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In this paper, an analytical formalism is developed for electron acceleration using two crossed and identical laser pulses in a plasma channel. The net electron energy is increased and the electron diffraction is decreased through the utilization of radially polarized (RP) crossed-focused laser pulses. The study investigates the impact of various parameters, such as laser amplitude, ion density, initial kinetic energy, injection angle, laser pulse duration, and spot size on electron energy gain within a preformed plasma ion channel. The presence of space-charge field confines the dynamic of electrons along the longitudinal direction. Consequently, the transverse component of the laser pulse vanishes along the propagation axis, whereas the longitudinal component provides a longitudinal force. This configuration leads to the observation of gain in energy of electrons in GeV at a laser intensity ∼ 10 19 W / cm 2 where the ion density is ∼ 10 23 m - 3 in plasma channel. [ABSTRACT FROM AUTHOR]

It is indispensable to accurately and sensitively identify and analyze the elemental composition of human blood serum. In the current study, human blood serums were analyzed for elements utilizing orthogonal dual pulse laser-induced breakdown spectroscopy (DP-LIBS) setup in He gas environment. Experimentally, a fundamental pulse Nd:YAG laser (1064 nm, 7 ns) was irradiated just above the material target to induce a luminous gas plasma. A third harmonic pulse Nd:YAG laser (355 nm, 7 ns) was subsequently focused on the material surface to initiate a target plasma to ablate the atoms from the blood serum film to be sent to the gas plasma region. Double pulse LIBS technique has been successfully applied to increase the LIBS signal intensity up to 8 folds of major, minor, and trace components in human blood serum. Furthermore, a number of emission lines that were indistinctly detected by single pulse LIBS were accurately identified with the use of the DP-LIBS. A variety of components from the human blood serum have been analyzed both qualitatively and quantitatively. Element concentrations measured in human blood are to be 8360 ppm, 219 ppm, 581 ppm, 785 ppm, 343 ppm, 293 ppm, and 12 ppm for C, Ca, K, Mg, P, Na, and Fe, respectively. The LIBS outcome results are in excellent agreement with the results acquired by applying the standard XRF technique. [ABSTRACT FROM AUTHOR]

A scheme for electron acceleration by self-focused q-Gaussian laser pulses in under-dense plasma has been presented. The relativistic increase in the mass of plasma electrons gives nonlinear response of plasma to the incident laser pulse resulting in self-focusing. Under the combined effects of the saturation nature of relativistic nonlinearity of plasma, self-focusing and diffraction broadening of the laser pulse, the beam width of the laser pulse evolves in an oscillatory manner. An electron initially on the pulse axis and at the front of the self-focused pulse, gains energy from it until the peak of the pulse is reached. When the electron reaches the tail of the pulse, the pulse begins to diverge. Thus, the deacceleration of the electron from the trailing part of the pulse is less, compared to the acceleration provided by the ascending part of the pulse. Hence, the electron leaves the pulse with net energy gain. The differential equations for the motion of electrons have been solved numerically by incorporating the effect of self-focusing of the laser pulse. [ABSTRACT FROM AUTHOR]

The paper discusses the results of studying the emission spectra and absolute radiation intensities of laser plasma generated by laser pulse on a xenon gas-jet target. A Nd:YAG laser, λ = 1064 nm, τ = 5.2 ns, Epulse = 0.8 J was used. The spectral range 3–20 nm was studied. Gas-jet targets were formed by a supersonic conical nozzle. Emission spectra of laser plasma were obtained and interpreted. Absolute radiation intensities were determined in a number of spectral bands under various conditions of gas-jet target excitation. [ABSTRACT FROM AUTHOR]

An analytical formalism is developed to study the radiation pressure hole boring ion acceleration of a CH foil in an underdense upstream plasma. The laser quickly converts the foil into an overdense plasma and exerts a strong forward ponderomotive force on the electrons. The electrons are pushed to the rear and detach from the ions to form a thin electron layer, followed by a hydrogen ion layer and a distant carbon ion layer. The triple layer of electrons, protons and carbon ions is accelerated by the radiation pressure; the space charge field plays an intermediary role in accelerating the ions. In the frame of the electron layer, moving with velocity v f z ^ , the upstream protons appear to be moving backward with velocity - v f z ^ . They get reflected back in the fast moving intense space charge field of the triple layer, acquiring velocity v f z ^ . In the lab frame, these protons have a velocity nearly twice the velocity of the electron layer. For a Gaussian (in time) laser pulse, a parabolic density profile of the upstream plasma is seen to produce a proton beam with narrow energy spread. For a normalized laser amplitude a 0 = 10 , one may obtain 180 MeV protons in a parabolically decreasing density profile of scale length 40 μ m. [ABSTRACT FROM AUTHOR]

The effect of the energy, the interval between the pulses, and the number of double laser pulses on the formation of the component and charge composition of laser plasma by laser spark spectrometry (LSS-1 spectrometer) was studied. The processes leading to the formation of mixed nanopowders of copper and aluminum oxides, precursors for the production of nanoceramics and films of CuAlO2 copper aluminates by the action of double laser pulses on a hybrid target consisting of cemented aluminum and copper plates, from AD1 and M2 alloys were investigated. It was shown that precursors for the manufacture of nanoceramics and nanofilms of CuAlO2 copper aluminates can be obtained by the successive action of a series of double laser pulses with energy of 53 mJ and an interval of 10 μs on a hybrid target. A closed glass weighing bottle containing the target was used for the products formed during interaction of the aluminum and copper ions with atmospheric oxygen. The size of the initial particles, determined by means of a high-resolution electron microscope, amounted to 30–45 nm. The particles were assembled into agglomerates and had a crystalline structure and spherical form. On account of the purely diffusion transfer mechanism of the fractals the size and amount of the fractal aggregates settling on the support situated at the bottom of the cuvette were several times greater than the amount of the products that settle on the side support. The main contribution to change in the intensity of the spectral lines for the Al and Cu atoms and ions and the AlO molecular bands comes from interaction of the second pulse with the condensation products formed in the channel after the action of the first pulse. With increase in the number of long-lived fractal aggregates in the air the intensity of molecular bands and lines decreases by ~1.5 times for Al III and by ~2 times for copper, which is due to active interaction of the long-lived large fractals that accumulate in the air with the incident radiation. [ABSTRACT FROM AUTHOR]

