Search

[Display omitted] • Metalloid nanoparticles (MNPs) of Mg–C and graphene fabricated via laser ablation. • Metalloid Mg–C nanoparticles inkjet printed for paper electronics. • Laser ablation used to alter the size and chemistry of nanoparticles after synthesis. Metalloid nanoparticles (MNPs) possess unique physicochemical properties but are challenging to create through biological or chemical routes. Using Pulsed Laser Ablation in Liquid (PLAL), Mg–C MNPs are fabricated from powders. The produced nanocolloids were ablated after the target was removed to tailor the particle size. MNPs with a mean size 300 nm could be reduced to 60 nm. Alternatively, MNPs with a mean size of 60 nm could be increased to 90 nm. The increase/decrease in size is controlled by the laser processing parameters and showcases the ability of PLAL for real-world applications that require meticulous control of size. The as-fabricated nanocolloids were successfully inkjet printed on paper, achieving a low resistivity of 75 Ω/square after 60 prints, highlighting their potential in printed electronics. To address a historical research gap, this article explored the impact of PLAL processing parameters, including fluence (1–2 J/cm2), pulse width (0.2–0.9 ns), repetition rate (10–20 kHz), and pH, factors often overlooked which is partly limiting applications. The influence of powder vs rod target on the PLAL process was addressed revealing that powders produce better size control and are easier to handle but they produce lower colloid concentrations. [ABSTRACT FROM AUTHOR]

Quartz material irradiated by femtosecond laser has increasingly attracted widespread attention for the micro-fabrication of photonic devices. Mechanism exploration is beneficial for accelerating the digital progress of laser processing. However, the mechanism between femtosecond laser and quartz is complicated and needs further theoretical investigation. This paper established the theoretical model based on the ionization model with the Drude equation to study the space–time evolution of free electron density and its influence on the absorption coefficient, reflectivity, and ablation depth. In addition, we achieved a 10 × 10 micro-holes array with a pore size less than 10 μm, cone angle less than 2° in a 0.25 mm thick quartz on the condition of a laser pulse energy Ep = 3 μJ, scanning velocity v = 0.1 mm/s, and defocusing distance Δf = −0.3 mm via the bottom-up femtosecond laser processing. The work gives a new insight into further understanding the ablation mechanism of transparent materials etching by the femtosecond laser. It provides a practical technical scheme for preparing commercial quartz photonic devices. [ABSTRACT FROM AUTHOR]

Ultrafast laser technology presents the unique capacity to process glass materials with an outstanding processing quality; however, combining high quality and high throughput is still a crucial issue because glass is brittle and highly heat sensitive. One strategy to overcome this limitation is to split in space the main laser beam into multiple beams for process parallelization. In the present paper, the simultaneous interaction of several femtosecond laser beams at the surface of fused silica targets is addressed experimentally and theoretically. This work is devoted to highlight the beams cooperation for inducing stress in the material. The experiment consists in irradiating the target with multiple laser pulses with a wavelength of 1030 nm and a duration of 500 fs. The induced stress is observed through post-mortem cross-polarized microscopy. A multiscale and multiphysics model describing laser energy deposition into the material and its mechanical response is developed. The influence of various laser parameters is studied: number and position of laser beams, repetition rate, and fluence. Both experimental and modeling results, which are in a good agreement, show significant cooperative effects for stress formation with large enough laser energy deposition, possibly leading to detrimental cracks. [ABSTRACT FROM AUTHOR]

Stimulated Raman Adiabatic Passage (STIRAP) and its variants, such as M-type chainwise-STIRAP, allow for efficiently transferring the populations in a multilevel system and have widely been used to prepare molecules in their rovibrational ground state. However, their transfer efficiencies are generally imperfect. The main obstacle is the presence of losses and the requirement to make the dynamics adiabatic. To this end, in the present paper, a new theoretical method is proposed for the efficient and robust creation and detection of deeply bound molecules in three-level Λ-type and five-level M-type systems via "Invariant-based shortcut-to-adiabaticity." In the regime of large detunings, we first reduce the dynamics of three- and five-level molecular systems to those of effective two- and three-level counterparts. By doing so, the major molecular losses from the excited states can be well suppressed. Consequently, the effective two-level counterpart can be directly compatible with two different "Invariant-based Inverse Engineering" protocols; the results show that both protocols give a comparable performance and have a good experimental feasibility. For the effective three-level counterpart, by considering a relation among the four incident pulses, we show that this model can be further generalized to an effective Λ-type one with the simplest resonant coupling. This generalized model permits us to borrow the "Invariant-based Inverse Engineering" protocol from a standard three-level Λ-type system to a five-level M-type system. Numerical calculations show that the weakly bound molecules can be efficiently transferred to their deeply bound states without strong laser pulses, and the stability against parameter variations is well preserved. Finally, the detection of ultracold deeply bound molecules is discussed. [ABSTRACT FROM AUTHOR]

Ultrafast optical spectroscopy is an effective experimental technique for accessing electronic and atomic motions in materials at their fundamental timescales and studying their responses to external perturbations. Despite the important insights that ultrafast techniques can provide on the microscopic physics of solids, undergraduate students' exposure to this area of research is still limited. In this article, we describe an ultrafast optical pump-probe spectroscopy experiment for the advanced undergraduate instructional laboratory, in which students can measure coherently excited vibrations of the crystal lattice and connect their observations to the microscopic properties of the investigated materials. We designed a simple table-top apparatus based on a commercial Er-fiber oscillator emitting 50-fs pulses at 1560 nm and at 100 MHz repetition rate. We split the output into two beams, using one of them as an intense "pump" to coherently excite phonons in selected crystals, and the other as a weaker, delayed "probe" to measure the transient reflectivity changes induced by the pump. We characterize the ultrafast laser pulses via intensity autocorrelation measurements and detect coherent phonon oscillations in the reflectivity of Bi, Sb, and 1T-TaS2. We then discuss the oscillation amplitude, frequency, and damping in terms of microscopic properties of these systems. Editor's Note: This paper provides an introduction to modern time-domain spectroscopy using ultrafast lasers, an experimental technique used to observe fundamentally important phenomena in condensed matter physics as well as in other fields. As a specific example, the authors demonstrate the generation and detection of coherent phonons in three solids. The paper provides an undergraduate-accessible discussion of the theory of coherent phonon spectroscopy in terms of classical harmonic oscillator physics. Then, a relatively low-cost ultrafast pump-probe spectroscopy system and the experimental procedures that the authors use in their experiment are described. Finally, typical experimental data and analysis methods are presented. This laboratory experiment is a welcome addition to the undergraduate physics curriculum, introducing a system that is suitable for examining a variety of ultrafast and nonequilibrium phenomena in an advanced instructional laboratory. [ABSTRACT FROM AUTHOR]

