We report a Nd:MgO:periodically poled lithium niobate-based 2 μm self -optical parametric oscillator (self-OPO) that enables co-tunable dual-wavelength emission and programmable pulse-burst encoded output. Laser gain and nonlinear frequency conversion are integrated in a single crystal. Field-programmable gate array-controlled stepwise acousto-optic Q-switching dynamically modulates the intracavity loss to regulate the sub-pulse number, spacing and amplitude. By tuning the crystal temperature from 76°C to 83.4°C, the two wavelength branches are tuned from 2.05/2.30 μm to a degenerate output at 2.168 μm. Alternating 1-3-1-3 burst sequences and amplitude-based information encoding are demonstrated. In the 1-3-1-3 mode, the oscillator delivers 1.92 W average output power, 10.6% slope efficiency and 6.94% optical-to-optical conversion efficiency. These results demonstrate source-level integration of wavelength tuning and temporal encoding in a single-crystal self-OPO.

The under-construction high-energy laser facility SG-X for the double-cone ignition scheme will deliver multiple picosecond laser beams with the crossing angle up to $60{}^{\circ}$. Here, we investigate the generation and transport of fast electrons driven by two relativistic picosecond laser pulses with an angle by particle-in-cell simulations. When the angle reaches $60{}^{\circ}$, the fast-electron generation decreases compared to that with an optimized angle around $20{}^{\circ}$. The decrease is associated with weaker and less stable interference-induced surface structures. The fast-electron generation can be significantly enhanced by shifting the crossing point of the pulses from the vacuum–plasma boundary into the plasma interior. The optimal crossing point is near the laser hole boring depth. We also find that an externally applied magnetic field can effectively guide fast-electron transport in this optimized geometry. The guiding saturates around a strength of $0.5\;\mathrm{kT}$ under the present simulation parameters, which is achievable in previous experiments.

High-quality single-shot measurement for the complete characterization of ultrafast light fields remains challenging. This paper proposes SS-TSPS-SPIDER, a single-shot scheme combining spectral phase interferometry for direct electric-field reconstruction (SPIDER) with two-step phase-shifting (TSPS). This design uses a non-polarizing beam splitter to combine two orthogonally incident sum-frequency pulses, from whose two outputs it acquires two spectral interferograms with a π-phase shift. Our experimental results demonstrate that the setup can measure the group delay dispersion of a 3-mm-thick BK7 glass with an error of less than 14.1 mrad over a 45 THz range centered at 375 THz, corresponding to a 10 dB spectral bandwidth, exhibiting superior measurement accuracy and a higher signal-to-noise ratio compared with traditional SPIDER. Thus, SS-TSPS-SPIDER is well suited for characterizing ultra-intense, low-repetition-rate or single-shot ultrashort pulses, which are vital in strong-field physics, attosecond science and other extreme-physics frontiers .

Fiber bending is a common and practical method to suppress transverse mode instability (TMI) in high-power fiber lasers. Tight bending and loose bending are respectively applicable to fiber lasers with different mode characteristics for TMI suppression. This study analyzes the applicability of the two approaches in conventional and low-numerical aperture (NA) fibers, finding that compared to conventional large-core fibers that predominantly use loose bending to improve TMI threshold, low-NA fibers have the potential to utilize both methods for TMI suppression, although their effectiveness differs significantly. Simulation results reveal that large-core low-NA fibers exhibit a more pronounced effect on TMI suppression by tight bending and there exists an optimal bending range for the maximum TMI threshold. Guided by these findings, a low-NA Yb-doped fiber with core/cladding diameters of 35/250 μm was fabricated and experiments were subsequently conducted. By optimizing bending, an 8-kW single-mode output tandem-pumping fiber amplifier is obtained.

