We characterize in a novel manner the physical properties of the low temperature Fermi gas in the degenerate domain as a function of temperature and chemical potential. For the first time we obtain low temperature $T$ results in the domain where several fermions are found within a de Broglie spatial cell. In this regime, the usual high degeneracy Sommerfeld expansion fails. The other known semi-classical Boltzmann domain applies when fewer than one particle is found in the de Broglie cell. We also improve on the understanding of the Sommerfeld expansion in the regime where the chemical potential is close to the mass and also in the high temperature regime. In these calculcations we use a novel characterization of the Fermi distribution allowing the separation of the finite and zero temperature phenomena. The relative errors of the three approximate methods (Boltzmann limit, Sommerfeld expansion, and the new domain of several particles in the de Broglie cell) are quantified.

We present the Virtual Beamline (VBL) application, an interactive web-based platform for visualizing high-intensity laser-matter interactions using particle-in-cell (PIC) simulations, with future potential for experimental data visualization. These interactions include ion acceleration, electron acceleration, $\gamma$-flash generation, electron-positron pair production, and attosecond and spiral pulse generation. Developed at the ELI Beamlines facility, VBL integrates a custom-built WebGL engine with WebXR-based Virtual Reality (VR) support, allowing users to explore complex plasma dynamics in non-VR mode on a computer screen or in fully immersive VR mode using a head-mounted display. The application runs directly in a standard web browser, ensuring broad accessibility. VBL enhances the visualization of PIC simulations by efficiently processing and rendering four main data types: point particles, 1D lines, 2D textures, and 3D volumes. By utilizing interactive 3D visualization, it overcomes the limitations of traditional 2D representations, offering enhanced spatial understanding and real-time manipulation of visualization parameters such as time steps, data layers, colormaps. Users can interactively explore the visualized data by moving their body or using a controller for navigation, zooming, and rotation. These interactive capabilities improve data exploration and interpretation, making VBL a valuable tool for both scientific analysis and educational outreach. The visualizations are hosted online and freely accessible on our server, providing researchers, the general public, and broader audiences with an interactive tool to explore complex plasma physics simulations. By offering an intuitive and dynamic approach to large-scale datasets, VBL enhances both scientific research and knowledge dissemination in high-intensity laser-matter physics.

With the advent of high repetition rate laser facilities, novel diagnostic tools compatible with these advanced specifications are required. This paper presents the design of an active gamma-ray spectrometer intended for these high repetition rate experiments, with particular emphasis on functionality within a PW level laser-plasma interaction chamber's extreme conditions. The spectrometer uses stacked scintillators to accommodate a broad range of gamma-ray energies, demonstrating its adaptability for various experimental setups. Additionally, it has been engineered to maintain compactness, electromagnetic pulse resistance, and ISO-5 cleanliness requirements while ensuring high sensitivity. The spectrometer has been tested in real conditions inside the PW-class level interaction chamber at the BELLA center, LBNL. The paper also outlines the calibration process thanks to a $^{60}$Co radioactive source.

Experimentally measured characteristics of a kHz laser-driven Cu plasma X-ray source that was recently commissioned at ELI Beamlines facility are reported. The source can be driven either by an in-house developed high contrast sub-20 fs near-infrared TW laser based on optical parametric chirped-pulse amplification technology, or by a more conventional Ti:sapphire laser delivering 12 mJ, 45 fs pulses. The X-ray source parameters obtained with the two driving lasers are compared. Measured photon flux of the order up to 10^{12} K{\alpha} photons/4{\pi}/s is reported. Furthermore, experimental platforms for ultrafast X-ray diffraction and X-ray absorption and/or emission spectroscopy based on the reported source are described.

