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A nanosecond Nd:YAG laser was used to study the laser ablation of aluminum foil in the phase explosion regime at a laser intensity range of 0.63–3.61 × 10 12 W / cm 2. Laser ablation and plasma characteristics were studied using microscopic ablation crater images, plasma emission spectra, and plasma plume images. Measured plasma density using a Stark width of Al I (396.2 nm) showed a strong linear correlation with crater size, with a Pearson correlation coefficient (r) of 0.97. To understand the origin of this linear correlation, plasma temperature was estimated using Bremsstrahlung emission from 512 to 700 nm. The estimated plasma temperature and aspect ratio of the plasma plume were negatively correlated, having r = − 0.76. This negative correlation resulted from a laser-plasma interaction, which heated the plasma and increased its hydrodynamic length. The percentages of laser energy used for plasma heating ( E p / E L ) and Al foil ablation ( E Al / E L ) were estimated from plasma temperature. Increased E Al / E L , such as crater size, with increasing laser intensity, confirms that greater mass ablation is the fundamental reason for the strong linear correlation between crater size and plasma density. [ABSTRACT FROM AUTHOR]

The role of the density gradient in the electron acceleration process by intense laser pulses for a plasma profile with a steep interface between vacuum and a strongly overdense plasma is investigated via particle-in-cell simulations with the Emi2d code. Laser pulses at relativistic intensities interacting with finite gradients at the laser–plasma interface favor collective electron motion in the underdense plasma provided that the pulse duration is long enough to form a standing wave structure. It is shown that the steepness of the gradient influences the evolution of the distribution of electrons that are injected into the dense plasma. Heating mechanisms of the electron bulk and a very energetic electron tail are identified. The heating of the targets evolves each time when bunches of electrons accelerate to relativistic energies and return to the laser–plasma interface. The heating dynamics have consequences on the ion front motion at the rear of the target. This is elaborated by determining the predominant hot electron populations and their temperatures that govern the expansion of the rear density profile. The role of the temporal dynamics of the hot electron populations is investigated with respect to the known analytic models for ion acceleration at the rear target, showing that those models are robust despite the important temporal increase in hot electron temperatures. [ABSTRACT FROM AUTHOR]

Laser-plasma interactions have been demonstrated to produce bright sources of energetic radiation including ions, electrons, photons across the electro-magnetic spectrum, and neutrons. Combinations of species can significantly increase information from non-destructive imaging. Here we demonstrate single-shot co-axial radiography with both x-ray and fast-neutron radiation from a laser-driven source using a pair of gated microchannel plate photomultiplier tube channels and a fast scintillator medium. The outlined system demonstrates recovery full-width-half-maximum of (18 ± 3) ns, which is sufficient to isolate x-rays from neutrons up to (72 ± 20) MeV and could be isolated only a short distance (2 m) from the target. [ABSTRACT FROM AUTHOR]

The detection of high-flux gamma beams from laser plasma interactions is always hampered by signal pileup. In this study, a gamma threshold detector based on the bubble chamber is designed to detect high-flux gamma beams. Through simulations, it has been demonstrated that this detector can detect gamma rays with energies above 5 MeV through photonuclear reactions, even at fluences as high as 1011 photons/cm2. In addition, by setting the detection threshold at 0.1 MeV/μm, a yield of up to 10−2 bubbles per gamma interaction can be achieved. Finally, the bubble chamber in the detection of a gamma ray from the inverse Compton scattering process is also discussed. [ABSTRACT FROM AUTHOR]

We introduce a new utilization of an Aerodynamic Lens Stack (ALS) for concentrating aerosols in the production of high energy (>200 keV) electrons through their interaction with intense( > 10 16 W/cm 2 ), ultra-short (30 fs) laser pulses. The lens was designed and simulated in COMSOL with various parameters such as inlet dimensions and backing pressures. Subsequently, the particle jet was analyzed using particle streak velocimetry (PSV). Following the characterization process, the jet was exposed to the laser, and the emission of electrons was investigated and described. Our results demonstrate the effectiveness of the lens in producing and focussing aerosols originating from liquid sources, underscoring its potential as a precise microtarget for laser interactions. [ABSTRACT FROM AUTHOR]

Ultra-intense lasers that ionize atoms and accelerate electrons in solids to near the speed of light can lead to kinetic instabilities that alter the laser absorption and subsequent electron transport, isochoric heating, and ion acceleration. These instabilities can be difficult to characterize, but X-ray scattering at keV photon energies allows for their visualization with femtosecond temporal resolution on the few nanometer mesoscale. Here, we perform such experiment on laser-driven flat silicon membranes that shows the development of structure with a dominant scale of 60 nm in the plane of the laser axis and laser polarization, and 95 nm in the vertical direction with a growth rate faster than 0.1 fs−1. Combining the XFEL experiments with simulations provides a complete picture of the structural evolution of ultra-fast laser-induced plasma density development, indicating the excitation of plasmons and a filamentation instability. Particle-in-cell simulations confirm that these signals are due to an oblique two-stream filamentation instability. These findings provide new insight into ultra-fast instability and heating processes in solids under extreme conditions at the nanometer level with possible implications for laser particle acceleration, inertial confinement fusion, and laboratory astrophysics. Ultrafast relativistic plasma instabilities accompany and influence laser matter interactions that accelerate particlebeams with potential applications in e.g radiotherapy or fussion fast ignition scenarios. Here, the authors use Small Angle X-ray Scattering to observe such instabilities on a femtosecond, tens of nanometer scale in solids, and draw conclusions on the underlying plasma dynamics. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the transition of fast electron generation mechanism from J × B heating to stochastic heating by varying preplasma scale length in the interaction of ultrashort (∼25 fs) high intensity (∼3–4 × 1019 W/cm2) laser with thin foil. At sharp plasma density laser interaction (contrast ∼2 × 10−10 at 1 ns, L/λ ≪ 1), fast electrons were observed along the laser propagation direction demonstrating J × B heating. Interestingly, fast electron temperature in this case was less than ponderomotive scaling. The reasons were identified to be the small excursion length of electron compared to laser wavelength in sharp density interaction along with energy loss while escaping through the rear surface. A simplistic model has been proposed to understand the energy loss mechanism from the rear surface. Next, preplasma was introduced gradually by varying the amplified spontaneous emission contrast and additional picosecond prepulse at different delays. It resulted in an increase in the energy and temperature of fast electrons. Most importantly, at larger scale length (L/λ ≫ 1), fast electron temperature beyond the ponderomotive limit was observed. The temperature scales with scale length as T ∝ L 0.59 and shows a saturation effect at longer scale length. The results indicate a gradual change in the fast electron generation mechanism to stochastic heating producing superponderomotive energy. Particle-in-cell simulation also very well reproduces our experimental findings. [ABSTRACT FROM AUTHOR]

