We demonstrate real-time wavefront correction in a high-energy high-average-power DiPOLE100/Bivoj laser using adaptive optics. A bimorph deformable mirror and a Shack–Hartmann wavefront sensor reduced wavefront error 10-fold and improved the Strehl ratio 11-fold. Design aspects such as the deformable mirror actuator geometry, optimal placement and loop frequency are discussed for integration into next-generation high-energy high-average-power lasers.

Femtosecond laser-induced filamentation typically exhibits pronounced spectral broadening, featuring a bright central white core encircled by concentric colored rings that span from the ultraviolet to the visible range and extend into the infrared. While ionization, self-steepening and self-phase modulation are widely accepted as explanations for the white spot, the underlying physics of colored rings remain inadequately understood by current models, such as Cherenkov radiation and four-wave mixing. In this study, inspired by the observation of similar discrete colored rings produced by cascaded four-wave mixing (CFWM) of intersecting beams, we systematically investigated the relationship between the colored rings in the white-light supercontinuum and CFWM. The CFWM model accurately predicted the correlation between color and divergence angles, thereby enhancing our understanding of spectral broadening in filamentation and providing guidance for optimizing the conversion efficiency and configuration of multi-wavelength ultrashort optical pulses in both spatial and spectral domains.

We present an experimental study of proton acceleration driven by femtosecond multi-PW lasers of three different prepulse parameters with the peak laser intensity of 1.2 × 1021 W/cm2 irradiating micrometre-thick metal foils. For 4-μm-thick copper foils, the highest-energy proton beam of 58.9 MeV is generated with the moderate-contrast laser, while the low-contrast or high-contrast lasers result in the lower proton cutoff energies. The one-dimensional hydrodynamic and two-dimensional particle-in-cell simulations indicate that the front preplasma of foils induced by the laser prepulse can enhance electron acceleration and in turn improve proton acceleration, while the rear preplasma will weaken the sheath field and be unfavourable for accelerating ions. For the case of the moderate contrast, the scale length of the front preplasma is long enough to generate high-temperature electrons compared to the high-contrast case, and the scale length of the rear preplasma is so short that the sheath field still remains strong compared with the low-contrast case, which is advantageous for generating high-energy protons. Meanwhile, a concrete map is theoretically given for accelerating higher-energy protons. This work extends the concept of the prepulse effect on target normal sheath acceleration (TNSA) to a wider range of laser parameters (multi-PW, 1021 W/cm2), representing an important step towards potential applications of TNSA-driven proton sources, especially considering that PW and even 10 PW laser facilities exist all around the world.

High-power laser beamlines typically operate with fixed focusing conditions, limiting the focal spot size and peak intensity. To mitigate these restrictions, prior studies used curved plasma mirrors to adjust the F-number to a specific value. Here, a double-plasma-mirror (DPM) system including spherical optics in a telescope configuration is implemented to adapt the F-number of a multi-petawatt (PW) laser beam resulting in adjustability within a range of intensities. The system is optimized to minimize focal aberrations. A dedicated imaging system is used to evaluate focus quality and the DPM reflectivity at the multi-PW level. Temporal contrast enhancement of the reflected beam is additionally demonstrated, as evidenced by higher particle yield and proton kinetic energy from nanometer-thick foils, compared to results without DPMs. These findings enable multi-PW laser facilities to explore more extreme laser–plasma conditions that require ultra-high temporal contrast and intensity, while expanding their capabilities in intensity adjustment beyond designed specifications.

A 2.05 μm holmium-doped yttrium lithium fluoride (Ho:YLF) master oscillator power amplifier system with both high average power and high pulse energy operating at a 1 kHz repetition rate is demonstrated, achieving a maximum output power of 280 W with a pulse width of 14.5 ns. The system comprises three-stage amplifiers, boosting a 20 W seed laser to output powers of 110, 205 and 280 W, corresponding to extraction efficiencies of 46.1%, 45.0% and 34.9%, respectively. At maximum output, the system exhibits excellent beam quality (Mx2 = 1.22 and My2 = 1.23) and power stability (root mean square = 0.5% over 30 min). To the best of our knowledge, this work reports the highest pulse energy (280 mJ) achieved for a 2 μm laser operating at a kHz repetition rate. In addition, a slice model of an end-pumped quasi-three-level laser amplifier was developed to analyze the output limitations of multi-stage Ho:YLF amplifiers based on rod geometry, providing theoretical support for the experimental results.

