Free-electron lasers (FELs) provide a revolutionary tool for capturing the structure and dynamics of matter in real time at the atomic scale. The size and cost of FELs can be substantially reduced by using laser wakefield acceleration (LWFA), which offers acceleration gradients orders of magnitude beyond radiofrequency technology, producing multi-GeV electron beams within tens of centimeters. This compactness opens the possibility of integrating multiple operating modes - from the EUV to X-rays including broadband operation - into one facility. Realizing this vision, however, faces key challenges: current LWFA bunches are too short to sustain sufficient radiation slippage, limiting FEL pulse energy at EUV wavelengths, while the large energy spread and emittance make X-ray lasing even more demanding. Here we present a LWFA-driven FEL scheme that addresses these challenges, enabling multi-mode operation spanning different wavelengths and bandwidths within a single facility. The scheme employs staged acceleration to reach multi-GeV energies while preserving beam quality, combined with a dual-chicane beamline that stretches the bunch to mitigate the radiation slippage for EUV FEL and tailors the energy chirp for diverse FEL bandwidth modes. Simulations demonstrate that the scheme can generate high-quality electron beams with energies up to 7 GeV and tunable energy chirp, enabling both FEL saturation from the EUV to X-ray wavelengths and large bandwidth operation with a bandwidth of up to 11

Successive innovations in particle accelerators have continually expanded the frontiers of scientific discovery. Laser wakefield accelerators promise to transform science, medicine, and industry, yet moving them from laboratory demonstrations to reliable real-world operation has remained a central, long-standing challenge. Here we report a field-deployable system that produced 100-MeV-class electron beams with 1

Focused very-high-energy electron (VHEE) beams can produce localized dose enhancement at selected depths, but irradiation of a finite target requires coordinated control of multiple focal positions, incidence directions, and beam weights while limiting exposure of nearby organs at risk (OARs). We present Focal-Point Scanning (FPS), a dose delivery and optimization method developed for laser wakefield accelerator (LWFA)-driven VHEE beams. The method is based on a two-dipole focusing system that produces single-plane beam convergence and allows the focal position to be varied by changing the magnetic field strength. FPS distributes focal points throughout the planning target volume and determines focal-point-specific incidence sectors according to the geometry of nearby critical OARs. The method was evaluated using the AAPM TG119 C-shape benchmark and one previously treated lung radiotherapy case. At matched target coverage, FPS reduced the TG119 Core mean dose by approximately one half relative to parallel VHEE and intensity-modulated x-ray plans, approaching the single-field proton pencil-beam-scanning reference. In the lung case, FPS maintained target coverage comparable to the clinical volumetric modulated arc therapy reference while reducing the mean dose to every evaluated OAR; spinal-cord mean and maximum doses decreased by 93.2

Laser-plasma accelerators have been the subject of extensive research in recent years. The electron beams they generate exhibit a broad energy spread. To conveniently characterize beams from laser wakefield acceleration (LWFA), electron spectrometers employing scintillating screens coupled with CCD cameras are typically used. In this work, we calibrate a series of DRZ phosphor screens and measure the spectra of the light they emit. The calibration was performed using the radio-frequency linear electron accelerator at Tsinghua University, which provided monoenergetic electron beams with peak energy of approximately 30 MeV.

MeV ultrafast electron diffraction (UED) is a widely used technique for ultrafast structural dynamics studies of matter in numerous areas. The development of the laser wakefield accelerator (LWFA) shows great potential for an advanced all-optical electron source based on LWFA in UED applications. Here we experimentally demonstrated that an LWFA-based device with a miniaturized permanent magnet beamline can generate and manipulate electron beams suitable for UED. During beam transport, the LWFA electron beams with intrinsically short duration undergo temporal stretching owing to the energy spread and are subsequently compressed by the following double-bend achromat. The optimized double-bend achromat can make the beamline isochronous such that the arrival time jitter induced by the shot-to-shot energy fluctuation can be eliminated, and allow the advantage of the natural laser-beam synchronization for LWFAs to emerge. With the energy filtering, the beam energy spread can be reduced to 3% (full-width at half-maximum), while a sufficient amount of charge (11.9 fC) per bunch for diffraction is retained. Using a laser-driven terahertz deflector, the beam length and arrival time jitter measured at the sample location are approximately 49.6 fs (root mean square (r.m.s.)) and 4.7 fs (r.m.s.), respectively, resulting in a temporal resolution of ~49.8 fs. Comprehensive start-to-end simulations indicate the potential of reducing the bunch length to ~10 fs (r.m.s.) with a lower energy spread of around 1.6%. Clear single-shot and multi-shot diffraction patterns of single-crystalline gold samples are obtained, and the derived lattice constant agrees well with the actual value. Our proof-of-principle experiments open the door to the detection of ultrafast structural dynamics using MeV LWFA beams, and pave the way for UED applications with sub-10 fs temporal resolution. Researchers demonstrate that a laser wakefield accelerator-based device with a miniaturized permanent magnet beamline can generate and manipulate electron beams suitable for ultrafast electron diffraction.

