A new near-infrared direct acceleration mechanism driven by Laguerre–Gaussian laser is proposed to stably accelerate and concentrate electron slice both in longitudinal and transversal directions in vacuum. Three-dimensional simulations show that a 2-μm circularly polarized ${\mathrm{LG}}_p^l$ (p = 0, l = 1, σz = −1) laser can directly manipulate attosecond electron slices in additional dimensions (angular directions) and give them annular structures and angular momentums. These annular vortex attosecond electron slices are expected to have some novel applications such as in the collimation of antiprotons in conventional linear accelerators, edge-enhancement electron imaging, structured X-ray generation, and analysis and manipulation of nanomaterials.

We report on a vortex laser chirped-pulse amplification (CPA) system that delivers pulses with a peak power of 45 TW. A focused intensity exceeding 1019 W/cm2 has been demonstrated for the first time by the vortex amplification scheme. Compared with other schemes of strong-field vortex generation with high energy flux but narrowband vortex-converting elements at the end of the laser, an important advantage of our scheme is that we can use a broadband but size-limited q-plate to realize broadband mode-converting in the front end of the CPA system, and achieve high-power amplification with a series of amplifiers. This method is low cost and can be easily implemented in an existing laser system. The results have verified the feasibility to obtain terawatt and even petawatt vortex laser amplification by a CPA system, which has important potential applications in strong-field laser physics, for example, generation of vortex particle beams with orbital angular momentum, fast ignition for inertial confinement fusion and simulation of the extreme astrophysical environment.

Proton radiography is a key diagnostics to measure and image the electric/magnetic field in laser-produced plasmas. A thin solid target is irradiated with an intense laser pulse to produce a proton beam. The accelerated proton can achieve higher energy with thinner target. In order to produce an extremely thin target, we have developed a large-area suspended graphene as a laser target for energetic ion sources. We describe the manufacturing process of the suspended graphene, and show the results of quality evaluations.

We produced $5\text{-}{\rm\mu}\text{J}$, 6.5-fs visible pulses at a repetition rate of 1 kHz using filamentation in a gas cell filled with krypton followed by spectral selection and phase compensation by a combination of dielectric mirrors. The visible pulses have a smooth spectrum from 520 to 650 nm with a shot-to-shot stability in each spectral component of better than 2% (standard deviation). This pulse compression scheme is simple and robust, and can be easily integrated into intense ultrashort-pulse laser systems.

All space–time coupling effects arising in an asymmetric optical compressor consisting of two non-identical pairs of diffraction gratings are described analytically. In each pair, the gratings are identical and parallel to each other, whereas the distance between the gratings, the groove density and the angle of incidence are different in different pairs. It is shown that the compressor asymmetry does not affect the far-field fluence and on-axis focal intensity. The main distinctive feature of the asymmetric compressor is spatial noise lagging behind or overtaking the main pulse in proportion to the transverse wave vector. This results in a degraded contrast but reduces beam fluence fluctuations at the compressor output. Exact expressions are obtained for the spectrum of fluence fluctuations and fluence root mean square that depends only on one parameter characterizing compressor asymmetry. The efficiency of small-scale self-focusing suppression at subsequent pulse post-compression is estimated.

In this work, a confined-doped fiber with the core/inner-cladding diameter of 40/250 μm and a relative doping ratio of 0.75 is fabricated through a modified chemical vapor deposition method combined with the chelate gas deposition technique, and subsequently applied in a tandem-pumped fiber amplifier for high-power operation and transverse mode instability (TMI) mitigation. Notably, the impacts of the seed laser power and mode purity are preliminarily investigated through comparative experiments. It is found that the TMI threshold could be significantly affected by the seed laser mode purity. The possible mechanism behind this phenomenon is proposed and revealed through comprehensive comparative experiments and theoretical analysis. Finally, a maximum output power of 7.49 kW is obtained with the beam quality factor of approximately 1.83, which is the highest output power ever reported in a forward tandem-pumped confined-doped fiber amplifier. This work could provide a good reference and practical solution to improve the TMI threshold and realize high-power high-brightness fiber lasers.

