We demonstrate the post-compression of the GW-level femtosecond pulse in a solid-state multi-pass cell (MPC) by the pre-chirp management method. When the laser pulse is positively pre-chirped, the 200 μJ 170 fs input pulse is compressed to 163 μJ 44 fs at the output, corresponding to a transmission of 81% and a pulse shortening factor of 3.86. When the laser pulse is negatively pre-chirped, the spectral evolution, as the pulse propagates in the MPC, is characterized and, eventually, the pulse duration is compressed to 51 fs, corresponding to a pulse shortening factor of 3.3. After the driving laser goes through the pre-chirp managed MPC device, the power stability and beam quality are almost preserved. The experimental results offer a viable path toward the post-compression of high-peak-power laser pulses.

Stimulated Raman scattering is a third-order nonlinear optical effect that is not only effective for wavelength converting laser output, but also for single longitudinal-mode output due to the absence of spatial hole burning. Diamond is a prominent Raman-active medium that has significant potential for linewidth narrowing and wavelength converting lasers at high power levels due to its high thermal conductivity, long Raman frequency shift and wide spectral transmission range. In this work we utilize diamond in a resonantly mode-matched external cavity to achieve cascaded Raman conversion of a 1064 nm laser. By fine-tuning the length of this external cavity, we can obtain narrow linewidth emission at 1240 and 1485 nm. When operating at maximum power, the measured linewidths were more than twofold narrower than the linewidth of the fundamental field. In addition, the noise levels of the Stokes fields are lower than that of the fundamental field throughout the entire noise frequency range, and the intrinsic linewidth of the second Stokes field, which is expressed at the hertz level (~3.6 Hz), is decreased by approximately three orders of magnitude compared to that of the pump. This work represents the first measurement and analysis of the linewidth and noise characteristics of cascaded diamond Raman lasers and, significantly, offers a new means by which high-power, narrow linewidth laser output can be produced from wavelength-converted laser systems.

An optical spectrometer system based on 60 channels of fibers has been designed and employed to diagnose light emissions from laser–plasma interactions. The 60 fiber collectors cover an integrated solid angle of $\pi$, enabling the measurement of global energy losses in a symmetrical configuration. A detecting spectral range from ultraviolet to near-infrared, with angular distribution, allows for the understanding of the physical mechanisms involving various plasma modes. Experimental measurements of scattered lights from a conical implosion driven by high-energy nanosecond laser beams at the Shenguang-II Upgrade facility have been demonstrated, serving as reliable diagnostics to characterize laser absorption and energy losses from laser–plasma instabilities. This compact diagnostic system can provide comprehensive insights into laser energy coupling in direct-drive inertial confinement fusion research, which are essential for studying the driving asymmetry and improving the implosion efficiencies.

An analytical expression for the focal intensity of a laser pulse was obtained for an asymmetric out-of-plane compressor with gratings of arbitrary surface shape. The focal intensity is most strongly affected by the linear angular chirp caused by the spatial shift of different frequencies on the second and third gratings. The chirp can be eliminated by simply rotating the fourth grating by an optimal angle, which significantly reduces the requirements for the grating quality. It is shown that the decrease in the focal intensity depends on the product of the grating surface root mean square and pulse spectrum bandwidth. With low-quality gratings, spectrum narrowing would not reduce focal intensity; contrariwise, it may even slightly increase it.

Mamyshev oscillators (MOs) exhibit the potential for generating high average power and ultrashort pulses. Herein, we construct an MO using flexible double-cladding ytterbium-fiber with a fusion-spliced-combiner pumped scheme. Consistent with the most reported research results, the offset filter separation significantly affects the pulse characteristics (spectrum, pulse duration, etc.). Notably, in comparison with red-shifting, blue-shifting the peak spectral emission of the grating filter relative to a constant central wavelength of the bandpass filter substantially enhances the laser output characteristics. This phenomenon, which has not been previously reported, results in an average power up to 2.23 W and a pulse duration as short as 49 fs. To our knowledge, this is the highest average power achieved in sub-50 fs pulse duration in the nonlinear polarization rotation-assisted mode-locked MO laser architecture. The presented technique offers unique scientific proof for developing ultrafast laser sources with higher average power and shorter pulse duration.

