We propose a spatially resolved B-integral measurement method for high-power laser drivers based on off-axis aberration characterization. Theoretical analysis confirms the feasibility and high precision of this approach, in which coma-shaped intensity modulation is intentionally introduced into the laser system, imprinting nonlinear phase modulation with a corresponding aberration profile. The B-integral is then extracted by measuring the coma component of the output beam using a Shack–Hartmann sensor. The experimental results demonstrate a 5.8% deviation between the measured and simulated B-integral values for coma aberration, showing that the proposed method significantly outperforms the defocus-based measurement method (67.4% error) in terms of error reduction. This method does not require modifications to the laser setup, offers a single-shot measurement capability and achieves high accuracy and excellent repeatability. The direct quantification of wavefront phase distortions provides a practical solution for nonlinear phase modulation diagnostics in high-power laser systems.

Spectral broadening in guided-wave optics, an effect intrinsic to the interplay of dispersion and nonlinearity, presents a major obstacle to achieving the high spectral purity required for applications in nonlinear frequency conversion and precision spectroscopy. This effect is especially detrimental in high-power cascaded Raman fibre lasers (CRFLs). Leveraging a concept analogous to wavefront shaping but implemented passively, we introduce and validate a novel architecture for CRFLs incorporating random fibre grating-assisted spectral tailoring. A theoretical model is developed to show that the randomized reflectance profile of the grating induces wavelength-selective feedback, promoting intracavity mode competition and noise suppression through enhanced coherent enhancement of selected spectral components. Experimentally, we demonstrate a maximum output power exceeding 1 kW at 1185 nm from the cascaded Raman fibre oscillator. The random grating provides enhanced spectral control, achieving a 3-dB linewidth of approximately 1.0 nm. Notably, it also significantly suppresses the spectral wings, reducing the 10- and 30-dB linewidths to 2.9 and 9.5 nm, respectively. This work represents the first implementation of built-in passive spectral tailoring in an all-fibre nonlinear dynamical system, offering insights into the control of complex light fields in both temporal and frequency domains throughout cascaded nonlinear processes.

We demonstrate that tailoring the laser–target interaction at the PW-class VEGA-3 facility (by controlling the focusing conditions, pulse duration, chirp sign and solid-target properties) enables the enhancement of ion flux, divergence and cutoff energy for high-energy-density physics experiments. The existence of optimal pulse duration, focusing conditions, target thickness and target material is experimentally demonstrated. We further show that a reduction in ion acceleration efficiency under best-compression conditions leads to delayed relative depletion of the hydrogen population compared to carbon ions, accompanied by a decrease in both ion flux and cutoff energy. For metallic targets, scintillator detectors reveal a more divergent and deflected proton beam than that produced from thick plastic targets. The product of the magnetic field strength and the interaction length acting on the ions is estimated to reach up to 400 MG μm, resulting in a ring-like spatial distribution of protons generated from aluminum and copper targets.

Multicore fiber is a prospective medium for high-power lasers. All-fiber cavities based on fiber Bragg gratings (FBGs) inscribed by femtosecond pulses in uncoupled cores generate beams independently at wavelengths defined by the individual FBG reflection. However, separate core generation spectra collapse into a single narrow and stable line at strong optical coupling between the cores. The developed model shows that the collapsed spectrum linewidth depends on the number of cores, their coupling strength and the geometric-mean reflection width of individual FBGs. It is revealed that physical mechanisms and quantitative features of linewidth broadening defined by spatial hole burning and Kerr effects are sufficiently modified in comparison with single-core lasers. A performed comparison of the theory with experiment demonstrates a fairly good correspondence of key characteristics, namely the generation wavelength, spectrum shape and the linewidth value depending on power. An extreme linewidth narrowing is predicted for a high-power multicore fiber laser with a greatly increased number of cores and their coupling strength.

