We report high-energy, high-efficiency second harmonic generation in a near-infrared all-solid-state burst-mode picosecond laser at a repetition rate of 1 kHz with four pulses per burst using a type-I noncritical phase-matching lithium triborate crystal. The pulses in each burst have the same time delay (${\sim}1~\text{ns}$), the same pulse duration (${\sim}100~\text{ps}$) and different relative amplitudes that can be adjusted separately. A mode-locked beam from a semiconductor saturable absorber mirror is pulse-stretched, split into seed pulses and injected into a Nd:YAG regenerative amplifier. After the beam is reshaped by aspheric lenses, a two-stage master oscillator power amplifier and 4f imaging systems are applied to obtain a high power of ${\sim}100~\text{W}$. The 532 nm green laser has a maximum conversion efficiency of 68%, an average power of up to 50 W and a beam quality factor $M^{2}$ of 3.5.

Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not been understood well yet, especially in dielectric targets. We present the first detailed two-dimensional particle-in-cell simulations of relativistic electron transport in a silicon target by including the field ionization and collisional ionization processes. An ionization wave is found propagating in the insulator, with a velocity dependent on laser intensity and slower than the relativistic electron velocity. Widely spread electric fields in front of the sheath fields are observed due to the collective effect of free electrons and ions. The electric fields are much weaker than the threshold electric field of field ionization. Two-stream instability behind the ionization front arises for the cases with laser intensity greater than $5\times 10^{19}~\text{W}/\text{cm}^{2}$ that produce high relativistic electron current densities.

A tunable ultrafast intensity-rotating optical field is generated by overlapping a pair of 20 Hz, 800 nm chirped pulses with a Michelson interferometer (MI). Its rotating rate can be up to 10 trillion radians per second ($\text{Trad}/\text{s}$), which can be flexibly tuned with a mirror in the MI. Besides, its fold rotational symmetry structure is also changeable by controlling the difference from the topological charges of the pulse pair. Experimentally, we have successfully developed a two-petal lattice with a tunable rotating speed from $3.9~\text{Trad}/\text{s}$ up to $11.9~\text{Trad}/\text{s}$, which is confirmed by our single-shot ultrafast frame imager based on noncollinear optical-parametric amplification with its highest frame rate of 15 trillion frames per second (Tfps). This work is carried out at a low repetition rate. Therefore, it can be applied at relativistic, even ultrarelativistic, intensities, which usually operate in low repetition rate ultrashort and ultraintense laser systems. We believe that it may have application in laser-plasma-based accelerators, strong terahertz radiations and celestial phenomena.

In this paper, we report the recent progress on the $1~\text{PW}/0.1~\text{Hz}$ laser beamline of Shanghai Superintense Ultrafast Laser Facility (SULF). The SULF-1 PW laser beamline is based on the double chirped pulse amplification (CPA) scheme, which can generate laser pulses of 50.8 J at 0.1 Hz after the final amplifier; the shot-to-shot energy fluctuation of the amplified pulse is as low as 1.2% (std). After compression, the pulse duration of 29.6 fs is achieved, which can support a maximal peak power of 1 PW. The contrast ratio at $-80~\text{ps}$ before main pulse is measured to be $2.5\times 10^{-11}$. The focused peak intensity is improved by optimizing the angular dispersion in the grating compressor. The maximal focused peak intensity can reach $2.7\times 10^{19}~\text{W}/\text{cm}^{2}$ even with an $f/26.5$ off-axis parabolic mirror. The horizontal and vertical angular pointing fluctuations in 1 h are measured to be 1.89 and $2.45~\unicode[STIX]{x03BC}\text{rad}$, respectively. The moderate repetition rate and the good stability are desirable characteristics for laser–matter interactions. The SULF-1 PW laser beamline is now in the phase of commissioning, and preliminary experiments of particle acceleration and secondary radiation under 300–400 TW/0.1 Hz laser condition have been implemented. The progress on the experiments and the daily stable operation of the laser demonstrate the availability of the SULF-1 PW beamline.