This document sets out the intention of the strong-field QED community to carry out, both experimentally and numerically, high-statistics parametric studies of quantum electrodynamics in the non-perturbative regime, at fields approaching and exceeding the critical or `Schwinger' field of QED. In this regime, several exotic and fascinating phenomena are predicted to occur that have never been directly observed in the laboratory. These include Breit-Wheeler pair production, vacuum birefringence, and quantum radiation reaction. This experimental program will also serve as a stepping stone towards studies of elusive phenomena such as elastic scattering of real photons and the conjectured perturbative breakdown of QED at extreme fields. State-of-the-art high-power laser facilities in Europe and beyond are starting to offer unique opportunities to study this uncharted regime at the intensity frontier, which is highly relevant also for the design of future multi-TeV lepton colliders. However, a transition from qualitative observational experiments to quantitative and high-statistics measurements can only be performed with large-scale collaborations and with systematic experimental programs devoted to the optimisation of several aspects of these complex experiments, including detector developments, stability and tolerances studies, and laser technology.

The emission of a photon by an electron in an intense laser field is one of the most fundamental processes in electrodynamics and underlies the many applications that utilize high-energy photon beams. This process is typically studied for electrons colliding head-on with a stationary-focus laser pulse. Here, we show that the energy lost by electrons and the yield of emitted photons can be substantially increased by replacing a stationary-focus pulse with an equal-energy flying-focus pulse whose focus co-propagates with the electrons. These advantages of the flying focus are a result of operating in the quantum regime of the interaction, where the energy loss and photon yield scale more favorably with the interaction time than the laser intensity. Simulations of 10 GeV electrons colliding with 10 J pulses demonstrate these advantages and predict a $5\times$ increase in the yield of 1-20 MeV photons with a flying focus pulse, which would impact applications in medicine, material science, and nuclear physics.

The EuPRAXIA project aims to construct two state-of-the-art accelerator facilities based on plasma accelerator technology. Plasma-based accelerators offer the possibility of a significant reduction in facility size and cost savings over current radio frequency (RF) accelerators. The two facilities - one laser-driven one a beam-driven - are envisioned to provide electron beams with an energy in the range of 1-5 GeV and beam quality comparable to existing RF machines. This will enable a versatile portfolio of applications from compact free-electron laser (FEL) drivers to sources for medical and industrial imaging. At the heart of both facilities is the use of plasma-based accelerator components and systems which encompass not only the accelerating medium itself, but also a range of auxiliary systems such as plasma-based electron beam optics and plasma-based mirrors for high-intensity lasers. From a technical standpoint, a high-degree of control over these plasma devices will be essential for EuPRAXIA to achieve its target performance goals. The ability to diagnose and characterize these plasma devices and to simulate their operation will be further essential success factors. Additionally, compatibility with extended operation at high-repetition rates and integration into the accelerator beamline will also prove crucial. In this work, we aim to review the current status of plasma components and related systems for both laser-driven and beam-driven plasma accelerators and to assess challenges to be addressed regarding implementation at future EuPRAXIA facilities.

Ultra-intense laser pulses can create sufficiently strong fields to probe quantum electrodynamics effects in a novel regime. By colliding a 60 GeV electron bunch with a laser pulse focussed to the maximum achievable intensity of $10^{23}$ Wcm$^{-2}$, we can reach fields much stronger than the critical Schwinger field in the electron rest frame. When the ratio of these fields $\chi_e\gg1$ we find that the hard ($>25$ \thinspace GeV) radiation from the electron has a substantial contribution from spin-light. 33% more photons are produced above this energy due to spin-light, the radiation resulting from the acceleration of the electron's intrinsic magnetic moment. This increase in high-energy photons results in 14% more positrons produced with energy above $25$ GeV. Furthermore, the enhanced photon production due to spin-light results in a 46% increase in the electron recoil radiation reaction. These observable signatures provide a potential route to observing spin-light in the strongly quantum regime ($\chi_e\gg1$) for the first time.

We reconsider the footprints of radiation friction in a head on collision of a bunch of relativistic charged particles with a laser pulse by demonstrating that in a dense enough bunch forward and backward radiation and radiation friction are coherently enhanced. This should make it possible to observe radiation friction effects in laser-matter interactions at much lower energies and laser intensities than accepted ever previously. A simple estimate for the energy losses of the particles in the bunch over the collision due to radiation friction in terms of laser and bunch parameters is derived and validated by comparing with the results of three dimensional particle-in-cell simulations.

