparing it with values obtained in a quasi-static diffraction measurement, we estimate the electron–phonon coupling in FeRh thin films as a function of laser excitation fluence. A model is presented which demonstrates that the transient state is paramagnetic and can be reached by a subset of the phonon bands. A complete description of the FeRh structural dynamics requires consideration of coupling strength variation across the phonon frequencies.

Energy-filtered dark-field imaging of nanoparticles by PINEM in 4D electron microscopy

Time-resolved dark-field imaging of alpha Fe2O3 nanoparticle and Ag nanowires using scattered electrons by selected crystal planes are realized by photon-induced near-field electron microscopy (PINEM) selecting probing electrons which absorb energy from a transient laser field during their passage through the target particles in a four-dimensional transmission electron microscope (4D-TEM). The high laser fluence illuminated on the particles causes significant part of probing swift electrons exchange energy with the laser light, creating enough PINEM electrons required for the dark-field imaging of particles with high spatiotemporal resolution at nanometer and femtosecond scale. Different from the bright-field PINEM imaging of particles where the outerspace with a close distance to the particle are illuminated by transmitted PINEM electrons, illumination is confined on the particles by selected scattered PINEM electrons, leading to a much more defined and sharp imaging of particles compared with a bright-field PINEM image. In combination with PINEM temporal gating and dark-field selective imaging, the PINEM dark-field imaging technique in the 4D-TEM enables the studies of structural dynamics of selective crystal planes or elements with high spatiotemporal resolution.

Estimating energy release performance of oxidizer-activated aluminum fuel particles under ultrafast stimulus

Aluminum (Al) particles are good fuel additives to improve the energy output performances of explosives. Under detonation environment, reaction delay of Al particles plays a key role in the energy release efficiency. Up to date, reaction delay of Al particles is still limited by the efficiency of mass and heat transfer from oxidizers to Al particles. To address this issue, a homogeneous fuel-oxidizer assembly has recently become a promising strategy. In this work, oxidizer-activated Al fuel particles (ALG) were prepared with glycidyl azide polymer (GAP) as the oxidizer. The ALG was in uniform spherical shape and core-shell structure with shell layer of around 5 nm which was observed by scanning electron microscope and transmission electron microscope. The localized nanoscale mid-IR measurement detected the uniform distribution of characteristic absorption bond of GAP in the shell layer which confirmed the homogenous fuel-oxidizer structure of ALG. A thermal gravimetric analysis of ALG at ultrafast heating rate of 1000 °C/min under argon atmosphere was conducted. The decomposition of GAP finished much earlier than that of GAP at heating rate of 10 °C/min. Under ultrafast high laser fluence, the reaction response of ALG was characterized and compared with that of micro-sized Al (μAl). With the increase of laser energy, the propagation distance of the shock wave increased. However, the velocity histories were nearly the same when energies were lower than 299 mJ or higher than 706 mJ. The propagation distance of the shock wave for ALG was 0.5 mm larger than that for μAl at 2.1 μs. The underwater explosion showed the peak pressure and the shock wave energy of the ALG-based explosive were both higher than those of the μAl-based explosive at 2.5 m. This study shows the feasibility to improve the energy release of Al-based explosives via using the oxidizer-activated Al fuel particles with energetic polymer as the oxidizer.