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This study presents the experimental investigation of the ignition and subsequent combustion spreading sequences of hydrogen jets issued from a single-hole nozzle into a constant-volume combustion chamber. The hydrogen jet flames, forced ignited using a laser-induced plasma ignition, were monitored using high-speed schlieren imaging and pressure trace measurements. The parameters varied include the laser ignition location (axial or radial positions), laser ignition timing and the ambient oxygen level (10–21 vol.%). An analysis of the jet flame evolution reveals that the reaction front of the hydrogen jet spreads from the forced ignition site to engulf the entire downstream jet volume and recedes towards the nozzle. The results reveal that the ignition parameters and ambient oxygen condition in which it occurs can impact the jet flame recession and stabilisation characteristics. When ignition occurs sufficiently downstream or at the jet head periphery, the flame may not attain a stable lift-off within the specified injection period. Additionally, lower ambient oxygen levels lead to slower flame recession towards the nozzle. Furthermore, the heat release profile of the hydrogen jet flame exhibits dependence on both the laser ignition parameters and ambient oxygen level. • Laser-plasma ignition. • Flame evolution. • Flame stabilisation. • Hydrogen direct-injection. [ABSTRACT FROM AUTHOR]

• We analyze the impact of plasma noise on Taiji using Wind's electron number density data. • Lomb–Scargle method is used to estimate the spectrum of plasma noise in 10−6 to 10−2 Hz. • The spectrum of plasma noise is fitted by power law and its effect on TDI is estimated. • It provides a basis for estimating plasma noises in similar gravitational wave observatories. In space-based laser interferometric gravitational wave antennas, plasma from the solar wind is an important noise floor source for laser interferometric measurements between two distant spacecraft. In this study, we aim to analyze the impact of solar wind on the inter-satellite laser interferometric measurements of the Taiji mission, a space-based laser interferometric gravitational wave antenna proposed by the University of Chinese Academy of Sciences. Based on the 6.5-year electron number density data from the National Aeronautics and Space Administration Wind spacecraft and considering the uneven sampling characteristics of the data, we employed the Lomb–Scargle spectral analysis method to study the impact of solar wind plasma on intersatellite laser interferometric measurements within the frequency range of 1 × 10 - 6 Hz to 0.01 Hz. The study shows that the effect of the plasma on the intersatellite laser interferometric measurement is approximately 1 pm/ Hz at 3.3 mHz, which is one order of magnitude smaller than the requirements on the displacement noise of the interferometric measurement of the Taiji mission, indicating that the noise due to plasma will not affect the aim of the Taiji mission to detect gravitational waves. The research can be applied to Taiji, Laser Interferometer Space Antenna, and future gravitational wave detection missions. [ABSTRACT FROM AUTHOR]

The silicon carbide (SiC) ceramic material was prepared by powder metallurgy processing route using spark plasma sintering (SPS) technique without any sintering additives. The effects of the SiC surface ablation by fiber laser and subsequent superficial incorporation of graphene nanoplatelets (GNPs) into the created microcraters were investigated in terms of their influence on the resulting tribological (i.e., friction and wear) behavior of the created SiC-graphene composite surfaces. It was clearly shown that the used laser treatment with the pulse duration in ms range led to desirable surface morphological changes, i.e., the creation of SiC ablated microrelief, suitable for GNPs incorporation. The friction and wear behavior of produced SiC-graphene composite surfaces was studied using translational ball-on-disc nanotribometer at room temperature and applied loading up to 1000 mN. The results showed that at all normal loads the wear rates of laser ablated surface materials were gradually decreasing as a result of frictional coefficient reduction. The observations of wear track topography indicated abrasive wear to be the dominant wear mechanism of the sintered SiC material. However, by incorporation of GNPs, the abrasive wear was significantly reduced by the graphene friction film created on the ablated SiC-graphene composite surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Coulomb implosion mechanism of the negatively charged ion acceleration in laser plasmas is proposed. When a cluster target is irradiated by an intense laser pulse and the Coulomb explosion of positively charged ions occurs, the negative ions are accelerated inward. The maximum energy of negative ions is several times lower than that of positive ions. We present the theoretical description and Particle-in-Cell simulation results of the Coulomb implosion mechanism, and show the evidence of the negative ion acceleration in the experiments on the high intensity laser pulse interaction with the cluster targets. [Copyright &y& Elsevier]

Laser plasmas have been produced using a xenon gas jet as a target. Spectra in the range of 5–20 nm were recorded using a transmission grating spectrograph. A quantitative spectral analysis is given of the dependence of the EUV source brightness ∼13.5 nm on two critical parameters, namely the initial target gas density and EUV absorption in the outermost, low-density target zone. [Copyright &y& Elsevier]

Stark broadening parameters are useful in solving various problems e.g., in astrophysics, opacity calculations, design of lasers, laser-produced plasma and for the evaluation of the physical conditions in stellar atmospheres. Our objectives in this research work are to obtain, for electron collisions, new atomic data for Stark broadening of astrophysically important S II lines using semi-classical perturbation (SCP) and modified semi-empirical (MSE) theory with the needed energy levels and oscillator strengths from NIST database. After calculating the Stark broadening data, we compared them with experimental and theoretical data. [ABSTRACT FROM AUTHOR]

This work aims to investigate the mechanisms governing H 2 jet flame evolution and stabilisation by precisely controlling the jet ignition location using a laser-induced plasma in compression-ignition engine-relevant conditions. The experiments examine the flame evolution with high-speed schlieren imaging and pressure trace measurements in an optically-accessible constant-volume combustion chamber over a range of ambient O 2 concentration (10–21 vol%) and temperature (600–800 K) conditions. Optical results reveal that in most cases, a localised flame kernel forms at the time and location of the laser-induced plasma and grows in connected regions to engulf the entire upstream and downstream jet volume of the ignition spot. The images also reveal that the flame lift-off is sensitive to ambient O 2 and temperature changes. The flame appears attached to the nozzle at 21 vol% O 2 , but becomes lifted at a lower ambient O 2 concentration and a colder temperature. A simplified numerical analysis suggests that edge-flame deflagration into stratified premixed fuel-ambient reactant streams explains the lift-off response to ambient O 2 and temperature changes. Furthermore, at the lowest tested O 2 concentration, the flame stabilisation occurs in leaner mixtures at the jet peripheral where it is likely exposed to stronger turbulence-chemistry interactions. [Display omitted] • Laser ignition of H2 jet in high-pressure high-temperature engine-related environment. • Optical study of H2 jet flame evolution in varied O2 and temperature conditions. • A localised flame kernel forms at ignition spot before spreading throughout the jet. • H2 flame lift-off is sensitive to ambient O2 or temperature changes. • Flame deflagaration and its sensitivity to ambient could explain lift-off responses. [ABSTRACT FROM AUTHOR]

The principal trend of the last decades is the use of laser systems generating ultrashort (femtosecond) laser pulses of gigawatt and terawatt power in various spheres of human activity, in particular, in atmospheric researches. One of the important challenges within this problem is the use of the unique nonlinear optical phenomena manifesting in the atmosphere as pulse self-focusing, light-induced ionization of the medium, plasma generation and laser filamentation for remote laser diagnostics of the aerosol-gas constituents and efficient delivery of concentrated optical energy over long distances in the atmosphere. This brings to the forefront the problem of increasing the actual length of the nonlinear interaction of an ultrashort laser pulse with medium to kilometer distances whereas real physical length of most existing optical paths is usually limited by several hundred meters. We propose and theoretically substantiate an effective way to solve the problem of long-range atmospheric filamentation by transforming the propagation medium itself using short laboratory traces and optical cuvettes with gases of increased (over-atmospheric) pressure. Following the scaling laws of the optical characteristics of pressurized medium, the coefficients describing the interaction between optical wave and medium increase along with the increase in gas pressure. By the numerical simulations in the framework of the nonlinear Schrodinger equation, we show that this makes it possible to emulate kilometers-long atmospheric traces for laser beams of centimeter diameter and terawatt pulse power on the laboratory scale (tens of meters). • Barometric scalability of the standard optical pulse filamentation model in gases is detailed. • The principles for building the equivalent optical traces in compressed air are addressed and verified. • Filamentation of a high-power laser pulse at kilometer range in air is substituted by the filamentation of a low-power pulse in compressed air. [ABSTRACT FROM AUTHOR]

