This paper provides an overview of the current status of ultrafast and ultra-intense lasers with peak powers exceeding 100 TW and examines the research activities in high-energy-density physics within China. Currently, 10 high-intensity lasers with powers over 100 TW are operational, and about 10 additional lasers are being constructed at various institutes and universities. These facilities operate either independently or are combined with one another, thereby offering substantial support for both Chinese and international research and development efforts in high-energy-density physics.

The use of ultra-high intensity laser beams to achieve extreme material states in the laboratory has become almost routine with the development of the petawatt laser. Petawatt class lasers have been constructed for specific research activities, including particle acceleration, inertial confinement fusion and radiation therapy, and for secondary source generation (x-rays, electrons, protons, neutrons and ions). They are also now routinely coupled, and synchronized, to other large scale facilities including megajoule scale lasers, ion and electron accelerators, x-ray sources and z-pinches. The authors of this paper have tried to compile a comprehensive overview of the current status of petawatt class lasers worldwide. The definition of ‘petawatt class’ in this context is a laser that delivers >200 TW.

The Atomic Weapons Establishment (AWE) is tasked with supporting Continuous At Sea Deterrence (CASD) by certifying the performance and safety of the national deterrent in the Comprehensive Test Ban Treaty (CTBT) era. This means that recourse to further underground testing is not possible, and certification must be achieved by supplementing the historical data with the use of computer calculation. In order to facilitate this, AWE operates some of the largest supercomputers in the UK. To validate the computer codes, and indeed the designers who are using them, it is necessary to carry out further experiments in the right regimes. An excellent way to meet many of the requirements for material property data and to provide confidence in the validity of the algorithms is through experiments carried out on high power laser facilities.

This paper reviews the different challenges that are encountered in the delivery of high power lasers as drivers for fusion energy. We will focus on diode-pumped solid-state lasers and we will highlight some of the main recent achievements when using ytterbium, cryogenic cooling and ceramic gain media. Apart from some existing fusion facilities and some military applications of diode-pumped solid-state lasers, we will show that diode-pumped solid-state lasers are scalable to inertial fusion energy (IFE)’s facility level and that the all-fiber laser scheme is very promising.

The properties of a series of phase measurement techniques, including interferometry, the Hartmann-Shack wavefront sensor, the knife-edge technique, and coherent diffraction imaging, are summarized and their performance in high power laser applications is compared. The advantages, disadvantages, and application ranges of each technique are discussed.

The development, the underlying technology and the current status of the fully diode-pumped solid-state laser system POLARIS is reviewed. Currently, the POLARIS system delivers 4 J energy, 144 fs long laser pulses with an ultra-high temporal contrast of 5×1012 for the ASE, which is achieved using a so-called double chirped-pulse amplification scheme and cross-polarized wave generation pulse cleaning. By tightly focusing, the peak intensity exceeds 3.5×1020 W cm-2. These parameters predestine POLARIS as a scientific tool well suited for sophisticated experiments, as exemplified by presenting measurements of accelerated proton energies. Recently, an additional amplifier has been added to the laser chain. In the ramp-up phase, pulses from this amplifier are not yet compressed and have not yet reached the anticipated energy. Nevertheless, an output energy of 16.6 J has been achieved so far.

Laser resistance and stress-free mirrors, windows, polarizers, and beam splitters up to 400 mm×400 mm are required for the construction of the series SG facilities. In order to improve the coating quality, a program has been in place for the last ten years. For the small-aperture pick-off mirror, the laser-induced damage threshold (LIDT) is above 60 J/cm2 (1064 nm, 3 ns), and the reflected wavefront is less than λ/4 (λ=633 nm). The Brewster-angle polarizing beam splitter (Φ50×10 mm) shows the best LIDT result, up to 29.8 J/cm2 (1064 nm, 10 ns) for a p-polarized wave in the 2012 damage competition of the XLIV Annual Boulder Damage Symposium. For the larger-aperture mirror and polarizer, the LIDT is above 23 J/cm2 (1064 nm, 3 ns) and 14 J/cm2 (1064 nm, 3 ns), respectively. The reflected wavefront is less than λ=3 (λ=633 nm) at the used angle.

Beam positioning stability in a laser-driven inertial confinement fusion (ICF) facility is a vital problem that needs to be fixed. Each laser beam in the facility is transmitted in lots of optics for hundreds of meters, and then targeted in a micro-sized pellet to realize controllable fusion. Any turbulence in the environment in such long-distance propagation would affect the displacement of optics and further result in beam focusing and positioning errors. This study concluded that the errors on each of the optics contributed to the target, and it presents an efficient method of enhancing the beam stability by eliminating errors on error-sensitive optics. Optimizations of the optical system and mechanical supporting structures are also presented.

We review the use of hollow-core photonic crystal fibre (HC-PCF) for high power laser beam delivery. A comparison of bandgap HC-PCF with Kagome-lattice HC-PCF on the geometry, guidance mechanism, and optical properties shows that the Kagome-type HC-PCF is an ideal host for high power laser beam transportation because of its large core size, low attenuation, broadband transmission, single-mode guidance, low dispersion and the ultra-low optical overlap between the core-guided modes and the silica core-surround. The power handling capability of Kagome-type HC-PCF is further experimentally demonstrated by millijoule nanosecond laser spark ignition and 100 J sub-picosecond laser pulse transportation and compression.

The driving mechanism of solar flares and coronal mass ejections is a topic of ongoing debate, apart from the consensus that magnetic reconnection plays a key role during the impulsive process. While present solar research mostly depends on observations and theoretical models, laboratory experiments based on high-energy density facilities provide the third method for quantitatively comparing astrophysical observations and models with data achieved in experimental settings. In this article, we show laboratory modeling of solar flares and coronal mass ejections by constructing the magnetic reconnection system with two mutually approaching laser-produced plasmas circumfused of self-generated megagauss magnetic fields. Due to the Euler similarity between the laboratory and solar plasma systems, the present experiments demonstrate the morphological reproduction of flares and coronal mass ejections in solar observations in a scaled sense, and confirm the theory and model predictions about the current-sheet-born anomalous plasmoid as the initial stage of coronal mass ejections, and the behavior of moving-away plasmoid stretching the primary reconnected field lines into a secondary current sheet conjoined with two bright ridges identified as solar flares.

We will review some of the requirements for a laser that would be used with a laser fusion energy power plant, including frequency, spatial beam smoothing, bandwidth, temporal pulse shaping, efficiency, repetition rate, and reliability. The lowest risk and optimum approach uses a krypton fluoride gas laser. A diode-pumped solid-state laser is a possible contender.