Direct laser acceleration has proven to be an efficient source of high-charge electron bunches and high brilliance x-rays. However, an analytical description of the acceleration in the interaction with varying plasma density targets is still missing. Here, we provide an analytical estimate of the maximum energies that electrons can achieve in such a case. We demonstrate that the maximum energy depends on the local electron properties at the moment when the electron fulfills the resonant condition at the beginning of the acceleration. This knowledge enables density shaping for various purposes. One application is to decrease the required acceleration distance needed to achieve the maximum electron energy. Another use for density tailoring is to achieve acceleration beyond the radiation reaction limit. We derive the energy scaling law that is valid for arbitrary density profile that varies slowly compared with the betatron period. Our results can be applied to electron heating in exponential preplasma of thin foils, ablating plasma plumes, or gas jets with long-scale ramp-up. [ABSTRACT FROM AUTHOR]

A scheme for a quasi-monoenergetic high-flux neutron source with femtosecond duration and highly anisotropic angular distribution is proposed. This scheme is based on bulk acceleration of deuteron ions in an optical trap or density grating formed by two counter-propagating laser pulses at an intensity of ∼ 1 0 16 W / c m 2 in a near-critical-density plasma. The deuterons are first pre-accelerated to an energy of tens of keV in the ambipolar fields formed in the optical trap. Their energy is boosted to the MeV level by another one or two laser pulses at an intensity of ∼ 1 0 20 W / c m 2 , enabling fusion reactions to be triggered with high efficiency. In contrast to previously proposed pitcher–catcher configurations, our scheme can provide spatially periodic acceleration structures and effective collisions between deuterons inside the whole target volume. Subsequently, neutrons are generated directly inside the optical trap. Our simulations show that neutron pulses with energy 2–8 MeV, yield 1018–1019n/s, and total number 106–107 in a duration ∼ 400 fs can be obtained with a 25 μm target. Moreover, the neutron pulses exhibit unique angularly dependent energy spectra and flux distributions, predominantly along the axis of the energy-boosting lasers. Such microsize femtosecond neutron pulses may find many applications, such as high-resolution fast neutron imaging and nuclear physics research. [ABSTRACT FROM AUTHOR]

We consider the Cauchy problem of the system of nonlinear Schrödinger equations with derivative nonlinearlity. This system was introduced by Colin and Colin (Differ Int Equ 17:297–330, 2004) as a model of laser-plasma interactions. We study existence of ground state solutions and the global well-posedness of this system by using the variational methods. We also consider the stability of traveling waves for this system. These problems are proposed by Colin–Colin as the open problems. We give a subset of the ground-states set which satisfies the condition of stability. In particular, we prove the stability of the set of traveling waves with small speed for 1-dimension. [ABSTRACT FROM AUTHOR]

In this work, we investigated the magnetic annihilation and reconnection and the resulted hot electron acceleration driven by double-beam intense laser pulses in two-layer near critical density (NCD) plasma target. The results are obtained by performing two-dimensional (2D) particle-in-cell (PIC) simulations. It is found that a quasi-mono-energetic peak can be formed in the energy spectrum of electrons accelerated by the process of magnetic field annihilation (MA) at cutoff energy. Electron spectra feature depends on the length of the second low-density layer. This suggests that the process of relativistic magnetic annihilation may be controlled in experiments by target design. [ABSTRACT FROM AUTHOR]

Overtaking collision of unidirectional dust acoustic waves in the Thomas-Fermi dense magnetoplasma has been investigated. The system consists of classical negatively charged dust particles with degenerate electrons and ions. Nonlinear Korteweg-de Vries (KdV) equation that characterizing the dust acoustic solitons in such a plasma model is derived. The system admits only rarefactive solitary waves. Hirota's bilinear method is used to investigate the overtaking collision of two and three-soliton solutions. The exchange of energies due to the overtaking collisions is affected by physical parameters such as the electron equilibrium density, the dust temperature, and the obliquity angle. This causes the solitons behavior to be alternated. The amplitude, and width increase as the dust temperature and electron density decrease or when the dust density increases. The magnetic field affects only the soliton's width. The phase shifts are also affected by the system parameters. The current study is an attempt to illuminate the properties of N-soliton in Thomas-Fermi dense magnetoplasma that are applicable in compact astrophysical objects such as white dwarfs and high-intensity laser-solid matter interaction experiments. [ABSTRACT FROM AUTHOR]

