International audienceELECTRONS in a plasma undergo collective wave-like oscillations near the plasma frequency. These plasma waves can have a range of wavelengths and hence a range of phase velocities1. Of particular note are relativistic plasma waves2,3, for which the phase velocity approaches the speed of light; the longitudinal electric field associated with such waves can be extremely large, and can be used to accelerate electrons (either injected externally or supplied by the plasma) to high energies over very short distances2á¤-4. The maximum electric field, and hence maximum acceleration rate, that can be obtained in this way is determined by the maximum amplitude of oscillation that can be supported by the plasma5á¤-8. When this limit is reached, the plasma wave is said to ᤘbreakᤙ. Here we report observations of relativistic plasma waves driven to breaking point by the Raman forward-scattering instability9,10 induced by short, high-intensity laser pulses. The onset of wave-breaking is indicated by a sudden increase in both the number and maximum energy (up to 44 MeV) of accelerated plasma electrons, as well as by the loss of coherence of laser light scattered from the plasma wave

The interaction of a 1053 nm picosecond laser pulse with a solid target has been studied for focused intensities of up to 10 19 W cm Ϫ2. The maximum ion energy cutoff E max ͑which is related to the hot electron temperature͒ is in the range 1.0-12.0 MeV and is shown to scale as E max ϷI 1/3. The hot electron temperatures were in the range 70-400 keV for intensities up to 5ϫ10 18 W cm Ϫ2 with an indication of a high absorption of laser energy. Measurements of x-ray/␥-ray bremsstrahlung emission suggest the existence of at least two electron temperatures. Collimation of the plasma flow has been observed by optical probing techniques.

In the 2015 review paper ‘Petawatt Class Lasers Worldwide’ a comprehensive overview of the current status of high-power facilities of ${>}200~\text{TW}$ was presented. This was largely based on facility specifications, with some description of their uses, for instance in fundamental ultra-high-intensity interactions, secondary source generation, and inertial confinement fusion (ICF). With the 2018 Nobel Prize in Physics being awarded to Professors Donna Strickland and Gerard Mourou for the development of the technique of chirped pulse amplification (CPA), which made these lasers possible, we celebrate by providing a comprehensive update of the current status of ultra-high-power lasers and demonstrate how the technology has developed. We are now in the era of multi-petawatt facilities coming online, with 100 PW lasers being proposed and even under construction. In addition to this there is a pull towards development of industrial and multi-disciplinary applications, which demands much higher repetition rates, delivering high-average powers with higher efficiencies and the use of alternative wavelengths: mid-IR facilities. So apart from a comprehensive update of the current global status, we want to look at what technologies are to be deployed to get to these new regimes, and some of the critical issues facing their development.

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.

No abstract

The Vulcan Nd : glass laser at the Central Laser Facility is a Petawatt (10 15 W) interaction facility available to the UK and international user community. The facility came online to users in 2002 and considerable experience has been gained operating the Vulcan facility in this mode. The facility is designed to deliver irradiance on target of 10 21 W cm −2 for a wide-ranging experimental programme in fundamental physics and advanced applications. This includes the interaction of super-high-intensity light with matter, fast ignition fusion research, photon induced nuclear reactions, electron and ion acceleration by light waves and the exploration of the exotic world of plasma physics dominated by relativity.

International audienceThe spatial extent of the plasma wave and the spectrum of the accelerated electrons are simultaneously measured when the relativistic plasma wave associated with Raman forward scattering of an intense laser beam reaches the wave breaking limit. The maximum observed energy of 94 MeV is greater than that expected from the phase slippage between the electrons and the accelerating electric field as given by the linear theory for preinjected electrons. The results are in good agreement with 2D particle-in-cell code simulations of the experiment

International audienceExperiments were performed using high-power laser pulses (greater than 50 TW) focused into underdense helium, neon, or deuterium plasmas (ne∼5×1019cm−3). Ions having energies greater than 300 keV were measured to be produced primarily at 90° to the axis of laser propagation. Ion energies greater than 6 MeV were recorded from interactions with neon. Images of the ion emission were also obtained, and it is possible that spatially resolved measurements of the ion energy spectrum can provide a method to estimate the intensity of the focused radiation in the interaction region