In the design and construction of ultra-high-peak-power laser systems, it is necessary to control the accumulated B-integral of the laser pulse, but currently there are no reasonable B-integral control standards for picosecond and femtosecond lasers. We systematically evaluate the influence of the B-integral on the output capability of picosecond and femtosecond laser systems for the first time, to our knowledge, taking Nd:glass lasers and Ti:sapphire lasers as examples. For picosecond lasers, the temporal domain compressibility and the small-scale self-focusing effect restrict the B-integral to 1.7 and 1.9, respectively. For femtosecond lasers, the B-integral is mainly restricted by the small-scale self-focusing effect and the far-field focusability, which limit the B-integral to 1.5 and 1.7, respectively. The restriction made by far-field focusability can be largely relaxed by inserting a deformable mirror. The study of the factors restricting the B-integral will provide guidance for the design of ultra-high-peak-power laser systems.

Accelerator-driven systems (ADSs) may offer a promising technology for energy production and transmutation of nuclear waste. Here we introduce the concept of utilizing high-intensity laser acceleration technology in realizing an ADS, with a focus on the use of thorium fuel in subcritical systems. We explore state-of-the-art laser-driven particle sources for neutron generation by nuclear fusion, spallation or photonuclear reactions and the prospect of reaching the flux of ${10}^{15}$ n/s required to drive a subcritical reactor. We review recent advances in high-power laser amplification and assess their technological readiness in view of integration in an ADS. Finally, we present a risk analysis of a laser-driven ADS in terms of laser and target development, radiation safety and operational stability. Our conclusion highlights the potential of laser-driven ADSs as a transformative approach to nuclear fission energy. With continued research and development, technological hurdles can be overcome to fully realize sustainable, green energy production that can meet global energy demands while addressing safety and environmental concerns.

In this work, we demonstrate the generation of high-performance tunable Raman solitons beyond 3 μm in a 10 cm, large-core (40 μm) fluorotellurite fiber. The pump source is a high-peak-power Raman soliton generated through soliton fission in a silica fiber. By further cascading the 10 cm highly nonlinear fluorotellurite fiber, this Raman soliton undergoes successive high-order soliton fission and soliton self-frequency shift with a tunable range of 2.7–3.3 μm. Such an ultra-short-length and ultra-large-core fiber significantly reduces the pulse width of the 3.3 μm Raman soliton to 55 fs, doubling the peak power to 2.3 MW compared to previous studies. Furthermore, owing to the seed’s high-repetition-frequency feature, the 3.3 μm Raman soliton’s power exceeds 2 W. These performance metrics represent the highest levels achieved for Raman solitons at wavelengths above 3 μm, offering a simple and effective new approach for generating high-peak-power femtosecond pulses in the mid-infrared spectral region.

High-energy, short-pulse laser-driven proton–boron (p–11B) fusion has attracted growing interest due to its aneutronic character and potential for clean energy generation. In this study, we report on two experimental campaigns carried out at the LFEX laser facility using petawatt-class laser systems (energy $\sim$1.2–1.4 kJ, pulse duration 2.7 ps, peak intensity $\sim$(2–3) × 1019 W/cm2). The experiments explored the influence of complex target geometries – including spherical, cylindrical and wedge-shaped configurations – on α-particle yield. Our results demonstrate that spherical targets can enhance α-particle production by up to two orders of magnitude compared to planar targets of identical composition and also lead to a noticeable shift of the α-particle energy spectrum toward higher values. Furthermore, we implemented a novel diagnostic technique for unambiguous α-particle detection using a CR-39 detector integrated into a Thomson parabola spectrometer. Particle-in-cell simulations performed with the Smilei code provide additional insight into the role of self-generated magnetic fields in modulating particle dynamics. These simulations highlight the critical interplay among target geometry, confinement effects and fusion efficiency. Overall, our findings underscore the potential of optimized target designs to significantly enhance fusion yield and α-particle output in p–11B fusion, with promising implications for the development of laser-driven α-particle sources and advanced clean energy concepts.