We demonstrate a high-power, flexibly tunable dual-pulse laser via temporal modulation techniques to overcome conventional systems’ fixed pulse width and temporal interval constraints, enhancing precision micro/nanofabrication and nonlinear photonics applications. By combining dispersion-engineered seed pulse shaping for adjustable pulse widths (5.6 ps and 0.38–0.47 ns) with optical-delay synchronized interval tuning (from –4 to 12.5 ns), the system achieves wide flexibility in pulse configuration. Furthermore, detailed nonlinear dynamics studies reveal the picosecond component exhibits reduced amplifier efficiency versus the nanosecond component, primarily due to peak-power-driven irreversible energy transfer to Raman-shifted wavelengths. This unique combination of features enables remarkable performance: 1092 W average power at 16 MHz with precisely tailored 15.9 ps/0.44 ns pulse widths and 4.2 ns temporal interval. This high-power tunability establishes a transformative material processing paradigm from precision machining to photonics, advancing fundamental nonlinear pulse science and setting new industrial laser standards.

We demonstrate a high-efficiency, high-power Er:CaF2 single-crystal fiber (SCF) continuous-wave (CW) laser pumped by a 976 nm laser diode. By carefully analyzing the thermal lensing effect and optimizing mode matching, we achieved a maximum CW output power of 10.02 W, corresponding to a slope efficiency as high as 32.2% for pump power below 25 W. To the best of our knowledge, this represents the highest output power ever reported for 2.8 μm SCF lasers, approximately an order of magnitude higher than previous results. In addition, a wavelength redshift beyond 2.8 μm was observed at high power, extending beyond the strong absorption region of water vapor. These results indicate that Er-doped CaF2 SCFs are promising candidates for high-power mid-infrared lasers.

We report a record-breaking 213.4 W continuous-wave diamond Raman laser operating at 1240 nm using polarization beam combining dual-fiber pumps and a quasi-Z-shaped cavity to suppress back-reflection. The secondary pump amplified the Stokes field without altering its polarization, confirming polarization-independent gain enhancement. Results demonstrate that high pump power, robust cavity design, reduced optical damage, temperature control of the mirror and crystal and parasitic Brillouin suppression were critical for maximizing Stokes output. The work surpasses the decade-old 154 W record, highlighting diamond’s potential in high-power applications.

Spectral coherent combining (SCC) offers a powerful approach to increase output power and shorten pulse duration. Here, we comprehensively investigate SCC of two beams to achieve the high combining performance. The preliminary analysis indicates that incident spectra and the transition region of the combiner both affect the combining process. The simulation results show that optimizing the overlapping spectral range, the transition width and start wavelength of the combiner can achieve high combining efficiency and high pulse quality. Guided by the simulation results, we built a femtosecond laser system based on the SCC of two fiber amplifiers, achieving 96.9% combining efficiency and high-quality 42-fs pulses. To the best of our knowledge, this is the first time that high combining efficiency and high pulse quality have been achieved simultaneously in a fiber femtosecond laser system based on SCC. This study provides design guidelines for the high-performance combination of beams covering different spectral regions.

We present time-dependent two-dimensional (2D) and three-dimensional (3D) fluid simulations of a gas cell with a variable length of 0–5 cm, designed for laser wakefield acceleration. The cell employs an output nozzle producing extended density ramps, which can facilitate the production of high-quality electron beams. In both geometries, the simulations demonstrate uniform density inside the cell. In the 3D case, the mean density inside the cell reaches a density nonuniformity below $1\%$ after 100 ms. The density equilibrium time, $\tau$, scales with the ratio of cell volume-to-outlet area, a relationship that is not captured by the 2D simulations showing five times shorter equilibrium time. We present a method to determine $\tau$ from fluid simulations, allowing the estimation of the minimum delay required to enable a uniform target density. Such uniformity prevents uncontrolled electron injection from density ripples, which has direct implications for optimizing beam quality and reproducibility in wakefield acceleration.