Acceleration of laser-induced plasma created as a result of three-step photoionization of atomic vapor by pulsed radiation of dye lasers pumped by copper-vapor lasers is studied experimentally. The acceleration was achieved due to the alternating magnetic field appearing upon propagation of a current pulse through an inductor located in direct proximity from the area of laser protoionization of atomic lutetium vapor. [ABSTRACT FROM AUTHOR]

Dry reforming of methane (DRM) is a highly endothermic process, with its development hindered by the harsh thermocatalytic conditions required. We propose an innovative DRM approach utilizing a 16 W pulsed laser in combination with a cost-effective Mo2C catalyst, enabling DRM under milder conditions. The pulsed laser serves a dual function by inducing localized high temperatures and generating *CH plasma on the Mo2C surface. This activates CH4 and CO2, significantly accelerating the DRM reaction. Notably, the laser directly generates *CH plasma from CH4 through thermionic emission and cascade ionization, bypassing the traditional step-by-step dehydrogenation process and eliminating the rate-limiting step of methane cracking. This method maintains a carbon-oxygen balanced environment, thus preventing the deactivation of the Mo2C catalyst due to CO2 oxidation. The laser-catalytic DRM achieves high yields of H2 (14300.8 mmol h−1 g−1) and CO (14949.9 mmol h−1 g−1) with satisfactory energy efficiency (0.98 mmol kJ−1), providing a promising alternative for high-energy-consuming catalytic systems. Dry reforming of methane (DRM) is a highly endothermic process, often limited by the severe thermocatalytic conditions it demands. Here the authors introduce a novel DRM method that employs a 16 W pulsed laser along with a cost-effective Mo2C catalyst, allowing DRM to proceed under milder conditions. [ABSTRACT FROM AUTHOR]

We report the optimization of the high-order harmonic generation (HHG) in the laser-induced gold plasma. It includes determination of the characteristics of heating pulses allowing formation of the gold plasma possessing suitable characteristics (plasma density, electron density, electron temperature, velocity of plasma), as well as determination of the optimal delay between heating picosecond pulses and driving femtosecond pulses. Time-resolved Au plasma spectra and images allowed determining the velocity of plasma spreading (2 × 104 m s-1), electron density (3 × 1016 cm-3), and electron temperature (0.8 eV) of gold plasma at the optimal fluence of heating 150 ps pulses allowing HHG up to the 53rd order at the conversion efficiency of 1 × 10− 5. We also report the modification of the blueshift of harmonics at different regimes of HHG and plasma formation. The harmonic splitting onto strong blue component and weak red component appeared at 3 × 1014 W cm-2 intensity of 806 nm pump. [ABSTRACT FROM AUTHOR]

The formation of a diamond-like carbon coating on a substrate as a result of the action of the radiation of an industrial laser (t ~ 20 ns, λ = 1.06 μm) on a target of the highly oriented pyrolytic UPV-1 graphite in a vacuum was investigated. It is shown that by changing the power density of the laser radiation on the surface of such a target, the velocity of scanning of the laser beam over the target surface, the laser pulse repetition frequency, and the temperature of the target, one can control the ratio between the sp2- and sp3-carbon bonds in the coating applied to a substrate. It was established that a diamond-like carbon coating with a predominant content of the sp3-bonded carbon is formed at a laser power density q ≥ 5.6∙108 W/cm2. In this case, it is advisable to select the laser pulse repetition frequency and the velocity of scanning of a laser beam over the surface of a target so that 10 to 14 laser pulses fall successively into one and the same area of the target surface. It is shown that, in the case where a target has a temperature T ≥ 423 K, the content of the sp3-linked carbon in the coating applied to a substrate decreases sharply, with the result that the properties of the coating deteriorate. [ABSTRACT FROM AUTHOR]

The paper considers the emission spectra and dependences of the emission intensity of a number of carbon lines in absolute units for laser plasma generated by laser pulse on CO2, CHF3, and CF4 gas jets on the gas pressure at the nozzle inlet. A pulsed Nd:YAG laser, λ = 1064 nm, τ = 5.2 ns, Eimp = 0.8 J was used. Gas-jet targets were formed by a supersonic conical nozzle, the pressure at the nozzle inlet varied in the range of 5–25 bar. The emission spectra of the investigated gases were compared and the reasons for the different dependences of the radiation intensity on the gas pressure at the nozzle inlet were analyzed. [ABSTRACT FROM AUTHOR]

The results of studying the spatial structure of the plasma flows that appear when a laser pulse of relativistic intensity (above 1018 W/cm2) is incident on the surface of a solid target are presented. The ring structure experimentally observed in the cross section of a plasma flow is shown to correspond to the toroidal equilibrium plasma configuration that appears in the strong magnetic fields of laser plasma. A model is proposed to describe astrophysical current jets consisting of a discrete sequence of toroidal equilibrium plasma structures. [ABSTRACT FROM AUTHOR]