In this paper we make an attempt to study the effect of a nanosecond prepulse on electron acceleration from microscopic solid particles. While standard scaling laws predict temperatures of ∼ 50 keV, our investigations showed an anomalous enhancement ( ∼ 200 keV) in electron temperatures from microscopic solids subjected to intense laser fields. Conventional isotropic expansion of the plasma target as a result of pre-pulse interaction is unable to explain the enhancement, prompting an experimental inquiry into the expansion form. Tentacle-like structures emerging from the spherical plasma are detected as an outcome of the pre-pulse interaction, with the region between the tentacles being targeted by the main laser pulse. We resort to PIC simulations to understand and predict the exact plasma condition that exists in this region. In this paper, we study a series of approximate pre-plasma conditions, particle shapes, and electron densities, examining them for their role in electron acceleration from this extended over-critical plasma target. [ABSTRACT FROM AUTHOR]

The described method is intended for application as a diagnostic tool for a nonstationary, short-lived plasma (in particular, for the laser-produced plasma). It is based on taking into account the lifetime of a laser-produced plasma, which is so short (several nanoseconds) that it is not enough for the ionization equilibrium to be established. Among mechanisms leading to appearance of an ion with a given charge Z in the plasma, only the electron-collisional ionization is considered, because contributions of other phenomena turn out to be negligible. The method is discussed as an example of a plasma excited on the Xe gas-jet target. The necessary collisional cross sections of ions from+7Xe to+16Xe have been calculated specifically for this study using a quantum-mechanical numerical simulation, with its principles and features being also presented in the paper. To demonstrate capabilities of the method, it has been applied to one of the experimental cases when the plasma was produced by the laser beam focused on the Xe gas-jet target. The time-integrated energy of laser radiation absorbed in the plasma was measured, and the absorption coefficient, μ, was derived from it with a correction for the plasma lifetime, which was several times shorter than the laser pulse. Using the method described here, the values of ⟨ Z ⟩ and then μ were calculated as a function of temperature. The time-averaged plasma temperature, T, in the above-mentioned experiment was believed to be equal to that at which the calculated and experimentally determined values of μ coincided. The following results were obtained: T = 42 eV, ⟨ Z ⟩ = 10.2. [ABSTRACT FROM AUTHOR]

Depending on the material properties of the system at hand, in some circumstances the application of a short pulse laser may initially bring a system into a highly non-equilibrium state wherein either the electron temperature may rise up while the lattice still remains cold, or conversely, because the heat capacity of electrons is usually different from that of lattice. In order to correctly describe the heat transport in those situations, therefore, one should properly split the non-equilibrium temperature into two different contributions: the electron temperature and the phonon temperature. By means of a recent two-temperature model (which fully agrees with the Maxwell-Cattaneo theory), in this paper we show that the values of those two temperatures may be always predictable during the thermal-shock propagation in nanowires, after having illustrated both that the employed theoretical model agrees with the basic tenets of continuum mechanics, and that it is mathematically well posed in the case of particular initial and boundary conditions. The main results of this paper could be used to deepen the concept of non-equilibrium temperature. [ABSTRACT FROM AUTHOR]

Inferring transient molecular structural dynamics from diffraction data is an ambiguous task that often requires different approximation methods. In this paper, we present an attempt to tackle this problem using machine learning. Although most recent applications of machine learning for the analysis of diffraction images apply only a single neural network to an experimental dataset and train it on the task of prediction, our approach utilizes an additional generator network trained on both synthetic and experimental data. Our network converts experimental data into idealized diffraction patterns from which information is extracted via a convolutional neural network trained on synthetic data only. We validate this approach on ultrafast electron diffraction data of bismuth samples undergoing thermalization upon excitation via 800 nm laser pulses. The network was able to predict transient temperatures with a deviation of less than 6% from analytically estimated values. Notably, this performance was achieved on a dataset of 408 images only. We believe that employing this network in experimental settings where high volumes of visual data are collected, such as beam lines, could provide insights into the structural dynamics of different samples. [ABSTRACT FROM AUTHOR]

In this paper, the laser pulse evolution arising from the field ionization during the interaction of a long laser pulse with gaseous hydrogen atoms is investigated using the kinetic 1D‐3 V Particle‐In‐Cell (PIC) Smilei simulation code. After performing various simulations, it is shown that the field ionization of hydrogen atoms has a non‐negligible effect on the evolution of the laser pulse compared to the pre‐ionized plasma case. The results of our simulations show that the amount of these evolutions is strongly dependent on the parameters of the laser and initial ionization assumed. In this regard, two main mechanisms are responsible for the changes in the generated radiations and then the evolution of the laser pulse. When the average degree of ionization is weak, the backscattered Raman radiations can provide the necessary conditions for the chaotic behavior to occur and the laser pulse to evolve. When the laser and plasma pulse parameters (such as the laser pulse amplitude, hydrogen atoms density, and the rise time of pulse) are selected so that a strong space charge field is formed, the wave breaking (which happened faster due to density changes during the field ionization) is the main factor for evolutions in the laser pulse. [ABSTRACT FROM AUTHOR]

The availability of high-power lasers open new frontiers of Terahertz (THz) optics. In this paper, we present a mechanism for the enhanced THz field generation from the laser wakefield excitation during the interaction of an amplitude-modulated laser filament with a magnetized plasma. The derivation of electric and magnetic wakefields in axially magnetized plasma is obtained using the perturbative approach. Amplitude-modulated laser filament generates a significantly stronger transverse current due to laser intensity redistribution by the amplitude modulation. The modulation index of the amplitude modulated laser pulse is used to control the transverse current at THz frequency. Fourfold enhancement takes place in THz field strength for higher values of the modulation index (0–0.4). Also, the conversion efficiency of this mechanism is estimated as 1 0 − 4 that can be enhanced for higher modulation index. Scaling laws are provided for controlling and optimization of generated THz field. This work may be crucial in exploring THz optical phenomena such as THz field-induced Kerr effects and many other nonlinear effects. [ABSTRACT FROM AUTHOR]