The characteristics of laser-produced metal hydride plasmas have been investigated in this work. The charge state and velocity of ions were determined by employing a time-of-flight technique in conjunction with an electrostatic deflection method. The ion velocities were found to be supersonic with values in the range of 104 to 105 m/s. The proportion of hydrogen ions was found to be lower than that of titanium ions. The ion emission behavior was studied by using a Faraday cup. When the total integrated space was taken into account, the ns pulsed laser was capable of producing hydrogen ion currents greater than one hundred mA. In order to understand the plasma generation process, we performed a comparative analysis between laser-generated plasma and arc plasma, and also investigated the effect of laser power density on the composition and velocity of the ions, the ablation properties of metal hydrides, and the maintainability of hydrogen ion emission. [ABSTRACT FROM AUTHOR]

Laser produced plasma extreme ultraviolet light source, as the exposure light source for next-generation lithography, faces urgent challenges due to its low conversion efficiency and significant debris contamination. Using a triple Langmuir probe, we conducted a study on the parameters and kinetic characteristics of tin droplet-based laser produced plasma that serves as extreme ultraviolet light source. In this paper, we report a design of triple Langmuir probe circuit based on the BWL (Bulk Wirewound Low-value) sampling resistor, which ensures that high-frequency signals remain undistorted during acquisition. Utilizing the "shadowgraph" method, we calculated the average deflection angles of droplet debris jets under different alignment conditions. Combining the diagnostic results from the probe, we found that the alignment accuracy between the laser and droplet directly influences the parameters of plasma. The parameters and kinetic characteristics of plasma were also diagnosed and analyzed at different angles and distances by moving the probe. Employing the triple Langmuir probe, measurements and analyses of laser produced plasma parameters and kinetic characteristics were achieved, providing a convenient method for diagnosing extreme ultraviolet lithography light sources. This work also offers an effective basis for optimizing the light sources. • Probe circuit based on a wirewound resistor ensures high fidelity in high-frequency signals. • Triple Langmuir probe combined with shadowgraph method for quantitative plasma analysis. • Multi-position detection reveals plasma's spatiotemporal distribution for comprehensive analysis. [ABSTRACT FROM AUTHOR]

We have prepared various low-density Gd targets to investigate the effect of concentration on the extreme ultraviolet (EUV) radiation near 6.7 nm and out-of-band emission from laser-produced plasma source. Results show that an increased EUV radiation intensity and narrow-band spectra from the low-density target was obtained. Comparing with the original solid Gd target, the intensity and spectral purity of the 6.7 nm EUV radiation from the 40 % mass concentration Gd target are enhanced 45 % and 74.5 %, respectively. And the FWHM of the spectra are decreased to one-half of that from the solid target. The measurements of the plasma electron density for various concentration targets shown that the low-density target exhibited lower plasma electron density, which reduced the self-absorption effect and the yield of the low-charge ions in the plasma, resulting in the enhancement of EUV radiation intensity as well as narrower band spectra output. Finally, the out-of-band radiation in the range of 325–385 nm from the 40 % concentration Gd target is decreased to approximately 60 % of the solid target case, while the angular distribution profile was significantly uniform. Our findings are beneficial to the Gd target as a new promising source candidate for the EUV nanolithography in the future. • The relationship between target concentration and EUV characteristics was obtained, the optimal target was determined. • The mechanism of low-density was analyzed by the measurements of plasma electron density using interferometry. • The OOB radiation of low-density targets was significantly decreases, the angular distribution profile was uniform. [ABSTRACT FROM AUTHOR]

Efficient evolution of electrolytic gas products is one of the mechanisms for increased material removal rate in laser-assisted electrolyte jet machining. However, the evolution mechanism of electrolytic gas products with multiple energy fields in laser-assisted electrolyte jet machining is not clear. In order to quantitatively characterize the laser-assisted facilitation of the evolution of electrolytic gas products, a gas quantification and detection device was designed and built in this paper. Compared to traditional electrolyte jet machining, laser-assisted electrolyte jet machining of 2024-T3 aluminum alloy increased the gas production by 52 % in 180 s. For the anode, the surface modification induced by laser texturing reduces the oxygen evolution potential and surface free energy and promotes gas nucleation and detachment. In addition, laser-induced conductive plasma can enhance transient currents for electrolyte jet machining and cause machining vibrations. The cathodic gas discharge phenomenon was characterized in conjunction with interelectrode gap visualization experiments and cathodic nozzle damage. Experimental results show that cathodic gas discharge depends on strong electric field and high laser pulse fluence. In summary, laser temperature rise, anode surface modification, laser-induced plasma, plasma recoil and cathode gas discharge can all contribute to the evolution of electrolytic gas products. [Display omitted] • A device for quantitative detection of electrolytic gas products was designed and fabricated. • Laser texturing can facilitate the evolution of oxygen on the anode surface. • The cathode gas evolution is accelerated by the cathode gas discharge at high laser pulse fluences. [ABSTRACT FROM AUTHOR]

• Efficiency of THz generation by the plasma of femtosecond optical filaments in air depends on the filament spatial structure; • THz yield from laser filaments is 1.5-fold increased by a thin turbulent layer of heated air placed in the femtosecond optical beam; • The effect is theoretically explained on the base of incoherent superposition of multiple linear dipole sources; Remote generation of electromagnetic waves in the terahertz (THz) by the volume of air medium gains increasing scientific interest due to the demand for this spectral range in solving various practical problems including those belonging to the nonlinear atmospheric optics. During self-focusing and filamentation of high-power femtosecond laser pulses in air, the source of THz radiation is the plasma of laser filaments. One of the main challenges of THz generation by a laser filament is increasing the value of optical energy conversion to the long-wavelength band. In this paper, we present the results of our studies on DC-biased THz generation during single-color filamentation in air of focused femtosecond Ti:Sapphire-laser pulses (800 nm, pulse energy up to 40 mJ). The distinctive feature of our study is that a femtosecond optical pulse propagates through a spatially-localized heated air layer containing randomly inhomogeneous refractive index perturbations, which mimics strong air turbulence. For the first time to our knowledge, we show, that the turbulent air layer formed at the beginning of the optical path allows increasing the yield of THz radiation up to 1.5 times due to the formation of multiple chaotically-arranged filaments resulting from random perturbations of the optical beam energy profile that reduces the subsequent THz (re)absorption in the filament plasma. [ABSTRACT FROM AUTHOR]