The emergence of petawatt lasers focused to relativistic intensities enables all-optical laboratory generation of intense magnetic fields in plasmas, which are of great interest due to their ubiquity in astrophysical phenomena. In this work, we study generation of spatially extended and long-lived intense magnetic fields. We show that such magnetic fields, scaling up to the gigagauss range, can be generated by interaction of petawatt laser pulses with relativistically underdense plasma. With three-dimensional particle-in-cell simulations we investigate generation of magnetic fields with strengths up to 10 10 G and perform a large multi-parametric study of magnetic field in dependence on dimensionless laser amplitude a 0 and normalized plasma density n e / n c . The numerical results yield scaling laws that closely follow derived analytical result B ∝ a 0 n e / n c , and further show a close match with previous experimental works. Furthermore, we show in three-dimensional geometry that the decay of the magnetic wake is governed by current filament bending instability, which develops similarly to von Kármán vortex street in its nonlinear stage. [ABSTRACT FROM AUTHOR]

THz radiation through a novel scheme based on a three-pulse configuration in two-dimensional ordinary and extraordinary modes was investigated. The electromagnetic radiation driven by the linear and nonlinear current density created by the laser-induced plasma mechanism has been evaluated. The numerical findings of the present study show that the electric field of THz radiation is significantly improved compared to the two-color scheme if the third harmonic is included. The asymmetric three-color femtosecond laser fields can be used to control the polarization state, radiation power, and the directivity of the THz radiation. With adjustable time delays between pulses, the polarization controllability of THz radiation from plasma, based on experimental conditions, can be achieved. With this scheme, not only tuning to circularly polarized THz radiation is feasible, but also linear or elliptical polarization can be realized by adjusting time delays. The effects of different laser profiles and wavelengths on ionization rate are considered. Variation of the electric field of the generated THz waves for both ordinary and extraordinary modes of photocurrent mechanism is examined numerically for various spatial laser profiles. The study indicates that a laser pulse profile can be used to control THz radiation. [ABSTRACT FROM AUTHOR]

In this work, a bi-stable behavior of laser ablation efficiency and quality was controlled by fluence and burst length. The plasma shielding of incoming laser radiation caused sudden jumps with a significant decrease in ablation efficiency for every even number of pulses in the burst. The attenuation of incoming laser radiation by plasma created by the previous pulse was incorporated into the toy model of burst ablation efficiency. The mathematical recurrence relation has been derived for the first time, binding ablation efficiency for the next pulse with the efficiency of the previous pulse, which predicts bi-stability, as well as sudden jumps occurring in ablation efficiency depending on the number of pulses in burst with the response to changes of the control parameter of peak laser fluence in the pulse. The modeling results using new recurrence relation showed stable and bi-stable ablation efficiency depending on burst fluence and the number of pulses, which agreed well with experimental data. The extremely efficient laser ablation has been achieved by optimizing the shielding effect using three pulses in the burst. [ABSTRACT FROM AUTHOR]

Terahertz pulse generation from multiterawatt laser surface plasma near thick solid targets and thin foils has been studied. Pulses with energies up to 7 μJ were detected in the spectral region <3 THz in the direction of specular reflection from the surface of the CaF2 target. The dependence of the terahertz pulse energy on the laser pulse intensity can be approximated by the power function . For a fixed laser pulse duration and variable energy the power index lies in the range , while for a fixed energy and variable duration . [ABSTRACT FROM AUTHOR]

Laser wakefield acceleration (LWFA) of electrons is a highly promising and advanced technique within the field of laser plasma physics, which enables the generation of remarkably high-energy electron beams over a comparatively short distance. In this paper, we have used different Gaussian-like laser pulse profiles of the same amplitude of electric field and laser intensity in magnetized plasma. Generated wakefield and energy gain are calculated analytically by using equation of motion and Maxwell's equation. Our results show that generated wakefield and energy gain are greatly affected by the shape of laser electric field profile. Pulse with broader electric field profile produces more effective LWFA under identical conditions of other parameters. Energy gain by electrons increases slightly with increase in the strength of external magnetic field. Results show that for the broadest laser profile, the magnetic field has more influence on wakefield production and electron energy gain. The role of laser pulse length is also analyzed. In this study, we have obtained a maximum of 151.6 MeV energy gain with experimentally feasible parameters. Our findings will assist researchers in selecting the most energy-efficient pulse profile for LWFA. [ABSTRACT FROM AUTHOR]

High-order harmonics generation in the laser-induced plasmas produced on the surfaces of lead-free perovskites is studied. We analyze the harmonics generation in (CH3NH3)2CuCl4 and (CH3NH3)2CuBr4 plasmas during their ablation by the femtosecond, picosecond, and nanosecond pulses. The modifications of the high-order harmonics spectra are studied using the -color pump scheme (800 nm and 400 nm, 40 fs pulses). The influence of the variations of laser chirp and pulse duration on the dynamics of high-order harmonics generation is examined. The spectral shift, chirp-related harmonic cutoff scaling, and the role of the pulse duration of converting and heating laser radiation are examined at different conditions of plasma formation and harmonic generation. The dependencies of the pulse duration and the fluence of heating pulses on the harmonic's blue shift are found. The effect of harmonics broadening and splitting on the two red- and blue-shifted components is demonstrated. [ABSTRACT FROM AUTHOR]