This paper primarily investigates the effect of the tilt of corner cube reflector (CCR) arrays on lunar laser ranging (LLR). A mathematical model was established to study the random errors caused by the tilt of the CCR arrays. The study found that, ideally, when the laser ranging pulse width is 10 picoseconds or less, it is possible to distinguish from which specific corner cubes within the CCR array each peak in the echo signal originates. Consequently, partial data from the echo can be extracted for signal processing, significantly reducing random errors and improving the single-shot precision of LLR. The distance obtained by extracting part of the echo can be reduced to the center position of the array, thereby providing multiple higher-precision ranging results from each measurement. This not only improves the precision of LLR but also increases the data volume. A simulation experiment based on the 1.2 m laser ranging system at Yunnan Observatories was conducted. By extracting one peak for signal processing, the single-shot precision improved from 32.24 mm to 2.52 mm, validating the theoretical analysis results. Finally, an experimental laser ranging system based on a 53 cm binocular telescope system was established for ground experiments. The experimental results indicated that the echo signal could identify the tilt state of the CCR array. By extracting the peak returned by the central CCR for signal processing, the ranging precision was greatly improved. Through theoretical analyses, simulation experiments, and ground experiments, a solution to reduce the random errors caused by the tilt of the CCR array was provided. This offers an approach to enhance the single-shot precision of future LLR and provides a reference for upgrading ground-based equipment at future laser ranging stations. [ABSTRACT FROM AUTHOR]

Intense laser pulses can be employed to generate plasma, carbon aggregates, and nanoparticles. The plasma produced by ns laser pulses impinging on carbon targets in a vacuum generates carbon vapors, atoms nucleation and growth of nano aggregates. Mass quadrupole spectrometry has permitted to analyze the mass of the carbon atoms and molecules produced in a vacuum by laser-generated plasma, discovering that the fullerene C20 and other small carbon aggregates have a high probability of being produced. In this paper, the conditions of C20 aggregate synthetization are presented, and their yield generation is approximately evaluated. It also calculated the process ablation yield, the maximum carbon energy acquired in the plasma, the plasma temperature and density, the adiabatic plasma expansion velocity, and the carbon ion charge state distributions. To this, measurements of time-of-flight (TOF) of ions have been performed using suitable ion collectors and ion energy analyzers. [ABSTRACT FROM AUTHOR]

The thermo-mechanical coupled behavior of biological tissues excited by a transient heating has been studied in this paper, in which the temperature-dependent physical properties are considered. A non-linear bio-thermo-mechanical coupled model with variable physical parameters has been proposed firstly in the context of the generalized theory with the dual-phase relaxation mechanism. An effective procedure constructed on an explicit finite difference scheme is then implemented to solve this non-linear model numerically. On this basis the thermo-mechanical coupled response and relative thermal damage within a skin tissue irradiated by a pulse laser has been explored. The temporal and spatial distributions of each physical field resulting from various cases have been obtained and illustrated. The results stated that the thermo-mechanical interaction induced by a laser heating would be inhibited by temperature-dependent physical parameters and this inhibition is more significant on the tissue displacement and normal stresses than tissue temperature. The thermal damage is also inhibited when the temperature dependence is considered and the time that healthy tissues can be tolerated would be a larger extension for its accumulative effect with tissue temperature. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate an ultrafast diamond Raman laser at 1240 nm with a pulse repetition rate of 956.62 MHz, a pulse duration of 39.5 ps, and an average power of up to 3.3 W based on synchronous pumping. The pump source is an electrical-pulse-modulated picosecond pulsed laser at 1064 nm with a repetition rate of 239.16 MHz and a pulse duration of 65.4 ps. A quadrupling repetition rate of the Raman pulse is achieved by synchronously amplifying both the forward and backward Raman pulses and the amplified Raman pulse undergoing two round trips in the resonator within one pump pulse period. The compression ratio of the pulse duration from the pump to the Raman is 1.66. This work offers a convenient and efficient method to significantly enhance the repetition rate of ultrafast crystalline Raman lasers and proves that a non-coherent ultrafast pump pulsed laser can be converted to a coherent mode-locked ultrafast Raman pulsed laser based on Raman conversion. [ABSTRACT FROM AUTHOR]

AbstractPulsed laser cladding provides a periodical thermal accumulation, enabling a greater temperature gradient and cooling rate inside the substrate, which can efficiently ameliorate the microstructure of the cladding layer. It is crucial to quantitatively investigate the mechanism of the interaction for the cladding process parameters on the transient evolution of the multi-field coupling to improve the cladding quality. In this paper, a 3-D model during the single-channel multilayer pulsed laser cladding process was constructed which is grounded on the temperature-variable physical properties parameters of the material. The integrated consideration in the masking impact of the molten powder waist beam on the pulsed laser beam, the molten pool liquid metal surface tension, the influence of buoyancy on the flow, and the transient evolution of the molten pool edge morphology. The temperature, flow, and stress fields of the single-channel multilayer cladding process were computed and resolved. The mechanism in multi-field coupling impact of laser pulse frequency, laser power, and pulse duty cycle on the single-channel multilayer cladding process was emphasized. The response surface equations between each influencing factor and the cladding temperature, temperature change gradient, and thermal stress were determined according to the response surface method, and the sensitivity of each parameter was attained from the Monte Carlo method. Using SEM to observe the profile and microstructure of the cladding layer, the material hardness distribution was measured experimentally, and the effectiveness of the model was confirmed. This research supplies an essential rationale for upgrading the quality of pulsed laser cladding layers. [ABSTRACT FROM AUTHOR]

As the weak link in electro-optical imaging systems, photodetectors have always faced the threat of laser damage. In this paper, we experimentally investigated the damage mechanism of the photodetector induced by the out-of-band laser. The damage thresholds of the mid-infrared pulsed laser for Charge Coupled Device (CCD) and HgCdTe detectors were determined through damage experiments. The analysis of the damage phenomena and data for both CCD and HgCdTe detectors clearly demonstrated that out-of-band mid-infrared pulsed lasers could entirely incapacitate CCD and HgCdTe detectors. Our analysis of the damage process and data revealed that the primary mechanism of damage to CCD and HgCdTe detectors by mid-infrared pulsed lasers was primarily thermal. This study serves as a reference for further research on the mid-infrared pulsed laser damage mechanisms of CCD and HgCdTe detectors, as well as for laser protection and performance optimization in imaging systems. [ABSTRACT FROM AUTHOR]