The temporal contrast requirements for high-power laser pulses have become increasingly stringent with rising irradiance levels. Over the past decade, in addition to discrete pre-pulses, spatiotemporal pulse pedestals have attracted significant attention as a major limiting factor for contrast quality in chirped-pulse amplification systems, primarily caused by imperfections in their stretching and compression optics. In this work, we present the first direct high-resolution single-shot measurement of these contributions in the spatiotemporal domain using an imaging spectrometer in combination with a two-dimensional self-referenced spectral interferometer.

Recent advancements in random distributed feedback Raman fiber lasers have promoted random Raman fiber lasers (RRFLs) as a novel laser source with significant progress. However, fully open cavity RRFLs suffer from suboptimal Stokes conversion efficiency and output power due to mode mismatch limitations. In this paper, we demonstrate the impact of end feedback and mode control on output Stokes wave characteristics. The random laser model incorporating multimode Raman interactions was established to theoretically simulate end feedback and output modal properties. Experimental studies were demonstrated through the construction of a fully open cavity RRFL. Higher end feedback reduces forward-propagating Stokes waves while amplifying backward-propagating light intensity. Transmission modes were effectively controlled through the design and optimization of tapered fiber. Consequently, 2081 W random Raman lasing was achieved in the fully open cavity RRFL. At maximum power, spectral purity exceeded 90%, representing the maximum output power reported for fully open cavity random lasers. This work provides important guidance for high-power laser generation and investigations of multimode nonlinear effects.

In this study, we present a low-numerical-aperture (NA) confined-doped fiber architecture that synergistically mitigates transverse mode instability (TMI) through combined optical waveguide engineering and spatially tailored gain distribution. The individual and combined benefits of low-NA fiber design and the confined-doped fiber design strategy on TMI mitigation are numerically investigated. Building upon these theoretical analyses, a self-developed fiber, featuring a core/cladding diameter of approximately 26/400 μm, a core NA of approximately 0.045 and a core doping ratio of approximately 75%, is fabricated. Further experimental validation in a master oscillator power amplifier demonstrates 6.74 kW output power with near-single-mode (M${}^2\sim$1.49) beam quality, validating the design’s efficacy. This study establishes a novel fiber design paradigm that concurrently addresses TMI mitigation, beam quality maintenance and power scalability, offering a viable pathway toward robust high-power fiber laser sources with near-diffraction-limited beam quality.

The impact of compressor gratings and transport optics imperfections on the power contrast ratio (PCR) is considered analytically, taking into account diffraction and all dispersion orders. All types of imperfections, including surface roughness, reflectivity fluctuations and surface dirt/damage/obscuration as well as the roughness and obscuration on the optics used to write holographic gratings are allowed for. For the same roughness and obscuration, the contribution to the PCR of the latter is significantly greater than the contribution of the gratings. Comparison of the PCR caused by obscuration and by roughness showed that at short times the latter prevails, whereas at long times the obscuration is dominant. The radiation scattered by the second and third gratings arrives at the target before the main pulse in the form of a vertical strip near the beam axis. Then this strip moves uniformly towards the axis, reaching it simultaneously with the main pulse.

We present quasi-continuous-wave (QCW) diode-pumped yellow–orange microchip lasers based on cooperative multi-phonon coupling and self-frequency doubling in Yb3+-doped YCa4O(BO3)3 crystals. QCW pumping at 100 Hz introduces cooling intervals that effectively suppress thermal accumulation. By optimizing the pump duty cycles, microchip yellow lasers at 565 nm and orange lasers at 590 nm were realized with peak powers of 125 and 102 W, respectively. The corresponding single-pulse energies were 4 mJ (yellow) and 2.4 mJ (orange). To the best of our knowledge, these results represent the highest reported peak power and single-pulse energy among all QCW yellow–orange microchip lasers. As a demonstration, the compact orange source was used to excite the fluorescent dye Cyanine 3.5, yielding a 20-fold enhancement in photoluminescence compared to conventional green lasers, indicating its great potential for flow cytometry applications with new laser wavelengths.