Preformed plasma channels are essential for guiding driver laser pulses over extended distances in laser wakefield accelerators (LWFAs), enabling the generation of multi-giga-electron volt electron beams for the applications of free-electron lasers and particle colliders. Optical-field ionization (OFI) heating provides a robust approach for creating laser-matched plasma channels across a broad range of parameters, owing to its density- and geometry-independent heating effect. Establishing predictive scaling laws between channel parameters and formation conditions is critical for the design of plasma channels capable of accelerating electrons from energies of hundreds of mega-electron volt up to tens of giga-electron volt. Through a combination of timescale analysis and numerical simulations, hydrodynamic expansion has been identified as the dominant mechanism governing density profile evolution during OFI channel formation, which leads to the similarity in density profiles under normalized conditions. As a result, this method preserves effective laser-guiding channel structures across a wide range of initial gas density (10(17)-10(19) cm(-3)) and initial ionization radius (10-100 mu m). For parabolic channels optimized for Gaussian laser drivers, scaling laws have been established, indicating that the on-axis density scales linearly with the initial gas density, while the matching radius exhibits an exponential dependence on both the initial gas density and the ionization laser radius. These findings provide a systematic framework for the parameter design and optimization of plasma channels in high-efficiency and high-energy LWFA applications.

Broad-bandwidth x-ray free-electron lasers (FELs) are critical scientific tools across diverse disciplines such as biology and chemistry. While substantial efforts have been devoted to achieving FEL bandwidth broadening, existing methods face limitations. This paper proposes a simple yet effective scheme for spectral broadening that utilizes a plasma wakefield accelerator (PWFA) to impart a large energy chirp to an electron beam. A specifically designed transport system then selectively injects the portion of the beam meeting the lasing requirements into the undulators for FEL generation. A start-to-end simulation demonstrates that the scheme can effectively manipulate the longitudinal and transverse phase space of the PWFA electron beam that subsequently generates a high-brightness x-ray FEL exhibiting a full-width bandwidth reaching 20%.

Femtosecond relativistic electron beams are key probes of ultrafast dynamics, and their pulse duration directly limits the achievable temporal resolution. Laser wakefield acceleration (LWFA) provides a compact source of such beams, but the injection-induced energy spread makes bunch compression sensitive to nonlinear longitudinal transport, motivating direct longitudinal phase space (LPS) measurements. Here, a terahertz transverse-deflecting cavity (THz-TDC) combined with a dipole magnet is used to reconstruct the nonlinear LPS of LWFA electron bunches compressed in a double-bend achromat (DBA), resolving a characteristic C-shaped distribution associated with higher-order longitudinal transport. At an average energy of approximately 4.55 MeV, the diagnostic achieves a temporal resolving power of 1.8 fs and an energy resolution of 6.0 keV, corresponding to a relative energy resolution of 0.13

Plasma wakefield acceleration in hollow plasma channels has emerged as a promising approach for positron acceleration, since an electron beam can drive wakes with a transversely uniform accelerating field and no intrinsic defocusing force for positrons. Recently, it was proposed that a transversely asymmetric electron beam can excite quadrupole-dominated wakefield in a hollow channel, enabling the formation of accelerating and focusing fields suitable for positrons. However, the self-consistent evolution and stability of such asymmetric drivers, which are crucial for sustaining a usable wake over long distances, remain insufficiently understood. In this work, we investigate the evolution modes of wakefield driven by asymmetric electron beams in hollow plasma channels using fully three-dimensional particle-in-cell simulations. We identify two distinct unstable scenarios: a reversal of quadrupole field polarity and continuous penetration of the driver into the plasma wall. By analyzing the transverse dynamics of the driver and the restoring forces provided by the channel ions, we establish simple physical criteria that ensure stable propagation. These results clarify the fundamental constraints governing asymmetric-driver evolution and provide practical guidance for realizing long-lived, quasi-steady wakes in hollow plasma channels.