• A PIC model is developed to investigate the plasma behaviors in laser damage processes under intense laser irradiation. • The evolution laws of plasma characteristics under intense laser irradiation are proposed to study from various aspects. • The particle ejection and the formation of craters are reproduced and the internal physical mechanisms are obtained. The laser-induced damage on KDP crystal optical surfaces under intense laser irradiation significantly limits the energy outputs of the high-power laser systems in many regions. The energy deposition in the non-heat stage of the laser-induced damage process is regarded as the main energy source, directly determining the laser-induced damage thresholds. It can cause severe damage to the optical surfaces under intense laser irradiation and significantly affect the final damage morphology on the optical surface. Nevertheless, there is still no available model that can well reproduce the behaviors of the plasma in the non-heat stage to reveal the internal physical mechanisms of the non-heat stage currently. Hence, a particle-in-cell (PIC) model is proposed to investigate the behaviors of the plasma in the non-heat stage. Afterward, the feature information of the plasma in the non-heat stage on the KDP crystal optical surface without surface defects under intense laser irradiation has been obtained from three aspects: the electron density, the electron phase-space distribution on the subatomic scale, and the electric field distribution at different times. Then two types of typical damage behaviors of particle ejection and the formation of the damaged craters on optical surfaces under intense laser irradiation are studied based on the developed model. Finally, the plasma behaviors in the processes of particle ejection and the formation of the damaged craters are well reproduced and the internal physical mechanisms of these two types of damage behaviors are obtained. To sum up, this work proposes a PIC model to investigate the plasma behaviors in the non-heat stage. Based on this, this work reveals the energy deposition mechanism of the non-heat stage in the process of the laser-induced damage on KDP crystal optical surfaces under intense laser irradiation and obtains the interaction laws between the intense laser and the plasma. Moreover, this work opens a door for the study on the non-heat stage of the laser-induced damage process on the optical surface from the subatomic scale, which is beneficial to the revelation of the internal physical mechanisms in the non-heat stage and the solution of the laser-induced damage issues in high-power laser systems. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) is a well-established technique widely used in fundamental research and diverse practical fields. Polarization-resolved LIBS, a variant of this technique, aims to improve the sensitivity, which is a critical aspect in numerous scientific domains. In our recent work we demonstrated that the degree of polarization (DOP) in the emission depends on the spatial location and time in a nano second laser generated aluminium plasma1. Present study investigates the effect of polarized emission on the estimation of plasma parameters. The plasma parameters are estimated using the conventional spectroscopic methods such as Boltzmann plot and line intensity ratio for the estimation of electron temperature and Stark broadening for estimating the electron density. The estimated plasma temperature using Boltzmann plot method shows large errors in electron temperature for the locations where DOP is higher. However, the electron density estimated using the Stark width does not show such variation. The observed ambiguity in temperature estimation using the Boltzmann plot method appears to be a consequence of deviation from expected Maxwell Boltzmann distribution of population of the involved energy levels. These findings highlight the need of assessing the DOP of the plasma before selecting the polarization for PRLIBS or temperature estimation using Boltzmann plots in elemental analysis. Figure shows the wavelength dependence of Degree of Polarization (DOP) of Al II emissions lines from different locations within the plasma plume at various time delays. At larger distances (3.5 mm and 4.5 mm), the DOP of emission lines shows a substantial wavelength dependence in comparison to the locations nearer to the sample. [Display omitted] • Dependence of degree of polarization of line emissions from laser produced plasma on emission wavelength • Plasma parameters are estimated using spectroscopic methods. • The estimated temperature from Boltzmann plot method shows significant errors for polarization-resolved data. • Results shows a possible deviation from MB distribution for different energy levels of a given species. • Information of the DOP of the emission is critical for estimation of plasma parameters using spectroscopy. [ABSTRACT FROM AUTHOR]

• High-energy coupling of laser-induced plasma electrolyte jet machining is realized. • The effect of laser beam refraction on machining is explored. • Compensation model for laser beam refraction is proposed. Laser-induced plasma electrolyte jet machining is a new hybrid machining method. This machining method utilizes the plasma impact effect and plasma to increase the inter-pole conductivity for material removal, with low laser energy loss, high material removal rate (MRR), and good surface quality. The advantages of laser machining and electrolyte jet machining are fully utilized. However, it is difficult to avoid refraction of the laser in the electrolyte column, which affects the efficient coupling of the laser to the electrolyte jet machining. In this paper, to improve the localization and MRR, a study is carried out to address the problem of energy utilization efficiency in laser-induced plasma electrolyte jet machining. A compensation model for the refraction of the laser beam in the electrolyte is proposed. Compensation improves the shape and positional accuracy of the laser beam coupled to the electrolyte beam during aluminum alloy machining. Compared before and after compensation, the MRR was improved by 30.2 %, and the groove localization was improved by 37.4 %. Realization of high energy coupling for laser electrolyte jet hybrid machining. [Display omitted] [ABSTRACT FROM AUTHOR]

In the realm of biological experimental research, bacterial deposition on scientific instruments' surfaces can compromise the integrity of experimental outcomes. Prolonged bacterial accumulation may even result in diminished instrument functionality, rendering them incapable of normal operation. Traditional chemical cleaning methods carry the risk of secondary contamination and are unsuitable for decontaminating precision optical or electronic instruments. Therefore, it is imperative to develop novel non-contact, waterless, contamination-free, and non-destructive decontamination methods. This paper introduces an innovative two-dimensional high-speed scanning sterilization technique based on high repetition rate laser-induced quasi-continuous plasmas. The experiment targeted Escherichia coli and Bacillus subtilis for decontamination, investigating the impact of laser energy, repetition rate, scanning rate, repetition scanning times, and focal distance on the inactivation rate. The results indicate that at a laser repetition rate of 15 kHz, an energy of 680 μJ/pulse, a repetition scanning of 10 times, and a focal distance of −50 mm, the decontamination efficiency reaches 26.7 mm2/min, with an inactivation rate exceeding 98 %, achieving rapid and efficient decontamination of bacteria adhering to the carrier. Furthermore, the paper explores the decontamination mechanism of laser-induced plasma, demonstrating that the primary mechanism of bacterial inactivation using this technique is the action of the plasma rather than the thermal ablation effect of laser irradiation. The proposed laser-based bacterial decontamination device is characterized by its compact design, integrability, ease of operation, and high inactivation effectiveness. This makes it a promising solution with broad applications in the fields of biological science, precision optoelectronics, medical devices, food processing, and more. Moreover, it integrates with LIBS technology to achieve the integrated development of identification and disinfection. [ABSTRACT FROM AUTHOR]

Single-crystal diamond has great potential applications in national defense, military, and aerospace fields. However, the high hardness, chemical inertness, and anisotropy bring great challenges to machine microstructures on the diamond. Here, iron plasma, generated by infrared nanosecond laser ablation of a Fe target, was utilized to etch single-crystal diamond. The EDS, Raman, and XPS analysis revealed the formation of iron carbide within the sputtered layer surrounding the diamond microgrooves, thereby confirming that the iron plasma reacts chemically with the diamond. It was observed that employing a reactive metal, such as iron, for etching diamond microgrooves yields improved morphological characteristics and enhanced etching efficiency compared to the use of a non-reactive metal, such as copper. Moreover, the process of material removal through laser-induced iron plasma etching of diamond was elucidated. Subsequently, a systematic investigation was conducted on the impact of processing parameters on the laser-induced iron plasma etching of diamonds. Various periodic microstructures with regular edges and no chipping and cracks were successfully processed on the diamond using suitable laser parameters. This study furnishes a novel approach for the efficient fabrication of high-quality microstructures on single-crystal diamonds. [ABSTRACT FROM AUTHOR]

Abstract: The plasma plume induced by dual-pulse laser ablation of a titanium target in vacuum was analyzed by the technique of cavity ringdown spectroscopy (CRDS). Large Doppler-splitting of the absorption spectral lines was observed which is due to increase of the velocity components parallel to the optical axis and specific features of the CRDS measurements. Vertical velocity component, the particle number density and plasma volume also show increase compared to the single-pulse laser ablation. The forward convolution best fit of absorption lineshapes was used to extract parameters describing dual-pulse laser ablation plasma plume. [Copyright &y& Elsevier]