High-power fiber lasers generate local heat load extremes during their operation, which increase the fiber temperature and lead to adverse thermal effects, such as transverse mode instability or cladding/coating thermal damage. The local temperature extremes are usually located near the end of a fiber where the pump power is delivered. In this paper, longitudinally inhomogeneous doping concentration profiles are applied to reduce the heat load extremes. Utilizing a new degree of freedom, it is shown by both simulations and measurements that the maximal temperature along the fiber can be effectively decreased by using active fibers with an increasing concentration profile in the direction of the pumping power. The concept is studied by a comprehensive numerical model that considers temperature-dependent parameters and is also demonstrated by measurement on an in-house built thulium-doped fiber laser formed by spliced sections with different concentrations. The output power of 54 W with the slope efficiency exceeding 62% was reached.

This paper introduces a high single-pulse energy, narrow-linewidth mid-infrared self-optical parametric oscillator (mid-IR SOPO) with a cavity length of 120 mm and a Nd:MgO:PPLN crystal. To achieve high single-pulse energy and high peak power in mid-IR light sources, a LiNbO3 electro-optic Q-switch (EOQ) is introduced for the first time in a mid-IR SOPO. A narrow-linewidth EOQ-SOPO rate equation is formulated, and experiments are conducted using a single Fabry–Pérot etalon. At a 500 μs pump pulse width, a 4.71 mJ single-pulse idler light at 3838.2 nm is achieved, with a linewidth of 0.412 nm, single-pulse width of 4.78 ns and peak power of 985 kW. At 200 μs, the idler light at 3845.2 nm exhibits a minimum linewidth of 0.212 nm.

An all-silica-fiber thulium-doped fiber laser emitting at 0.82 μm on the transition from 3H4 to the ground state 3H6 outputs 105 W continuous-wave power and 555 W quasi-continuous-wave instantaneous power with 0.96% duty cycle in 240 μs rectangular pulses. The system comprises a double-clad thulium-doped fiber designed and fabricated in-house, incorporated into an all-fiber cavity and cladding-pumped by diode lasers at 0.79 μm. Co-lasing at 1.9 μm counteracts population trapping in 3F4. The slope efficiency reaches 64% and 77.5% under quasi-continuous-wave and continuous-wave operations, respectively. Under quasi-continuous-wave conditions, the beam quality M2 becomes 2.2 (beam parameter product: 0.57 mm mrad) and 2.45 (0.64 mm mrad) in orthogonal directions at approximately 250 W of instantaneous output power. In addition, a modified quasi-continuous-wave setup is continuously wavelength-tunable from 812 to 835 nm. We believe this is the first reported demonstration of high-power laser operation of the 3H4 → 3H6 transition in a thulium-doped fiber.

A technique developed to accurately simulate the amplification of back-reflected light through a multi-petawatt laser system is presented. Using the Frantz–Nodvik equation, we developed an iterative algorithm to simulate the amplification of the main beam as it propagates through solid-state multipass amplifiers, while also accounting for back-reflections from experimental targets and the residual gain within the crystals. Our technique builds on the theoretical model by estimating the energy levels after multiple passes through all amplifiers and refining the simulated data using a brute-force optimization algorithm. We also demonstrate an application of this tool aimed at evaluating machine safety: optimizing the laser system to minimize crystal gain in the post-pulse regime and, consequently, the amplification of back-reflections, while taking advantage of the B-integral.