Surface plasmon (SP) based electron acceleration has been investigated during the interaction of short, ultra-intense (I > 1019 W/cm2) laser pulse with periodically modulated solid target. Laser contrast conditions are required to preserve the structural integrity of the target. Two dimensional (2D) particle-in-cell (PIC) simulations report emission of energetic (~ 78 MeV) electron bunches along grating surface for grazing incident of laser pulse at an optimum angle 4° with respect to target surface. The energy and flux of emitted electrons for grazing laser incidence were found to be strongly enhanced as compared to the incident angles satisfying the resonant condition for surface plasma wave's excitation. [ABSTRACT FROM AUTHOR]

Self-focusing emerges as a nonlinear optical phenomenon resulting from an intense laser field and plasma interaction. This study investigates the self-focusing behavior of Gaussian laser beams within magnetized plasma environments utilizing a novel approach, source-dependent expansion. By employing source-dependent expansion, we explore the intricate dynamics of laser beam propagation, considering the influence of plasma density and external magnetic fields. The interplay between the beam's Gaussian profile and the self-focusing mechanism through rigorous mathematical analysis and numerical simulations, particularly in the presence of plasma-induced nonlinearities, is elucidated here. Our findings reveal crucial insight into the evolution of laser beams under diverse parameters, including the ponderomotive force, relativistic factors, plasma frequency, polarization states, external magnetic field, wavelength, and laser intensity. This research not only contributes to advancing our fundamental understanding of laser–plasma interactions but also holds promise for optimizing laser-driven applications. [ABSTRACT FROM AUTHOR]

We theoretically investigate the polarized terahertz (THz) generation in laser–gas interaction using circularly polarized (CP) two-color laser pulses with uncommon frequencies. We show that these laser pulses can be applied to generate polarized THz radiation, and the polarization of THz radiation, which ranges from linear to circular, can be controlled in a flexible manner by manipulating the laser parameters, such as the relative phase and phase angle. Furthermore, in contrast to traditional harmonic frequency combinations, the polarization states of the incommensurate lasers undergo complex evolution with the phase angle, resulting in a noteworthy influence on the THz yield. The obtained results could deepen our understanding of polarized THz radiation generation. [ABSTRACT FROM AUTHOR]

There are numerous applications of terahertz (THz) imaging in many fields. However, current THz imaging is generally based on scanning technique due to the limited intensity of the THz sources. Thus, it takes a long time to obtain a frame image of the target and cannot meet the requirement of fast THz imaging. Here, we demonstrate a single-shot direct THz imaging strategy based on a broadband intense THz source with a frequency range of 0.1~23 THz and a THz camera with a frequency response range of 1~7 THz. This THz source was generated from the laser–plasma interaction, with its central frequency at ~12 THz. The frame rate of this imaging system was 8.5 frames per second. The imaging resolution reached 146.2 μm. With this imaging system, a single-shot THz image for a target object with a size of more than 7 cm was routinely obtained, showing a potential application for fast THz imaging. Furthermore, we proposed and tested an image enhancement algorithm based on an improved dark channel prior (DCP) theory and multi-scale retinex (MSR) theory to optimize the image brightness, contrast, entropy and peak signal-to-noise ratio (PSNR). [ABSTRACT FROM AUTHOR]

The investigation of tuneable and energy-efficient terahertz (THz) generation has become a prominent field of study due to its significant ramifications in various disciplines, including chemical analysis and medical research. This study selects two co-propagating Hermite-cosh-Gaussian (HchG) laser beams with positively chirped frequencies for analysis. The laser beam exhibits interaction with a collisionless underdense plasma in the presence of a static transverse magnetic field. The interaction between laser and plasma exhibits nonlinear characteristics, leading to the creation of THz radiation with high energy efficiency. The primary objective of this study is to conduct an analytical examination of the correlation between THz conversion efficiency, normalised transverse distance, and plasma frequency. Additionally, the analysis will consider various laser parameters, including the Hermite polynomial mode index (s), decentred parameter (a), and frequency chirp (b). The results show that in off-resonant condition THz conversion efficiency quickly decreases and approaches to zero for normalised THz frequencies. The observed phenomenon entails an augmentation in the normalized amplitude of terahertz (THz) waves, accompanied by a displacement of the peak towards greater normalized transverse distance values. This occurrence is contingent upon the variation of the Hermite polynomial mode index within the range of 0 t o 2. As the chirp parameter (b) is increased from 0.0011 t o 0.0099 , the normalised terahertz (THz) amplitude exhibits an increase with respect to the normalised transverse distance for values of s equal to 0,1 a n d 2. The proposed methodology demonstrates significant use in generating high-intensity, adjustable, and energy-efficient terahertz (THz) radiation sources through the manipulation of the decentred parameter and Hermite polynomial mode index values. [ABSTRACT FROM AUTHOR]

Single-shot X-ray phase-contrast imaging is used to take high-resolution images of laser-driven strong shock waves. Employing a two-grating Talbot interferometer, we successfully acquire standard absorption, differential phase-contrast, and dark-field images of the shocked target. Good agreement is demonstrated between experimental data and the results of two-dimensional radiation hydrodynamics simulations of the laser–plasma interaction. The main sources of image noise are identified through a thorough assessment of the interferometer's performance. The acquired images demonstrate that grating-based phase-contrast imaging is a powerful diagnostic tool for high-energy-density science. In addition, we make a novel attempt at using the dark-field image as a signal modality of Talbot interferometry to identify the microstructure of a foam target. [ABSTRACT FROM AUTHOR]