The thermodynamic state of a high-temperature laser-induced emitting plasma has been studied based on numerical simulation data. Laser-induced X-ray radiation characteristics versus wavelength and intensity of an incident Nd-laser pulse have been discussed for those ranges of these parameters where the condition for compression of an inertial-confinement fusion target by an X-ray pulse is met. Another object of investigation was the thermodynamic state of a plasma produced by a laser-induced X-ray radiation pulse acting on plane targets made of light materials that are most in demand as materials for a target outer layer (so-called ablator), within which a target-compressing pressure is developed. The thermodynamic characteristics of the plasma produced by the laser pulse have been compared with those of the plasma produced by the pulse of laser-induced X-ray radiation. [ABSTRACT FROM AUTHOR]

The high-power pulsed laser beams can use for matter ablation which is not only prevalent in science fiction movies but discovered by several technological fields ranging from the manufacturing of micro and nanoscale features to biomedical imaging applications.In the present work, the contemporary technical setup, integrated with the spatially, temporally, and semi-spectrally resolved optical emission imaging of colliding laser-produced plasma has been employed to study plasmas formed by 1064 nm pulsed laser ablation of the Aluminum target in a vacuum. The species emissions from the stagnation layer were mapped as a function of both locations from the surface of the target and time from the laser pulse. The fast-optical imaging technique, based on new digital analysis mechanisms and algorithms, has been utilized as a diagnostic tool to investigate the geometrical characterization and related features of the interaction zone formed by homogenous target material. The study provides a considerable amount of detailed data of the interaction zone which extends the understanding of the behaviour of particular species within colliding laser-produced plasmas. The plasma parameters such as total intensity and area density were measured from the spatiotemporal analysis based on an integrated digital image processing code. The results explain the characterizations of the stagnation layer life cycle and dynamical decay of the species emission and related features. Our experimental investigations show that through appropriate engineering based on the modified observational setup, the properties of the stagnation layer can be controlled with relative ease, making colliding plasma systems a flexible platform for the study of many complex physical systems. [ABSTRACT FROM AUTHOR]

Based on the dynamic behavior of laser keyhole, the time characteristics of coupling discharge of heat source in pulsed laser–induced twin TIG welding (LITTW) are studied. The behaviors of arc plasma and laser keyhole were directly observed by high-speed camera and auxiliary illumination source. The physical characteristics of arc plasma were analyzed by spectrometer and arc quality analyzer. A physical model is established to reveal the regulation mechanism of time characteristics of coupling discharge. It is found that after laser pulse action, the coupling discharge between keyhole plasma and double-arc plasma does not end immediately, and its time depends on the existence time of keyhole. During hybrid welding, when the combined force of arc pressure and Marangoni force can overcome the gravity, the liquid metal is forced out of the keyhole and the keyhole remains open. Improving the electron density of arc plasma and arc voltage and reducing the diameter of arc conductive channel by selecting appropriate parameters is the key to prolong the existence time of keyhole, which is beneficial to improve the welding penetration. The coupling enhancement of double-arc electromagnetic field in LITTW can effectively suppress keyhole backfill and increase the duty ratio of coupling discharge. When the total current intensity is 200 A, compared with laser-induced single TIG welding (LISTW), the existence time of keyhole in LITTW increases by 77%, the duty ratio of coupling discharge increases by 12%, and the weld penetration increases by 29.2%. [ABSTRACT FROM AUTHOR]

Organic–inorganic lead halide perovskite nanocrystals (NCs) have received the phenomenal attention of researchers in the last few years due to their advanced optical properties and developments in simple synthetic procedures. In this work, we demonstrate the effect of Ni-dopant on the ultrafast third-order nonlinear optical (NLO) properties of two-dimensional (2D) CsPbBr3 NCs using 60 fs laser pulses at a wavelength of 400 nm. Based on the probe pulse intensity, pure CsPbBr3 NCs exhibited saturable absorption and reverse saturable absorption (RSA). The doping of NCs by Ni at different concentrations significantly modified the nonlinear absorption mechanism where the RSA was followed by the SA with growing input laser intensity. The nonlinear refractive index of Ni-doped CsPbBr3 NCs decreased when compared with the pure CsPbBr3. In addition, the NLO properties of these 2D NCs are correlated with the efficiency of the high-order harmonics generated during propagation of the two-color (800 + 400 nm) and single-color (800 nm) chirp-free (35 fs) and negatively/positively chirped pulses through the laser-induced plasmas produced on the surface of undoped and Ni-doped perovskite NCs. The ablation of Ni-doped NCs allowed increasing the harmonic yield compared to undoped CsPbBr3 NCs. Our studies undoubtedly demonstrate the advanced lower and higher order NLO properties of Ni-doped 2D CsPbBr3 NCs. [ABSTRACT FROM AUTHOR]

Particle-in-cell (PIC) simulations are a widely-used tool to model kinetics-dominated plasmas in ultrarelativistic laser-solid interactions (dimensionless vectorpotential a0 > 1). However, interactions approaching subrelativistic laser intensities (a0 ≲ 1) are governed by correlated and collisional plasma physics, calling for benchmarks of available modeling capabilities and the establishment of standardized testbeds. Here, we propose such a testbed to experimentally benchmark PIC simulations of laser-solid interactions using a laser-irradiated micron-sized cryogenic hydrogen-jet target. Time-resolved optical shadowgraphy of the expanding plasma density, complemented by hydrodynamics and ray-tracing simulations, is used to determine the bulk-electron-temperature evolution after laser irradiation. We showcase our testbed by studying isochoric heating of solid hydrogen induced by laser pulses with a dimensionless vectorpotential of a0 ≈ 1. Our testbed reveals that the initial surface-density gradient of the target is decisive to reach quantitative agreement at 1 ps after the interaction, demonstrating its suitability to benchmark controlled parameter scans at subrelativistic laser intensities. Relativistic laser-solid interactions are simulated via particle-in-cell (PIC) approaches, while subrelativistic regimes rely on radiation-hydrodynamics formulations. To validate the methods at the transition from relativistic to subrelativistic laser intensities, the authors propose a testbed to experimentally benchmark PIC simulations. [ABSTRACT FROM AUTHOR]