The longitudinal fields of a tightly focused Laguerre–Gaussian (LG) laser can be used to accelerate electron pulse trains when it is reflected from a solid plasma. However, the normal transverse mode of laser beams in high-power laser systems is approximately Gaussian. A routine and reliable way to obtain high-intensity LG lasers in experiments remains a major challenge. One approach involves utilizing a solid plasma with a ‘light fan’ structure to reflect the Gaussian laser and obtain a relativistic intense LG laser. In this work, we propose a way to combine the mode transformation of a relativistic laser and the process of electron injection and acceleration. It demonstrates that by integrating a nanowire structure at the center of the ‘light fan’, electrons can be efficiently injected and accelerated during the twisted laser generation process. Using three-dimensional particle-in-cell simulations, it is shown that a circularly polarized Gaussian beam with ${a}_0=20$ can efficiently inject electrons into the laser beam in interaction with the solid plasma. The electrons injected close to the laser axis are driven by a longitudinal electric field to gain longitudinal momentum, forming bunches with a low energy spread and a small divergence angle. The most energetic bunch exhibits an energy of 310 MeV, with a spread of 6%. The bunch charge is 57 pC, the duration is 400 as and the divergence angle is less than 50 mrad. By employing Gaussian beams, our proposed approach has the potential to reduce experimental complexity in the demonstrations of twisted laser-driven electron acceleration.

This paper introduces a novel fiber-based picosecond burst-mode laser system capable of operating at high power and high repetition rates. A pulse-circulating fiber ring was developed as a burst generator, achieving an intra-burst repetition rate of 469 MHz without the need for a high-repetition-rate seed source. This design also allows for flexible adjustment of the number of sub-pulses, burst repetition rate and burst shape. In addition, a master oscillator power amplifier was employed to analyze the amplification characteristics of bursts. The system demonstrated a maximum average power of 606 W, with a measured sub-pulse duration of 62 ps and the highest sub-pulse peak power of 980 kW. To the best of our knowledge, this marks the highest average power obtained in burst-mode ultrafast lasers. Such a laser system holds potential for applications in precision manufacturing, high-speed imaging, high-precision ranging and other diverse domains.

Tightly focused proton beams generated from helical coil targets have been shown to be highly collimated across small distances, and display characteristic spectral bunching. We show, for the first time, proton spectra from such targets at high resolution via a Thomson parabola spectrometer. The proton spectral peaks reach energies above 50 MeV, with cutoffs approaching 70 MeV and particle numbers greater than 10${}^{10}$. The spectral bunch width has also been measured as low as approximately 8.5 MeV (17% energy spread). The proton beam pointing and divergence measured at metre-scale distances are found to be stable with the average pointing stability below 10 mrad, and average half-angle beam divergences of approximately 6 mrad. Evidence of the influence of the final turn of the coil on beam pointing over long distances is also presented, corroborated by particle tracing simulations, indicating the scope for further improvement and control of the beam pointing with modifying target parameters.

Rapid advancements in high-energy ultrafast lasers and free electron lasers have made it possible to obtain extreme physical conditions in the laboratory, which lays the foundation for investigating the interaction between light and matter and probing ultrafast dynamic processes. High temporal resolution is a prerequisite for realizing the value of these large-scale facilities. Here, we propose a new method that has the potential to enable the various subsystems of large scientific facilities to work together well, and the measurement accuracy and synchronization precision of timing jitter are greatly improved by combining a balanced optical cross-correlator (BOC) with near-field interferometry technology. Initially, we compressed a 0.8 ps laser pulse to 95 fs, which not only improved the measurement accuracy by 3.6 times but also increased the BOC synchronization precision from 8.3 fs root-mean-square (RMS) to 1.12 fs RMS. Subsequently, we successfully compensated the phase drift between the laser pulses to 189 as RMS by using the BOC for pre-correction and near-field interferometry technology for fine compensation. This method realizes the measurement and correction of the timing jitter of ps-level lasers with as-level accuracy, and has the potential to promote ultrafast dynamics detection and pump–probe experiments.