The high mechanical and chemical properties of SiC make it difficult to texture and modify its surface using such conventional methods as mechanical machining and wet etching. Among possible alternative strategies, Atmospheric Pressure Plasmas (APPs) could be used, cutting cost and time, but much still has to be understood about their feasibility for the surface treatment of ceramic materials. In this work, the effectiveness of a commercial corona discharge system in modifying the surface of SiC has been evaluated, focusing on its positive effect on the joint strength of adhesively bonded plasma-treated SiC. The objective of the study has been to observe the surface changes, in terms of chemical composition and texture, that take place as a result of exposure to corona plasma and to compare the obtained results with previous studies on laser and low-pressure plasma textured SiC samples. These very first results, derived from characterization and mechanical testing, suggest that this approach could be a promising alternative. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we report an innovative pump-probe based experimental set up, to study the melting, subsequent evaporation, plasma formation and re-deposition in a thin film coated on a glass substrate under different ambient conditions and laser fluences. The ambient conditions restrict the expansion of the plasma plume. At high ambient pressure, plume expansion stops closer to the substrate and gets re-deposited at the site of the ablation. This helps in the identification of multiple processes and their temporal evolutions during the melting, expansion and re-deposition stages. The ambient conditions affect the plasma plume formed upon ablation, thus modulating the transmission of probe laser pulses, which provides information about the plume dynamics. Further, the study offers valuable insights into the laser-based ablation of thin film coatings, which will have implications in situ cleaning of view ports on large experimental facilities such as tokamaks and other systems e.g. coating units, pulsed laser deposition, Laser induced forward transfer, Laser surface structuring, etc. • An innovative experimental method to study laser surface interaction. • Effect of ambience and laser fluence on the ablation and redeposition is studied. • The redeposition is validated with micro-Raman and SEM analysis. • Observed IB absorption up to an extented duration of a few 100s of ns. • The study offers insights into laser ablation, surface structuring, PLD and LIFT. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methane conversion is investigated by employing the hybrid SD-LIP method. • Methane dissociation rate is measured by making use of FTIR spectroscopy. • Decomposition of methane is mainly revealed according to the vibrational peaks of sp/sp2 C–H stretching bonds. • *Corresponding dissociation rate in SD-LIP is notably enhanced compared to that of LIP. • Dissociation rate demonstrates two-fold enhancement increasing the spark discharge voltage up to 6.5 kV. The widespread utilization of fossil fuels cause to significantly elevate greenhouse gas emissions. Consequently, the developments of the innovative methods are essential to convert methane into the green energy. Recently, significant effort is made to enhance the performance of the plasma-based conversion technologies. Here, the dissociation rate of methane into heavier hydrocarbon compounds are carefully determined by making use of a hybrid laser-induced plasma (LIP) and spark discharge (SD). Fourier-transform infrared (FTIR) spectroscopy reveals a couple of characteristic peaks after laser triggering, whose intensities notably increase at higher applied voltages. The corresponding peaks indicate the formation of heavier compounds including sp and sp2 C–H stretching bonds. The findings elucidate that the methane decomposition rate notably elevates in favor of hybrid SD-LIP against that of traditional LIP. It is worth noting that the simultaneous ablative effect of the catalyst surface to remove the carbon soot by the successive laser shots could prevent the catalytic deactivation leading to the sustained performance. [ABSTRACT FROM AUTHOR]

• Two types of the combined laser with different laser irradiation mechanisms is proposed for a 2D C/SiC-Ti 3 SiC 2 composite. • An in-situ observation measurement is developed to obtain the instantaneous combined laser irradiation behaviors. • An efficient, phenomenological multi-scale ablation model is established and revealed the "accelerated" ablation behavior under the combined laser irradiation. The combined laser has been applied in laser processing due to the accelerated damage behavior and processing efficiency. However, the best-combined scheme is uncertain for C/SiC composites due to multiple ablation modes and damage effects at various input laser parameters. In this paper, the combined laser, composing the continuous-wave and short-pulsed or long-pulsed lasers, is experimentally investigated in terms of the efficiency of ablation behavior. An in-situ observation system is established to obtain the instantaneous ablation process. The numerical simulation procedure, which includes an efficient and phenomenological multi-scale ablation model, is also proposed to reveal the ablation mechanism of the combined laser. The experimental and numerical results reveal the governing ablation mechanism of the different composed schemes: When combined with continuous-wave laser, the short-pulsed laser induces the plasma impact effect can reduce the oxidation resistance of the 2D C/SiC-Ti 3 SiC 2 composite, whereas the long-pulsed laser can significantly accelerate the ablation rate. The multi-scale ablation model in this work can provide an effective analytical tool for studying the efficient processing mechanisms of the combined laser. [ABSTRACT FROM AUTHOR]

• Harmonic generation in Cu 2±x Se nanocrystals varying the stoichiometric ratio of Cu/Se. • Smaller clusters, atoms/ions, or tiny nanoparticles show resonance enhancement in HHG. • Suitable for upscaling HHG by altering the material composition. • Altering stoichiometric ratio as new degrees of freedom to form coherent short-wavelength sources. Altering the composition of various solid elements will influence the high-order harmonic generation in laser-induced plasma, paving the way for analysis of the properties of the materials used in this process. In this study, we demonstrate a significant enhancement in harmonic intensities and a variation of harmonics in Cu 2±x Se nanocrystals by adjusting the stoichiometric ratio of Cu/Se. We investigate the influence of the target, heating pulse, and driving pulse on the intensity and cut-off higher order harmonics to evaluate the role of the stoichiometric ratio in steering the harmonic emission. The theoretical calculations of harmonics generation, based on strong-field approximation, in the atomic plasma of Cu and Se are presented. [ABSTRACT FROM AUTHOR]

• β-Bi 2 O 3 NPs were synthesized by pulsed laser ablation of Bi target in atmospheric air at different power densities. • The LIBS method was used to study the effect of laser plasma composition and temperature on nanoparticle formation under nonequilibrium conditions. • The particles obtained by PLA of Bi in atmospheric air consist of stoichiometric and non-stoichiometric tetragonal bismuth oxide, and also contain carbonates and nitrates on the surface. • β-Bi 2 O 3 nanoparticles with NO 3 – groups on the surface show high photocatalytic activity in RhB decomposition under UV and visible light. Purposeful synthesis of bismuth oxide nanoparticles (NPs) of various crystal modifications is important for biomedicine, photocatalysis and other applications. In this work, pulsed laser ablation of a metallic Bi target in atmospheric air is used to obtain β-Bi 2 O 3 NPs. The effect of the Nd:YAG laser radiation power density (1064 nm, 7 ns) in the range of 0.1–1.2 GW/cm2 on the features of formation of NPs under nonequilibrium conditions is studied, for which the spectra of laser-induced plasma are recorded and analyzed, the plasma composition is determined, and the temperature of the plasma plume is estimated. The NPs are comprehensively characterized using TEM, XRD, FTIR, Raman, and UV–Vis spectroscopies, and electrophoretic light scattering, which make it possible to determine their morphology, crystal structure, chemical composition, and optical properties. The photocatalytic activity of the resulting nanopowders in the Rhodamine B dye decomposition reaction is assessed. [ABSTRACT FROM AUTHOR]

