Optical vortices are structures of the electromagnetic field with a spiral phase ramp about a point-phase singularity, carrying orbital angular momentum (OAM). Recently, OAM has been imprinted to short-wavelength radiation through high-order harmonic generation (HHG), leading to the emission of attosecond twisted beams in the extreme-ultraviolet (XUV) regime. We explore the details of the mapping of the driving vortex to its harmonic spectrum. In particular, we show that the geometry of the harmonic vortices is convoluted, arising from the superposition of the contribution from the short and long quantum paths responsible of HHG. Finally, we show how to take advantage of transverse phase-matching to select twisted attosecond beams with different spatiotemporal properties.

High-power femtosecond lasers beyond $5~\unicode[STIX]{x03BC}\text{m}$ are attractive for strong-field physics with mid-infrared (IR) fields but are difficult to scale up. In optical parametric chirped-pulse amplification (OPCPA) at mid-IR wavelengths, a nonlinear crystal is vital, and its transmittance, dispersion, nonlinear coefficient and size determine the achievable power and wavelength. OPCPA beyond $5~\unicode[STIX]{x03BC}\text{m}$ routinely relies on semiconductor crystals because common oxide crystals are not transparent in this spectral range. However, the small size and low damage threshold of semiconductor crystals fundamentally limit the peak power to gigawatts. In this paper, we design a terawatt-class OPCPA system at $5.2~\unicode[STIX]{x03BC}\text{m}$ based on a new kind of oxide crystal of $\text{La}_{3}\text{Ga}_{5.5}\text{Nb}_{0.5}\text{O}_{14}$ (LGN). The extended transparent range, high damage threshold, superior phase-matching characteristics and large size of LGN enable the generation of 0.13 TW seven-cycle pulses at $5.2~\unicode[STIX]{x03BC}\text{m}$. This design fully relies on the state-of-the-art OPCPA technology of an octave-spanning ultrafast Ti:sapphire laser and a thin-disk Yb:YAG laser, offering the performance characteristics of high power, a high repetition rate and a stable carrier–envelope phase.

Narrowband microwave generation with tuneable frequency is demonstrated by illuminating a photoconductive semiconductor switch (PCSS) with a burst-mode fibre laser. The whole system is composed of a high-power linearly polarized burst-mode pulsed fibre laser and a linear-state PCSS. To obtain a high-performance microwave signal, a desired envelope of burst is necessary and a pulse pre-compensation technique is adopted to avoid envelope distortion induced by the gain-saturation effect. Resulting from the technique, homogenous peak power distribution in each burst is ensured. The maximum energy of the laser burst pulse reaches 200 μJ with a burst duration of 100 ns at the average power of 10 W, corresponding to a peak power of 4 kW. When the PCSS is illuminated by the burst-mode fibre laser, narrowband microwave generation with tuneable frequency (0.80–1.12 GHz) is obtained with a power up to 300 W. To the best of the authors’ knowledge, it is the first demonstration of frequency-tuneable narrowband microwave generation based on a fibre laser. The high-power burst-mode fibre laser reported here has great potential for generating high-power arbitrary microwave signals for a great deal of applicable demands such as smart adaptive radar and intelligent high-power microwave systems.

Compared with end pumping fiber combiner, one of the advantages for side pumping combiner is the unlimited pumping points, which means multi-point or cascaded side pumping can be realized. However, the loss mechanism of the cascaded structure is rarely discussed. In this paper, we present the numerical and experimental investigation about the loss mechanism of a two-stage-cascaded side pumping combiner based on tapered-fused technique. The influence of loss mechanism on the coupling efficiency and thermal load of the fiber coating is analyzed according to simulations and experiments with different tapering ratios for the first stage. Based on the analysis, a cascaded component with total pump coupling efficiency of 96.4% handling a pump power of 1088 W is achieved by employing 1018 nm fiber laser as the pump source. Future work to further improve the performance of a cascaded side pumping combiner is discussed and prospected.

Temporal contrast is one of the crucial physical determinants which guarantee the successful performance of laser–matter interaction experiments. We generally reviewed the influences on the temporal contrast in three categories of noises based on the requirement by the physical mechanisms. The spatiotemporal influences on temporal contrast at the focal region of the chromatic aberration and propagation time difference introduced by large-aperture broadband spatial filters, which were spatiotemporally coupled with compression and focusing, were calculated and discussed with a practical case in SG-II 5 PW ultrashort petawatt laser. The system-wide spatiotemporal coupling existing in large-aperture broadband ultrashort petawatt lasers was proved to be one of the possible causes of temporal contrast degradation in the focal region.