This paper presents a flexible method for directly generating an orthogonally polarized dual-wavelength double pulse Pr: YLF visible laser. A theoretical model is established to reveal the oscillation mechanism of the orthogonally polarized dual-wavelength double pulse laser. Theoretical results demonstrate that the ratio of orthogonally polarized dual-wavelength laser intensity and master-slave pulse energy, along with the time delay between the master and slave pulses, can be controlled by the insertion angle of the acousto-optic element and the double step losses of the signal generator. These theoretical results have been verified in experiments. We obtained a maximum output power of 145 mW for the orthogonally polarized dual-wavelength double pulse laser, with π-polarization at 604 nm and σ-polarization at 607 nm. At a pulse repetition frequency (PRF) of 10 kHz, the pulse widths of the master and slave pulses are measured to be 29.6 ns and 65.4 ns, respectively. [ABSTRACT FROM AUTHOR]

Thermal diffusivity is an essential thermophysical factor for designing thermal protection materials. At present, the laser flash method is widely employed for measuring thermal diffusivity, and reasonable determination of experimental parameters is a prerequisite for accurate measurement. In this paper, high-purity graphite is used as the reference specimen, and measurement temperature ranges from 25 °C to 1500 °C. Besides, experimental investigations on the influence of the laser flash method such as specimen thickness, laser pulse energy, and temperature increase rate on the measurement of thermal diffusivity for high-purity graphite are carried out. The results indicate that for high-purity graphite samples, a sample thickness of 3 mm is more appropriate. Additionally, the setting of laser pulse voltage and width is related to the measurement temperature, and the measurement results are more easily affected by the laser pulse width. When measuring temperatures below 600 °C, it is necessary to set both the laser pulse width and voltage to the smallest possible values, provided that a stable signal can be collected. When the temperature is above 600 °C, the laser pulse voltage does not affect the measurement results, but the influence of laser pulse width still needs to be considered to a certain extent. It is only when the measured temperature exceeds 900 °C that neither the laser pulse voltage nor the laser pulse width influences the measurement results. Furthermore, the temperature increase rate has a relatively small impact on the measurement results and can be adjusted according to the measured temperature. The research results can provide a basis for the calibration of experimental parameters in the high-temperature flash method measuring instrument. [ABSTRACT FROM AUTHOR]

Laser micromachining has been used as an alternative to producing microfluidics structures and simplifying the conventional soft lithography process. In this paper we characterize the excimer laser micromachining parameters and demonstrate its application by producing several microfluidic structures in polydimethylsiloxane (PDMS). The parameters include the number of laser pulses, laser energy and rectangular variable aperture (RVA) in both x- and y-directions. We found that the laser energy and pulse rate affect the depth of micromachining d channels, while RVA in both x- and y-directions affects the width of the channels. Repetition of laser scan does not change the channel width but significantly changes the channel depth. Proper adjustment for laser energy and pulse rate is required to fabricate a desired channels depth. In order to demonstrate the microfabrication capability of an excimer laser with the optimal operating parameters, several microfluidic structures were micromachining d into PDMS with a KrF excimer laser. [ABSTRACT FROM AUTHOR]

The paper aims at studying the impact of gravity and laser pulse on the overall structure of the generalized thermoelasticity equations concerning a standardized elastic isotropic half-space. Using four generalized thermoelasticity theories, i.e. the Green-Naghdi (GN) theory, Green-Lindsay (GL) theory, Lord-Schulman (LS) theory, and Coupled Theory (CT), the authors applied the formulation. In the physical sphere, they attained the analytical expressions for the (Mechanical and Maxwell's) stresses distribution, displacement components, and temperature through utilizing the normal mode analysis. Moreover, they calculated these expressions numerically and plotted the conforming graphs to demonstrate and make comparisons between theoretical findings. The paper concludes that the impact of gravity and laser pulse field is highly significant. [ABSTRACT FROM AUTHOR]

This research paper explores the integration of AlexNet-guided femtosecond laser processing (GFLP) techniques in optical materials and devices to achieve significant advancements in nanofabrication. The combination of deep learning, specifically utilizing the AlexNet architecture, and ultrafast laser processing offers a novel approach for precise and efficient manipulation of materials at the nanoscale. The paper presents a comprehensive investigation of the synergistic effects of deep learning and femtosecond laser processing on various optical materials, highlighting their potential for creating intricate nanostructures and improving device performance. Experimental results demonstrate the enhanced precision, speed, and versatility of this approach compared to traditional methods. Moreover, the study sheds light on the underlying mechanisms governing the interaction between laser pulses and materials, providing valuable insights for further optimization and applications in emerging fields such as photonics, optoelectronics, and quantum technology. [ABSTRACT FROM AUTHOR]

Purpose: This paper adopts a modified Taguchi approach to develop empirical relationships to the performance characteristics (output responses) in terms of process variables and demonstrated their validity through comparison of test data. The method suggests a few tests as per the orthogonal array and provides complete information for all combinations of levels and process variables. This method also provides the estimated range of output responses so that the scatter in the repeated tests can be assessed prior to the tests. Design/methodology/approach: In order to obtain defect-free products meeting the required specifications, researchers have conducted extensive experiments using powder bed fusion (PBF) process measuring the performance indicators (namely, relative density, surface roughness and hardness) to specify a set of printing parameters (namely, laser power, scanning speed and hatch spacing). A simple and reliable multi-objective optimization method is considered in this paper for specifying a set of optimal process parameters with SS316 L powder. It was reported that test samples printed even with optimal set of input variables revealed irregular shaped, microscopic porosities and improper melt pool formation. Findings: Finally, based on detailed analysis, it is concluded that it is impossible to express the performance indicators, explicitly in terms of equivalent energy density (E_0ˆ*), which is a combination of multiple sets of selective laser melting (SLM) process parameters, with different performance indicators. Empirical relations for the performance indicators are developed in terms of SLM process parameters. Test data are within/close to the expected range. Practical implications: Based on extensive analysis of the SS316 L data using modified Taguchi approach, the optimized process parameters are laser power = 298 W, scanning speed = 900 mm/s and hatch distance = 0.075 mm, for which the results of surface roughness = 2.77 Ra, relative density = 99.24%, hardness = 334 Hv and equivalent energy density is 4.062. The estimated data for the same are surface roughness is 3.733 Ra, relative density is 99.926%, hardness is 213.64 Hv and equivalent energy density is 3.677. Originality/value: Even though equivalent energy density represents the energy input to the process, the findings of this paper conclude that energy density should no longer be considered as a dependent process parameter, as it provides multiple results for the specified energy density. This aspect has been successfully demonstrated in this paper using test data. [ABSTRACT FROM AUTHOR]