Stimulated photon-photon scattering is a predicted consequence of quantum electrodynamics that has yet to be measured directly. Measuring the cross-section for stimulated photon-photon scattering is the aim of a flagship experiment for NSF OPAL, a proposed laser user facility with two, 25-PW beamlines. We present optimized experimental designs for achieving this challenging and canonical measurement. A family of experimental geometries is identified that satisfies the momentum- and energy-matching conditions for two selected laser frequency options. Numerical models predict a maximum signal exceeding 1000 scattered photons per shot at the experimental conditions envisaged at NSF OPAL. Experimental requirements on collision geometry, polarization, cotiming and copointing, background suppression, and diagnostic technologies are investigated numerically. These results confirm that a beam cotiming shorter than the pulse duration and control of the copointing on a scale smaller than the shortest laser wavelength are needed to robustly scatter photons on a per-shot basis. Finally, we assess the bounds that a successful execution of this experiment may place on the mass scale of Born-Infeld nonlinear electrodynamics beyond the Standard Model of physics.

Generation of quasi-monoenergetic ions by intense laser is one of long-standing goals in laser-plasma physics. However, existing laser-driven ion acceleration schemes often produce broad energy spectra and limited control over ion species. Here we propose the acceleration mechanism, boosted Coulomb explosion, initiated by a standing wave, which is formed in a pre-expanded plasma by the interference between a continuously incoming main laser pulse and the pulse reflected by a solid target, where the pre-expanded plasma is formed from a thin layer on the solid target by a relatively strong pre-pulse. This mechanism produces a persistent Coulomb field on the target front side with field strengths on the order of TV/m for picoseconds. We experimentally demonstrate generation of quasi-monoenergetic deuterons up to 50 MeV using an in-situ D$_2$O-deposited target. Our results show that the peak energy can be tuned by the laser pulse duration.

We present the first experimental realization of a four-dimensional (4D) plasma hologram capable of recording and reconstructing the full spatiotemporal information of intense laser pulses. The holographic encoding is achieved through the interference of a long object pulse and a counter-propagating short reference pulse, generating an ionized plasma grating that captures both spatial and temporal characteristics of the laser field. A first-order diffractive probe enables the retrieval of encoded information, successfully reconstructing the spatiotemporal profiles of Gaussian and Laguerre-Gaussian beams. The experiment demonstrates the ability to encode artificial information into the laser pulse via spectral modulation and retrieve it through plasma grating diffraction, high-lighting potential applications in ultraintense optical data processing. Key innovations include a single-shot, background-free method for direct far-field spatiotemporal measurement and the obser-vation of laser focus propagation dynamics in plasma. The plasma grating exhibits a stable lifetime of 30-40 ps and supports high repetition rates, suggesting usage for high-speed optical switches and plasmatic analog memory. These advancements establish plasma holography as a robust platform for ultrafast laser manipulation, with implications for secure optical communication, analog computing,and precision spatiotemporal control of high-intensity lasers.

We present a modular user-oriented simulation toolbox for studying highharmonic generation in gases. The first release consists of the computational pipeline to 1) compute the unidirectional IR-pulse propagation incylindrical symmetry, 2) solve the microscopic responses in the whole macroscopic volume using a 1D-TDSE solver, 3) obtain the far-field harmonic field using a diffraction-integral approach. The code comes with interfaces and tutorials, based on practical laboratory conditions, to facilitate the usage and deployment of the code both locally and in HPC-clusters. Additionally, the modules are designed to work as stand-alone applications as well, e.g., 1D-TDSE is available through Pythonic interface.