The mechanisms governing generation and amplification of laser-driven electromagnetic pulses (EMPs) in the picosecond (ps) regime remain insufficiently understood. Here, we present a unified theoretical and experimental framework that demonstrates dual-picosecond laser irradiation of solid targets can synergistically enhance EMP emission. By integrating particle-in-cell simulations with three-dimensional electromagnetic modeling, we reveal that the increasing laser focal power density amplifies hot electron emission and strengthens neutralization currents, leading to giant EMP radiations. Experimentally, we validate these predictions at the XG-III and SG-II U picosecond petawatt laser facilities, achieving a record-breaking EMP field strength of 3.08 MV/m – substantially exceeding previously reported values from ps-laser–solid interactions. Furthermore, we demonstrate that EMP characteristics can be precisely tuned via laser and target parameters, enabling controllable, high-field electromagnetic sources. Our findings provide deep insight into the physics of laser-driven EMP amplification and establish a robust platform for developing next-generation high-intensity electromagnetic emitters.

We present recent results on high-power guiding and laser wakefield acceleration in the ELectron Beam Accelerator (ELBA) beamline at ELI Beamlines, using the L3-HAPLS laser system (13 J, 30 fs, 0.2 Hz). By employing self-waveguiding in a 20 cm plasma channel in helium, we achieved stable acceleration of electron beams to energies of approximately 5 GeV. A novel all-reflective optical setup, including an off-axis reflective axicon, enabled efficient acceleration at 0.2 Hz and guiding at repetition rates up to 3.3 Hz. This compact single laser, single-compressor implementation of plasma channels for electron acceleration stabilizes electron pointing and enhances energy gain without requiring modifications to the laser system, paving the way for broader adoption of the technology across user facilities.

We present a deterministic method for the spatio-spectral characterization of intense ultrashort laser pulses via far-field speckle analysis. By mapping vacuum propagation to a linear forward model, we replace slow, error-prone iterative algorithms with a direct least-squares minimization. This enables high-speed retrieval of spectrally resolved wavefronts with rigorous uncertainty quantification. Demonstrated at the ATLAS-3000 petawatt facility, our in situ architecture utilizes only a pinhole mask for both attenuation and speckle generation. By eliminating complex downstream optics and minimizing systematic errors, this approach provides a robust, real-time diagnostic essential for the optimization of high-intensity lasers.

We demonstrate a high-power InnoSlab amplifier based on a multi-segmented composite ytterbium-doped yttrium aluminum garnet (Yb:YAG) crystal. A systematic comparison was performed of the laser amplification output performance of multi-segmented and conventional Yb:YAG crystals to demonstrate the feasibility of using gain media with multiple doping concentrations in InnoSlab laser amplifiers. We achieved an amplified output of 245 W based on the multi-segmented composite Yb:YAG crystal InnoSlab amplifier, with a beam quality of M2 = 1.21 × 1.25 and an optical-to-optical efficiency of 38.9%. Thanks to the unique doping structure of the composite crystal, compared to homogeneous dopant crystals, the average output power, optical-to-optical efficiency and beam quality were significantly improved. Exceptional output power stability with a root mean square fluctuation of 0.11% and pointing stability of approximately 7.5 μrad were achieved.

The results of numerical simulation of spatial noise filtering prior to the stage of nonlinear temporal compression of PW laser pulses are presented. It is shown that small-scale self-focusing (filamentation instability) can be substantially suppressed in a diffraction-grating optical compressor, since the spatial frequencies in the instability region lag behind or overtake the main pulse. This effect in an asymmetric compressor is weaker than in a symmetric one, despite a more efficient smoothing of spatial fluence fluctuations.

Continuous-wave diamond Raman lasers (DRLs) operated at high pump power commonly suffer from power roll-off and output instability, even when high-thermal-conductivity gain media are employed. These degradations originate from thermally induced cavity-mode mismatch and cavity-length drift, which limit further power scaling. In this work, we establish a thermo–optical chain-linked model that quantitatively describes the coupled evolution of thermal deposition, equivalent thermal lensing, intracavity-mode matching and output power in high-power DRLs, providing a direct physical link between pump power and cavity-length compensation. Based on this model, a peak–valley co-location criterion is proposed to determine the optimal cavity-length compensation point. Both theoretical and experimental results show that the output power exhibits a single-peak dependence on cavity-length offset, while the power stability follows a U-shaped distribution, and their extrema coincide at an optimal compensation value ΔL*. By operating at ΔL*, the maximum Stokes output power increases from 27 to 32 W, and the root mean square power fluctuation decreases from 4.8% to 3.2%. These results demonstrate that thermal-lens-induced performance degradation can be effectively mitigated by cavity-length compensation using a single control parameter, providing a practical design rule for simultaneous enhancement of output power and stability in high-power Raman laser systems.