The widely-used magnesium alloy AZ91D is light-weight and energy-saving with good castability and mechanical performance. The traditional machining way for magnesium and its alloys is the high-speed mechanical contact cutting, which usually leads to uncontrollable intense ignition with some notable heat-induced machining defects. However, it has been rarely reported that the non-contact precision laser machining is used for cutting the magnesium and its alloys. The problems such as the local heat effect, the heat-induced defects and the local ignition as well as the vapor-plasma plume usually encountered during laser machining of magnesium and its alloys. Hence, in this study, a hybrid laser cutting way of femtosecond laser layered ring hole-cutting using the assist gas and E-field is reported to machine micro holes in the AZ91D material. The effect of the lateral E-field and assist gas on the hole formation characteristics was demonstrated for femtosecond laser cutting of the AZ91D sheets. It was indicated that the use of the lateral E-field and assist gas suppressed the ignition as well as the vapor-plasma plume. The hole depth was increased by the external assistance used especially the lateral nitrogen blowing. The hole wall formation quality was improved by using the lateral E-field and compressed air blowing, while it got poorer if using the lateral nitrogen blowing. The ignition-induced carbonization was effectively suppressed by the assist gas used. The hole depth, microstructure and micro hardness were improved by using the lateral E-field and assist gas. • Femtosecond laser hole-cutting of AZ91D is first reported using E-field and assist gas. • Nearly no heat-induced defects were found despite laser-induced ignition with plasma. • Lateral E-field and assist gas suppressed ignition and vapor-plasma plume. • Lateral E-field and assist gas increased hole depth and improved microstructure. • Assist gas used effectively suppressed the ignition-induced carbonization. [ABSTRACT FROM AUTHOR]

Laser produced plasma ions implantation has a great potential to change various characteristics of the polymer after irradiation, such as, surface, structural, optical and electrical properties. For this purpose, polymer CR- 39 is implanted by laser produced Ni plasma ions at various fluences ranging from 75 × 1013 to 95 × 1016 ions/cm2. The ion energy estimated by Thomson parabola technique using CR-39 detectors was 540 KeV. Digital optical microscopic analysis illustrates the formation of granular morphology for all ion fluences. However, at the maximum fluence (95 × 1016 ions/cm2), distinct and well organized grains with sub-granular morphology are observed. Confocal microscopic analysis shows the development of micro/nano sized caters, voids, ion tracks, clusters and bumps for various fluences of Ni ions ranging from 75 × 1013 to 60 × 1015 ions/cm2. Whereas, at the maximum ion fluence (95 × 1016 ions/cm2), hillock like features are observed. Raman spectroscopy analysis shows the formation of carbonaceous structures along with new bonds of Ni–C O in implanted CR-39. Reduction in transmittance value from 92.2% to 60.8% is observed with increase in ion fluence from 75 × 1013 to 95 × 1016 ions/cm2. The electrical conductivity of implanted CR-39 increases by increasing the ion fluence. Formation of conductive layer and carbonaceous structures are considered to be accountable for improvements in electrical conductivity of implanted target polymer. The observed stopping power or Linear Energy Transfer (LET) of 540 KeV Ni ions in CR-39 is 72.88 eV/Ǻ and their corresponding depth is 686 nm. • To investigate the surface, structural, topographical, optical and electrical properties of Ni ion implanted CR-39. • Formation of ion induced well defined granular morphology is perceived. • The estimated surface temperature of implanted surface increases up to 7.1 × 104 K. • Linear Energy Transfer (LET) of 540 KeV Ni ions in CR-39 is 72.88 eV/Ǻ and their corresponding depth is 537.3 nm. • Electrical conductivity of implanted CR-39 increases monotonically by increasing ion fluence. [ABSTRACT FROM AUTHOR]

• Laser surface modification improves bonding strength for 316L and TA1 bipolar plate. • Laser generates morphological reconstruction, pollutant removal and oxide generation. • Laser-treated surface exhibits good reliability under atmospheric exposure. • Laser surface modification is competitive in further application to hydrogen fuel cell. Safety and service life of hydrogen fuel cell is significantly affected by the bonding interface between polar plate and gasket, however, tremendous difference in physiochemical properties challenges the bonding strength between metallic polar plate and gasket, and sealing failure commonly occurs at bonding interface under the combined effect of assembly stress and hash service environment. This study investigates the influences of surface modifications on bonding strength of metallic polar plate (e.g. stainless steel and titanium) and gasket, and both techniques of laser and plasma surface modifications are utilized to alter surface characteristics of metallic polar plate with comparison to primer coating, where the processing parameters are optimized by orthogonal experiments. Laser surface modification increases the bonding strength by 355% and 285% for stainless steel and titanium compared to untreated condition, respectively, while plasma surface modification results in an improvement of 123% for titanium and little increase for stainless steel. It is observed that laser generates micro-/nano- hierarchical structure and induces oxidation reaction of elemental Ti and Fe, contributing to bonding strength through interfacial interlocks and stronger interactions with gasket molecules. Moreover, laser-treated titanium surface exhibits higher stability under atmospheric exposure, and loses 30% of initial bonding strength after 24 h exposure, however, 30% reduction of bonding strength is found for plasma-treated surface only after 6 h exposure. Therefore, laser surface modification is competitive in enhancing bonding strength between metallic polar plate and gasket, and this study provides support for potential application prospects of surface modification technology in the field of hydrogen fuel cell. [ABSTRACT FROM AUTHOR]

This research aims to develop a feedback control laser processing system using artificial intelligence. Real-time online measurement of hole depth for blind hole processing is challenging. In this study, electric fields were used to detect laser-induced plasma signals and a neural network was used to predict the hole depth to overcome this difficulty. This electric field was generated by a pair of electrode plates placed above the drilled surface to provide hundreds of volts of DC voltage. During laser processing, laser-induced plasma interferes with the electric field and generates a detection signal. This signal is sent back to the neural network to estimate the hole depth. This study also trained a neural network to predict the machining parameters required for a given hole depth and diameter. If the error in the hole size after processing exceeds the threshold value, the feedback control system will perform immediate compensation processing to reduce the error. This avoids the difficulty of relocating the material. Therefore, this study integrated laser processing, online laser-induced plasma detection, and neural network-based parameter estimation to form an advanced feedback control laser machining system that can solve the problems of processing parameter prediction, real-time hole depth measurement, and compensation processing relocation encountered during the processing process. The experimental results demonstrate that the proposed method can effectively compensate for processing and reduce errors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Laser Ignition was investigated at high initial chamber pressures and temperatures. • Flame kernel evolution and growth were studied using shadowgraphy. • Flame front developed faster in hydrogen-air mixtures than in CNG-air mixtures. • Leaner fuel-air mixtures are more prone to two-stage combustion. • Laser ignition has potential in high compression ratio hydrogen engines. Engine combustion typically involves the preparation of fuel-air mixture, ignition, combustion, and pollutant formation. The ignition phenomena distinguish them by ensuring a dependable operation under any working environment, which also affects downstream processes and events. The experimental study focuses on understanding the early stages of flame-kernel evolution in laser-induced spark-ignited combustion of hydrogen and natural gas-air mixtures in a constant-volume combustion chamber (CVCC). Experiments were conducted for five initial pressures (4–20 bar, in the intervals of 4 bar) and three initial temperatures (373, 473, 573 K) in the CVCC to investigate the flame kernel evolution. Initial temperature and pressures simulated typical engine conditions with different compression ratios. A Q-switched Nd: YAG laser emitting 1064 nm wavelength with a pulse width of 6–9 ns was used for ignition by producing laser plasma in the CVCC. The flame kernel evolution and combustion analysis of hydrogen were compared to the baseline stoichiometric natural gas-air mixture. The results indicated that the flame front developed differently and burned faster in hydrogen-air mixtures when micro-explosions happened in the wavefront than in the natural gas-air mixture. The Flame kernel evolution and growth were studied using a high-speed CMOS camera by employing the Shadowgraphy technique. Excess chamber pressure–time history under different operating conditions was recorded and analysed for each test condition during these experiments. The time to attain the maximum pressure for the stoichiometric CNG-air mixture was approximately equal to the time to attain the maximum pressure for λ = 2.5 to 3 for hydrogen-air mixture. At 4 bar initial chamber pressure, the maximum excess chamber pressure for the stoichiometric mixture of CNG was 10.5 bar, and it took ∼ 205 ms to reach the peak pressure. However, the peak pressure for hydrogen at this condition was 15.5 bar, and it took only 5.2 ms to attain this pressure. Flame kernel images for the hydrogen-air mixture showed significantly faster growth than the stoichiometric CNG-air mixture. The third lobe was visible in all cases, including different initial temperatures and pressures in the CNG-air mixture. [ABSTRACT FROM AUTHOR]