This document serves as a preface to a special topic collection in the journal "Physics of Plasmas" that focuses on the study of relativistic plasma in supercritical fields. The collection includes papers from a mini-conference held at the 2022 meeting of the American Physical Society Division of Plasma Physics. The objective of the mini-conference was to bring together researchers from different physics communities to address the physics of matter in extreme astrophysical objects and high-power laser systems. The papers in the collection cover topics such as electron-positron pair production, extreme astrophysics, radiation reaction, and vacuum physics. The mini-conference aimed to facilitate knowledge exchange and inspire future research in this emerging field of plasma physics. The authors of this document, Alec G. R. Thomas and Stepan S. Bulanov, declare that they have no conflicts of interest to disclose and were supported by the U.S. Department of Energy Office of Science Offices of High Energy Physics and Fusion Energy Sciences. [Extracted from the article]

We have analyzed the effects of the spreads in experimental parameters on the reliability of speeds and angular distributions extracted from a generic surface-scattering experiment based on planar laser-induced fluorescence detection. The numerical model assumes a pulsed beam of projectile molecules is directed at a surface. The spatial distribution of the scattered products is detected by imaging the laser-induced fluorescence excited by a thin, pulsed sheet of laser light. Monte Carlo sampling is used to select from realistic distributions of the experimental parameters. The key parameter is found to be the molecular-beam diameter, expressed as a ratio to the measurement distance from the point of impact. Measured angular distributions are negligibly distorted when this ratio is <∼10%. Measured most-probable speeds are more tolerant, being undistorted when it is <∼20%. In contrast, the spread of speeds or of corresponding arrival times in the incident molecular beam has only very minor systematic effects. The thickness of the laser sheet is also unimportant within realistic practical limits. These conclusions are broadly applicable to experiments of this general type. In addition, we have analyzed the specific set of parameters designed to match the experiments on OH scattering from a liquid perfluoropolyether (PFPE) surface in the Paper I [Roman et al., J. Chem. Phys. 158, 244704 (2023)]. This reveals that the detailed form of the molecular-beam profile is important, particularly on apparent angular distributions, for geometric reasons that we explain. Empirical factors have been derived to correct for these effects. [ABSTRACT FROM AUTHOR]

Paper-based electronics with carbon nanomaterials incorporated have several advantages including recyclability, biodegradability, non-toxicity, low cost and ease of fabrication and disposal. Herein, carbon nanoparticles (CNPs) were fabricated by Pulsed Laser Ablation in Liquid (PLAL) using three different liquid mediums, i.e. deionised (DI) water, ethanol and a magnesium-based solution. The as-fabricated nanocolloids were used as conductive inks and deposited on paper substrates. The resulting nanoparticle (NP) coatings were subjected to electrical resistivity tests via 4-point probe. Ultraviolet–Visible spectroscopy (UV–Vis) studies were conducted to determine the presence of nanomaterials. All nanocolloids produced within DI water had three distinct UV–Vis absorbance peaks at 200, 216 and 225 nm while nanocolloids produced in ethanol exhibited more peaks and significantly higher absorbance values in the range from 210 nm to 300 nm. Dynamic Light Scattering and field emission scanning electron microscopy (FESEM) were used to analyse samples for particle size and morphology respectively. The liquid medium in which PLAL was conducted was found to significantly affect the NP mean size, conductivity and surface chemistry of the resulting NPs. DI water produced smaller nanoparticles (NPs) (10–82 nm) than ethanol (60–143 nm) and magnesium-based solution (263–1389 nm) within the process parameters studied herein. The laser scan speed and fluence have a combined effect on the NP mean diameter. The surface chemistry of the NPs produced in the magnesium-based solution was analysed via X-ray photoelectron spectroscopy and it was found that the Mg, Li and Si atoms are adsorbed by the carbon NPs leading to higher conductivity of the coated paper substrates. [Display omitted] • This paper studies the effect of liquid medium on nanoparticle mean size during Pulsed Laser Ablation in Liquid (PLAL). • A complex liquid medium (magnesium-based solution) is used for the first time during PLAL of carbon targets. • The effect of laser scan speed and fluence on the nanoparticle size and conductivity is investigated. [ABSTRACT FROM AUTHOR]

Nanostructures incorporating copper oxide (CuO), a narrow bandgap p-type semiconductor, are well suited for applications such as gas/biosensors, field emission devices, and photodetectors. However, the use of CuO nanocomponents in these applications is currently limited by the availability of fabrication and in situ processing techniques. In this paper, we show that the electrical and mechanical properties of CuO nanowire (NW) networks can be adjusted through sequential processing with nanosecond laser radiation. This new two-stage process involves selective breakage/cleaving of CuO NWs with an initial set of laser pulses, followed by irradiation with a second set of laser pulses applied in an optimized orientation to tailor bonding and junction formation between pairs and bundles of previously separated CuO NWs. We find that stage one processing introduces a high concentration of oxygen vacancies in NWs leading to the nucleation of dislocations and high strain. This localized strain is responsible for the breaking of individual NWs, while the high oxygen vacancy concentration modifies the electrical conductivity within each NW. The second stage involves re-orientation of the laser beam, followed by additional laser irradiation of the NW network. This has been found to result in the bonding of NWs and the creation of junctions in regions where CuO NWs are in contact. Laser-induced heating under these conditions produces melting in the contact areas between NWs and is accompanied by the reduction of CuO to form Cu2O as verified via XPS and Raman analysis. XRD and TEM observations demonstrate that plastic deformation within CuO NWs dominates in stage one laser processing. The enhancement of electrical conductivity observed, following stage two processing, is attributed due to an increase in the concentration of laser-induced oxygen vacancies as well as the formation of localized bridging and junction sites in the overall NW network. [ABSTRACT FROM AUTHOR]