Pump-probe experiments using dual ultrashort X-ray pulses provide unique opportunities for resolving non-equilibrium dynamics initiated by intense X-ray excitation. Betatron radiation from laser wakefield accelerators offers femtosecond duration, micrometer-scale source size, and intrinsic synchronization with the driving laser, making it a promising candidate for compact ultrafast X-ray sources. Here, we experimentally demonstrate a high-flux, dual-pulse betatron X-ray source based on a density-tailored gas-mixture target. Two electron bunches are generated within a single plasma wakefield through ionization-induced and shock-front-triggered injection, subsequently producing twin X-ray pulses. The measured electron spectra and dual-component X-ray angular profiles, together with particle-in-cell simulations, identify the contributions of the two electron populations to the radiation. The total X-ray photon yield reaches the level of 10^10 photons per shot with a 40-TW laser system. These results establish a compact, single-stage route toward high-flux dual-pulse betatron sources for laboratory-scale ultrafast X-ray spectroscopy.

MethodsThis was a retrospective cohort study that enrolled patients with LARC who received short-course radiotherapy (SCRT, 25 Gy in 5 fractions) at the Radiation Therapy Center of Fudan University Shanghai Cancer Center between January 2023 and October 2025. Patients were divided into an integrated workflow group and a conventional workflow group according to the treatment procedure. In the integrated workflow group, simulation, treatment planning, and radiotherapy delivery were all performed on the United Imaging uRT-linac 506c system, with daily fan-beam computed tomography (FBCT)-based image-guided radiation therapy (IGRT). In the conventional workflow group, patients underwent computed tomography simulation with a Siemens (SOMATOM Definition AS) scanner followed by radiotherapy on a Varian EDGE linear accelerator, with daily cone-beam computed tomography (CBCT)-based IGRT. This study was approved by the Ethics Committee of Fudan University Shanghai Cancer Center (2201250-16). Setup errors were recorded in three translational directions: vertical (VRT), longitudinal (LNG), and lateral (LAT) and three rotational directions: YAW, PITCH, and ROLL. Equivalence was assessed using Hodges-Lehmann (HL) median difference estimation. Predefined equivalence margins were ±2 mm for translational errors and ±1° for rotational errors.ResultsA total of 60 patients were enrolled in this study, including 30 patients in the integrated workflow group and 30 patients in the conventional workflow group. For translational directions, the HL median differences for VRT, LNG, and LAT were -0.030 mm, -0.020 mm, and 0.020 mm, respectively. The HL median difference for three-dimensional vector error was -0.018 mm. All 95% confidence intervals fell entirely within the ±2 mm equivalence margin. For rotational directions, the HL median differences for YAW, PITCH, and ROLL were 0.090°, -0.300°, and -0.200°, respectively, with all 95% confidence intervals within the ±1° margin. Clinical equivalence in setup accuracy was demonstrated across all directions.ConclusionThe integrated radiotherapy workflow using the United Imaging uRT-linac 506c demonstrates clinical equivalence in setup accuracy compared with the conventional workflow for SCRT in patients with LARC. In addition, this integrated approach shows potential advantages in reducing treatment duration and alleviating treatment-related financial burden, suggesting its applicability in selected clinical settings.Background and purposeFor locally advanced rectal cancer (LARC), short-course radiotherapy (SCRT) has emerged as a research hotspot in recent years and has shown potential advantages when combined with consolidation immunochemotherapy. This study employed a retrospective cohort design to compare the setup accuracy between an integrated CT-linear accelerator workflow and a conventional workflow in SCRT for LARC, and to evaluate their clinical equivalence.