• Laser ignition of a lean methane/air mixture by dual-color femtosecond pulses is investigated. • A strong wavelength effect in fs laser ignition (fs-LI) is found. • The role of the ionization enhancement in the wavelength effect is clarified. • The mechanism of fs-LI is ascribed to the non-resonant photochemical ignition. Laser ignition (LI) is promising for green combustion of lean-fuel mixtures with controllable ignition timing and location. It was recently discovered that despite the inferior energy deposition and low thermal temperature in femtosecond (fs) laser-induced plasma, fs laser pulses can achieve a robust ignition of lean-fuel mixture through forming a "line" kernel by filamentation. Here, to clarify fs-LI mechanism, we investigated a dual-color (DC: 800 nm at 1.5 mJ and 400 nm at 0.43 mJ, ∼50 fs) fs-LI of a lean methane/air mixture with an equivalence ratio of φ = 0.87. An optical emission spectroscopy study was conducted to probe the N 2 + and OH emissions and characterize the ignition success rate. It was demonstrated that fs-LI can be achieved at a lower minimum ignition energy (MIE) (<0.46 mJ) by the DC scheme than that (>0.7 mJ) by a single-color (SC: 800 nm at 2.0 and 2.4 mJ, ∼50 fs) scheme, indicating a strong wavelength effect on the successful ignition. A pump-probe measurement was carried out to reveal the effect of the ionization enhancement on the successful ignition. It was found that only when the two-color fs pulses are temporally overlapped, the OH yield is strongly enhanced and the MIE is decreased. By comparing the variation trend of the fluorescence intensity of OH with that of the direct ionization product N 2 +, we ascribed fs-LI to a non-resonant photochemical ignition mechanism, in which the enhancement in the multiphoton/tunnel ionization of the lean-fuel mixture by the high-energy 400-nm photon can increase the yields of the reactive radicals through various dissociation and chain reaction pathways, and thus result in the successful ignition at the micro-joule level. This work unravels the essential role of the non-resonant photochemical ignition mechanism in fs-LI, and provides a promising route for the ignition of lean-fuel engines by compact ultrashort-pulsed lasers in the filamentation regime. [ABSTRACT FROM AUTHOR]

• Absorption non-uniformities within aggregates increase with increasing aggregate sizes, and may contribute to excessive absorption and anomalous cooling effects observed in TiRe-LII experiments on metal nanoparticles. • For the aggregates considered, primary particles within the aggregate may be shielded from the E-field at certain orientations leading to a larger degree of absorption and emission non-uniformity, however, orientation has a less than 10 % impact on the random orientation value. • Sintering-induced overlap can enhance the absorption properties of the aggregate due to increased electrical conductivity and morphological changes towards an elongated structure that promotes the antenna effect. Analyzing time-resolved laser-induced incandescence (TiRe-LII) data from metal nanoparticle aerosols requires a detailed understanding of their absorption and emission characteristics. This work investigates how non-uniform absorption within metal nanoparticle aggregates, aggregate morphology and orientation, and sintering of primary particles may affect TiRe-LII signals from metal nanoparticle aerosols. The multi-sphere T-matrix method is used to compute the absorption properties of aggregates with point contact between primary particles, while the discrete dipole approximation method is used when primary particles overlap. It was found that absorption non-uniformities within aggregates increase with increasing aggregate sizes, and may contribute to excessive absorption and anomalous cooling effects. For the anisotropic aggregates considered, the total absorption cross-section depends weakly on orientation. It was also found that the sintering of primary particles can enhance the absorption cross-section of metal aggregates. [ABSTRACT FROM AUTHOR]

Self-absorption effect is always encountered in laser-induced breakdown spectroscopy (LIBS) and immediately distorts the calibration curves especially for the elemental determination of complex materials. With the aim to provide an expeditious approach for LIBS measurements susceptible to self-absorption effect, an exploratory study for sample preparation by powder mixing is implemented, and the self-absorption of laser-induced plasma beryllium emissions is investigated as a function of the dilution factor. For comparison, boric acid and wax powder are separately used as typical binding agent to mix with beryl powder to produce two sets of pressed pellets with sequential gradient of beryllium content variation. For the resonant lines most prone to self-absorption of Be II emission doublet at 313.042 nm and 313.107 nm, the beryllium spectral line shapes can be directly regulated and improved in the case of both sets of pellets as the dilution factor increases. In addition, the self-absorption effect for the strongly emitting beryllium spectral lines is further assessed by calculating the self-absorption coefficients based on the radiation transport equation. With regard to the both types of binder as diluent, when the dilution factor for beryl increases to 10 with a weight percent of 0.386% for beryllium in the pellet, the SA values may exponentially increase in general to around 0.8 and eventually asymptotically approaches to 1 without exception. Thus the self-absorption effect of laser-induced beryl plasma emissions can be readily overcome with sample preparation by powder mixing. By contrast with laser pulse irradiance in the present work, the dilution factor for powder mixing plays a dominant role in eliminating self-absorption effect. This research proposes a potentially effective approach to reduce self-absorption in laser-induced plasma emissions. [Display omitted] • Sample preparation by powder mixing is used to overcome plasma self-absorption. • The beryllium spectral line shapes can be regulated and improved. • Laser-induced beryl plasma self-absorption can be eliminated eventually. • The effect of laser pulse irradiance on self-absorption is binder-type dependent. • Dilution factor for powder mixing dominates the eliminating of self-absorption. [ABSTRACT FROM AUTHOR]

We studied the tolerance of one species of quinoa achenes from ecotype RQ252 to simulated extraplanetary conditions in a vacuum chamber (high low-pressure 10–2 to 10-7 Torr, UV laser simulated plasma radiation, and cryogenic temperature). The selection of this ecotype of quinoa achenes was a condition to previous studies, where RQ252 shows evidence of high efficacy in grow adaptation in the South America Puna between 3800–4500 m asl subjected to low oxygen and increased UV radiation exposition. After extraplanetary experiment exposure, we evaluated quinoa tolerance to experimental conditions through germination and early growth responses under a controlled laboratory standard atmosphere. Rate and final germination subjected to high low-pressure treatments during 4 h, 8 h, and 16 h were not different to control. Laser plasma application accelerated the germination rates. Final germination always reaches values up to 90%. SEM-EDS analysis showed structural changes on the pericarp surface, especially in high low-pressure and high low pressure + plasma treatments. EDS revealed that the quinoa pericarp subjected to different treatments showed changes in mineral content. Potassium ions decreased under high low-pressure and high low pressure + laser plasma irradiation (between 32 and 42%) but increased in a prolonged vacuum (35%) and more when plasma was added (96%). Early growth was affected by the different treatments, being the radicle length the most affected parameter. Our results suggest that quinoa achene ecotype RQ252 viability has excellent tolerance to extraplanetary conditions. • Quinoa viability has a great tolerance to extraplanetary conditions. • Quinoa achenes are viable after high low-pressure and laser irradiation conditions. • Quinoa sprouts seem to be a good fresh food alternative for long term space missions. [ABSTRACT FROM AUTHOR]