Slits have been widely used in laser–plasma interactions as plasma optical components for generating high-harmonic light and controlling laser-driven particle beams. Here, we propose and demonstrate that periodic thin slits can be regarded as a new breed of optical elements for efficient focusing and guiding of intense laser pulse. The fundamental physics of intense laser interaction with thin slits is studied, and it is revealed that relativistic effects can lead to enhanced laser focusing far beyond the pure diffractive focusing regime. In addition, the interaction of an intense laser pulse with periodic thin slits makes it feasible to achieve multifold enhancement in both laser intensity and energy transfer efficiency compared with conventional waveguides. These results provide a novel method for manipulating ultra-intense laser pulses and should be of interest for many laser-based applications. [ABSTRACT FROM AUTHOR]

Magnetosonic (MS) waves, i.e., ion Bernstein mode waves, are one of the common plasma waves in the Earth's magnetosphere, which are important for regulating charged particle dynamics. How MS waves propagate in the magnetosphere is critical to understanding the global distribution of the waves, but it remains unclear. Although previous studies present that MS waves can be reflected by fine-scale density structures, the dissipation of waves by background plasma has long been neglected. In this study, we perform one-dimensional (1-D) particle-in-cell (PIC) simulations to study the propagation of MS waves through density structures, where both absorption and reflection have been included. We find that absorption is as important as reflection when considering the propagation of MS waves through density structures, and both of them are strongly dependent on the shape of density structures. Specifically, the reflectivity of MS waves is positively and negatively correlated with the height and width of density structures, respectively, while the absorptivity of MS waves has a positive correlation with both the height and width of density structures. Our study demonstrates the significance of absorption during the propagation of MS waves, which may help better understand the distribution of MS waves in the Earth's magnetosphere. [ABSTRACT FROM AUTHOR]

Foam targets have gained considerable importance over the last decade in laser–matter interaction. They find widespread applications such as in inertial confinement fusion and secondary sources for particles and radiation. At the same time, the advent of high repetition-rate laser systems, be they short-pulse in the tens of femtosecond regime or in the kilo-Joule nanosecond regime, calls for equally high repetition rate targetry systems. A well-established repetition-rate targetry system is the tape target. In this article, we present the successful marriage of a tape target delivery system with 3D-printed foam targets produced by two photon polymerization. [ABSTRACT FROM AUTHOR]

Efficient generation of 13.5 nm light with increased conversion efficiency and output power is important for Extreme Ultraviolet (EUV) lithography applications. In this study, we present a computational investigation of plasma dynamics and EUV generation from laser-driven plasma, with specific focus on the influence of magnetic fields, ranging up to 50 T. Simulations show that the plasma expansion is restricted based on the direction and strength of the magnetic field, resulting in an anisotropic plasma confinement, which in turn allows for radiation escape with a reduced loss. Moreover, angle-dependent measurements show an increase in in-band EUV (2% bandwidth around 13.5 nm) yield, reaching a peak enhancement of up to 40% when a magnetic field is applied, particularly when it is oriented perpendicular to the laser axis. The ability to control plasma dynamics by magnetic field offers exciting prospects for optimizing EUV radiation sources. [ABSTRACT FROM AUTHOR]

Time-of-flight estimates of the kinetic energy of magnetically insulated bunches of moderately relativistic runaway electrons (RAEs) were obtained with the use of an air diode equipped with a drift section. The measurements have demonstrated that the bunch energy can be controlled by changing the conditions for RAE emission in an air diode with a sharply inhomogeneous electric field, which can be done by varying the cathode geometry and material and the length of the cathode-anode gap. It has been demonstrated that if the measured electron current peaks are resolved to within 10 ps, and the bunch duration and spread in RAE emission moments are close to this resolution, the characteristic energies of the bunches can be estimated with an accuracy of ≈10%. Examples of energy measurements are given for paraxial and tubular bunches accelerated at cathode potentials of up to −250 kV. The estimated characteristic energies of the bunches, even not corrected for drift losses in the fill gas, turned out to be greater than the energies that could be achieved for bunches accelerated in a vacuum diode with due account for the variations in diode voltage. [ABSTRACT FROM AUTHOR]

The editorial in "Frontiers in Physics" discusses the historical significance of nuclear physics and its impact on scientific progress, technological advancements, and medical applications. It highlights the emergence of high-intensity lasers as a new tool for exploring nuclear processes and outlines the challenges and opportunities in laser-driven nuclear physics research. The editorial introduces a Research Topic comprising 18 research papers from prestigious institutions worldwide, focusing on experimental and theoretical aspects of laser-driven nuclear reactions, advanced particle sources, and computational methods for nuclear physics. The papers cover a wide range of topics, including fusion experiments, particle acceleration, and nuclear excitation studies, showcasing the interdisciplinary nature of the field and its potential for practical applications. [Extracted from the article]

Additive manufactured (AM) foams in the context of high-power laser–matter interaction have emerged as a topic of significant interest. Printed foam targets provide a highly controlled environment for laser interaction and permit a high degree of versatility in terms of average density, spatial structure, and materials. These features are of great value to a variety of applications, including inertial confinement fusion and generation of intense x-rays and gamma rays. This paper describes an approach to the design and fabrication of AM foams for laser–plasma interaction experiments, including the selection of cellular structure, optimization of mechanical properties using a finite element approach, and foam printing on dielectric and conducting substrates. [ABSTRACT FROM AUTHOR]

The formation of e± plasmas within pulsar magnetospheres through quantum electrodynamics (QED) cascades in vacuum gaps is widely acknowledged. This paper aims to investigate the effect of photon polarization during the QED cascade occurring over the polar cap of a pulsar. We employ a Monte Carlo-based QED algorithm that accurately accounts for both spin and polarization effects during photon emission and pair production in both single-particle and particle-in-cell (PIC) simulations. Our findings reveal distinctive properties in the photon polarization of curvature radiation (CR) and synchrotron radiation (SR). CR photons exhibit high linear polarization parallel to the plane of the curved magnetic field lines, whereas SR photons, on average, demonstrate weak polarization. As the QED cascade progresses, SR photons gradually dominate over CR photons, thus reducing the average degree of photon polarization. Additionally, our study highlights an intriguing observation: the polarization of CR photons enhances e± pair production by approximately 5 per cent, in contrast to the inhibition observed in laser–plasma interactions. Our self-consistent QED-PIC simulations in the corotating frame reproduce the essential results obtained from single-particle simulations. [ABSTRACT FROM AUTHOR]

