In 2019 we published the extensive review paper ‘Petawatt and exawatt class lasers worldwide’ in High Power Laser Science and Engineering. We are delighted that the review has achieved over 1000 citations on Google Scholar and over 750 on Web of Science. We take this opportunity to reflect on the current state of the field.

An exawatt-class peak-power laser architecture, based on a single, large-aperture Nd:mixed-glass amplifier combined with a technique called chirped pulse juxtaposed with beam amplification (CPJBA) is proposed to significantly extend laser capabilities beyond the present 10 PW state-of-the-art for ultra-high-intensity lasers. CPJBA utilizes a space–time coupled chirped-beam pulse to enhance the temporal compression of a fixed-aperture grating pair in a novel six-grating compressor arrangement. With this, an appropriately structured, 20-ns stretched pulse can be compressed to a transform limit of 100 fs using a maximum grating aperture of 2 m. This enables the extraction of 25 kJ of energy from a single, large-aperture Nd:glass beamline while staying below the B-integral threshold. This paper presents the numerical modeling of the various novel sub-systems required for this exawatt-class laser architecture. In particular, the unique spatial and temporal pulse distortions present during amplification using CPJBA, and the strategies used to mitigate them, are discussed.

Polarized particle sources have a plethora of applications, ranging from deep-inelastic scattering to nuclear fusion. One crucial challenge in laser–plasma interaction is maintaining the initial polarization of the target. Here, we propose the acceleration of spin-polarized helium-3 from near-critical density targets using high-intensity Laguerre–Gaussian laser pulses. Three-dimensional particle-in-cell simulations show that magnetic vortex acceleration with these modes yields high polarization at the $90\%$ level, while also providing low-divergence beams.

Transverse mode instability (TMI) is a primary limitation for power scaling in high-brightness fiber lasers. This paper reports observation of the TMI effect in the process of supercontinuum generation, and demonstrates a 993 W linearly polarized supercontinuum ranging from 800 to 2000 nm through an amplifier-based structure. To mitigate TMI, three strategies are implemented: repetition rate doubling to reduce peak power and mitigate the thermal loading; reducing the bending radius of the gain fiber to suppress higher-order modes; optimizing the polarization extinction ratio of the pre-amplifier. TMI-induced beam quality degradation and power-scaling limitation resemble those of conventional fiber lasers. In particular, burr-like spectral fluctuations in supercontinuum sources are observed upon the onset of TMI. This work deepens the understanding of TMI mechanisms in broadband laser systems and offers critical guidance for power scaling of high-power supercontinuum sources.

We report here the characteristics of a high-power continuous-wave mid-infrared (mid-IR) fiber light source based on nested anti-resonant hollow-core fiber (AR-HCF) filled with HBr gas. A homemade hundred-watt-level 2 μm narrow-linewidth fiber laser is constructed as the pump source. The pump source is forward injected into the AR-HCF through a single-pass configuration. A maximum output power of 10.4 W at 4.16 μm with excellent beam quality (M2) of approximately 1.05 is achieved in a 4.8 m long AR-HCF at gas pressure of 9.9 mbar, with a slope efficiency of 20% relative to the absorbed pump power. The mid-IR light source maintains good stability during long-term operation. To the best of our knowledge, this is the highest output power for silica-based fiber light sources beyond 4 μm. This work demonstrates the significant capability of power scaling in a gas-filled AR-HCF mid-IR light source.

A setup based on magnetic levitation technologies was created to demonstrate credible solutions in the area of cryogenic fuel target (CFT) noncontact transport and their repeatable injection. A necessary element is a levitating CFT carrier made from Type-II, high-temperature superconductors (HTSCs). This paper discusses four principal categories: (1) a tandem HTSC–carrier configuration; (2) a linear permanent magnet guideway to maintain a friction-free acceleration of the HTSC–carrier; (3) a spring mechanism for driving the HTSC–carrier; (4) an optical tracking system to control the HTSC–carrier and injected targets motion. In demo experiments (T = 80 K), a magnetic track oriented S-N-S (size 360 mm × 24 mm × 5 mm) had a large cross-sectional gradient ΔВ = 0.33 T at the edges of the track forming the so-called ‘magnetic wall’ to provide a lateral stability of the HTSC–carrier trajectory. Acceleration and braking of the HTSC–carrier containing two surrogate targets was recorded, followed by targets injection with a rate of 10–25 Hz.

Laser-driven plasma wakefield acceleration (LWFA) offers exceptionally high acceleration gradients and can produce high-brightness electron beams. However, the laser-to-electron energy conversion efficiency typically remains limited to a few percent. Theoretically, the self-mode transition from LWFA to beam-driven plasma wakefield acceleration (PWFA) provides a pathway for fully utilizing the laser energy. Here, we demonstrate the single-stage LPWFA (hybrid LWFA–PWFA) scheme, validated through comparative experiments using a 300 TW tightly focused laser interacting with sub-critical density nitrogen gas targets. The experiments produce an electron beam with charge of approximately 31 nC above 6 MeV and approximately 116 nC above 2 MeV. The laser-to-electron energy conversion efficiency is approximately 6.1% (>6 MeV) and 16.4% (>2 MeV), respectively. Particle-in-cell simulations confirm that the single-stage LPWFA mechanism depletes the laser energy and enables continual electron injection. This high-charge, multi-MeV electron beam has great value in the generation of high-brightness $\unicode{x3b3}$-rays and high-flux neutron sources.