The Shenguang-II Upgrade (SG-II Up) facility is an under-construction high-power laser driver with eight beams, 24 kJ energy, 3 ns pulse duration and ultraviolet laser output, in the Shanghai Institute of Optics and Fine Mechanics, China. The prototype design and experimental research of the prototype final optics assembly (FOA), which is one of the most important parts of the SG-II Up facility, have been completed on the ninth beam of the SG-II facility. Thirty-three shots were fired using 1-${\it\omega}$ energy from 1000 to 4500 J and 3-${\it\omega}$ energy from 500 to 2403 J with a 3 ns square pulse. During the experiments, emphasis was given to the process of optical damage and to the effects of clean-gas control. A numerical model of the FOA generated by the Integrated Computer Engineering and Manufacturing code for Computational Fluid Dynamics (ICEMCFD) demonstrated that a flux within $1{-}5~\text{l s}^{-1}$ and a 180 s period is effectual to avoid contaminant sputtering to the optics. The presence of surface ‘mooning’ damage and surface spots located outside the clear aperture are induced by contaminants such as wire, silica gel and millimeter order fiber and metal.

We report the development of a stable high-average power X-ray source generated by the interaction of ultrashort laser pulses (35 fs, 1 mJ, 1 kHz) with a solid target in air. The achieved source stability, which is essential for the applications foreseen for these laser-driven plasma accelerators, is due to the combination of precise positioning of the target on focus and the development of a fast rotating target system able to ensure the refreshment of the material at every shot while minimizing positioning errors with respect to the focal spot. This vacuum-free laser-plasma X-ray source provides an average dose rate of 1.5 Sv/h at 30 cm and a repeatability better than 93% during more than 36 min of continuous operation per target.

Pulse contrast is a crucial parameter of high peak-power lasers since the prepulse noise may disturb laser–plasma interactions. Contrast measurement is thus a prerequisite to tackle the contrast challenge in high peak-power lasers. This paper presents the progress review of single-shot cross-correlator (SSCC) for real-time contrast characterization. We begin with the key technologies that enable an SSCC to simultaneously possess high dynamic range ($10^{10}$), large temporal window (50–70 ps) and high fidelity. We also summarize the instrumentation of SSCC prototypes and their applications on five sets of petawatt laser facilities in China. Finally, we discuss how to extend contrast measurements from time domain to spatiotemporal domain. Real-time and high-dynamic-range contrast measurements, provided by SSCC, can not only characterize various complex noises in high peak-power lasers but also guide the system optimization.

Experiments have shown that the ion energy obtained by laser–ion acceleration can be optimized by choosing either the appropriate pulse duration or the appropriate target thickness. We demonstrate that this behavior can be described either by the target normal sheath acceleration model of Schreiber et al. or by the radiation pressure acceleration model of Bulanov and coworkers. The starting point of our considerations is that the essential property of a laser system for ion acceleration is its pulse energy and not its intensity. Maybe surprisingly we show that higher ion energies can be reached with reduced intensities.

To reduce the seed length while maintaining the advantages of the cuboid KDP-type crystal, a long-seed KDP crystal with size $471~\text{mm}\times 480~\text{mm}\times 400~\text{mm}$ is rapidly grown. With almost the same high cutting efficiency to obtain third harmonic generation oriented samples, this long-seed KDP-type crystal can be grown with a shorter seed than that of the cuboid KDP-type crystal. The full width at half maximum of the high-resolution X-ray diffraction of the (200) crystalline face is 28.8 arc seconds, indicating that the long-seed KDP crystal has good crystalline quality. In the wavelength range of 377–1022 nm, the transmittance of the long-seed KDP crystal is higher than 90%. The fluence for the 50% probability of laser-induced damage (LID) is $18.5~\text{J}/\text{cm}^{2}$ (3 ns, 355 nm). Several test points survive when the laser fluence exceeds $30~\text{J}/\text{cm}^{2}$ (3 ns, 355 nm), indicating the good LID performance of the long-seed KDP crystal. At present, the growth of a long-seed DKDP crystal is under way.

We present the workflow of the design, realization and testing of deformable mirrors suitable for high power diode pumped solid-state lasers. It starts with the study of the aberration to be corrected, and then it continues with the design of the actuators position and characteristic. In this paper, we present and compare three deformable mirrors realized for multi-J level laser facilities. We show that with the same design concept it is possible to realize deformable mirrors for other types of lasers. As an example, we report the realization of a deformable mirror for femtosecond lasers and for a CW $\text{CO}_{2}$ laser.

The fiber laser based on an oscillating-amplifying integrated structure has the potential to benefit from the advantages of a fiber laser oscillator and amplifier with the characteristics of strong anti-back-reflected light ability and high efficiency. Here, we achieved a 3.5-kW near-single-mode (M2 ∼ 1.24) oscillating–amplifying integrated fiber laser with an active fiber length of 8 m in the oscillating section and 17.6 m in the amplifying section. While operating at the maximum power, the optical-to-optical conversion efficiency is 87.0%, and the intensity of stimulated Raman scattering is about 23.61 dB lower than that of the signal light. To the best of the authors’ knowledge, this is the highest output power of an oscillating–amplifying integrated fiber laser, accompanied with the best beam quality and the highest efficiency.

Two different pulse cleaning techniques for ultra-high contrast laser systems are comparably analysed in this work. The first pulse cleaning technique is based on noncollinear femtosecond optical-parametric amplification (NOPA) and second-harmonic generation (SHG) processes. The other is based on cross-polarized wave (XPW) generation. With a double chirped pulse amplifier (double-CPA) scheme, although temporal contrast enhancement in a high-intensity femtosecond Ti:sapphire chirped pulse amplification (CPA) laser system can be achieved based on both of the techniques, the two different pulse cleaning techniques still have their own advantages and are suitable for different contrast enhancement requirements of different laser systems.