Sapphire crystals have a special lattice structure, which causes anisotropy in their processing quality due to anisotropy of the physical and mechanical properties. Laser-induced plasma assisted ablation (LIPAA) is a new processing technology used to process transparent, hard, and brittle materials. LIPAA is regarded as a photoelectric composite processing method that makes the material removal and surface generation mechanisms more complicated. In this study, a surface generated by LIPAA processing showed much higher quality than a surface generated by direct laser ablation. Moreover, LIPAA has the advantage of a lower etching energy threshold than that of infrared laser direct ablation. Infrared laser-induced plasma assisted ablation was performed on different sapphire crystal orientations to explore the influence of anisotropy on LIPAA processing. The LIPAA material removal rates for different sapphire planes were presented and compared with results for direct laser ablation-focused ion beam (FIB) processing. The results showed that thermal removal was most dominant during LIPAA processing of sapphire. The material removal rate was highest in the [10 1 ‾ 0] direction and lowest in the [11 2 ‾ 0] direction. [ABSTRACT FROM AUTHOR]

The precise machining of silicon carbide composite (SiC–SiC) as a high-tech material with extraordinary characteristics is required for different applications in aerospace, light weight construction and car industry. Laser machining enable new approaches for fabrication processes but the regularly applied ablation processes can cause damage to the SiC–SiC material. Here we propose and demonstrate a new approach for gentle SiC–SiC machining making use of a laser-induced plasma for reactive species generation enabling chemical material removal processes. A fs-laser (775 nm, 150 fs, 1 kHz) was focussed to a CF 4 /O 2 gas mixture igniting a laser-induced plasma (LIP) approximately 100 μm in front of a SiC–SiC sample. This LIP initiate material removal processes of the textured, multiphase SiC–SiC sample without a mechanical damage of the SiC–SiC composite structure. Different surface features such as etching of the cover SiC layer, etching of the SiC matrix and exposure, thinning and sharpen of the SiC fibres, underetching of the fibres has been observed. Across the whole etched area, no mechanical damage such as cracks, delamination's, broken fibres were observed so that a gentle machining process can be expected. [Display omitted] • Etching of superhard SiC–SiC by a reactive, laser-induced plasma (LIP) was achieved. • Preferential etching of the matrix causes the exposure of fibres due to processing. • Selective etching of the various SiC–SiC phases causes specific surface morphologies. • Damage-free machining of the SiC–SiC composites by lasers is shown. [ABSTRACT FROM AUTHOR]

The research has examined the effects of CO 2 dilution on ignition characteristics in H 2 /air mixtures. An ignition kernel was initiated by a laser-induced plasma in H 2 /air/CO 2 mixtures with a bulk velocity of 6.5 m/s. An infrared camera was used to measure radiation intensity emitted from H 2 O and ignition probabilities. A high-speed schlieren image system was utilized to measure ignition kernel areas and ignition time. High-speed chemiluminescence was performed to examine OH* intensities. Numerical simulations were conducted using GRI 3.0 mechanisms to calculate reaction rates and laminar flame speeds. The ignition probability is highest for the undiluted mixtures and decreases with increasing the CO 2 dilution fraction at constant adiabatic temperatures. A prolonged ignition time is observed at elevated CO 2 dilution concentrations. Increasing the CO 2 mole fraction decreases the ignition kernel growth, the integrated OH* intensity, and the integrated radiation intensity for each adiabatic temperature. CO 2 reacts with H radicals and decreases the production of OH*, OH, and H 2 O. The CO 2 dilution in the H 2 /air flames significantly contributes to the reduced reaction rate and flame speed, resulting in the low ignition probability. The high ignition probability is found at the large integrated OH* intensity in all cases. The ignition probability is high at the large integrated radiation intensity under the constant adiabatic flame temperatures. The OH* intensity is a critical parameter to estimate the ignition probability in the diluted lean hydrogen flames. • The effects of CO 2 dilution on the ignition process have been studied in lean premixed H 2 /Air flames. • The ignition probability decreases with increasing the CO 2 dilution fraction. • An increase in the CO 2 dilution fraction in the mixtures reduces OH* intensity and radiation intensity emitted from H 2 O. • The presence of CO 2 in the mixtures decreases reaction rates and flame speed. [ABSTRACT FROM AUTHOR]

Superhydrophobic functional surfaces are widely used in medical treatment, pipeline transportation, and ship corrosion protection and have great potential in the field of anti-icing. Ultrafast laser-induced plasma micromachining (LIPMM) combined with a chemical modification of a fluoroalkyl low surface-energy substance (Novec) was used to fabricate superhydrophobic surfaces with periodic layered micro-nano arrays on Ti6Al4V. The wettability, droplet collision behavior and wear resistance of surfaces with different physical and chemical properties were analyzed. In terms of static anti-icing, based on the classical nucleation theory, the icing-delay performance of different surfaces was analyzed. Ice adhesion strength and frosting properties were also studied. It was found that the micro-nano structure surface fabricated by LIPMM had strong hydrophobicity (contact angle of 164°, roll-off angle of 1.0°), high icing delay time (3072 s, 4 μL of water droplet on the surface at −10 °C), low ice adhesion strength (38.2 kPa), and better durability. Additionally, the droplets bounced off this surface after colliding at different angles (0°, 5°, 10°, and 20°). This study provides a feasible solution for fabricating anti-icing surfaces on Ti6A14V. • Micro-nanostructures machined by laser-induced plasma micromachining promote the growth and attachment of compounds. • The influence of structures and chemical elements on surface wettability is studied. • The wettability and droplet collision behavior of surfaces were analyzed. • The static anti-icing properties of the Micro-nanostructures were investigated. [ABSTRACT FROM AUTHOR]

Femtosecond-laser ablation is becoming increasingly popular due to its advantageous characteristics such as reduced fractionation and improved lateral resolution. However, since the emission from the resulting laser-induced plasmas is reduced and relatively short-lived, optical spectroscopy analyses with fs lasers (LIBS) are often carried out with enhancement strategies, such as double-pulse LIBS. For orthogonal double pulse set ups, characterizing the spatio-temporal excitation of the fs-LIP can be useful to fully optimize the scheme. This work aims to characterize the structure of a fs-laser induced plasma in atmospheric pressure, illustrating the general behavior of the plasma plume for different target materials (metals and dielectrics), and further obtain insight about the emission and excitation characteristics of the plume for pure copper and PVC samples. The results show a clear two-component structure of the metallic plumes, composed by a fast-displacing upper component that presents higher excitation and higher ionization degree and a slow, almost static component that remains near the sample surface throughout the complete evolution. On the contrary, PVC presented only one fast-displacing component which was seen not to be homogeneous in terms of excitation. As a general feature, in the present study conditions, all the plasma plumes induced in different samples presented an intensity-dominating fast component, with discrepancies in the presence and relative intensity of the slow component. [Display omitted] • Characterization of fs-laser induced plasma plume behavior on different matrices. • General two-component structure for metals, with brighter fast component. • Study of excitation conditions in each component of a metallic (Cu) plasma plume. • Excitation and spatio-temporal distribution of species in a dielectric (PVC) plume. [ABSTRACT FROM AUTHOR]

Gadolinium is a compelling candidate for the next-generation 6.x nanolithography light source. We present a systematically study on the spectral purity at 6.7 nm in the gadolinium laser produced plasma. Variations in extreme ultraviolet spectra are observed over a wide range of laser focal spot sizes and laser pulse energies due to the combined effect of plasma temperature and opacity. When varying laser focal spot size, ionic populations of Gd ions at different electron temperatures were estimated by the collisional-radiative model for the explanation of changes in the spectral profile. When adjusting the laser pulse energy, modifications in the electron density profile were measured through Nomarski interferometry, and the related optical depth was quantified assisted with a one-dimensional radiation transfer model. Results show that, appropriate laser energy and focal spot size are necessary to achieve the high spectral purity, and with a lens with focal length of f = 175 mm and a laser pulse energy of 100 mJ, a spectral purity of Gd plasma up to 3.7% over range of 5.5–10 nm is achieved. • Discloses that spectral purity of laser plasma is affected by both the ion charge state and optical depth. • Measure electron density distribution at different laser energies. • Quantifies the optical depth of the laser plasma at different laser energies. [ABSTRACT FROM AUTHOR]