While high-power 780 nm pulsed lasers are essential for atom interferometry, scaling existing sources is restricted by nonlinear effects and material damage. In this work, we demonstrate a robust 780 nm source based on single-pass frequency doubling in a lithium triborate crystal. The source is driven by a high-power 1560 nm master oscillator fiber power amplifier. Frequency doubling is performed at a maximum fundamental power of 68.7 W, achieving an average output power of 17.2 W at 780 nm at a conversion efficiency of 25.03%. The source operates at a 10 MHz repetition rate with a pulse duration of approximately 2 ns and excellent beam quality (M2 ≈ 1.06). To the best of our knowledge, this represents the highest average power reported for a nanosecond 780 nm source, offering a scalable solution for high-flux quantum sensing.

Circular laser beam polarization is known to be an alternative tool to increase the damage resistance of optical components to ultraviolet (UV) laser irradiation. In this work, we carefully study its influence on the nonlinear processes mainly responsible for laser damage, which are the Kerr effect and the photo-ionization process. In particular, we show that the circular polarization benefit in the UV domain is mainly observable on thick optical samples. Whatever the laser beam spatial shape is, there is no gain when using circular polarization with thin optical components for nanosecond UV laser beam when the fluence is lower than 25 J/cm2. Moreover, our measurements show that laser polarization has no impact on damage growth.

Backward Raman amplification (BRA) in plasma, as a promising amplification technique, has been theoretically predicted to achieve multi-petawatt peak powers using millimeter-scale plasmas. However, under stronger intensity or high plasma densities, self-focusing, filamentation and degradation of pulse focusability often arise. To address these, we propose a scheme that suppresses laser pulse filamentation in high-density plasmas by employing a structured plasma. This approach exploits the balance between self-focusing and diffraction in different layers, thereby preserving the Gaussian profile and focusability of laser pulses. Nonlinear envelope models and particle-in-cell simulations confirm that the structured plasma not only improves energy conversion efficiency but also maintains excellent focusability. In contrast to conventional BRA, our scheme promotes the transition to the high-gain region, offering the merits of high efficiency, high spatial mode quality and great focusability, which may be a key step for the improvement of the competitiveness and practicality of plasma-based amplifiers.

The pulse width, temporal contrast and focal spot are critical parameters to characterize the performance of petawatt-scale femtosecond laser systems. In this study, based on the Shenguang II femtosecond petawatt laser facility, we systematically investigate the influence of spatial-temporal coupling on chirped pulses during the optical parametric amplification, parametric fluorescence in the frontend-small-signal amplification, wavefront distortion in high-energy amplification and spatial dispersion induced by large-aperture optical components – all affecting the pulse width and temporal contrast. Through comprehensive optimization, we achieve a focused spot approaching the diffraction limit of approximately 4 μm alongside a remarkable temporal contrast exceeding 1011 at 10 ps before the pulse peak under the full performance of pulse energy higher than 30 J and pulse width of 20–30 fs. This in-depth work provides insight toward the ideal outputs for future femtosecond petawatt lasers.

Enhancing laser–plasma coupling in picosecond petawatt laser–solid interactions is important for generating intense particle and radiation sources. Here, we report experiments and particle-in-cell simulations of dual petawatt-class picosecond laser pulses interacting with planar metal foils at the SG-II Upgrade facility. In the most directly matched comparison, dual-pulse irradiation increases the electron cutoff energy from 9.3 to 33.8 MeV, enhances the total electron yield per steradian by a factor of 8.64 and raises the charge of electrons above 5 MeV by a factor of 30.22. The effective electron temperature is correspondingly increased. The peak electromagnetic pulse amplitude and neutron yield also increase. Simulations show that the first pulse reshapes the front-side plasma conditions, leading to stronger coupling of the delayed second pulse and enhanced electron acceleration via direct laser acceleration. These results suggest that dual-pulse driving provides an effective route to tailoring laser–foil coupling through temporal control and enhancing multiple secondary sources.