Tailored diode laser single emitters with long (6 mm) resonators and wide (1.2 mm) emission apertures that operate with 940 nm emission wavelength were assembled in novel edge-cooled vertically stacked arrays, and used to construct a compact and highly efficient fiber coupled pump source for Yb:YAG pulsed high-energy class solid-state lasers. The novel configuration is shown to allow repetition rates of 200 Hz at 1 ms pulse duration, at an output power of 130 W per single emitter. The emission of two stacked arrays was then optically combined to realize pump modules that deliver 6 kW peak power (pulse energy 6 J) from a 1.9 mm core diameter fiber, with wall plug efficiency of 50%. This represents a significant improvement in terms of duty cycle and electro-optical efficiency over conventional sources. The pump module has been successfully tested at the Max Born Institute, Berlin during trials for pumping of disk lasers.

The interaction of relativistically intense lasers with opaque targets represents a highly non-linear, multi-dimensional parameter space. This limits the utility of sequential 1D scanning of experimental parameters for the optimization of secondary radiation, although to-date this has been the accepted methodology due to low data acquisition rates. High repetition-rate (HRR) lasers augmented by machine learning present a valuable opportunity for efficient source optimization. Here, an automated, HRR-compatible system produced high-fidelity parameter scans, revealing the influence of laser intensity on target pre-heating and proton generation. A closed-loop Bayesian optimization of maximum proton energy, through control of the laser wavefront and target position, produced proton beams with equivalent maximum energy to manually optimized laser pulses but using only 60% of the laser energy. This demonstration of automated optimization of laser-driven proton beams is a crucial step towards deeper physical insight and the construction of future radiation sources.

Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion. Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a challenging task. In this work, we report, for the first time to the best of our knowledge, the time-dependent measurement of the reflected light of a terawatt laser pulse from the laser-produced plasma of low-Z foam material of overcritical density. The experiments have been performed with the ABC laser, with targets constituted by foam of overcritical density and by solid media of the same chemical composition. We implemented in the MULTI-FM code a model for the light reflection to reproduce and interpret the experimental results. Using the simulations together with the experimental results, we indicate a criterion for estimating the homogenization time of the laser-produced plasma, whose measurement is challenging with direct diagnostic techniques and still not achieved.

Laser-induced damage (LID) on high-power laser facilities is one of the limiting factors for the increase in power and energy. Inertial confinement fusion (ICF) facilities such as Laser Mégajoule or the National Ignition Facility use spectral broadening of the laser pulse that may induce power modulations because of frequency modulation to amplitude modulation conversion. In this paper, we study the impact of low and fast power modulations of laser pulses both experimentally and numerically. The MELBA experimental testbed was used to shape a wide variety of laser pulses and to study their impact on LID. A 1D Lagrangian hydrodynamic code was used to understand the impact of different power profiles on LID.

The laser system PALS, as a driver of a broad-beam ion source, delivered deuterons which generated neutrons with energies higher than 14 MeV through the $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{}^{7}\mathrm{Li(d,n)}{}^{8}\mathrm{Be}$ reaction. Deuterons with sub-MeV energy were accelerated from the front surface of a massive $\mathrm{CD}_{2}$ target in the backward direction with respect to the laser beam vector. Simultaneously, neutrons were emitted from the primary $\mathrm{CD}_{2}$ target and a secondary LiF catcher. The total maximum measured neutron yield from ${}^{2}\mathrm{D(d,n)}{}^{3}\mathrm{He}$, ${}^{7}\mathrm{Li(d,n)}{}^{8}\mathrm{Be}$, ${}^{12}\mathrm{C(d,n)}{}^{13}\mathrm{N}$ reactions was ${\sim } 3.5 ({\pm }0.5) \times 10^{8}\ \mathrm{neutrons/shot}$.

We demonstrate a diode-pumped femtosecond Yb:CaGdAlO4 (Yb:CALGO) laser with a semiconductor saturable absorber mirror (SESAM) for stable mode-locking operation. A perfect beam profile is measured under 10 W output power with $M_{x}^{2}$ = 1.017 and $M_{y}^{2}$ = 1.016 in the horizontal and vertical directions, respectively. At the repetition rate of 71.66 MHz, the optical pulse duration is 247 fs and the pulse energy is 140 nJ at the central wavelength of 1041 nm, corresponding to a peak power of 0.56 MW. In addition, we also generate continuous wave (CW) power of more than 15 W with TEM00 mode, corresponding to an optical-to-optical efficiency of 44.1%.