Laser–plasma acceleration of ions has been of interest for the past few decades. An effective way to enhance laser-driven proton acceleration is to improve laser absorption in plasmas. In this study, we show that lithium (Li) is the most promising candidate for accelerating protons with better absorption among target light weight materials used for ion acceleration. For this, two-dimensional particle-in-cell (PIC) simulations were performed to investigate the acceleration of ions and protons with a high-power laser (with an amplitude a0=10 and a pulse duration of 30 fs) to determine the optimal lithium target thickness for maximum energies. The maximum energy of Li ions is achievable with a target thickness of 40 nm, while the maximum proton energy can be achieved for a 30nm thickness of the target. Moreover, a series of PIC simulations were also performed with targets of different atomic numbers and thicknesses to understand lithium's performance for the acceleration of protons. Compared to other targets, such as Al (Aluminum), C (Carbon), and Be (Beryllium), the Li target has a significant enhancement in proton energy, which can be used as an alternative target to enhance proton and ion energies in future experiments. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) is an emerging technique in geochemistry that allows rapid in-situ analysis of the elemental composition and concentration of minerals by laser ablation of the material surface and measurement of the light emitted by the resulting plasma. However, this type of application is still under development for geochemical analyses. Indeed, it is still difficult to know how minerals are ablated under laser pulses in the context of LIBS geochemical analysis using a high-power Q-switched Nd:YAG laser operating at 1064 nm with pulse durations on the order of nanoseconds. Important questions remain unanswered regarding the volume sampled by the laser beam on the minerals to be analyzed, as well as the plasmas induced by the laser on the minerals in air at atmospheric pressure. The objective of this work is to provide insight into laser-mineral interactions within the framework of LIBS geochemical analysis of ore samples with emphasis on the characterization of plasmas and laser ablation craters under ambient air at atmospheric pressure. We study the crater morphology in the three main phases of a palladium ore fragment (Lac des Iles mine, Canada), namely plagioclase feldspar, amphibole and sulfides [Mohamed et al., Geostand Geoanal Res 45:539, (2021)] We performed four series of laser shots (50, 250, 500 and 1000 shots) in the three mineral phases and characterized the morphology of the craters obtained by scanning electron microscopy and optical coherence tomography. It turns out that laser ablation is most effective in plagioclase, presumably due to its lower thermal conductivity. In addition, the temperature and electron density of the plasma were determined for each phase from the iron and nickel lines of LIBS spectra taken 4 µs after the laser shots. They are between 6300 and 8600 °C and about 2 × 1017 cm−3, respectively. [ABSTRACT FROM AUTHOR]

The dynamics of heterogeneous angularly colliding (Al–Cu) laser-produced plasmas with varying input laser pulse energies on each target are studied using fast imaging and optical emission spectroscopic techniques. The stagnation layer formed at the collision front consists of both Al and Cu species, and its intensity varied with the variation in laser pulse energy. Multispecies stagnation region formation and the variation of spectral line intensity with laser pulse energy are studied using the optical emission spectroscopic technique. The depositions of interaction regions are analyzed using the XRD, EDAX, FESEM, and AFM techniques. The intermetallic compound formation is possible using this technique, and the composition can be varied by varying the input laser pulse energies. The major benefits are the flexibility of controlling parameters and the simplicity of experimental setup for the formation of intermetallic compounds. Thus, angular target geometry for colliding laser-produced plasma is proposed to efficiently mix different metals with control over the composition of deposited films. [ABSTRACT FROM AUTHOR]

A terahertz NH3 laser optically pumped by "long" (~100 μs) pulses of an electron-beam-sustained-discharge CO2 laser is demonstrated for the first time. The NH3 laser pulses and the "long" pulses of the CO2 laser are simultaneously measured with nanosecond resolution. The duration and the delay of the NH3 laser pulse relative to the pump pulse are measured depending on the pulse energy of the pump CO2 laser. The following emission wavelengths of the terahertz NH3 laser were observed upon pumping by the 9R(30) line of the CO2 laser: 67.2, 83.8, and 88.9 μm. [ABSTRACT FROM AUTHOR]

A computer code is developed for processing primary images obtained in the pepper-pot emittance measurement technique, which makes it possible to estimate emittance in a single measurement. The code uses a pepper-pot mask image on a scintillator screen obtained by means of laser plasma radiation. This image is used to find positions of holes of the mask and its rotation angle. The pepper-pot technique is applied to measure emittance of a carbon ion beam extracted from the laser-produced plasma, which is generated by CO2 laser pulses at the focal power density on the target of about 1011 W/cm2. Some results of image processing and calculation of the emittance are presented. [ABSTRACT FROM AUTHOR]

The possibility of implementing the relativistic self-trapping of an ultraintense laser pulse in a plasma with an inhomogeneous density profile is proved using the three-dimensional kinetic particle-in-cell simulation. The necessary focusing conditions of laser light are determined depending on the gradient length of the plasma density. The comparison of the efficiency of the laser-induced acceleration of electrons with the case of a homogeneous plasma indicates that the appropriate choice of the position of the focus of laser light and the size of the focusing spot on the density profile ensures the relativistic self-trapping of the laser pulse and its use in innovative applications with the same efficiency as in the case of a homogeneous target. [ABSTRACT FROM AUTHOR]