The refractive index of a liquid serves as a fundamental parameter reflecting its composition, thereby enabling the determination of component concentrations in various fields such as chemical research, the food industry, and environmental monitoring. Traditional methods for refractive index (RI) measurement rely on light deflection angles at interfaces between the liquid and a material with a known refractive index. In this paper, the authors present a new differential refractometer for the highly sensitive measurement of RI differences between two liquid samples. Using a configuration with two cells equipped with flat parallel plates as measuring elements, the instrument facilitates accurate analysis. Namely, the sensor signals from both the solution and the solvent cuvette are generated simultaneously with one laser pulse, reducing the possible fluctuations in the laser radiation intensity. Our evaluation shows the high sensitivity of RI measurements < 7 × 10 − 6 ), so this differential refractometer can be proposed not only as a high-sensitivity sensing tool that can be used for mobile detection of nanoparticles in solution samples but also to determine the level of environmental nano-pollution using water (including rain, snow) samples from various natural as well as industrial sources, thus helping to solve some important environmental problems. [ABSTRACT FROM AUTHOR]

The peculiar nonlinear optical responses of two-dimensional (2D) materials endow them highly attractive for photonics applications. This review systematically discusses the performance of pulsed lasers employing 2D materials as their modulation device. First, it is crucial to categorize 2D materials that can act as saturable absorbers, encompassing a range of substances such as Graphene, Black Phosphorus, Topological Insulators, MXene, and even heterojunction. Furthermore, a thorough investigation is conducted to analyze the performance indexes to study the nonlinear characteristics of 2D materials in the pulse generation. Especially, the focus is on the 1.5 μ m band ultrafast lasers utilizing 2D materials. This paper also provides a comprehensive analysis of the obstacles and prospects in 2D materials preparation, and their utilization in the pulse laser systems. [ABSTRACT FROM AUTHOR]

Achieving ignition in inertial confinement fusion requires significant heating and compression of the thermonuclear fuel. One of the most efficient ways to achieve such conditions is spherical compression of the target initiated by specially profiled laser pulses. Any irradiation asymmetries and target imperfections break the symmetry of the compression and are seeds for the growth of hydrodynamic instabilities. As a result, the initial small amplitudes grow significantly and break the effective target compression, which is critical for successful ignition. The paper numerically studies the evolution of ice–ablator small perturbations in a direct drive target. The simulations consider the target dynamics with two different numerical hydrocodes. As a result of Rayleigh–Taylor instability development during both acceleration and deceleration phases, the perturbations grow significantly and could violate the ignition if the initial amplitude is larger than the critical value of several hundred nm: for successful ignition, the amplitude should be compared or smaller than a 100 nm. The effect of perturbations propagating from the distributed interface to the internal smooth layers is also observed. [ABSTRACT FROM AUTHOR]

One of the effective ways to achieve drilling of Carbon fiber reinforced polymer (CFRP) materials is to use short pulse lasers. However, the existing cutting thermal damage, such as the heat-affected zone (HAZ), can weaken the CFRP mechanical properties. In this paper, a heterogeneous mesoscopic model of transient distribution of short pulse laser ablation heat flow is built to fully explore the formation and extension mechanism of thermal damage. The significant difference in laser interaction thermal effects between fibers and resin leads to the formation of HAZ with exposed fibers. The interface effect exists in the ablation process, which aggravates the matrix damage. The ablation of carbon fibers occurs within the duration of a single laser pulse, and the degree of ablation depends on the pulse energy. Under the coupling of the thermal conduction effect along the fiber axis and the thermal accumulation effect between pulses, the matrix damage extends significantly during the cooling stage. Large pulse repetition frequency increases heat accumulation between pulses and increases matrix damage. There is a new erosion mechanism in that the thermal accumulation behavior leads to the falling off of fragmented carbon fiber filaments. The accuracy of the model was verified through different pulse ablation tests, and the average error of ablation morphology is 11.28%. [ABSTRACT FROM AUTHOR]

This paper presents a study on the optimisation of laser pulse parameters using an optimal control theory based adaptive simulated annealing technique. The objective of this study is to obtain a cost-effective laser pulse that can selectively excite the vibrational state and cause photo-dissociation of the C–H bond in a methane molecule. We have optimised both sinusoidal and linear ramped pulses using the proposed technique, and incorporated a linear chirping in the field as well. The results demonstrate the effectiveness of the proposed approach in designing laser pulses for targeted molecular excitation and dissociation. [ABSTRACT FROM AUTHOR]

We investigate the effect of pre-bunched relativistic electron beams on the output power of a free electron laser by two electron beams in a theoretical study. In general, this highly coherent and stable pulse of laser is known as the best investigator of basic importance for present-day science. Free electron lasers are the best candidates for exploring nature at ultrasmall spatial and ultrafast temporal scales. In this paper, we have considered the distribution function of relativistic electron beams as a water-bag, and the configuration of the wiggler pump has assumed a helical magneto-static wiggler. By a set of nonlinear, 1D, coupled differential equations the wave-particle interaction problem has been analyzed. With the aid of MATLAB-based Runge-Kutta algorithm numerical solution has been obtained. Saturation profiles in different cases of pre-bunching phase region of beams have been plotted. Out-coming has shown that the saturation length decreases by about 7.2%. However, the amplitude of the output pulse increased by about 209.3% in comparison to the non-pre-bunched relativistic electron beams. [ABSTRACT FROM AUTHOR]

In this paper, we study changes in the phase shift and length, as well as the spatial structure of birefringent microtracks induced in the bulk of fused silica in the tight focusing regime (numerical apertures NA = 0.45 and 0.55) by laser pulses with a wavelength of 1030 nm, durations of 0.3 and 0.6 ps, and variable energy. It is shown that the phase shift and the length of the microtracks increase monotonically with the pulse energy, while their spatial structure is transformed from an array of longitudinal channels with transverse subwavelength periodicity along the polarization vector into a three-dimensional hierarchical structure with additional periodicity about the wavelength along the radiation propagation axis. For the first time, it has been found that the period ΛE in three-dimensional hierarchical structures decreases by almost a factor of 2, which corresponds to an increase in the refractive index difference induced in the microtracks to . [ABSTRACT FROM AUTHOR]

This paper deals with an analytical study of shock waves propagating in heterogeneous metallic mediums. A shock wave travels through most media at a speed higher than ordinary wave. The propagation of a shock wave created by a laser impact over a metallic surface is considered here. In the process of Shock wave generation, a high-pressure surface level is reached using a nanosecond laser pulse that heats the surface of the material and generates adense plasma expansion. The pressure reaches few GPa so that shockwaves are generated and propagated in the bulk of the material. Whitham method, a powerful analytical method for shock waves, has been employed to obtain the analytical relations for shock velocity, shock strength and pressure behind the freely propagating shock. Numerical calculations have been performed for shock velocity, shock strength, pressure, adiabatic sound velocity, and compression behind the shock (?) and their variation with propagation distance have been discussed. A sharp decrease in shock velocity and pressure behind the shock whereas a steadily increasing shock strength with propagation distance has been observed. Particle velocity, adiabatic sound velocity and compression parameter also show a gradual decrease as the shock advances in the medium. Effect of overtaking disturbances has been evaluated by considering Yadav's approach. [ABSTRACT FROM AUTHOR]