High-power continuous-wave single-frequency Er-doped fiber amplifiers at 1560 nm by in-band and core pumping of a 1480 nm Raman fiber laser are investigated in detail. Both co- and counter-pumping configurations are studied experimentally. Up to 59.1 W output and 90% efficiency were obtained in the fundamental mode and linear polarization in the co-pumped case, while less power and efficiency were achieved in the counter-pumped setup for additional loss. The amplifier performs indistinguishably in terms of laser linewidth and relative intensity noise in the frequency range up to 10 MHz for both configurations. However, the spectral pedestal is raised in co-pumping, caused by cross-phase modulation between the pump and signal laser, which is observed and analyzed for the first time. Nevertheless, the spectral pedestal is 34.9 dB below the peak, which has a negligible effect for most applications.

Multilayer dielectric gratings typically remove multiple-grating pillars after picosecond laser irradiation; however, the dynamic formation process of the removal is still unclear. In this study, the damage morphologies of multilayer dielectric gratings induced by an 8.6-ps laser pulse were closely examined. The damage included the removal of a single grating pillar and consecutive adjacent grating pillars and did not involve the destruction of the internal high-reflection mirror structure. Comparative analysis of the two damage morphological characteristics indicated the removal of adjacent pillars was related to an impact process caused by the eruption of localized materials from the left-hand pillar, exerting impact pressure on its adjacent pillars and eventually resulting in multiple pillar removal. A finite-element strain model was used to calculate the stress distribution of the grating after impact. According to the electric field distribution, the eruptive pressure of the dielectric materials after ionization was also simulated. The results suggest that the eruptive pressure resulted in a stress concentration at the root of the adjacent pillar that was sufficient to cause damage, corresponding to the experimental removal of the adjacent pillar from the root. This study provides further understanding of the laser-induced damage behavior of grating pillars and some insights into reducing the undesirable damage process for practical applications.

A new specially correlated partially coherent beam named nonuniform multi-Gaussian correlated (NMGC) partially coherent beam is introduced. The correlation functions of such beam in $x$ and $y$ directions are different from each other, i.e., nonuniform correlation function in one direction and multi-Gaussian correlated Schell-model function in the other direction. The propagation properties of an NMGC partially coherent beam in free pace are demonstrated, and we find that the intensity distribution of such beam exhibits self-focusing and self-shifting effect in one direction and self-shaping effect in the other direction on propagation. The correlation-induced self-focusing and self-shaping effect will be useful in some applications, where the high power and shaped laser is required, such as material thermal processing and laser carving.

Measured highly elevated gains of proton–boron (HB11) fusion (Picciotto et al., Phys. Rev. X 4, 031030 (2014)) confirmed the exceptional avalanche reaction process (Lalousis et al., Laser Part. Beams 32, 409 (2014); Hora et al., Laser Part. Beams 33, 607 (2015)) for the combination of the non-thermal block ignition using ultrahigh intensity laser pulses of picoseconds duration. The ultrahigh acceleration above $10^{20}~\text{cm}~\text{s}^{-2}$ for plasma blocks was theoretically and numerically predicted since 1978 (Hora, Physics of Laser Driven Plasmas (Wiley, 1981), pp. 178 and 179) and measured (Sauerbrey, Phys. Plasmas 3, 4712 (1996)) in exact agreement (Hora et al., Phys. Plasmas 14, 072701 (2007)) when the dominating force was overcoming thermal processes. This is based on Maxwell’s stress tensor by the dielectric properties of plasma leading to the nonlinear (ponderomotive) force $f_{\text{NL}}$ resulting in ultra-fast expanding plasma blocks by a dielectric explosion. Combining this with measured ultrahigh magnetic fields and the avalanche process opens an option for an environmentally absolute clean and economic boron fusion power reactor. This is supported also by other experiments with very high HB11 reactions under different conditions (Labaune et al., Nature Commun. 4, 2506 (2013)).