A broadband, antireflective metasurface optic on a silica substrate is subjected to laser-induced damage-threshold measurements to quantify its performance under exposure to high-intensity/fluence laser pulses in the near-infrared at four pulse durations, ranging from 20 fs to 1.4 ns. The performance of the metasurface is benchmarked against that obtained from an equivalent bare fused-silica substrate that did not receive reactive-ion-etching metasurface treatment. Results showed that the damage threshold of the antireflective metasurface was always lower than the input-surface damage threshold of the untreated substrate. The damage initiations with nanosecond and picosecond pulses resulted in localized modification and removal of the nanostructures, whereas the onset of laser-induced modification with 20-fs pulses in a vacuum environment manifested as changes in the optical and electronic properties without significant material removal. The broader goal of this work is to develop a preliminary understanding of the laser-induced failure mechanisms of silica-based metasurface optics.

Coherent beam combining (CBC) of laser arrays is increasingly attracting attention for generating free-space structured light, unlocking greater potential in aspects such as power scaling, editing flexibility and high-quality light field creation. However, achieving stable phase locking in a CBC system with massive laser channels still remains a great challenge, especially in the presence of heavy phase noise. Here, we propose an efficient phase-locking method for a laser array with more than 1000 channels by leveraging a deep convolutional neural network for the first time. The key insight is that, by elegantly designing the generation strategy of training samples, the learning burden can be dramatically relieved from the structured data, which enables accurate prediction of the phase distribution. We demonstrate our method in a simulated tiled aperture CBC system with dynamic phase noise and extend it to simultaneously generate orbital angular momentum (OAM) beams with a substantial number of OAM modes.

Ultraintense laser–plasma experiments generate a variety of high-energy radiations, including nonlinear inverse Compton scattered (NCS) X-rays, which are expected to be a key experimental observable as we transition into the quantum electrodynamic plasma regime. However, there is also a high bremsstrahlung X-ray background that reduces our ability to observe NCS X-rays. Previous numerical studies comparing NCS and bremsstrahlung emissions fail to capture the full temporal emission of both processes. We present for the first time two-dimensional particle-in-cell (PIC) and three-dimensional hybrid-PIC EPOCH simulations that capture up to 150 ps of the laser–plasma interaction and directly compare the NCS and bremsstrahlung emissions for a plastic target for intensities of ${10}^{20}{-}{10}^{23}$ W/cm2. We present angular distribution plots where the NCS emission is seen to dominate at intensities greater than 5$\times {10}^{21}$ W/cm2 and the target design is seen to successfully divert the bremsstrahlung signal away from the NCS lobe regions, making the experimental observation of nonlinear inverse Compton scattering at lower intensities more likely.

High-power 808 nm vertical-cavity surface-emitting laser (VCSEL) chips have unique characteristics for neodymium-doped yttrium aluminum garnet (Nd:YAG) laser pumping compared with conventional edge-emitting laser bars, including a chip surface with high reflectivity, near flat top distribution in the near field, larger emitting width and smaller divergence. A novel symmetrical pump cavity with an inter-reflective chamber was invented by introducing even-numbered pumping geometry and removing the conventional internal reflector. Several optical tuning measures were taken to improve the uniformity of the pumping distribution, including power and spectrum balancing in the cross-section and the long axis of the laser rod, a diffuse mechanism in the pump chamber by a frosted flow tube and optional eccentric pumping geometry. A series of VCSEL pumping experiments were conducted and optical tuning measures were evaluated through distribution profiles and efficiencies. A new design philosophy for the VCSEL side-pumped Nd:YAG laser cavity was finally developed.

This paper introduces a novel ray-tracing methodology for various gradient-index materials, particularly plasmas. The proposed approach utilizes adaptive-step Runge–Kutta integration to compute ray trajectories while incorporating an innovative rasterization step for ray energy deposition. By removing the requirement for rays to terminate at cell interfaces – a limitation inherent in earlier cell-confined approaches – the numerical formulation of ray motion becomes independent of specific domain geometries. This facilitates a unified and concise tracing method compatible with all commonly used curvilinear coordinate systems in laser–plasma simulations, which were previously unsupported or prohibitively complex under cell-confined frameworks. Numerical experiments demonstrate the algorithm’s stability and versatility in capturing diverse ray physics across reduced-dimensional planar, cylindrical and spherical coordinate systems. We anticipate that the rasterization-based approach will pave the way for the development of a generalized ray-tracing toolkit applicable to a broad range of fluid simulations and synthetic optical diagnostics.