We deduce a complete wave propagation equation that includes inhomogeneity of the dielectric constant and present this propagation equation in compact vector form. Although similar equations are known in narrow fields such as radio wave propagation in the ionosphere and electromagnetic and acoustic wave propagation in stratified media, we develop here a novel approach of using such equations in the modeling of laser beam propagation in nonlinear media. Our approach satisfies the correspondence principle since in the limit of zero-length wavelength it reduces from physical to geometrical optics.

On behalf of all at High Power Laser Science and Engineering we would like to congratulate the team at Lawrence Livermore National Laboratory (LLNL) on demonstrating fusion ignition at the National Ignition Facility. This major scientific achievement was realized on the 5 December 2022 at the LLNL and announced at a press briefing on the 13 December 2022 by the United States Department of Energy’s National Nuclear Security Administration. This was a historic milestone and the culmination of decades of effort.

The rapid development of high-intensity laser-generated particle and photon secondary sources has attracted widespread interest during the last 20 years not only due to fundamental science research but also because of the important applications of this developing technology. For instance, the generation of relativistic particle beams, betatron-type coherent X-ray radiation and high harmonic generation have attracted interest from various fields of science and technology owing to their diverse applications in biomedical, material science, energy, space, and security applications. In the field of biomedical applications in particular, laser-driven particle beams as well as laser-driven X-ray sources are a promising field of study. This article looks at the research being performed at the Institute of Plasma Physics and Lasers (IPPL) of the Hellenic Mediterranean University Research Centre. The recent installation of the ZEUS 45 TW laser system developed at IPPL offers unique opportunities for research in laser-driven particle and X-ray sources. This article provides information about the facility and describes initial experiments performed for establishing the baseline platforms for secondary plasma sources.

Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus, both in position and angle, is critical to many laser applications such as optical guiding, laser–plasma acceleration, and laser-produced secondary radiation. We present an online, non-destructive laser diagnostic, capable of measuring the transverse position and pointing angle at focus. The diagnostic is based on a unique double-surface-coated wedged-mirror design for the final steering optic in the laser line, producing a witness beam highly correlated with the main beam. By propagating low-power kilohertz pulses to focus, we observed spectra of focus position and pointing angle fluctuations dominated by frequencies below 70 Hz. The setup was also used to characterize the excellent position and pointing angle correlation of the 1 Hz high-power laser pulses to this low-power kilohertz pulse train, opening a promising path to fast non-perturbative feedback concepts even on few-hertz-class high-power laser systems.

An optically addressed liquid crystal modulator for wavefront control of 1053 nm laser beam is reported in this paper. Its working principle, control method and spatial phase modulation capability are mainly introduced. A new method of measuring the relationship between gray level and phase retardation is proposed. The rationality of the curve is further confirmed by designing special experiments. According to the curve, several spatial phase distributions have been realized by this home-made device. The results show that, not only the maximum phase retardation is larger than $2\unicode[STIX]{x03C0}$ for 1053 nm wavelength, but also the control accuracy is high. Compared with the liquid crystal on silicon type spatial light modulator, this kind of modulator has the advantages of generating smooth phase distribution and avoiding the black-matrix effect.

We present the first steps of a design of the optimal parameters for a full Bragg X-Ray free electron laser (BX-FEL). Aiming towards a future source of coherent X-ray radiation, operating in the strong Compton regime, we envisage the system to be the seed for an advanced light source or compact medical X-ray source. Here we focus on the design of the accelerator parameters: maximum gradient, optimal accelerated charge, maximum efficiency, and ‘wake coefficient’, which relates to the decelerating electric field generated due to the motion of a charged-line or train of charged-lines. Specifically, we demonstrate that the maximum efficiency has optimal value and given the fluence of the materials, the maximum accelerated charge in the train is constant. These two results might be important in any future design.

Nowadays, inertial confinement fusion (ICF) research related to noncontact positioning and transport of free-standing cryogenic targets is playing an increasingly important role in this field. The operational principle behind these technologies is the magnetic acceleration of the levitating target carrier (or sabot) made from Type-II, high-temperature superconductors (HTSCs). The physics of interaction among levitation, guidance and propulsion systems is based on a quantum levitation of high-pinning HTSCs in the mutually normal magnetic fields. This paper discusses current target delivery strategies and future perspectives to create different permanent magnet guideway (PMG) systems for ICF target transport with levitation. In particular, several PMG building options for optimizing both suspension and levitation of ICF targets using an HTSC-sabot will be analyzed. Credible solutions have been demonstrated for both linear and round PMGs, including the ones with a cyclotron acceleration process to realize high-running velocities of the HTSC-sabot for a limited magnetic track. Focusing on physics, we describe in detail the main aspects of the PMG building and the results obtained from computations and proof of principle experiments. High-pinning HTSC magnetic levitation promises a stable and self-controlled levitation to accelerate the ICF targets placed in the HTSC-sabots up to the required injection velocities of 200 m/s and beyond.