Based on the laser flash method, the selection of experimental parameters on the accuracy of measurement results for measuring thermal diffusivity is investigated in this paper. High purity graphite is employed as the experimental material. Three experimental parameters are taken into consideration, including specimen thickness, laser pulse power, and laser pulse width. Firstly, the principle of the laser flash method is introduced. Then, a numerical simulation model is established and independence tests are performed. In order to investigate the impact of different experimental parameters to the precision of the measurement results using the laser flash method, six thicknesses of the specimens, five laser pulse powers, and five laser pulse widths are selected for numerical simulation and LFA 427 measurement experiments. Finally, an orthogonal design method with three-factor and three-level is constructed to investigate the influence degree of these three factors on the measurement results. It is found that the laser pulse width has the most significant influence, while the laser pulse power has the least impact. For high purity graphite specimens, it is required to choose a thicker specimen, a lower laser pulse power, and a smaller laser pulse width to ensure better measurement accuracy. [ABSTRACT FROM AUTHOR]

Coherent Doppler wind lidar (CDWL) uses transmitted laser pulses to measure wind velocity distribution. However, the echo signal of CDWL is easily affected by atmospheric turbulence, which can decrease the signal-to-noise ratio (SNR) of lidar. To improve the SNR, this paper proposes a pulse accumulation method based on the cross-correlation function to estimate the phase of the signal. Compared with incoherent pulse accumulation, the proposed method significantly enhances the correlation between signals from different periods to obtain high SNR gains that arise from pulse accumulation. Using simulation, the study evaluates the effectiveness of this phase estimation method and its robustness against noise in algorithms which analyze Doppler frequency shifts. Furthermore, a CDWL is developed for measuring the speed of an indoor motor turntable and the outdoor atmospheric wind field. The phase estimation method yielded SNR gains of 28.18 dB and 32.03 dB for accumulation numbers of 500 and 1500, respectively. The implementation of this method in motor turntable speed measurements demonstrated a significant reduction in speed error—averaging 9.18% lower than that of incoherent accumulation lidar systems. In experiments that measure atmospheric wind fields, the linear fit curve slope between the measured wind speed and the wind speed measured via a commercial wind-measuring lidar can be reduced from 1.146 to 1.093. [ABSTRACT FROM AUTHOR]

Carbon nanodots (CNDs) produced in pure water by the ablation of graphite with a nanosecond laser pulse exhibit weak photoluminescence. A small addition of polyethyleneimine (PEI) to the aqueous suspension of CNDs causes a significant increase in emissions. This paper presents experimental and theoretical studies of the emission properties of CND/PEI systems. The obtained CNDs responded to even trace amounts of PEI in solution (~0.014% v/v), resulting in a significant increase in the initial weak blue emission of CNDs and PEI taken separately. Morphology and size measurements showed that particle aggregation occurred in the presence of the polymer. A decrease in the calculated Stokes shift values was observed with increasing PEI content in the solution. This indicates a reduction in the number of non-radiative transitions, which explains the increase in the emission intensity of the CND/PEI systems. These results therefore confirmed that the increase in the emission of CND/PEI systems is caused by particle aggregation. Kinetic studies proved that the process is controlled mainly by diffusion, the initial stage of which has a dominant influence on determining the optical properties of the system. [ABSTRACT FROM AUTHOR]

The VEGA-3 laser system at the Centro de Láseres Pulsados delivers laser pulses up to 1 PW at 1 Hz repetition rate, focused to intensities up to 2.5 × 10 20 W cm−2. A versatile and compact solid target suitable for up to 0.05 Hz is presented which can operate in the challenging petawatt laser environment close to the laser-plasma interaction. Strips are spooled in a tape target system to deliver a solid density target to the laser focus for every shot. Results are presented for different tape materials and thicknesses, and a shot-to-shot standard deviation of the cut-off energy of 1.5% was obtained for Kapton reinforced aluminium tapes of 9 µ m thickness. Experimental ion spectra are recorded by a Thomson Parabola Ion Spectrometer coupled with a scintillator screen; and an antenna array is used for the characterization of electromagnetic pulses. The results of both diagnostics show a good shot-to-shot stability of the system. [ABSTRACT FROM AUTHOR]

The advent of fast washout and high frequency laser ablation systems has reduced blurring and greatly improved the throughput of analyses performed using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). However, historical laser synchronisation issues have limited the number of elements aquired in a single run when using quadrupole-based ICP-MS. Aliasing noise results from incorrect synchronisation between the MS acquisition time and laser firing rate, and is made more prevalent by fast washout cells. Oversampling at high Hz is a possible solution to aliasing, yet remains unexplored for the context of multiplexed elemental bioimaging. In this paper we determined the minimum laser firing rates required to prevent aliasing for any MS dwell time, and provide an equation for calculating aliasing noise. The effects of oversampling were explored using simulations and the ablation of gelatine standards and murine brains. Higher firing rates were found to reduce aliasing and increase signal, but increased the risks of sample damage and raised backgrounds. Aliasing was found to be insignificant at firing rates and dwell times greater than 200 Hz and 2 ms for a typical (20 ms full-width at 10% of maximum) fast washout cell. At these parameters, the noise from aliasing was overwhelmed by noise from other sources and synchronisation was a non-issue. This allowed facile selection of acquisition and dwell times to increase the number of targeted elements or favour those with low sensitivity. Nine elements were collected in a single analysis of a murine brain at 25 pixels per second with no visible aliasing. Use of these parameters will greatly increase throughput and multiplexing capabilities when using high frequency laser ablation with quadrupole-based ICP-MS. [ABSTRACT FROM AUTHOR]

In recent studies, it has been shown that under optimal dual pulse irradiation, it is possible to generate anomalous relativistic temperature (> 500 keV) electron emission even with mJ/pulse lasers at 1/100th of the relativistic intensity when micrometer droplets of methanol are used as a high repetition rate target. In this paper, we present the results of doping these droplets with CH3I to bring out a 30-fold enhancement in electron emission. Experiments and simulations presented here find a route to enhance electron emission driven by two plasmon decay instability. Improving compact laser plasma based sources of MeV electrons, x-ray emission schemes that use a high repetition rate, and mJ/pulse laser systems is important not only for basic science but also applications of imaging and radiography. [ABSTRACT FROM AUTHOR]