Large-aperture gratings are core components for pulse compression in kilojoule petawatt laser systems. The wavefront or amplitude error originating from fabrication and assembly of these gratings can be transformed into near-field modulation during propagation of the laser pulse. In severe cases, near-field modulation would induce laser damage on gratings and downstream optics. In this study, a three-dimensional near-field propagation model is developed based on ray tracing and diffraction propagation theory, allowing one to quantify the effect of each grating in the compressor independently. We investigate near-field propagation properties of the mosaic grating-based compressor in detail; the impacts of periodic wavefront error and mosaic gap error of the mosaic grating on near-field modulation are analyzed and evaluated, with two measured wavefronts introduced for further analysis. This work offers theoretical insights for estimating the fabrication requirement of gratings and reducing the risk of laser damage.

Fiber-coupled laser pumps with low size, weight and power consumption (SWaP) have become more and more compelling for applications in both industrial and defense applications. This study presents an innovative approach employing the spectral beam combining technique and double-junction laser diode chips to create efficient, high-power, high-brightness fiber-coupled packages. We successfully demonstrated a wavelength-stabilized pump module capable of delivering over 560 W of ex-fiber power with an electro-optical conversion efficiency of 55% from a 135 μm diameter, 0.22 numerical aperture fiber. The specific mass and volume metrics achieved are 0.34 $\mathrm{kg}/\mathrm{kW}$ and 0.23 ${\mathrm{cm}}^3/\mathrm{W}$, respectively. The module exhibits a stabilized spectrum with a 3.6 nm consistent interval of two spectral peaks and a 4.2 nm full width at half maximum across a wide range of operating currents.

We demonstrate a Yb:CaGdAlO4 (Yb:CALGO) bulk regenerative amplifier (RA) capable of delivering a peak power of 0.112 TW at a 1 kHz repetition rate. By integrating a home-built ultrabroadband nonlinear polarization evolution (NPE) mode-locked fiber oscillator, a set of custom-designed spectral shapers and the broad emission bandwidth Yb:CALGO gain medium, an amplified bandwidth of 18.2 nm and an output pulse duration of 137 fs are achieved. Thanks to the thermally insensitive dual-crystal cavity design and the quasi-continuous pumping thermal management scheme, the RA achieves a maximum pulse energy output of 21.01 mJ. Under the constraint of avoiding crystal damage, the compressed pulse energy reaches 17.6 mJ. To the best of our knowledge, this represents the highest pulse energy and peak power ever achieved from a Yb:CALGO RA. The power stability over 30 minutes is measured to be 0.506%, and the beam quality factor M2 is 1.16 × 1.12.

We report experimental optical and thermodynamical studies of convection cooling for face cooling of laser amplifier disks. Amplifier maquettes are used to explore the flow regime in laser relevant conditions, and to measure heat exchange coefficients $h$. We thus benchmark analytical and numerical predictions, based on common models of turbulence. The ${y}^{+}$ model appears best suited to compute $h$ in the laminar regime, and the Reynolds-Average Navier–Stokes model in the weakly turbulent regime. By strioscopic imaging, we examine the optical properties of the flows, in particular the onset of a striation instability occurring well before the transition to turbulence. At higher Reynolds numbers, the unstable thermal layer is shown to be pushed back onto the surface, suppressing effectively the wavefront distortions from striations. This super-forced thermal regime may be of high interest for very high thermal loads.

An experimental study of the equation of state for metallic powders under impact loading was carried out at a high-energy laser facility. A laser-ablatable micro-target was obtained to satisfy the laser equation of state for experimental study, and the precise characterization of the initial density was realized. The technique boosts the pressure of copper powder to 1400 GPa. The data consistency can effectively distinguish the data trends under different initial densities (~4.05 and 4.50 g/cm3). Experimental data can effectively distinguish the differences between the high-pressure Thomas–Fermi model and the Thomas–Fermi–Kirzhnits model, providing strong support for the WEOS-Pα model of the Institute of Applied Physics and Computational Mathematics, which is more in line with the actual state description of the material. This experimental technique can be extended to study the high-pressure physical properties of other powder particles.