We present the characterization of intensity distributions and the beam wavefront along the caustic of an iodine photodissociation laser beam at the Prague Asterix Laser System. Its $700\;\mathrm{J},300\;\mathrm{ps}$ laser pulse was attenuated by neutral-density optical filters and focused by an $f/2.2$ aspherical lens. In multiple planes at and around the focus position ($\pm 7\times \mathrm{Rayleigh}\kern0.17em \mathrm{length}$), we measured fluence distributions by far-field imaging with a nonlinearity-corrected camera. We used these measurements to retrieve the beam wavefront by a phase retrieval algorithm with dynamic input–output mixing. We then propagated the beam to the focus position and to the lens position. The calculated peak intensity at the focus position was $7.9\times {10}^{18}\;\mathrm{W}/{\mathrm{cm}}^2$, and $300\;\mathrm{J}$ (43% of the pulse energy) was contained within the intensity region above the relativistic intensity threshold of $0.8\times {10}^{18}\;\mathrm{W}/{\mathrm{cm}}^2@1315.2\;\mathrm{nm}$.

Laser–target interactions generate intense electromagnetic pulses (EMPs) that can interfere with measurements and damage equipment. In this paper we show that applying a magnetic field to nanosecond pulse laser–target interactions decreases the magnitude of EMPs. We demonstrate this effect in two experiments with different geometries (spherical versus planar), laser intensities ($\sim {10}^{13}$ versus $\sim {10}^{15}$ W/cm${}^2$) and applied field strength (12 versus 0.1 T) that both observed suppression of EMPs in approximately the 1 GHz band (by factors of $0.65\times$ and $0.32\times$, respectively). We then observe the opposite effect at high intensities with a picosecond pulse: for planar experiments with laser intensities of approximately ${10}^{19}$ W/cm${}^2$ and magnetic fields of 6–10 T, the magnitude of EMPs is increased by a factor of $1.75\times$. These results provide a benchmark for models of EMP generation, but suggest that magnetic fields are not a viable solution for mitigating EMPs in the high-intensity laser facilities where they are most damaging.

We report a high-power broadband flat supercontinuum laser system based on a large-mode-area (LMA) low-loss fluorotellurite fiber cascaded with an LMA chalcogenide fiber. To effectively expand the coverage of the mid-infrared supercontinuum spectrum and enhance its flatness, a novel femtosecond Raman-soliton laser with high peak power is used as the pump source. When pumping the fluorotellurite fiber, a supercontinuum extended to 4.2 μm can be obtained, with an output power of 8.12 W. Subsequently, we further pumped an LMA As2S3 fiber. At the maximum input power, the output power of the supercontinuum can reach 2.6 W, with the spectral edge extending to 5.7 μm, a 10-dB bandwidth spanning 2–4.7 μm and favorable power stability retained. To the best of our knowledge, this is the first laser system that uses a fluorotellurite fiber as a transition fiber and further cascades the chalcogenide fiber to generate mid- and long-wave infrared supercontinuum, achieving the highest output power of a mid- to long-wave infrared supercontinuum laser generated in As2S3 fiber reported to date.

LiGaS2 crystals are prospective media for optical parametric oscillators. In such systems efficiency and maximum power output are often limited by the laser-induced damage threshold (LIDT) of nonlinear crystals. In addition, most nonlinear crystals have a high refractive index and consequently large Fresnel losses, thus encouraging the use of antireflection coatings. However, antireflection coatings are known to compromise the LIDT. This work presents results of the LIDT testing of LiGaS2 nonlinear crystals in untreated, antireflection-coated and antireflection-microstructured variations. The tests were performed using a one-on-one method with pulsed lasers operating at 1.57, 2.09 and 2.5 μm wavelengths with pulse durations of 9, 149 and 12 ns, respectively. The paper covers damage site feature investigation and LIDT comparison of antireflection coating and antireflection microstructures. The key finding of the work is that antireflection microstructures can provide an increase in transmittance for both the pump and the signal, while maintaining a high LIDT.