Understanding the complex plasma dynamics in ultra-intense relativistic laser-solid interactions is of fundamental importance for applications of laser-plasma-based particle accelerators, the creation of high-energy-density matter, understanding planetary science, and laser-driven fusion energy. However, experimental efforts in this regime have been limited by the lack of accessibility of over-critical densities and the poor spatiotemporal resolution of conventional diagnostics. Over the last decade, the advent of femtosecond brilliant hard X-ray free-electron lasers (XFELs) has opened new horizons to overcome these limitations. Here, for the first time, we present full-scale spatiotemporal measurements of solid-density plasma dynamics, including preplasma generation with tens of nanometer scale length driven by the leading edge of a relativistic laser pulse, ultrafast heating and ionization at the main pulse arrival, the laser-driven blast wave, and transient surface return current-induced compression dynamics up to hundreds of picoseconds after interaction. These observations are enabled by utilizing a novel combination of advanced X-ray diagnostics including small-angle X-ray scattering, resonant X-ray emission spectroscopy, and propagation-based X-ray phase-contrast imaging simultaneously at the European XFEL-HED beamline station.

Laser wakefield accelerators (LWFAs) offer acceleration gradients up to 1000 times higher than those of conventional radio-frequency accelerators, offering a pathway to significantly more compact and cost-effective accelerator systems. This breakthrough opens up new possibilities for laboratory-scale light sources. All-optical inverse Compton scattering (AOCS) sources driven by LWFAs produce high-brightness, quasi-monochromatic X rays with micrometer-scale source sizes, delivering the spatial coherence and resolution required for X-ray phase-contrast imaging (XPCI). These features position AOCS X-ray sources as promising tools for applications in biology, medicine, physics, and materials science. However, previous AOCS-based imaging studies have primarily focused on X-ray absorption imaging. In this work, we report successful experimental demonstrations of edge-enhanced in-line XPCI using energy-tunable, quasi-monochromatic AOCS X rays. With a spatial resolution of ∼20 μm, our results clearly show the potential of high-resolution, AOCS-based XPCI applications.

Wavelength-tunable ultra-intense femtosecond lasers may enable breakthroughs in diverse areas of science spanning attosecond science, particle acceleration and beyond. Conventional crystal-based methods are limited by gain bandwidth and damage thresholds, which restrict their wavelength tunability. Plasma-based frequency conversion, unconstrained by material damage, offers a promising alternative. Here, a novel scheme named Frequency Downshifting Stair (FDS) based on plasma bubble filling control is presented. The FDS enables arbitrary frequency down-conversion of ultra-intense femtosecond pulses and yields chirp-free laser pulses. It can achieve near-100

Radiotherapy utilizing very-high-energy electron (VHEE) beams in the range of 50–300 MeV has gained significant interest over the past two decades due to their advantageous dose characteristics, deep tissue penetration capabilities, and potential for ultrahigh dose-rate treatments. Laser wakefield accelerators (LWFAs) are particularly well suited for generating VHEE beams in a compact setup, thanks to their substantially higher accelerating gradients compared to conventional radio-frequency accelerators. To meet the demands of clinical applications, a comprehensive dosimetry study of LWFA-generated VHEE beams in a preclinical treatment configuration is essential. In this study, a VHEE beam with a maximum energy over 160 MeV was produced using a compact and stable LWFA prototype operating at 1 Hz. The beam was subsequently transported through a quadrupole triplet to eliminate low-energy components and reduce pointing jitter, followed by a scatterer and collimator to create a uniform circular radiation field with an 8-mm diameter. Using this beam, we measured the three-dimensional dose distribution within a solid-water phantom and evaluated the feasibility of multifield intensity-modulated irradiation by delivering 400 VHEE beams from 20 different angles into the phantom. This resulted in a 16-mm-diameter dose plateau peak, with the relative uniformity of approximately 2.8%, and the entrance dose was only 20% of the peak value. These findings demonstrate the feasibility and robustness of LWFA-based VHEE beams for treating deep-seated tumors, highlighting the need for dedicated engineering and preclinical studies in this promising direction.