We report on the design and first results from experiments looking at the formation of radiative shocks on the Shenguang-II (SG-II) laser at the Shanghai Institute of Optics and Fine Mechanics in China. Laser-heating of a two-layer CH/CH–Br foil drives a $\sim 40$ km/s shock inside a gas cell filled with argon at an initial pressure of 1 bar. The use of gas-cell targets with large (several millimetres) lateral and axial extent allows the shock to propagate freely without any wall interactions, and permits a large field of view to image single and colliding counter-propagating shocks with time-resolved, point-projection X-ray backlighting ($\sim 20$ μm source size, 4.3 keV photon energy). Single shocks were imaged up to 100 ns after the onset of the laser drive, allowing to probe the growth of spatial nonuniformities in the shock apex. These results are compared with experiments looking at counter-propagating shocks, showing a symmetric drive that leads to a collision and stagnation from $\sim 40$ ns onward. We present a preliminary comparison with numerical simulations with the radiation hydrodynamics code ARWEN, which provides expected plasma parameters for the design of future experiments in this facility.

Processes of laser energy absorption and electron heating in an expanding plasma in the range of irradiances $I\unicode[STIX]{x1D706}^{2}=10^{15}{-}10^{16}~\text{W}\,\cdot \,\unicode[STIX]{x03BC}\text{m}^{2}/\text{cm}^{2}$ are studied with the aid of kinetic simulations. The results show a strong reflection due to stimulated Brillouin scattering and a significant collisionless absorption related to stimulated Raman scattering near and below the quarter critical density. Also presented are parametric decay instability and resonant excitation of plasma waves near the critical density. All these processes result in the excitation of high-amplitude electron plasma waves and electron acceleration. The spectrum of scattered radiation is significantly modified by secondary parametric processes, which provide information on the spatial localization of nonlinear absorption and hot electron characteristics. The considered domain of laser and plasma parameters is relevant for the shock ignition scheme of inertial confinement fusion.

We demonstrate an all-fiber high-power linearly polarized supercontinuum source with polarization-maintaining photonic crystal fibers (PM-PCFs) as the nonlinear medium. The source exhibits an average output power of 3.8 W with a flat spectrum from 480 nm to 2100 nm at the $-$10 dB level, except for the residual pump peak. The polarization extinction ratio (PER) is measured to be greater than 20 dB at selected sample wavelength points (532 nm, 1064 nm and 1550 nm) at the highest pump power level and greater than 20 dB at all wavelengths from 800 nm to 1500 nm at the low pump power level. We also experimentally study the spectral properties when the pump light propagates along different axes of the PM-PCF. The results show that propagating parallel to the slow axis enables a broader spectrum in the PM-PCF in this case, probably due to matching of the dispersion properties with the pump light, which is qualitatively in accordance with the numerical simulation. To our best knowledge, this is the first demonstration of a watt-level linearly polarized supercontinuum source generated from PM-PCFs in an all-fiber structure.

In inertial fusion energy (IFE) research, a number of technological issues have focused on the ability to inexpensively fabricate large quantities of free-standing targets (FSTs) by developing a specialized layering module with repeatable operation. Of central importance for the progress towards plasma generation with intense thermonuclear reactions is the fuel structure, which must be isotropic to ensure that fusion will take place. In this report, the results of modeling the FST layering time, $\unicode[STIX]{x1D70F}_{\text{Form}}$, are presented for targets which are shells of ${\sim}4~\text{mm}$ in diameter with a wall made from compact and porous polymers. The layer thickness is ${\sim}200~\unicode[STIX]{x03BC}\text{m}$ for pure solid fuel and ${\sim}250~\unicode[STIX]{x03BC}\text{m}$ for in-porous solid fuel. Computation shows $\unicode[STIX]{x1D70F}_{\text{Form}}<23$  s for $\text{D}_{2}$ fuel and $\unicode[STIX]{x1D70F}_{\text{Form}}<30$  s for D–T fuel. This is an excellent result in terms of minimizing the tritium inventory, producing IFE targets in massive numbers (${\sim}$1 million each day) and obtaining the fuel as isotropic ultrafine layers. It is shown experimentally that such small layering time can be realized by the FST layering method in line-moving, high-gain direct-drive cryogenic targets using $n$-fold-spiral layering channels at $n=2,3$.