The double stream gas puff-based laser-produced plasma is studied as a source of soft X-ray radiation in nm wavelength spectral range. Dynamics of plasma induced by Nd:YAG laser beam and its emission is simulated with radiation-magnetohydrodynamic code Zstar. The modeling results for krypton gas stream in an annular helium jet as a circumferential gas for various picosecond and nanosecond laser pulses corresponding to the experiments are presented. The spatial–spectral features and temporal behavior of the soft X-ray and EUV emission are investigated. Under ps pulse, the gas is rapidly ionized in the laser beam channel, but it does not have enough time to shift sensibly during the pulse, and the plasma electron density grows against the background of almost constant ion density during the ionization in the laser radiation field. There is ionization instability only capable to be developed in ps range. At ns pulse, the gas ionization and heating leads to gas pushing out of the channel, and the formation of a divergent compression wave transforming into the shock wave. Behind the compression wave front, conditions arise for the development of Rayleigh–Taylor-type instability. The instability leads to the redistribution of plasma temperature and density, and to the formation of increased soft X-ray emission spots. Time evolution of spatial distributions and spectral characteristics of emitted SXR radiation is analyzed for different laser pulses. Transient effects in multicharged ion plasma are discussed, fundamental understanding of those is required for optimization of plasma radiation source. A conversion efficiency of laser energy into soft X-ray wavebands from krypton plasma is scanned by laser parameters and analyzed. [ABSTRACT FROM AUTHOR]

Three groups of charged particles are recorded at the impact of the laser radiation pulse with a metal target in a rarefied gas medium. The optical range laser radiation intensity is ~109 W/cm2. A possibility of using a Langmuir probe for diagnosing plasma processes with nanosecond resolution is demonstrated. [ABSTRACT FROM AUTHOR]

It has been experimentally shown that a low-power vacuum pinch discharge with laser ignition can emit a beam of abnormally accelerated electrons with maximum energies per unit charge almost an order of magnitude higher than the voltage across the discharge gap. It has been found that the intensity of the X-ray radiation generated when the beam is applied to the target significantly decreases with an increase in the laser pulse energy. The maximum energy of X-ray quanta is inversely proportional to the mass of the cathode substance ablated by laser radiation during discharge ignition. Possible mechanisms of the electron-beam generation process have been discussed. [ABSTRACT FROM AUTHOR]

The interaction of an ultrashort (~10 fs) laser pulse with a relativistic intensity (≳1018 W/cm2) with a cluster medium characterized by a random distribution of large, submicron clusters of heavy atoms has been studied. Matching conditions for the parameters of the cluster medium and the laser pulse have been determined under which the yield of hot electrons is maximal at a given laser energy. The stochastic dynamics of laser-heated electrons in the Coulomb fields of clusters after the passage of the pulse determines the formation of a plateau with signatures of quasimonochromaticity in the energy spectrum of electrons in the ponderomotive energy range, which is important for the generation of the secondary electromagnetic radiation. [ABSTRACT FROM AUTHOR]

Underwater laser ablation can be employed both as a means to produce nanoparticles and to texturize surfaces of various materials. In this approach, a stationary or flowing water layer above the target surface confines laser induced plasma which cools to form short lived cavitation bubbles, positively influencing the amount of removed material per laser pulse. Plasma and cavitation bubble evolution additionally give rise to bubbles which may persist in the water throughout the ablation process. These bubbles are known to have a detrimental effect on material removal rates particularly in stationary water, but the quantitative influence of bubble dimensions and position on removed material volume is currently unknown. Here we show the laser intensity profile changes induced by bubbles located at 0–0.4 Rayleigh lengths above a stainless steel surface and couple these changes to removed crater volume. Our results show that water flowing at Reynolds numbers in the range of 1–100 positively contribute to crater volumes for pulse frequencies up to 1 kHz. At 1 kHz, it was found bubbles have insufficient time to flow from the vicinity of the laser spot, regardless of the Reynolds number within the range investigated. These conclusions assist in selecting an appropriate combination of laser and flow conditions to optimize laser ablation material removal rate. [ABSTRACT FROM AUTHOR]

Laser plasma-based particle accelerators attract great interest in fields where conventional accelerators reach limits based on size, cost or beam parameters. Despite the fact that particle in cell simulations have predicted several advantageous ion acceleration schemes, laser accelerators have not yet reached their full potential in producing simultaneous high-radiation doses at high particle energies. The most stringent limitation is the lack of a suitable high-repetition rate target that also provides a high degree of control of the plasma conditions required to access these advanced regimes. Here, we demonstrate that the interaction of petawatt-class laser pulses with a pre-formed micrometer-sized cryogenic hydrogen jet plasma overcomes these limitations enabling tailored density scans from the solid to the underdense regime. Our proof-of-concept experiment demonstrates that the near-critical plasma density profile produces proton energies of up to 80 MeV. Based on hydrodynamic and three-dimensional particle in cell simulations, transition between different acceleration schemes are shown, suggesting enhanced proton acceleration at the relativistic transparency front for the optimal case. Laser-produced plasma can be used for particle acceleration in different schemes. Here the authors demonstrate proton acceleration from the intense ultrashort laser pulse interaction with micron-sized cryogenic hydrogen jet. [ABSTRACT FROM AUTHOR]