The second and final year of the Erasmus Plus programme ‘Innovative Education and Training in high power laser plasmas’, otherwise known as PowerLaPs, is described. The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme, where teaching takes place in five separate institutes with a range of different aims and styles of delivery. The ‘in-class’ time is limited to 4 weeks a year, and the programme spans 2 years. PowerLaPs aims to train students from across Europe in theoretical, applied and laboratory skills relevant to the pursuit of research in laser plasma interaction physics and inertial confinement fusion. Lectures are intermingled with laboratory sessions and continuous assessment activities. The programme, which is led by workers from the Hellenic Mediterranean University and supported by co-workers from the Queen’s University Belfast, the University of Bordeaux, the Czech Technical University in Prague, Ecole Polytechnique, the University of Ioannina, the University of Salamanca and the University of York, has just finished its second and final year. Six Learning Teaching Training activities have been held at the Queen’s University Belfast, the University of Bordeaux, the Czech Technical University, the University of Salamanca and the Institute of Plasma Physics and Lasers of the Hellenic Mediterranean University. The last of these institutes hosted two 2-week-long Intensive Programmes, while the activities at the other four universities were each 5 days in length. In addition, a ‘Multiplier Event’ was held at the University of Ioannina, which will be briefly described. In this second year, the work has concentrated on training in both experimental diagnostics and simulation techniques appropriate to the study of plasma physics, high power laser matter interactions and high energy density physics. The nature of the programme will be described in detail, and some metrics relating to the activities carried out will be presented. In particular, this paper will focus on the overall assessment of the programme.

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 study the optimization of collisionless shock acceleration of ions based on hydrodynamic modelling and simulations of collisional shock waves in gaseous targets. The models correspond to the specifications required for experiments with the $\text{CO}_{2}$ laser at the Accelerator Test Facility at Brookhaven National Laboratory and the Vulcan Petawatt system at Rutherford Appleton Laboratory. In both cases, a laser prepulse is simulated to interact with hydrogen gas jet targets. It is demonstrated that by controlling the pulse energy, the deposition position and the backing pressure, a blast wave suitable for generating nearly monoenergetic ion beams can be formed. Depending on the energy absorbed and the deposition position, an optimal temporal window can be determined for the acceleration considering both the necessary overdense state of plasma and the required short scale lengths for monoenergetic ion beam production.

The development of laser performance models having real-time prediction capability for the OMEGA EP laser system has been essential in meeting requests from its user community for increasingly complex pulse shapes that span a wide range of energies. The laser operations model PSOPS provides rapid and accurate predictions of OMEGA EP laser-system performance in both forward and backward directions, a user-friendly interface and rapid optimization capability between shots. We describe the model’s features and show how PSOPS has allowed real-time optimization of the laser-system configuration in order to satisfy the demands of rapidly evolving experimental campaign needs. We also discuss several enhancements to laser-system performance accuracy and flexibility enabled by PSOPS.

A simple, compact, double-pass pumped Nd:YVO4 thin disk laser is demonstrated. Its continuous-wave performance with different Nd doping concentrations and thicknesses is investigated experimentally. The maximum output power of 17.7 W is achieved by employing a 0.5 at.% doped sample, corresponding to an optical-to-optical efficiency of 46% with respect to the absorbed pump power. In addition, a numerical analysis and an experimental study of the temperature distribution, and thermal lens effect of the Nd:YVO4 thin disk, are presented considering the influence of the energy transfer upconversion effect and the temperature dependence of the thermal conductivity tensor. The simulated results are in good agreement with the experimental results.

A developing application of laser-driven currents is the generation of magnetic fields of picosecond–nanosecond duration with magnitudes exceeding $B=10~\text{T}$. Single-loop and helical coil targets can direct laser-driven discharge currents along wires to generate spatially uniform, quasi-static magnetic fields on the millimetre scale. Here, we present proton deflectometry across two axes of a single-loop coil ranging from 1 to 2 mm in diameter. Comparison with proton tracking simulations shows that measured magnetic fields are the result of kiloampere currents in the coil and electric charges distributed around the coil target. Using this dual-axis platform for proton deflectometry, robust measurements can be made of the evolution of magnetic fields in a capacitor coil target.

We demonstrated a high-power long-wave infrared laser based on a polarization beam coupling technique. An average output power at $8.3~\unicode[STIX]{x03BC}\text{m}$ of 7.0 W was achieved at a maximum available pump power of 107.6 W, corresponding to an optical-to-optical conversion of 6.5%. The coupling efficiency of the polarization coupling system was calculated to be approximately 97.2%. With idler single resonance operation, a good beam quality factor of ${\sim}1.8$ combined with an output wavelength of $8.3~\unicode[STIX]{x03BC}\text{m}$ was obtained at the maximum output power.

We address the power scaling issue in end-pumped laser rod amplifiers by studying, experimentally and numerically, the magnitude of thermal lensing in a high-energy diode-pumped Yb:YAG crystal. The spatio-temporal temperature profile of the gain medium and the focal length of the induced thermal lens are determined numerically. The influence of the repetition rate and pumping power on the temperature distribution is analyzed. Experimental measurements covered repetition rates between 1 and 10 Hz and up to 4 kW pumping power.