Quasi-Bessel beams produced by axiparabolas are increasingly used in high-intensity laser applications, yet their longitudinal profiles exhibit unwanted oscillations that limit their effectiveness. Here we identify the physical origin of these distortions and develop a general strategy to control the on-axis intensity of extended focal lines. By combining analytical insight with numerical and experimental validation, we show how both smooth and sharply structured longitudinal profiles can be reliably produced. This establishes a robust framework for tailoring quasi-Bessel beams in regimes relevant to laser–plasma acceleration, advanced photon sources and other high-field applications.

The double-cone ignition (DCI) scheme offers a promising approach to high-gain inertial confinement fusion with reduced laser drive energy. The hydrodynamic evolution at the fuel–cone interface during implosion is critical to ignition performance. Herein, we present a combined experimental and simulation study of interfacial hydrodynamics in DCI experiments performed on the ShenGuang-II Upgrade laser facility, employing picosecond time-resolved Cu Kα X-ray radiography and three-dimensional radiation-hydrodynamics simulations. We demonstrate that X-ray pre-ablation of the gold-cone inner wall generates a slow-velocity gold pre-plasma, and the resulting tangential velocity shear between this pre-plasma and the high-speed CH fuel flow triggers the Kelvin–Helmholtz instability (KHI). This instability significantly enhances gold–fuel mixing, induces severe radiative cooling via bremsstrahlung losses and thereby degrades ignition conditions. To mitigate this issue, we propose and experimentally validate a CH inner-wall coating for the gold cone. This coating suppresses the formation of gold pre-plasma, reduces the KHI growth rate and substantially lowers the gold mass fraction in the central colliding plasma area. Excellent agreement between experimental measurements of Cu Kα transmittance and simulation results confirms the effectiveness of the coating strategy. These findings offer a practical method for improving DCI performance and offer important insights into the dynamics of KHI in high-energy-density interfacial flows.

Designing multilayer dielectric gratings (MLDGs) for high-power laser systems requires minimizing local enhancement of the electric-field intensity (EFI) while maximizing the diffraction efficiency (DE). By introducing an extended modal analysis that incorporates both propagation and interfacial phases, the periodic dependence of DE and EFI on the matching layer thickness is revealed. A phase-matching design framework that aligns the DE peak with the EFI valley is established, with the peak EFI relocated from the interior of the grating structure to the air interface, achieving substantial internal field suppression. The results lie within manufacturable tolerance windows to achieve optimal performance trade-offs. The robustness of the framework is validated by changing the grating material from low-index (SiO2) to high-index (HfO2) dielectrics. This work facilitates the comparison of design limits across materials, concurrently generates fabrication tolerances and offers solutions from material selection to preparation feasibility for designing MLDGs for chirped-pulse amplification and spectral beam combining systems.

Efficient generation of microjoule-level long-wave mid-infrared pulses at high repetition rates remains challenging because conventional difference-frequency generation (DFG) systems typically rely on white-light-seeded optical parametric amplification (OPA) chains with limited overall efficiency. Here we demonstrate a Raman-shifted multi-pass-cell-driven DFG scheme for tunable 5.6–11 μm mid-infrared generation. A He–CO${}_2$ molecular-gas multi-pass cell (MPC) efficiently converts 1025 nm pump pulses into a 1.10–1.25 μm signal through Raman-dominated red shifting, with a filtered-signal conversion efficiency of 17%–32% at repetition rates up to 40 kHz. The generated signal is combined with a synchronized 1025 nm pump beam and converted in a LiGaS${}_2$ crystal. The system delivers 179 mW at 6 μm, corresponding to 4.5 μJ pulses and a pump-to-idler efficiency of 6.4%, and 168 mW at 7 μm with a maximum quantum efficiency of 41%. By replacing the OPA-based signal-generation chain with an efficient Raman-shifted molecular-gas MPC, this architecture offers a scalable route toward high-repetition-rate, high-energy long-wave mid-infrared ultrafast sources.