We report on the development of a highly directional, narrow energy band, short time duration proton beam operating at high repetition rate. The protons are generated with an ultrashort-pulse laser interacting with a solid target and converted to a pencil-like narrow-band beam using a compact magnet-based energy selector. We experimentally demonstrate the production of a proton beam with an energy of 500 keV and energy spread well below 10 % , and a pulse duration of 260 ps. The energy loss of this beam is measured in a 2 μ m thick solid Mylar target and found to be in good agreement with the theoretical predictions. The short time duration of the proton pulse makes it particularly well suited for applications involving the probing of highly transient plasma states produced in laser-matter interaction experiments. This proton source is particularly relevant for measurements of the proton stopping power in high energy density plasmas and warm dense matter. [ABSTRACT FROM AUTHOR]

We use the qualitative, simplified modeling, and approximately self-consistent nonlinear-optical approaches to explain the nature of the regime under which relativistically intense laser pulses propagate in a plasma to distances exceeding the Rayleigh length considerably, as was found earlier by numerical simulation. Such a regime requires certain matching of the size of the laser spot with the plasma density and the laser pulse intensity. It corresponds to the so-called self-trapping of radiation, which has been well known since the 1960s for the quadratic nonlinearity of the medium's dielectric permittivity and, as has been established, takes place for the relativistic plasma nonlinearity as well. The case of the plasma with a near-critical density is considered as it is of greatest interest in the context of practical applications. Synchronization of chaotic motions of the electrons accelerated by the laser pulse in the self-trapping regime is discussed. [ABSTRACT FROM AUTHOR]

The high intensities reached today by powerful lasers enable us to explore the interaction with matter in the relativistic regime, unveiling a fertile domain of modern science that is pushing far away the frontiers of plasma physics. In this context, refractive-plasma optics are being utilized in well established wave guiding schemes in laser plasma accelerators. However, their use for spatial phase control of the laser beam has never been successfully implemented, partly due to the complication in manufacturing such optics. We here demonstrate this concept which enables phase manipulation near the focus position, where the intensity is already relativistic. Offering such flexible control, high-intensity high-density interaction is becoming accessible, allowing for example, to produce multiple energetic electron beams with high pointing stability and reproducibility. Cancelling the refractive effect with adaptive mirrors at the far field confirms this concept and furthermore improves the coupling of the laser to the plasma in comparison to the null test case, with potential benefits in dense-target applications. Intense laser interaction with matter creates plasma which can act as a nonlinear optical medium. Here the authors demonstrate plasma as a refractive optics for relativistic intensity radiation, evident by the acceleration of multiple electron beams from a single laser pulse passing through the plasma. [ABSTRACT FROM AUTHOR]

Optical and photo-thermal effects have emerged in many fields, including thermal characterization, spectroscopy, transportation, and non-destructive examinations. In this study, the Moore-Gibson-Thompson (MGT) thermoelastic model is used to explore the photo-thermal coupling of an isotropic, homogeneous, semiconducting and thermomagnetic solid. The heat conduction law is modified to include the time derivative of fractional order and theoretically formulate the system of governing equations. Using the extended Mittag–Leffler functions as nonsingular kernels, the Atangana and Baleanu derivatives considers the features of fractional derivatives. As measured by an external reference frame, it is taken into account that the medium rotates with a constant angular velocity about the axis of symmetry. The cavity boundaries undergo thermal shock and time-varying heat flux. It has been shown that the Laplace transform method is a powerful technique for solving such problems that link the plasma and heat transfer with phase delays. It is finally aimed to describe the numerical results for changes in carrier density as a function of time and radial distance, temperature increment, strain, thermal stresses, and displacement using a photo-induced carrier with different values of physical relaxation time and fractional operator. [ABSTRACT FROM AUTHOR]

We present a new experimental setup for high-order harmonic generation in laser-produced plasmas, allowing the generation of coherent VUV and EUV light, as well as characterisation of the laser-produced plasmas by studying the emitted harmonics. We have successfully generated high-order harmonics in laser-produced Al, Ni, Ag, In, and Sn plasmas. Large differences in harmonic spectra and signal yields have been observed for these different targets. Harmonics up to order 25, corresponding to a wavelength of 62.4 nm and photon energy of 19.9 eV, have been measured with tin plasmas. Scanning laser parameters and delay between pump and fundamental laser pulses allows us to optimise the harmonic yield and observe the temporal dynamics of the laser-produced tin plasma. [ABSTRACT FROM AUTHOR]

The theory of terahertz (THz) waves generation at the incidence of the focused p-polarized laser pulse on the plasma boundary is developed. The angular, spectral, and energy characteristics of the THz signal are studied as the function of the focusing degree and the incidence angle of laser radiation, as well as the plasma density. The frequency dependence of the THz signal energy is considered and it is established that the emission spectrum contains the broad line, and its position for tight focusing of laser radiation is determined by its reciprocal duration. The radiation pattern of the THz pulse is studied and it is shown that the decrease in the size of the laser pulse focal spot leads to the increase in the angle of radiation with respect to the normal to the plasma boundary, and for the tight focusing of the laser pulse, THz waves are emitted almost along the plasma-vacuum interface. It is established that the energy of the THz pulse noticeably increases when the p-polarized laser pulse is incident almost along the normal onto the near-critical plasma at the angle of total reflection, and the transverse size of the laser pulse decreases. It is shown that the emission of high-power THz pulses with the sufficiently high conversion rate occurs at the almost normal incidence of ultrashort tightly focused laser radiation on the boundary of near-critical plasma with rare electron collisions. [ABSTRACT FROM AUTHOR]