The commissioning of multi-petawatt class laser facilities around the world is gathering pace. One of the primary motivations for these investments is the acceleration of high-quality, low-emittance electron bunches. Here we explore the interaction of a high-intensity femtosecond laser pulse with a mass-limited dense target to produce MeV attosecond electron bunches in transmission and confirm with three-dimensional simulation that such bunches have low emittance and nano-Coulomb charge. We then perform a large parameter scan from non-relativistic laser intensities to the laser-QED regime and from the critical plasma density to beyond solid density to demonstrate that the electron bunch energies and the laser pulse energy absorption into the plasma can be quantitatively described via the Zero Vector Potential mechanism. These results have wide-ranging implications for future particle accelerator science and associated technologies. [ABSTRACT FROM AUTHOR]

The propagation of electromagnetic beams carrying orbital angular momentum l is investigated in a cold collisionless plasma where a static magnetic field is applied in the axial direction. The relativistic and ponderomotive nonlinearities are taken into consideration simultaneously. A stationary nonlinear Schrödinger equation is derived using the Wentzel–Kramers–Brillouin method and the slowly varying envelope approximation. The critical condition for the self-trapped mode is achieved as a function of orbital angular momentum (OAM), magnetic field, and initial laser intensity of the beam. The response of the medium to the two types of polarizations, i.e., left circular polarization (LCP) and right circular polarization (RCP), is compared, and it is observed that the RCP laser shows better focusing than the LCP laser and also requires a smaller beam radius for achieving the self-trapped mode. The effect of applied magnetic field and OAM of the laser is also studied on the beam width evolution. The laser is found to be focused earlier in the cases of a larger applied magnetic field. A Laguerre–Gaussian laser with higher OAM is observed to show efficient self-focusing. This study enables exploration in the fields of particle acceleration, electron bunch generation, x-ray sources, and more. [ABSTRACT FROM AUTHOR]

The ion kinetic effect on the formation of intense laser-driven collisional shock waves is investigated via hybrid fluid-particle-in-cell simulations. It is found that the ion heat flux dominates the shock formation, which is considerably larger than the electron heat flux in the shock region. The rise of the temperature due to the laser energy deposition drives a heatwave into the overdense plasma, creating an electron–ion energy exchange zone between the critical surface and heat wave front. The heated ions, which are generated at the electron–ion energy exchange zone via the friction force, are found to travel to the high-density region and cause a tail distribution gain. Despite the small quantity, the heated tail ions contribute most of the ion heat flux during the shock formation. Additionally, as the electron heat flux decreases, the population of the heated tail ions is reduced, leading to a fall in the ion heat flux. This results in the delay or even suppression of the shock formation, because the ions are in a non-equilibrium state in the vicinity of the shock region, the ratio of the downstream ion temperature to the upstream ion temperature tends to a modestly decrease in comparison to the theory. The study provides a clear picture of the formation process of laser-driven shock waves. [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]

Nonlinear interaction of two or three synchronized coplanar filaments was demonstrated to generate plasma gratings with high electron density capable of effectively exciting samples. This excitation was further enhanced by multi-photoionization and electron collision. Consequently, an increase in laser pulse energy led to a decrease in the full width at half maxima (FWHM) of spectral lines, primarily observed in breakdown spectroscopic lines due to electron signal enhancement. Moreover, by measuring the emission line intensity as a function of time delay and excitation laser pulse energy, the radiative lifetime and self-absorption correlation coefficient of neutral atomic and ionic lines were determined to exhibit longed plasma lifetimes in the presence of filament interaction. The enhancement was particularly notable when using three coplanar coupled filaments for excitation, as it resulted in a plasma lifetime increase of approximately 50–60 ns compared to that when using two filaments for atomic lines. These findings indicate that high-electron density in plasma gratings could improve the application of filament-induced breakdown spectroscopy by enhancing spectral resolution, radiative lifetime, and spectral reproducibility. [ABSTRACT FROM AUTHOR]

In the paper, we demonstrate the application of X-ray spectroscopy with high spatial resolution to study magnetic reconnection in laboratory astrophysical experiments performed with nano- and pico-second duration laser facilities at a moderate laser density on the target of <1018 W/cm2. A brief overview of the commonly used experimental schemes is given. Atomic kinetic calculations for the L-shell spectra of Ne- and F‑like Fe ions (iron, Z = 26) demonstrate the high sensitivity of the measurements to changes in plasma parameters. The scope of the different diagnostic approaches to measure electron temperature and laser plasma density is discussed. It is shown that transitions in Ne-like ions are a universal tool for measuring plasma parameters, both in the region of laser interaction with the target and in the reconnection zone. [ABSTRACT FROM AUTHOR]

Direct laser acceleration of electrons in near-critical-density (NCD) carbon nanotube foams (CNFs) has its advantages in the high-efficiency generation of relativistic electrons and broadband x-rays. Here, we report the first simultaneous measurement on the spectra of laser-driven electrons and x-rays from CNFs at moderately relativistic intensities of around 5 × 10 19 W / c m 2 . The density and thickness of the CNFs were scanned in the experiments, indicating the optimized electron temperature of 5.5 MeV and x-ray critical energy of 5 keV. Two-dimensional particle-in-cell simulations confirm that the electrons, with a temperature significantly higher than the pondermotive scale, are directly accelerated by the laser along the NCD plasma channel, while the bright x-rays are emitted by these electrons through betatron radiation or Thomson backscattering inside the channel. The simultaneously generated electrons and x-rays, automatically synchronized with the femtosecond laser driver, are suitable for applications such as bi-modal radiography. [ABSTRACT FROM AUTHOR]