The use of very high-energy electron (VHEE) beams for radiotherapy has been actively studied for over two decades due to their advantageous dose distribution, deep penetration depth, and great potential of ultrahigh dose-rate irradiation. Recently, laser-plasma wakefield accelerator (LWFA) has emerged as a promising method for the compact generation of VHEE beams, due to its substantially higher accelerating gradients compared to traditional radio-frequency accelerators. However, how to compactly deliver the LWFA-based VHEE beams of relatively large energy spread and create a maximum dose deeply inside the body remains very challenging. In this article, we present a simple dose delivery scheme utilizing only two dipole magnets for LWFA-based VHEE treatment. By adjusting the magnet strengths, the electron beams can be guided along different angular trajectories toward a precise position as deep as 20 cm within a water phantom, creating a maximum dose over the target region and significantly reducing the entrance dose. Supported by Monte Carlo simulations, such a beam delivery approach is demonstrated to be insensitive to the beam energy spread and meanwhile capable of controlling precisely the dose-peak position in both lateral and longitudinal directions. As such, a uniform dose peak can be generated by the weighted sum of VHEE beams that reach different dose-peak depths. These results demonstrate that LWFA-based VHEE beams can be compactly delivered into a deep-seated tumor region in a controllable manner, thus advancing the development of the VHEE radiotherapy toward the practical clinical applications in the near future.

Radiotherapy using very-high-energy electron (VHEE) beams (50-300 MeV) has attracted considerable attention due to its advantageous dose deposition characteristics, enabling deep penetration and easy manipulation by magnetic components. One promising approach to compactly delivering these high energy electron beams in a cost-effective manner is laser wakefield acceleration (LWFA), which offers ultra-strong accelerating gradients. However, the transition from this concept to a functional machine intended for tumor treatment remains elusive. Here we present the self-developed pro- totype for LWFA-based VHEE radiotherapy, exhibiting compactness (occupying less than 5 m2) and long-term operational stability (validated over a period of one month). Subsequently, we employ this device to irradiate a tumor implanted in a mouse model. Following a dose delivery of 5.8 +/- 0.2 Gy with precise tumor conformity, all irradiated mice exhibit pronounced control of tumor growth. For comparison, this tumor-control efficacy is similar to that achieved using commercial X-ray radiotherapy equipment operating at equivalent doses. These results demonstrate a compact and stable laser-driven VHEE system dedicated for preclinical studies involving small animal models and its promising prospects for future clinical translation in cancer therapy.

Supercontinuum (SC) generation in bulk materials offers a versatile, broadband coherent light source for ultrafast spectroscopy and nonlinear optics. The filamentation process underlying SC generation is primarily governed by three critical parameters: input pulse energy, focusing numerical aperture, and crystal thickness. Using femtosecond pulses and sapphire crystals, we systematically investigate how these parameters affect SC energy stability. Depending on the number of pulse-splitting events, filamentation can manifest in either single- or multi-filament regimes, with the latter leading to undesirable spectral modulation and thus requiring avoidance. Our study reveals that within the single-filament regime, two distinct dynamical states can arise: a critical state, in which pulse-splitting dynamics and SC spectra evolve rapidly with increasing input pulse energy, and a steady state, which ensures optimal stability. Experimental results show that steady-state SC generation yields the highest stability, exceeding that of the driving laser. These findings deepen the physical understanding of filamentation and provide clear guidelines for parameter selection to achieve stable SC in bulk media, offering practical insights for optimizing broadband coherent sources in ultrafast applications.

Flat-top beam, known for its ability to generate a consistently even irradiation area, holds vast utility in many fields of scientific and industrial applications. In this paper, a reflective laser beam shaping method based on two axisymmetric aspheric mirrors (AAMs), a polarizing beam splitter (PBS) and two quarter wave plates (QWPs) is proposed to transform Gaussian beam into flat-top beam. Compared to alternative beam shaping methods, the method using AAMs demonstrates distinct advantages on notably high energy efficiency and unique capability to generate parallel beams. Thanks to its relative simplicities of design, manufacture and tunability, AAMs-shaping further enhances its appeal in applied research scenarios.

This paper provides an overview of the current status of ultrafast and ultra-intense lasers with peak powers exceeding 100 TW and examines the research activities in high-energy-density physics within China. Currently, 10 high-intensity lasers with powers over 100 TW are operational, and about 10 additional lasers are being constructed at various institutes and universities. These facilities operate either independently or are combined with one another, thereby offering substantial support for both Chinese and international research and development efforts in high-energy-density physics.