Fractional Brownian motion (fBm) is an important scale-invariant Gaussian non-Markovian process with stationary increments, which serves as a prototypical example of a system with long-range temporal correlations and anomalous diffusion. The fBm is traditionally defined for the Hurst exponent $H$ in the range $-1/2

Creating a plasma dominated by strong-field QED (SFQED) effects is a major goal of new multi-PW laser facilities. This is motivated by the fact that the fundamental dynamics of such plasmas is poorly understood and plays an important role in the electrodynamics of extreme astrophysical environments such as pulsar magnetospheres. The most obvious observable for which such a regime has been reached is the production of a bright flash of x-rays, but distinguishing this from other sources of hard x-rays (e.g., bremsstrahlung) is a major challenge. Here we show that the photons from the X-ray flash are highly polarised, as compared to the unpolarised background, i.e., polarisation is an indicator that the SFQED plasma has really produced. For a laser of intensity $10^{21}$ Wcm$^{-2}$ impinging on a solid Al target, the photons of the flash with energy $>10$\thinspace keV are $>65\%$ polarised.

Material damage thresholds pose a fundamental limit to chirped pulse amplification (CPA) in high-power laser systems. Plasma-based amplification via stimulated Brillouin scattering (SBS) offers a damage-free alternative, yet its effectiveness has been hindered by instabilities that constrain interaction length. In this study, we report the first experimental demonstration of SBS amplification driven by a flying focus in a 3-mm plasma channel. The flying focus is generated using chromatic aberration from spherical lenses, with its velocity precisely measured by an interferometric ionization method achieving 6.6 fs timing resolution. At a focus velocity near -c, SBS amplification is realized at pump and seed intensities more than two orders of magnitude lower than in conventional setups, yielding a conversion efficiency of 14.5%. These results validate flying focus as a powerful tool for extending interaction lengths and enabling efficient plasma-based laser amplification at reduced intensities.

The interaction of an ultraintense Nd:glass laser pulse with a near-critical plasma self-organizes into a highly efficient $\gamma$-ray source. Three-dimensional particle-in-cell simulations demonstrate that relativistic self-focusing, aided by a self-generated electron cavity, enhances the laser intensity by more than an order of magnitude, driving the system into the radiation-reaction-dominated regime, i.e. one where the electrons lose a substantial amount of their energy as hard radiation. Peak photon emission occurs near $0.5$ times the relativistic critical density, with a $\gamma$-photon yield exceeding $20\%$ of the laser energy. Compared to Ti:Sa lasers of the same power, the longer duration of Nd:glass laser pulses leads to an order of magnitude increase in $\gamma$-photon number in the extreme conversion efficiency regime, making them particularly well-suited for photonuclear physics applications. These findings point to a robust and scalable mechanism for compact, ultra-bright $\gamma$-ray generation in the multi-petawatt regime.

This study explores nanoparticle-assisted electron injection as a method for controlling beam charge in laser wakefield acceleration through particle-in-cell simulations. We systematically investigate how the material (Li through Au) and size (50-200 nm) of nanoparticles influence electron injection dynamics and beam charge. Our results demonstrate that beam charge (10-600 pC) can be effectively controlled by adjusting these parameters. We identify a saturation threshold in the nanoparticle electric field strength, beyond which beam charge depends on the total number of atoms in the nanoparticle rather than on the electron density after ionization. Significant electron injection occurs across multiple plasma wave periods with distribution patterns influenced by nanoparticle properties leading to increased beam charge but a broader energy spread. These findings offer practical guidelines for experimental implementation of nanoparticle-assisted injection in laser wakefield accelerators to tailor electron beam characteristics for various applications.

The interaction between relativistic electron beams and intense laser fields has been extensively studied for generating high-energy radiation. However, achieving coherent radiation from such interactions needs to precisely control the phase matching of the radiationg electrons, which has proven to be exceptionally challenging. In this study, we demonstrate that coherent attosecond radiation can be produced when a laser pulse interacts at grazing angle with a relativistic electron beam. The electrons oscillate in the laser field and are modulated with a superluminal phase, coherent ultrashort pulse trains are produced in the far field at the Cherenkov angle. This is verified by theoretical modeling and numerical simulations, including three-dimensional particle-in-cell (PIC) simulations and far-field time-domain radiation simulations. Based on our proposed scheme, high-repetition-rate, compact, and high-energy attosecond pulse sources are feasible.