Employing the dual laser plasma technique, we measured the extreme ultraviolet (EUV) photoabsorption spectrum of F 2 + ions, spanning the energy range from 53 to 93 eV with an energy resolution (E / Δ E) of 866. The measured spectrum is carefully analyzed by comparing with the available reference data and theoretical calculation using the Cowan code. We identify prominent transitions to the Rydberg series 2 s 2 2 p 2 n s / n d and 2 s 2 p 3 n p from the ground level and remarkable transitions to the 2 s 2 2 p 2 ( 1 D) n d 2 D states from the 2 s 2 2 p 3 2 D metastable level. Transition energies and line profile parameters are determined by fitting the identified absorption features. The calibration of the spectrometer with well-known transitions allows us to provide line positions for well-resolved resonances with an uncertainty of 20 meV. The reported experimental data of F 2 + significantly contribute to the fundamental atomic database, offering valuable benchmarks for theoretical calculations with potential applications in astrophysics and plasma sciences. • Extreme ultraviolet photoabsorption of doubly-charged F is measured using dual laser plasma technique. • Transitions from both the ground level 2s22p34S and the metastable level 2s22p32D are identified. • Line profile parameters for the autoionization states are determined by fitting indivual resonances. • The obtained atomic data offer valuable benchmarks for theoretical models with potential applications in astrophysics and plasma sciences. [ABSTRACT FROM AUTHOR]

This investigation aims to understand the enhancement characteristics of plasma-assisted combustion in oxy-coal combustion. A 1064 nm Nd:YAG laser was added into a laminar flow reactor to produce laser-induced plasmas (LIPs). The high-speed visualization of the coal flame was used to reveal combustion's progress and evolution following laser-induced breakdown. To the best of our knowledge, this is the first time LIP has been applied to the optimization of pulverized coal combustion. The optical emission spectroscopy (OES) demonstrats that LIPs can generate adequate free electrons and ions during combustion. When the laser's pulse interval exceeds 60 ms, the LIP has a beneficial impact on combustion. For the heterogeneous reaction, the thermal effect generated by LIP only improves the intensity of flame radiation by 11–33 %. In contrast, the combination of chemical and thermal effects of plasma can result in significant enhancements of radiation intensity for high-volatile coals, with improvements of 76–203 %. Following laser-induced breakdown, the ignition delay time also decreases from lignite to anthracite, and the flame's peak intensity occurs earlier. [ABSTRACT FROM AUTHOR]

Laser electrolytic hybrid machining methods still present a more significant challenge regarding material removal rates due to the high energy loss of the laser in the electrolyte column and the low conductivity electrolyte column between the electrodes. In this paper, a laser-induced plasma electrolyte jet machining method is proposed for the first time to overcome the above problems. Specifically, the short propagation distance of the laser beam in the electrolyte column in the laser-induced plasma electrolyte jet machining method reduces the laser energy loss. In addition, a plasma is formed between the cathode and anode to reduce the ohmic voltage drop between the electrodes. Compared to conventional laser-electrolytic hybrid machining, the introduction of plasma into electrolyte jet machining leads to a significant difference in machining performance. The evolution of laser-induced plasma channels and the enhancement of plasma shocks under the jet liquid film are demonstrated. The material removal mechanism and laser-induced plasma electrolyte jet machining characteristics are comprehensively investigated. The grooves were finally machined using the proposed laser-induced plasma electrolyte jet machining method, and a material removal rate of 2.23 mm3/min was obtained. This study significantly increased the material removal rates of the laser electrolytic hybrid machining technique. [Display omitted] • This paper presents a novel laser-induced electrolyte jet machining (LIPEJM) method. • The material removal mechanism of LIPEJM is investigated. • An equivalent circuit model is proposed to reveal the effect of plasma on EJM. [ABSTRACT FROM AUTHOR]

Polarization, broadening, and splitting in Fraunhofer-type absorption (FTA) spectra are observed in colinear Double-Pulse Lase-Induced Breakdown Spectroscopy (DP LIBS). Effects are attributable to the Optical Stark Effect (OSE) induced by the electric field of the second laser pulse within the first pulse-created plasma. This effect manifests exclusively in back-directed Laser-Induced Plasma (LIP) emission and during the presence of the second laser pulse. Notably, the OSE is absent in LIBS observations orthogonal to the direction of the laser beams. [Display omitted] • Some Fraunhofer-type absorption lines are polarized in the Double Pulse Laser-induced breakdown spectroscopy in back-directed laser-induced plasma emission geometry. • Polarization in Fraunhofer-type absorption is attributed to the Optical Stark effect induced by the electric field generated by the focused second laser beam. [ABSTRACT FROM AUTHOR]

The structural properties, angle-integrated total and magnetic sublevel excitation cross sections, alignments of the residual ion, and polarization properties of the line emission are investigated for the plasma-embedded atomic system. This is done using the developed distorted wave approach which solves the Dirac equation by employing a modified Debye potential to represent the screened interaction in plasmas. The effective Hamiltonian is employed to obtain the level energies as functions of the screening parameters. The Coulomb interaction is replaced by shielded Coulomb interaction during the collision dynamics. As an illustrating example, detailed calculations are carried out for the 1 s 2 → 1 s 2 p 3 , 1 P 1 excitations of the plasma-embedded He atom by electron impact. Our results suggest that the energy levels are pushed towards continuum as the effect of (plasma) confinement increases. The cross sections decreases monotonically if the screening effect is enhanced continuously, while the alignments of the residual He + ion and polarizations of the fluorescence emission change slightly for the corresponding screening parameters. A comparison of our results in the absence of the screening potential with other available experimental and theoretical data shows satisfactory agreement. The present study not only provides a helpful approach to study the influence of plasma effect, but also has important applications in laser produced plasmas, stellar atmospheres, fusion research plasmas and so on. • A relativistic approach is proposed/suggested to precisely predict the electronic structures and collision processes. • Cross section and characteristic of fluorescence emission of the He atom confined in the plasma conditions are studied. • The present work has important implications for astrophysics and laboratory plasma. [ABSTRACT FROM AUTHOR]

[Display omitted] Laser induced plasma micro-machining (LIPMM) has proved its superiority in micro-machining of hard and brittle materials due to less thermal defects, smaller heat affected zone and larger aspect ratio compared to conventional laser ablation. In order to improve characteristics and stability of induced plasma, this paper proposed magnetically controlled LIPMM (MC-LIPMM) to achieve a good performance of processing single-crystal silicon which is widely used in solid state electronics and infrared optical applications. A comprehensive study on surface integrity and geometrical shape was conducted based on the experimental method. Firstly, the mechanism of MC-LIPMM including laser-plasma, laser-materials interactions and transport effects was theoretically analyzed. Then a series of experiments was conducted to completely investigate the effect of magnetic field intensity, pulse repetition frequency, and bubble behavior on surface integrity and geometrical shape of micro channels. It revealed that magnetic field contributed to maximum reduction of 12.64% for heat affected zone and 62.57% for width while maximum increase of 26.23% for depth and 90.26% for aspect ratio. This research confirms that MC-LIPMM can improve the machining characteristics of silicon materials and cavitation bubbles shows an apparently negative impact on the surface morphology. [ABSTRACT FROM AUTHOR]