Laser Wakefield Acceleration (LWFA) has emerged as a groundbreaking approach for generating ultra-high energy electron beams over short distances, revolutionizing the field of particle acceleration. In this paper, we investigate the novel concept of employing sin-Gaussian laser pulse for enhanced LWFA performance. sin-Gaussian pulses combine the advantageous features of both sinusoidal and Gaussian pulse shapes, offering unique opportunities for generating the plasma wakefield and optimizing electron acceleration. We present a comprehensive theoretical analysis of the interaction between a sin-Gaussian laser pulse and an underdense plasma medium, elucidating the intricate dynamics of the wakefield excitation and electron acceleration. Through analytical study, we demonstrate that the sin-Gaussian pulse configuration leads to a significant energy gain (Maximum gain of 2.06 GeV with chosen parameters) for plasma electrons. Furthermore, we explore the effects of varying key parameters such as the laser electric field amplitude and beam waist on the acceleration performance. Our findings reveal the underlying physics governing the interplay between these parameters and the resulting electron energy spectra for LWFA outcomes. [ABSTRACT FROM AUTHOR]

In this paper, the dependence of the sublimation temperature of soot particles synthesized during the combustion of various hydrocarbons, depending on their size and structure, is obtained. The experimental approach is based on the analysis of the thermal radiation of particles heated to the sublimation temperature by a nanosecond laser pulse. The sublimation temperature of soot particles was measured using the two-color pyrometry method. In this paper, it is proposed to use the average size of primary particles to compare data in different flames. It is established, that the sublimation temperature of soot particles depends mainly on the stage of their formation, which is characterized by an increase in average size. It is shown, that with an increase in the average particle size from 12 to 23 nm, their sublimation temperature increases significantly from 2700 to 4500 K. This reflects a significant difference in the thermodynamic and optical properties of the so-called "young" and "mature" soot particles, which must be taken into account when developing methods of soot diagnostics and in the thermo-physical analysis of combustion and pyrolysis processes with the formation of soot. [ABSTRACT FROM AUTHOR]

The pulse laser using a saturable absorber as a passive device has the advantages of narrow pulse width, high repetition rate, and high pulse energy. Low‐dimensional materials have attracted research interest in recent years due to their excellent saturable absorption properties, ultra‐fast carrier response speed, high damage threshold, and so on. This paper gives a brief review of the state‐of‐the‐at 2 µm solid‐state lasers using saturable absorbers. The output performance of lasers in repetition rate, pulse energy, pulse width, and wavelength are summarized. The paper is expected to provide a development direction of novel materials as saturable absorbers in 2 µm solid‐state lasers. [ABSTRACT FROM AUTHOR]

Ultrafast laser pulses can redistribute charges in Mott insulators on extremely short time scales, leading to the fast generation of photocarriers. It has recently been demonstrated that these photocarriers can form a novel η -paired condensate at low temperatures, featuring a staggered superconducting pairing field. In this conference paper, we discuss the origin of the η -paired hidden phase and its optical response, which may be detected in a pump-probe experiment. The hidden phase may be relevant for possible light-induced superconductivity in Mott insulators. [ABSTRACT FROM AUTHOR]

The graphene paper microsieves can be applied in the filtration of biological fluids or separation of solid particles from exploitation fluids. To produce graphene paper microsieves for specific applications, good control over fabrication should be achieved. In this study, a laser ablation method using a picosecond laser was applied to fabricate graphene paper microsieves. Holes in the microsieves were drilled using pulsed laser radiation with a pulse energy from 5 to 100 µJ, a duration of 60 ps, a wavelength of 355 nm, and a repetition rate of 1 kHz. The impact method was applied using 10 to 100 pulses to drill one hole. To produce holes of a proper diameter which could separate biological particles of a certain size (≥10 µm), optimum parameters of graphene paper laser ablation were defined using the MATLAB software taking into account laser pulse energy, repetition rate, and a desired hole diameter. A series of structural tests were carried out to determine the quality of an edge and a hole shape. Experimental results and Laguerre–Gauss calculations in MATLAB were then compared to perform the analysis of the distribution of diffraction fringes. Optimum experimental parameters were determined for which good susceptibility of the graphene paper to laser processing was observed. [ABSTRACT FROM AUTHOR]

In this paper, we have applied a holographic time-of-flight technique with a nanosecond laser pulse to perform time-resolved measurements of optically induced gratings in bent-core nematics formed by a new kind of liquid crystal (LC). The effects of the electric field, laser pulse energy, temperature, and light intensity pattern on the photocharge transport process were investigated systematically. The results indicate that some peculiar features, such as high photosensitivity, relatively large mobility, and negative conductivity anisotropy, were present in the studied soft-matter system. Furthermore, a coupling between the optically induced grating and electrically induced convection was observed, which revealed a competitive state between them via the transport process. Thus, a better understanding of the carrier transport process involving photosensitivity and response time will help to tailor LC devices toward novel optical applications. [ABSTRACT FROM AUTHOR]

Major components of electrical motors are toroidal cores made of stacked electrical steel sheets. All common joining methods cause a degradation of the magnetic properties of the toroidal cores. In this paper, pulsed laser beam welding in vacuum is used to join the individual electrical steel sheets. It is shown that the magnetic behaviour of the toroidal cores can be influenced by variation of process parameters like beam power and working pressure. [ABSTRACT FROM AUTHOR]

This paper deals with double-pulse laser-induced breakdown spectroscopy (LIBS) underwater, which is a promising analytical method for elemental analysis in the deep sea up to a water depth of 6000 m. A double-pulse laser with a wavelength of 1064 nm is used, which provides a pulse energy of up to 266 mJ for each laser pulse (in single pulse mode), a pulse width of 5–7 ns and a pulse delay in the range of 0.5 to 20 µs. In the double-pulse LIBS method, the first laser pulse creates a cavity on the material surface, and then the second laser pulse forms the plasma in this cavity. It is expected that the plasma is affected by the cavity's size and lifetime. For this reason, the influence of focus position, pulse energy and pulse delay on the cavity and plasma formation at shallow water depth has been investigated. [ABSTRACT FROM AUTHOR]