Electron acceleration is investigated in a plasma wake generated via the interaction of a high-intensity laser pulse with the plasma in the presence of a perpendicular magnetic field. For this purpose, using the Maxwell equation, the wakefield profile in the perpendicularly magnetized plasma is obtained and then using the magnetized wakefied the electron energy and momentum equations are numerically solved. It turns out that the electron acceleration in a magnetized wake having a different profile than unmagnetized one increases with the perpendicular magnetic field strength so that in presence of a magnetic field with a strong enough amplitude the acceleration goes beyond the resonance regime. The numerical results demonstrate that the electron could be significantly accelerated in a low-amplitude laser-driven wake in presence of an external perpendicular magnetic field which can be superseded the high-amplitude laser-driven wake acceleration regime. Furthermore, we concluded in such systems that the electron acceleration is drastically sensitive to amplitude and initial phase of the wakefield as well as the initial energy of the electron. [ABSTRACT FROM AUTHOR]

Betatron x-ray sources from laser-plasma interaction are characterized by compactness, ultrashort duration, broadband spectrum and micron source size. However, high-quality measurements with good statistics, especially in a single shot, require fluxes and energies beyond the current capabilities. Here, we propose a method to enhance the flux and brightness of the betatron sources without increasing the laser energy. By irradiating an edge of a microtape target with a femtosecond laser, a strong surface plasma wave (SPW) is excited at the edge and travels along the lateral plasma-vacuum interfaces. Tens of nC of electrons are peeled off and accelerated to superponderomotive energies by the longitudinal field of the SPW, whilst undergoing transverse betatron oscillations, leading to emission of hard x-rays. Via three-dimensional particle-in-cell simulations, we demonstrate that a tabletop 100 TW class femtosecond laser can produce an ultrabright hard x-ray pulse with flux up to 107 photons eV−1 and brilliance about 1023 photons s−1 mm−2 mrad−2 0.1%BW−1, paving the way for single-shot x-ray measurements in ultrafast science and high-energy-density physics. High-quality measurements with good statistics, especially in a single shot, require fluxes and energies beyond the current capabilities of laserbased betatron x-ray sources. Here, the authors propose a method to enhance the flux and brightness of such sources without increasing the laser energy, paving the way for single-shot x-ray measurements in ultrafast science. [ABSTRACT FROM AUTHOR]

Spectral measurements play a vital role in understanding laser–plasma interactions. The ability to accurately measure the spectrum of radiation sources is crucial for unraveling the underlying physics. In this article, we introduce a novel approach that significantly enhances the efficiency of binary sinusoidal transmission grating spectrometers. The grating was tailored especially for Extreme Ultraviolet (EUV) measurements. The new design, High Contrast Sinusoidal Transmission Grating (HCSTG), not only suppresses high diffraction orders and retains the advantageous properties of previous designs but also exhibits a fourfold improvement in first-order efficiency. In addition, the HCSTG offers exceptional purity in the first order due to effectively eliminating half-order contributions from the diffraction pattern. The HCSTG spectrometer was employed to measure the emission of laser-produced Sn plasma in the 1–50 nm spectral range, achieving a spectral resolution of λ/Δλ = 60. We provide a comprehensive analysis comparing the diffraction patterns of different STGs, highlighting the advantages offered by the HCSTG design. This novel, efficiency-enhanced HCSTG spectrometer opens up new possibilities for accurate and sensitive EUV spectral measurements. [ABSTRACT FROM AUTHOR]

The laser wakefield acceleration (LWFA) scheme is now a superb and potent instrument for industry, medicine, fusion, and other uses. With the aid of this technique, high-quality electron beams can be generated, which might eventually be employed to create small, portable X-ray sources. Using a linearly polarized Gaussian laser pulse, the present work focuses on examining electron acceleration in an under-dense plasma having a ramp profile with different density-hill widths. Two-dimensional Fourier–Bessel Particle-In-Cell simulation (2D-FBPIC) code shows that optimizing the laser parameters and plasma density profile maximizes the energy gain and minimizes the normalized rms emittance in the x, y directions inside the plasma bubble. For 10 and 90 μ m density-hill widths, respectively, the optimal emittance value is reported to be ϵ x ∼ 3.10 mm.mrad in the x-direction and ϵ y ∼ 2.63 mm.mrad in the y-direction. At a density-hill width of 90 μ m , it is also observed that the charge trapped inside the bubble is 44.91 pC. With this density-hill width and a plasma channel length of 3.84 mm, our simulation findings show an energy gain of 0.38 GeV to the electron-bunch accelerated inside the bubble. [ABSTRACT FROM AUTHOR]

We introduce a novel, gaseous target optical shaping laser set-up, capable to generate short scale length, near-critical target profiles via generated colliding blast waves. These profiles are capable to maintain their compressed density for several nanoseconds, being therefore ideal for laser-plasma particle acceleration experiments in the near critical density plasma regime. Our proposed method overcomes the laser-target synchronization limitations and delivers energetic protons, during the temporal evolution of the optically shaped profile, in a time window of approximately 2.5 ns. The optical shaping of the gas-jet profiles is optimised by MagnetoHydroDynamic simulations. 3D Particle-In-Cell models, adopting the spatiotemporal profile, simulate the 45 TW femtosecond laser plasma interaction to demonstrate the feasibility of the proposed proton acceleration set-up. The optical shaping of gas-jets is performed by multiple, nanosecond laser pulse generated blastwaves. This process results in steep gradient, short scale length plasma profiles, in the near critical density regime allowing operation at high repetition rates. Notably, the Magnetic Vortex Acceleration mechanism exhibits high efficiency in coupling the laser energy into the plasma in the optically shaped targets, resulting to collimated proton beams of energies up to 14 MeV. [ABSTRACT FROM AUTHOR]