We report on mode-locked thulium-doped fiber lasers with high-energy nanosecond pulses, relying on the transmission in a semiconductor saturable absorber (SESA) and a carbon nanotube (CNTs-PVA) film separately. A section of an SMF–MMF–SMF structure multimode interferometer with a transmission peak wavelength of ∼2003 nm was used as a wavelength selector to fix the laser wavelength. When the SESA acted as a saturable absorber (SA), the mode-locked fiber laser had a maximum output power of ∼461 mW with a pulse energy of ∼0.14 μJ and a pulse duration of ∼9.14 ns. In a CNT-film-based mode-locked fiber laser, stable mode-locked pulses with the maximum output power of ∼46 mW, pulse energy of ∼26.8 nJ and pulse duration of ∼9.3 ns were obtained. To the best of our knowledge, our experiments demonstrated the first 2 μm region ‘real’ SA-based dissipative soliton resonance with the highest mode-locked pulse energy from a ‘real’ SA-based all-fiberized resonator.

The process of high energy electron acceleration along the surface of grating targets (GTs) that were irradiated by a relativistic, high-contrast laser pulse at an intensity $I=2.5\times 10^{20}~\text{W}/\text{cm}^{2}$ was studied. Our experimental results demonstrate that for a GT with a periodicity twice the laser wavelength, the surface electron flux is more intense for a laser incidence angle that is larger compared to the resonance angle predicted by the linear model. An electron beam with a peak charge of ${\sim}2.7~\text{nC}/\text{sr}$, for electrons with energies ${>}1.5~\text{MeV}$, was measured. Numerical simulations carried out with parameters similar to the experimental conditions also show an enhanced electron flux at higher incidence angles depending on the preplasma scale length. A theoretical model that includes ponderomotive effects with more realistic initial preplasma conditions suggests that the laser-driven intensity and preformed plasma scale length are important for the acceleration process. The predictions closely match the experimental and computational results.

Experimental and simulation data [Moreau et al., Plasma Phys. Control. Fusion 62, 014013 (2019); Kaymak et al., Phys. Rev. Lett. 117, 035004 (2016)] indicate that self-generated magnetic fields play an important role in enhancing the flux and energy of relativistic electrons accelerated by ultra-intense laser pulse irradiation with nanostructured arrays. A fully relativistic analytical model for the generation of the magnetic field based on electron magneto-hydrodynamic description is presented here. The analytical model shows that this self-generated magnetic field originates in the nonparallel density gradient and fast electron current at the interfaces of a nanolayered target. A general formula for the self-generated magnetic field is found, which closely agrees with the simulation scaling over the relevant intensity range. The result is beneficial to the experimental designs for the interaction of the laser pulse with the nanostructured arrays to improve laser-to-electron energy coupling and the quality of forward hot electrons.

We report on a compact and robust self-referenced optical frequency comb with a tunable repetition rate, generated by an all-polarization-maintaining (PM) mode-locked Er-doped fiber laser. The spacing between comb teeth can be tuned above 300 kHz at a repetition rate of 101 MHz. The repetition rate and the carrier–envelope offset of the laser are stabilized separately, and the relative residual phase noises are determined to be $336~\unicode[STIX]{x03BC}\text{rad}$ and 713 mrad (1 Hz–1 MHz). The accurate frequency characteristics and the stable structure show great potential for the use of such a comb in applications of precision measurements.

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.

White-light continuum can be induced by the interaction of intense femtosecond laser pulses with condensed materials. By using two orthogonal polarizers, a self-induced birefringence of continuum is observed when focusing femtosecond laser pulses into bulk fused silica. That is, the generated white-light continuum is synchronously modulated anisotropically while propagating in fused silica. Time-resolved detection confirms that self-induced birefringence of continuum shows a growth and saturation feature with time evolution. By adjusting laser energy, the transmitted intensity of continuum modulated by self-induced birefringence also varies correspondingly. Morphology analysis with time evolution indicates that it is the focused femtosecond laser pulses that induce anisotropic microstructures in bulk fused silica, and the anisotropic structures at the same time modulate the generated continuum.

We report on the successful demonstration of a 150 J nanosecond pulsed cryogenic gas cooled, diode-pumped multi-slab Yb:YAG laser operating at 1 Hz. To the best of our knowledge, this is the highest energy ever recorded for a diode-pumped laser system.