External seeded free-electron lasers (FELs) have exhibited substantial progress in diverse applications over the last decade. However, the frequency up-conversion efficiency in single-stage seeded FELs, particularly in high-gain harmonic generation (HGHG), remains constrained to a modest level. This limitation restricts its capability to conduct experiments within the ‘water window’. This paper presents a novel method for generating coherent X-ray FEL pulses in the water window region based on the HGHG scheme with multi-stage harmonic cascade. Without any additional modifications to the HGHG configuration, simulation results demonstrate the generation of intense 3 nm coherent FEL radiation using an external ultraviolet seed laser. This indicates an increase of the harmonic conversion number to approximately 90. A preliminary experiment is performed to evaluate the feasibility of this method. The proposed approach could potentially serve as an efficient method to broaden the wavelength coverage accessible to both existing and planned seeded X-ray FEL facilities.

We are showing a significant enhancement in the temporal contrast by reducing the coherent noise of the 10 PW laser system at the Extreme Light Infrastructure - Nuclear Physics facility. The temporal contrast was improved by four orders of magnitude at 10 picoseconds and by more than one order of magnitude at 50 picoseconds before the main peak. This improvement of the picosecond contrast is critical for the experiments using thin solid targets.

For the pulse shaping system of the SG-II-up facility, we propose a U-shaped convolutional neural network that integrates multi-scale feature extraction capabilities, an attention mechanism and long short-term memory units, which effectively facilitates real-time denoising of diverse shaping pulses. We train the model using simulated datasets and evaluate it on both the simulated and experimental temporal waveforms. During the evaluation of simulated waveforms, we achieve high-precision denoising, resulting in great performance for temporal waveforms with frequency modulation-to-amplitude modulation conversion (FM-to-AM) exceeding 50%, exceedingly high contrast of over 300:1 and multi-step structures. The errors are less than 1% for both root mean square error and contrast, and there is a remarkable improvement in the signal-to-noise ratio by over 50%. During the evaluation of experimental waveforms, the model can obtain different denoised waveforms with contrast greater than 200:1. The stability of the model is verified using temporal waveforms with identical pulse widths and contrast, ensuring that while achieving smooth temporal profiles, the intricate details of the signals are preserved. The results demonstrate that the denoising model, trained utilizing the simulation dataset, is capable of efficiently processing complex temporal waveforms in real-time for experiments and mitigating the influence of electronic noise and FM-to-AM on the time–power curve.

Laser systems based on coherent beam combination (CBC) that rely on tiled pupil architecture intrinsically carry digital capabilities independently applicable to all three essential characteristics of a laser pulse: amplitude, phase and polarization. Those capabilities allow the far-field energy distribution to be flexibly tailored in real time. Operation in the femtosecond regime at high repetition rates gives access to a wide range of applications requiring both high peak and average powers. We address the task of independent peak versus average power adjustment needed for applications seeking to decouple nonlinear phenomena associated with GW peak power from the thermal load inherent to kW average power operation. The technical solutions proposed are presented in the framework of the Ecole Polytechnique XCAN CBC laser platform (61 independent channels) with an emphasis on thermal management measures implemented to ensure its nominal operation.

In this paper, we prove that the third near-infrared (NIR-III) window high-power laser with wavelength in the range of 1600–1800 nm can be obtained by the coherent Raman fiber amplification technique through theoretical and experimental study. Detailed numerical simulation reveals that the nonlinear dynamics of the Raman fiber amplification in the polarization-maintaining double-clad erbium-ytterbium co-doped fiber is similar to that of the Mamyshev oscillator. Through the spectral filtering effect induced by finite Raman gain, we can obtain a high-quality Raman pulse. According to the theoretical results, we design a simple Raman fiber amplification laser and finally obtain a high-quality watt-level NIR-III window laser pulse in which the central wavelength is about 1650 nm and the pulse width can reach 85 fs. The experimental results correspond to the simulation results. Such nonlinear effect is universal in all kinds of fibers, and we think this technology can provide a great contribution to the development of ultrafast fiber lasers.