High-energy gamma-ray spectroscopy is crucial for studying and advancing the application of high-energy photons in areas such as strong-field physics, high-energy-density science and laboratory astrophysics. However, high-energy gamma-ray spectroscopy in the multi-MeV to GeV range faces significant challenges in precise spectral reconstruction. This study presents a machine learning-based inversion approach that combines a spectrometer design with advanced deconvolution algorithms. We develop a gamma-ray spectrometer optimized through Monte Carlo simulations for maximum positron yield and minimal noise. A two-stage neural network framework is proposed based on the structure of the spectrometer: a denoising autoencoder suppresses statistical noise in measured positron spectra, while a U-Net architecture solves the ill-posed inverse problem to reconstruct incident gamma spectra. This approach establishes a method for gamma-ray diagnostics in strong-field quantum electrodynamics experiments and high-energy photon sources.

Synchronization of common-seed ultrashort pulses from parallel chirped pulse amplification (CPA) and compression systems, with accuracy comparable with the pulse duration, is hindered by the inherent environmental noise present in the laboratory. If the pulses are produced in high-repetition-rate systems, they can be monitored in real-time and their relative delay fluctuations can be efficiently suppressed. However, at lower repetition rates, the laser pulses themselves do not provide the information about the delay for compensation at the required pace. Demonstrated here is the coherent combination of two ultrashort pulses from a dual arm CPA laser system and dual optical compressors at low repetition rate, using an assisting continuous wave laser beam. In this way, the relative delay fluctuations in the common focus of the two pulses reached 325 as root mean square (rms), corresponding to $\lambda /8$, over 45 minutes of operation at 10 Hz, while their short-term measured stability was 78 as rms, corresponding to $\lambda /34$, over 100 s.

This paper presents the design and implementation of a distributed control system for the laser wakefield acceleration (LWFA) facility at the Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences. This system is developed to support artificial intelligence (AI) integration and automated tuning. Built on the Experimental Physics and Industrial Control System, it provides real-time monitoring, device control, alarm handling and data archiving. To enhance modularity and scalability, unified multiuser interfaces were developed using Control System Studio within a microservice architecture. Remote direct memory access was adopted to remove bottlenecks in high-throughput image data transmission, and a hybrid storage framework combining MySQL, InfluxDB and MinIO was implemented for efficient data storage and management. The system has been comprehensively tested in both laboratory and operational environments. This work offers a practical solution for the intelligent evolution of LWFA facilities, laying the groundwork for future AI-driven laser–plasma accelerator systems.

A technique developed for capturing and monitoring the back-reflected (BR) laser light in experiments utilizing the world’s most powerful laser (high-power laser system, HPLS) at the Extreme Light Infrastructure - Nuclear Physics facility is presented. We address the challenge of characterizing BR light generated during the first laser shots delivered on thin-foil targets by using two optical setups: a full-aperture image relay system capable of imaging the full beam profile along the propagation of the laser beam path and a small-aperture monitoring (SAM) system that captures low levels of BR energy in the range of a few tens of millijoules to over 100 mJ. SAM characterizes the temporal profile of the BR pulses with a resolution of 0.3 ns. We model the amplification of BR light along the laser chain, which correlates the measured back-reflection with the target reflectivity. Our techniques allow for precise monitoring of the BR beam dynamics ensuring at the same time the safety of the HPLS.

High-energy nanosecond pulses at wavelengths beyond 2.5 μm in the mid-infrared (mid-IR) region are of significant interest for applications such as polymer processing, minimally invasive surgery, laser ranging and infrared countermeasures. While rare-earth-doped fluoride fibers provide a compact and robust platform for mid-IR pulse generation, achieving millijoule (mJ)-level nanosecond pulses beyond 3 μm remains challenging. In this work, we demonstrate high-energy nanosecond pulse generation at 3.17 μm using a master oscillator power amplifier based on a 980 nm diode-pumped Er3+/Dy3+ co-doped fluoride fiber. Seeded by an actively Q-switched oscillator operating at a 1 kHz repetition rate, the system delivers 0.68 mJ of pulse energy with a pulse width of 132 ns and a peak power of 4.8 kW, while maintaining single-transverse-mode operation (M2 = 1.2–1.3). To the best of our knowledge, this work represents the first report on mJ-level nanosecond pulse generation beyond 3 μm from a fiber-based system.