Accurate spatio-temporal and spatio-spectral metrology is critical to the characterization and use of ultra-short, high-power lasers. The emergence of few-cycle pulses, with bandwidths of tens or hundreds of nanometers, poses a significant challenge to existing metrology techniques. This is due to a combination of large discrepancies in sensor sensitivity and significant variations in the pulse’s spectral intensity at those wavelengths. In this paper, the authors propose spectral filtering and stitching of the measurements as a robust, simple solution that enhances the dynamic range of the measurements, allowing accurate few-cycle pulse reconstruction. This enhancement is demonstrated using INSIGHT – the most commonly used spatio-spectral measurement device – as well as using the IMPALA technique and spatially resolved Fourier transform spectrometry.

High-brightness picosecond green lasers are important for precision processing and advanced manufacturing, yet lithium triborate (LBO)-based picosecond second-harmonic generation often faces a trade-off between brightness and temperature bandwidth. Here we treat the longitudinal phase-mismatch trajectory as a design degree of freedom and propose a brightness-oriented adiabatic trajectory that jointly optimizes conversion efficiency and beam quality. Through parametric trajectory screening and longitudinal temperature-profile mapping, the proposed trajectory was implemented in a 50-mm-long LBO crystal. Experiments produced 79.87 W of picosecond green output at 532.286 nm, corresponding to a light-to-light conversion efficiency of 62.4%, with a beam quality factor of ${M}^2=1.24$. Compared with a conventional efficiency-oriented adiabatic trajectory, the proposed trajectory increased brightness by suppressing beam quality degradation rather than maximizing conversion efficiency alone. We further introduce the brightness temperature bandwidth, which reached 25°C for the proposed trajectory, 39% larger than the 18°C value obtained with the conventional trajectory, but smaller than the corresponding efficiency temperature bandwidth of 34°C. This difference indicates that an efficiency-defined bandwidth can overestimate the practically usable operating range.

Multi-beam-pumped optical parametric chirped-pulse amplification (OPCPA) systems suffer from parasitic parametric diffraction caused by nonlinear cross-coupling among intense laser beams, which severely degrades conversion efficiency. Although quasi-parametric amplification has been proposed to suppress cascaded nonlinear effects, its quantitative effectiveness in mitigating multi-beam parametric diffraction has remained experimentally unexplored. In this work, we experimentally demonstrate a quasi-parametric chirped-pulse amplification (QPCPA) scheme that actively depletes idler waves in a Sm-doped yttrium calcium oxyborate crystal to suppress parametric diffraction. We characterize the dependence of parametric diffraction on the pump beam angle and intensity, and evaluate the suppression performance provided by idler dissipation. Experimental results in a two-beam-pumped configuration show that the QPCPA scheme reduces pump-to-diffraction conversion by more than 60% compared to conventional OPCPA. Robust cross-coupling suppression is maintained across a range of operating conditions. By establishing a clear experimental link between idler dissipation and diffraction suppression, this work provides a practical pathway for scalable energy enhancement in multi-beam nonlinear combining systems, supporting the advancement of high-energy OPCPA architectures.

Laser wakefield acceleration, characterized by the extremely high electric field gradient exceeding $100\;\mathrm{GV}/\mathrm{m}$, is regarded as a compact and cost-affordable technology for the next generation of particle colliders and light sources. However, it has always been a major challenge to effectively increase the energy transfer efficiency from the laser to the accelerated beam, while ensuring the beam quality remains suitable for practical applications. This study demonstrates two-step dechirping of a nanocoulomb-class accelerated electron beam using shorter laser pulses. The electron beams with an energy spread of 5% can be generated with the energy transfer efficiency of 10%–30% in a large parameter space. For example, an electron beam with an energy of 420 MeV, a charge of 5.5 nC and an energy spread of approximately 10% can be produced using an 8.3 J laser pulse with a duration of 7.2 fs.