We present a fully three-dimensional kinetic framework for modeling intense short pulse lasers interacting with dielectric materials. Our work modifies the open-source particle-in-cell code EPOCH to include new models for photoionization and dielectric optical response. We use this framework to model the laser-induced damage of dielectric materials by few-cycle laser pulses. The framework is benchmarked against experimental results for bulk silica targets and then applied to model multi-layer dielectric mirrors with a sequence of simulations with varying laser fluence. This allows us to better understand the laser damage process by providing new insight into energy absorption, excited particle dynamics and nonthermal excited particle distributions. We compare common damage threshold metrics based on the energy density and excited electron density.

A dual-beam platform is developed for all-optical Thomson/Compton scattering, with versatile parameter tuning capabilities including electron energy, radiation energy, radiation polarization, etc. By integrating this platform with a 200 TW Ti:sapphire laser system, we demonstrate the generation of inverse Compton scattering X-/gamma-rays with tunable energies ranging from tens of keV to MeV. The polarization of X-/gamma-rays is manipulated by adjusting the polarization of the scattering laser. In the near future, by combining this platform with multi-PW laser facilities, our goal is to explore the transition from nonlinear Thomson scattering to nonlinear Compton scattering, ultimately verifying theories related to strong-field quantum electrodynamics effects induced by extreme scattering.

A reduced dispersion relation for multibeam laser–plasma instability is derived. The dispersion relation includes the combined effects of self-coupling and interaction with other beams by sharing a common scattered light (SL modes) and by sharing a common plasma wave (SP modes). The latter two have the most prominent collective effects of all. We have solved the dispersion relation numerically for stimulated Raman scattering, and set different beam configurations and polarizations to discuss the spatial distributions of the temporal growth rate. The instability in the beam overlapping region is complicated, but there are still a few simple rules that govern the system, such as the dominancy of SL modes and subdominancy of backscattering and SP modes. The maximum growth rate always occurs at these special modes, or a new mode formed by combining two or three of the special modes. The reduced model provides us with the ability to understand the underlying physics of multibeam instabilities under general laser and plasma conditions.

We propose a B-integral management strategy for manipulating the nonlinear effects by employing a discrete single-crystal fiber (SCF) configuration, enabling direct amplification of 2-μm femtosecond pulses at high repetition rates without additional pulse picking, stretching and compression. The system delivers an average power of more than 56 W at 75.45 MHz with extremely high extraction efficiency (>55%) and near-diffraction-limited beam quality (M2 < 1.2). The dynamic evolution of the optical spectra and temporal properties in the power amplifier reveals that detrimental nonlinear effects are largely suppressed due to the low accumulated nonlinear phase shift in the discrete SCF layout. This straightforward, compact and relatively simple approach is expected to open a new route to the amplification of 2-μm ultrashort pulses at MHz and kHz repetition rates to achieve high average/peak powers, thereby offering exciting prospects for applications in modern nonlinear photonics.

We present a high-power mid-infrared single-frequency pulsed fiber laser (SFPFL) with a tunable wavelength range from 2712.3 to 2793.2 nm. The single-frequency operation is achieved through a compound cavity design that incorporates a germanium etalon and a diffraction grating, resulting in an exceptionally narrow seed linewidth of approximately 780 kHz. Employing a master oscillator power amplifier configuration, we attain a maximum average output power of 2.6 W at 2789.4 nm, with a pulse repetition rate of 173 kHz, a pulse energy of 15 μJ and a narrow linewidth of approximately 850 kHz. This achievement underscores the potential of the mid-infrared SFPFL system for applications requiring high coherence and high power, such as high-resolution molecular spectroscopy, precision chemical identification and nonlinear frequency conversion.