Multi-plane light conversion (MPLC) is a versatile technique that enables arbitrary manipulation of optical fields, and is numerically investigated as a novel avenue for coherent beam combining (CBC) applications. The optical parameters have been investigated to guide the MPLC design, indicating that the number of phase planes and plane spacing serve as pivotal factors. The channel scalability is simulated, revealing that the plane spacing should be increased in a larger array to maintain high performance under a few-plane limit. CBC of up to 1027 lasers has been numerically demonstrated with near-diffraction-limited beam quality (M2 of 1.16 and combining efficiency close to 100%) with only seven phase plates. Beam steering is investigated, revealing that steering capability is related to both the number of multiplexed modes in MPLC and their mode fidelities, and the main-lobe power ratio of 87.1% at one divergence angle is achieved in a 10-mode MPLC with five phase plates.

In this work, an innovative scheme is proposed that exploits the response of magnetized plasmas to realize a refractive index exceeding unity for right circularly polarized waves. Using two- and three-dimensional particle-in-cell simulations with the OSIRIS 4.0 framework, it is shown that a shaped magnetized plasma lens (MPL) can act as a glass/solid-state-based convex lens, enhancing laser intensity via transverse focusing. Moreover, by integrating three key ingredients, a tailored plasma lens geometry, a spatially structured strong magnetic field and a suitably chirped laser pulse, simultaneous focusing and compression of the pulse has been achieved. The simulations reveal up to a 100-fold increase in laser intensity, enabled by the combined action of the MPL and the chirped pulse profile. With recent advances in high-field magnet technology, shaped plasma targets and controlled chirped laser systems, this approach offers a promising pathway toward experimentally reaching extreme intensities.

We present an experimental study on electron and X-ray generation from the interaction of a hundreds of TW femtosecond laser with microchannels. Leveraging the guiding effect of the channel structure on both the laser and electrons, a well-collimated electron beam is achieved, with a beam charge of 1.5 nC (>10 MeV), a slope temperature of 9.1 MeV and a nearly constant divergence angle (~14°) over a broad energy range (10–50 MeV). Meanwhile, we demonstrate a ring-shaped X-ray source generated through bremsstrahlung radiation mechanism from electrons collision with channel walls, exhibiting a characteristic energy of 90 keV and emittance of 0.8 mm mrad. Three-dimensional simulations elucidate the underlying acceleration dynamics. It is found that elongated channels facilitate the formation of well-collimated electron beams. These results establish the foundation for applications of channel guided electrons and secondary radiation sources and represent a key step toward the controlled manipulation of particle sources in laser-driven plasmas.

We report on the development of a carrier-envelope phase (CEP)-stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad root mean square. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability and sub-two-cycle pulse durations. Similar to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source, this newly developed system is accessible to the international research community in peer-reviewed open user calls of the Extreme Light Infrastructure European Research Infrastructure Consortium.

A high-power, efficient pulsed amplifier based on a laser diode end-pumped ytterbium-doped yttrium aluminum garnet (Yb:YAG) rod was demonstrated. The crystal’s reabsorption was effectively minimized by optimizing the amplifier’s parameters through numerical simulations, leading to a power extraction efficiency of up to 56%. A compensation method was applied to correct the beam distortion caused by thermally induced birefringence in the Yb:YAG rod. Furthermore, a remarkably low depolarization rate of 2.2% was achieved, along with an average power output of 483 W. The beam quality factor (M2) of the amplified signal was improved to below 1.3, following compensation of the thermally induced spherical aberration using a phase plate. To the best of our knowledge, this achievement represents the highest average power and efficiency for fundamental mode operation in an Yb:YAG rod amplifier at room temperature.

The traditional design of laser drivers for inertial confinement fusion (ICF) is highly dependent on coherent laser light fields, which have significant advantages in achieving harmonic conversion and enhancing amplification efficiency. However, they also bring the core challenge of achieving uniform irradiation. This paper investigates the dynamic evolution process of uniform irradiation of multi-mode spatiotemporal light fields and analyzes the influence mechanism of spatiotemporal coherence on irradiation uniformity with different integration times. By balancing the relationship between the spatiotemporal coherence of the light field and uniform irradiation, we explore a possible scheme to alleviate the beam smoothing problem while satisfying the basic requirements of laser amplification and high-efficiency harmonic conversion. Based on this scheme, the overall architecture of the ICF laser driver is constructed.

Cylindrical vector (CV) $\gamma$ rays can introduce spatially structured polarization as a new degree of freedom for fundamental research and practical applications. However, their generation and control remain largely unexplored. Here, we put forward a novel method to generate CV $\gamma$ rays with tunable hybrid polarization via a rotating electron beam interacting with a solid foil. In this process, the beam generates a coherent transition radiation field and subsequently emits $\gamma$ rays through nonlinear Compton scattering. By manipulating the initial azimuthal momentum of the beam, the polarization angle of $\gamma$ rays relative to the transverse momentum can be controlled, yielding tunable hybrid CV polarization states. Three-dimensional spin-resolved particle-in-cell simulations demonstrate continuous tuning of the polarization angle across $\left(-90{}^{\circ},\ 90{}^{\circ}\right)$ with a high polarization degree exceeding 60%. Our work contributes to the development of structured $\gamma$ rays, potentially opening up new avenues in high-energy physics, nuclear science and laboratory astrophysics.