Parameters (thickness, electron density) of the laser target in the form of ultrathin foil are determined that provide maximum (~10%) conversion ratio of short relativistically intense laser pulses into a train of several coherent attopulses. Attopulse amplitude, duration are determined, conversion ratio of laser energy into the energy of attopulses is determined and the possibility of its increase using several successively located targets is shown. [ABSTRACT FROM AUTHOR]

The review aims to present the current state of research on the resonance plasma heating by high-power laser radiation in the presence of a strong magnetic field. It is demonstrated that modulation instability with a modulation period equal to the wavelength of the driven plasma wave occurs upon propagation of a low-amplitude pulse parallel to the magnetic field in a subcritical-density plasma in the ECR region. The magnitude of the driven longitudinal electric field grows substantially with increase in the pulse amplitude. In the process, the energy imparted to plasma electrons by the laser radiation increases severalfold relative to the case of an isotropic plasma. The physical mechanism of strong heating of electrons consists in transformation of the modulation instability into stochastic regime at high amplitudes. Propagation of an extraordinary laser wave in plasma in the region of parametric resonance at twice the upper hybrid frequency is analyzed in the case of wave propagation perpendicular to the magnetic field. Considerable auxiliary heating of electrons due to laser-wave decay into upper hybrid plasmons and excitation of the Bernstein waves takes place under such interaction as well. It follows from the electric-field distribution at the time of laser pulse arriving to the right boundary of the plasma layer that strong absorption of the transverse electric field of the laser pulse and enhancement of the longitudinal field occur in the region of parametric upper-hybrid resonance, which is accompanied by the appearance of the reflected electromagnetic wave at the upper hybrid frequency. [ABSTRACT FROM AUTHOR]

Optimizing the laser wakefield accelerator (LWFA) requires control of the intense driving laser pulse and its stable propagation. This is usually challenging because of mode mismatching arising from relativistic self-focusing, which invariably alters the velocity and shape of the laser pulse. Here we show how an intense pre-pulse can prepare the momentum/density phase-space distribution of plasma electrons encountered by a trailing laser pulse to control its propagation. This can also be used to minimize the evolution of the wakefield thus enhancing the stability of the LWFA, which is important for applications. [ABSTRACT FROM AUTHOR]

Spectra and structures of near-surface plasma torches were studied experimentally by measuring the specific mass loss and plume luminosity caused by dual-pulse laser radiation at wavelengths 1064 and 532 nm on titanium in air as functions of the time between laser pulses and their sequence. Dependences of the laser-plasma temperature and concentration of charged particles on the paired laser pulse parameters were established at laser radiation power densities q1064 ≤ 3.1·109 and q532 ≤ 2.7·109 W/cm2 for λ = 1064 and 532 nm. The optimal conditions for recording erosion plasma spectra had the initial effect from second-harmonic radiation with a time interval between pulses of 4–5 μs; for specific mass loss, 3–6 μs. The results were important for enhancing the efficiency of laser emission spectral analysis and laser-plasma processing of materials. [ABSTRACT FROM AUTHOR]

Various recently emerged applications of mid-infrared pulses for high-order harmonic generation in laser plasmas produced on the surfaces of various materials are reviewed. Among them are (a) the highorder harmonic generation in Ag, Sn, fullerene, and graphene nanoparticle-containing plasmas using tunable two-color mid-infrared pulses, (b) efficiency dependence on the generating particle properties in the case of two-color high-harmonic generation of the longer-wavelength radiation in the plasmas, and (c) high-order sum and difference frequency generation using tunable two- and three-color commensurate and incommensurate mid-infrared pumps of graphite plasma. These studies demonstrate the perspectives of the frequency conversion of mid-infrared radiation in the extended laser-produced plasmas. [ABSTRACT FROM AUTHOR]

We have studied the intensity of the spectral lines for the main components in clay: Al I 309.4 nm, Al II 358.7 nm, Mg II 279.6 nm, Ti II 323.6 nm vs. the position of the object relative to the focus of the optical system when the samples are exposed to single laser pulses from a YAG:Nd3+ laser. We have determined the permissible ranges for positioning the object relative to the focus of the optical system (positive and negative defocusing) for which there is practically no change in the reproducibility of the intensity for the spectral lines for red and white clay samples. We show that the position of the object relative to the focus of the optical system should be within the range ΔZ ~ ±1.5 mm for optimal laser pulse energies for the analyte spectral lines. We have calculated the radiation flux density for different laser pulse energies and different distances from the focus to the object. We have shown experimentally that reducing the radiation flux density leads to a decrease in the intensity of the analyte spectral lines. [ABSTRACT FROM AUTHOR]

Appearance of three groups of charged particles upon interaction of an optical laser pulse with intensity of ~109 W/cm2 with a metal target in a dilute-gas environment is discovered. Measured electron temperature of the laser-produced plasma agrees well with the results of model calculations carried out to estimate electron temperature in the region of absorption of laser radiation for parameters corresponding to conditions of presented experiments. [ABSTRACT FROM AUTHOR]

The formation and heating of laser plasma when silicon is irradiated in ambient air by pulsed laser radiation with wavelengths of 355 and 532 nm at radiation power density up to 5 GW/cm2 has been experimentally investigated. An increased efficiency of the formation and heating of ablation plasma is observed when nanosecond pulses with a wavelength of 355 nm are leading in the bichromatic irradiation of silicon. [ABSTRACT FROM AUTHOR]

Three groups of charged particles are recorded at the impact of the laser radiation pulse with a metal target in a rarefied gas medium. The optical range laser radiation intensity is ~109 W/cm2. A possibility of using a Langmuir probe for diagnosing plasma processes with nanosecond resolution is demonstrated. [ABSTRACT FROM AUTHOR]