We introduce a versatile high-repetition-rate solid tape target system suitable for relativistic laser-plasma driven secondary sources. We demonstrate the operation and stability monitoring based on a petawatt laser focused at 1 Hz. Experiments were carried out at the VEGA-3 laser system of the Centro de Láseres Pulsados facility where results for different tape materials and thicknesses are presented. Experimental proton spectra were recorded by a Thomson parabola spectrometer and a time-of-flight detector. In addition, non-invasive detectors, such as a target charging monitor and ionization chamber detectors, were tested as metrology for the stability of the source. Degradation of the proton signal at high-repetition-rate operation was observed and it was solved by online optimization of the relative focus position of the target and laser beam parameters. We report the use of the tape target for bursts of 1000 shots at 1 Hz with mean cut-off energies of about 10 MeV in optimized interaction conditions.

Nonlinear compression experiments based on multiple solid thin plates are conducted in an ultra-high peak power Ti:sapphire laser system. The incident laser pulse, with an energy of 80 mJ and a pulse width of 30.2 fs, is compressed to 10.1 fs by a thin-plate based nonlinear compression. Significant small-scale self-focusing is observed as ring structures appear in the near-field of the output pulse at high energy. Numerical simulations based on the experimental setup provide a good explanation for the observed phenomena, offering quantitative predictions of the spectrum, pulse width, dispersion and near- and far-field distributions of the compressed laser pulse.

We present results of frequency tripling experiments performed at the Hilase facility on a cryogenically gas cooled multi-slab ytterbium-doped yttrium aluminum garnet laser system, Bivoj/DiPOLE. The laser produces high-energy ns pulses at 10 Hz repetition rate, which are frequency doubled using a type-I phase-matched lithium triborate (LBO) crystal and consequently frequency summed using a type-II phase-matched LBO crystal. We demonstrated a stable frequency conversion to 343 nm at 50 J energy and 10 Hz repetition rate with conversion efficiency of 53%.

Understanding the physics of electromagnetic pulse (EMP) emission and nozzle damage is critical for the long-term operation of laser experiments with gas targets, particularly at facilities looking to produce stable sources of radiation at high repetition rates. We present a theoretical model of plasma formation and electrostatic charging when high-power lasers are focused inside gases. The model can be used to estimate the amplitude of gigahertz EMPs produced by the laser and the extent of damage to the gas jet nozzle. Looking at a range of laser and target properties relevant to existing high-power laser systems, we find that EMP fields of tens to hundreds of kV/m can be generated several metres from the gas jet. Model predictions are compared with measurements of EMPs, plasma formation and nozzle damage from two experiments on the VEGA-3 laser and one experiment on the Vulcan Petawatt laser.

The flexible delivery of single-frequency lasers is far more challenging than that of conventional lasers due to the onset of stimulated Brillouin scattering (SBS). Here we present the successful delivery of 100 W single-frequency laser power through 100 m of anti-resonant hollow-core fiber (AR-HCF) in an all-fiber configuration, with the absence of SBS. By employing a custom-designed AR-HCF with a mode-field diameter matching that of a large-mode-area panda fiber, the system achieves high coupling efficiency without the need for free-space components or fiber post-processing. The AR-HCF attains a transmission efficiency of 92%, delivering an output power of 100.3 W with a beam quality factor (M2) of 1.22. The absence of SBS is confirmed through monitoring backward light, which shows no increase in intensity. This all-fiber architecture ensures high stability, compactness and efficiency, potentially expanding the application scope of single-frequency lasers in high-precision metrology, optical communication, light detection and ranging systems, gravitational wave detection and other advanced applications.