Here, we report on terahertz (THz) radiation generation in air driven by the fundamental and second harmonic of Yb:KGW laser pulses with durations of a few hundred femtoseconds. It was found that the spectrum of generated THz pulses surprisingly spans up to 50 THz, which is comparable to that usually obtained using much shorter Ti:sapphire laser pulses. The broad bandwidth is attributed to a strong spatiotemporal reshaping of the pump pulses in a filament. The achieved energy conversion efficiency is comparable to the one usually obtained from much shorter pump pulses and could be further improved by an optimized experimental setup. The obtained results indicate that compact Yb-based sources provide an attractive alternative to much larger and expensive laser systems. [ABSTRACT FROM AUTHOR]

One of the interesting topics of recent research is the study of the Weibel electromagnetic instability growth rate in the interaction of high-intensity lasers with the dense plasma of fusion fuel pellets. In this paper, the effect of stresses caused by laser ponderomotive force on the growth rate of Weibel instability in the nonlinear phase is investigated. The growth of the nonlinear phase of Weibel instability growth rate, which is the saturation phase of Weibel instability, in the presence of stress leads to viscosity turbulence. The results show that the coefficient of reduction of fuel viscosity in the presence of the stress flow is about 0.0014 due to the anomalous transfer mechanism caused by the nonlinear growth of the Weibel instability. [ABSTRACT FROM AUTHOR]

Ultrashort electron beams with femtosecond to picosecond bunch durations offer unique opportunities to explore active research areas ranging from ultrafast structural dynamics to ultra‐high dose‐rate radiobiological studies. It presents a straightforward method to generate relativistic electron beams in ambient air via the tight focusing of a few‐cycle, mJ‐class femtosecond infrared laser. It demonstrates experimentally that electrons can reach up to 1.4 MeV at a dose‐rate of 0.15 Gy/s, providing enough dose rate for radiation therapy applications. 3D Particle‐In‐Cell simulations confirm that the acceleration mechanism is based on the relativistic ponderomotive force and show theoretical agreement with the measured electron energies and divergence. Relativistic peak intensities up to 1019 Wcm−2 are reached in ambient air due to a very low B‐integral accumulation during focusing, which prevents intensity clamping. Furthermore, it discusses the scalability of this method with the continuing development of mJ‐class high average power lasers, and providing a promising approach for FLASH radiation therapy. [ABSTRACT FROM AUTHOR]

We investigate the generation of terahertz (THz) radiation from laser-wakefield acceleration (LWFA) in a helium gas jet. We consider a three-dimensional setup incorporating a realistic gas density distribution and use particle-in-cell simulations to study the interaction of a femtosecond intense laser pulse with the gas medium. Our results show that LWFA can efficiently produce THz radiation. In the simulations, we use multiple probes to record the electric and magnetic fields arising from the interaction. In addition, we compare the results of fixed and moving window simulation boxes used to capture electromagnetic fields in the THz range. We demonstrate that a moving window with a 600 μm width can be significantly useful for THz studies. We further analyze the spectrum of spatially and temporally resolved electromagnetic radiation and its emission angle. Our results are consistent with experimental data. Our findings provide valuable insights into the potential of LWFA as a strong source of THz radiation. [ABSTRACT FROM AUTHOR]

Using the quantum hydrodynamic model, quantum effects (QEs) on threshold intensity required for Brillouin amplification and Brillouin gain coefficients (BGCs) of magnetized semiconductor-plasmas are investigated. Expressions are obtained for threshold intensity and BGCs with including and excluding QEs. Numerical analysis is performed for the n-InSb/CO2 laser system. It is found that QEs become significant at high pump intensity and dominate over plasma mode dispersion at low doping levels. The minimization of threshold intensity and enhancement of BGCs by one order of magnitude is observed by incorporating QEs (via Bohm potential) in the analysis. The analysis leads to a better understanding of the Brillouin amplification in magnetized semiconductor-plasmas. [ABSTRACT FROM AUTHOR]

Recent magnetospheric observations and three‐dimensional (3D) kinetic simulations have shown that plasma wave activities are significantly enhanced around the reconnection x‐line, implying that the reconnection process is fully 3D. However, how the turbulence affects the local reconnection process has been poorly understood so far. We find by means of large‐scale particle‐in‐cell simulation in 3D system that the local reconnection rate can be significantly enhanced, reaching 0.4, which is much larger than theoretical predictions for two‐dimensional (2D) reconnection. The large reconnection rate is associated with large energy conversion rate and strong electron acceleration. The enhancement of the reconnection rate is caused by local increases of electron momentum transport and pressure gradient force induced by turbulence, which can not occur in 2D system. The result is expected to give better interpretations to in‐situ satellite observations where magnetic reconnection proceeds in 3D system. Plain Language Summary: Magnetic reconnection is an important process in space physics to convert the magnetic field energy into particle kinetic energy. In this study, we investigate reconnection rate, a physical quantity that measures the speed of magnetic reconnection by using fully kinetic simulation, in which both electrons and ions are particles. We find very fast local reconnection processes in three‐dimensional system that far exceeds expectation. It indicates that magnetic reconnection is a three‐dimensional process. The high reconnection rate comes from the electrons rather than ions. And the main reason is the increasing of electron momentum transport and pressure gradient caused by strong turbulence, leading to a strong magnetic reconnection process in the current sheet. Key Points: Magnetic reconnection can be strongly intensified in turbulent current sheet with the local reconnection rate exceeding 0.4High reconnection rate is caused by local enhancements of electron momentum transport and pressure gradient force induced by turbulenceReconnection process is essentially 3D, suggesting that local satellite observations may be insufficient in capturing the global process [ABSTRACT FROM AUTHOR]

The past decade has seen tremendous progress in the production and utilization of vortex and vector laser pulses. Although both are considered as structured light beams, the vortex lasers have helical phase fronts and phase singularities, while the vector lasers have spatially variable polarization states and polarization singularities. In contrast to the vortex pulses that carry orbital angular momentum (OAM), the vector laser pulses have a complex spin angular momentum (SAM) and OAM coupling. Despite many potential applications enabled by such pulses, the generation of high-power/-intensity vortex and vector beams remains challenging. Here, we demonstrate using theory and three-dimensional simulations that the strongly-coupled stimulated Brillouin scattering (SC-SBS) process in plasmas can be used as a promising amplification technique with up to 65% energy transfer efficiency from the pump beam to the seed beam for both vortex and vector pulses. We also show that SC-SBS is strongly polarization-dependent in plasmas, enabling an all-optical polarization control of the amplified seed beam. Additionally, the interaction of such structured lasers with plasmas leads to various angular momentum couplings and decouplings that produce intense new light structures with controllable OAM and SAM. This scheme paves the way for novel optical devices such as plasma-based amplifiers and light field manipulators. High-intensity vortex and vector laser pulses can enable a wide range of applications; however, their generation remains challenging. The manuscript demonstrates that the strongly-coupled stimulated Brillouin scattering in plasma can be used as a promising amplification technique for both vortex and vector laser pulses, and thus paves the way for novel optical devices. [ABSTRACT FROM AUTHOR]

Interaction of intense lasers with nm thick targets provides an attractive regime for the acceleration of ions of all types. Acceleration of heavy ions however is undermined in the presence of low charge contaminant species due to their higher charge-to-mass ratio. Here we show narrow-band acceleration of very heavy Au ions from ~15 nm Au foils driven by a sub-Petawatt laser, with spectral peaks of 1.5 ± 0.5 GeV at fluxes on the order of 1012 particles per steradian. 3D and 2D particle-in-cell simulations show a complex interplay between different acceleration mechanisms at different stages of the interaction, suggesting the spectrally peaked Au ion bunches stem from strong radiation pressure acceleration on a heavy-ion dominant plasma in the moments just before transparency, followed by an efficient acceleration due to transparency-enhanced mechanisms. Acceleration of heavy ions is difficult in presence of low charge contaminants due to their high charge-to-mass ratio. The authors use ultra-thin Au foils to efficiently accelerate both contaminants and heavy ions, discussing the interplay between distinct acceleration mechanisms at different stages of interaction via particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

Relativistically intense laser light interacting with solid density targets can accelerate protons to multi-MeV energies via the target normal sheath acceleration process. The use of hollow hemisphere targets with a hollow conical region to focus protons of selected energies, for applications such as isochoric heating of matter and for the fast ignition approach to inertial confinement fusion, is explored for laser intensity ∼ 10 20 Wcm−2. Specifically, the effects of having the cone tip open or closed is investigated experimentally and via a programme of scaled particle-in-cell simulations. The open cone configuration is found to result in proton focusing in the energy range of 9 to 24 MeV, and produce an annular profile for higher energy components, up to 55 MeV, while the spatial distribution of lower energy components remains unchanged. By contrast, for the closed cone case, the focusing effect is diminished by the fields present on the inner wall of the cone tip. Simulations reveal that strong electrostatic and magnetic fields present on the inner surfaces of the target induce the focusing effect with the open cone, but also result in proton divergence in the case of the closed cone. Additionally, the simulations demonstrate the possibility to tailor the cone geometry to select the energy range over which the focusing occurs. [ABSTRACT FROM AUTHOR]

The nonlinear effects of an magnetized plasma of a system including two kinds of electrons with Kappa distribution, warm ions, in the presence of an electron beam have been investigated. The nonlinear differential equation governing this system is derived using the reduction perturbation approach. The propagation of waves in plasma settings is significantly impacted by the electron beam's existence as a unique component. The results demonstrate that soliton waves propagating in the proposed plasma environment experience changes in their amplitude, phase speed, and nonlinear coefficient owing to the presence of the electron beam. The current results demonstrate that the electron number density of the beam may be used to regulate the propagation of ion acoustic waves in plasmas. The outcomes obtained have applications in plasma laser interaction. [ABSTRACT FROM AUTHOR]

The beam-plasma particles distribution function is one of the parameters which plays an important role in the energy-traveling mechanism of the relativistic electrons generated by the laser-plasma interaction in the Inertial Confinement Fusion Plasma. This paper investigates an analytical expression of the beam-plasma particles distribution function effect such as the Kappa, Semi-relativistic Maxwellian and bi- Maxwell distributions on the Weibel electromagnetic instability growth rate in strongly coupled plasmas under the low-frequency wave condition. The obtained results show that the maximum growth rate of the beam- plasma particles with semi-Maxwell distribution function is based on the temperature anisotropy parameter, density gradient, quantum and relativistic parameters has the highest possible value compared to the other two beam-plasma particles distribution functions. Also, the bi-Maxwellian distribution function has a more stable growth rate than the Kappa and the semi-Maxwell distribution functions. [ABSTRACT FROM AUTHOR]