The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes to increase achievable ion energies and conversion efficiencies. Whilst the evolving nature of laser-plasma interactions can limit the effectiveness of individual acceleration mechanisms, it can also enable the development of hybrid schemes, allowing additional degrees of control on the properties of the resulting ion beam. Here we report on an experimental demonstration of efficient proton acceleration to energies exceeding 94 MeV via a hybrid scheme of radiation pressure-sheath acceleration in an ultrathin foil irradiated by a linearly polarised laser pulse. This occurs via a double-peaked electrostatic field structure, which, at an optimum foil thickness, is significantly enhanced by relativistic transparency and an associated jet of super-thermal electrons. The range of parameters over which this hybrid scenario occurs is discussed and implications for ion acceleration driven by next-generation, multi-petawatt laser facilities are explored.

(2016). Optically controlled dense current structures driven by relativistic plasma aperture-induced diffraction. Nature Physics, 12, 505-512. DOI: 10.1038/nphys3613 General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights.Take down policy The Research Portal is Queen's institutional repository that provides access to Queen's research output. Every effort has been made to ensure that content in the Research Portal does not infringe any person's rights, or applicable UK laws. If you discover content in the Research Portal that you believe breaches copyright or violates any law, please contact openaccess@qub.ac.uk. AbstractThe collective response of charged particles to intense fields is intrinsic to plasma accelerators and radiation sources, relativistic optics and many astrophysical phenomena. Here we show that the fundamental optical process of diffraction of intense laser light occurs via the self-generation of a relativistic plasma aperture in thin foils undergoing relativistic induced transparency. The plasma electrons collectively respond to the resulting near-field diffraction pattern, producing a beam of energetic electrons with spatial structure which can be controlled by variation of the laser pulse parameters. It is shown that static electron beam, and induced magnetic field, structures can be made to rotate at fixed or variable angular frequencies depending on the degree of ellipticity in the laser polarization. The concept is demonstrated numerically and verified experimentally. It is a viable step towards optical control of charged particle dynamics in laser-driven sources. * Electronic address: paul.mckenna@strath.ac.uk 1 The formation of current structures due to the collective response of charged particles to a perturbation is one of the most fundamental properties of plasma. This is manifest in plasma dynamics ranging from flares and X-ray jets on the sun to disruptive instabilities in fusion plasmas. This feature is also exploited to great effect in the development of compact laser-based particle accelerators and radiation sources, which have wide-ranging potential applications in science, medicine and industry. Controlling the collective motion of plasma electrons in response to perturbation produced by intense laser light is key to the development of these novel sources. Pertinent examples in plasma with density low enough for laser light to propagate (underdense plasma) include the self-generated plasma cavity or 'bubble' produced in laser-driven wakefield acceleration [1] and plasma channels [2]. These structures are formed principally by the ponderomotive force induced by the propagating laser pulse, which expels electrons from the regions of high laser intensity, and by self-generated fields induced by the current displacement [3]. Sh...

The properties of high energy density plasma are under increasing scrutiny in recent years due to their importance to our understanding of stellar interiors, the cores of giant planets 1 , and the properties of hot plasma in inertial confinement fusion devices 2 . When matter is heated by X-rays, electrons in the inner shells are ionized before the valence electrons. Ionization from the inside out creates atoms or ions with empty internal electron shells, which are known as hollow atoms (or ions) 3,4,5 . Recent advances in free-electron laser (FEL) technology 6,7,8,9 have made possible the creation of condensed matter consisting predominantly of hollow atoms. In this Letter, we demonstrate that such exotic states of matter, which are very far from equilibrium, can also be formed by more conventional optical laser technology when the laser intensity approaches the radiation dominant regime 10 . Such photon-dominated systems are relevant to studies of photoionized plasmas found in active galactic nuclei and X-ray binaries 11 . Our results promote laser-produced plasma as a unique ultra-bright x-ray source for future studies of matter in extreme conditions as well as for radiography of biological systems and for material science studies 12,13,14,15 .

Bright proton beams with maximum energies of up to 30MeV have been observed in an experiment investigating ion sheath acceleration driven by a short pulse (<50 fs) laser. The scaling of maximum proton energy and total beam energy content at ultra-high intensities of ∼10²¹ W cm^-2 was investigated, with the interplay between target thickness and laser pre-pulse found to be a key factor. While the maximum proton energies observed were maximised for lm-thick targets, the total proton energy content was seen to peak for thinner, 500 nm, foils. The total proton beam energy reached up to 440 mJ (a conversion efficiency of 4%), marking a significant step forward for many laser-driven ion applications. The experimental results are supported by hydrodynamic and particle-in-cell simulations

Article:Oks, E., Dalimier, E., Faenov, A. Ya et al. (16 more authors) (2017) Using X-ray spectroscopy of relativistic laser plasma interaction to reveal parametric decay instabilities : A modeling tool for astrophysics. Optics Express. pp. 1958-1972. ISSN 1094 https://doi.org/10.1364/OE.25.001958 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.Using X-ray spectroscopy of relativistic laser plasma interaction to reveal parametric decay instabilities: a modeling tool for astrophysics faenov.anatoly@photon.osaka-u.ac.jp Abstract: By analyzing profiles of experimental x-ray spectral lines of Si XIV and Al XIII, we found that both Langmuir and ion acoustic waves developed in plasmas produced via irradiation of thin Si foils by relativistic laser pulses (intensities ~10 21 W/cm 2 ). We prove that these waves are due to the parametric decay instability (PDI). This is the first time that the PDI-induced ion acoustic turbulence was discovered by the x-ray spectroscopy in laserproduced plasmas. These conclusions are also supported by PIC simulations. Our results can be used for laboratory modeling of physical processes in astrophysical objects and a better understanding of intense laser-plasma interactions. A. Pikuz, V. M. Romanova, and T. A. Shelkovenko, "High-performance X-ray spectroscopic devices for plasma microsources investigations," Phys. Scr. 50(4), 333-338 (1994 1122-1127 (1981). 39. P. Maine, D. Strickland, P. Bado, M. Pessot, and G. Mourou, "Generation of ultrahigh peak power pulses by chirped pulse amplification," IEEE J. Quantum Electron. 24(2), 398-403 (1988). 40. A. I. Akhiezer and R. V. Polovin, "Theory of wave motion of an electron plasma," Sov. Phys. JETP 3, 696-705 (1956). 41. W. Lünow, "On the relativistic non-linear interaction of cold plasma with electro-magnetic waves," Plasma Phys.10(9), 879-897 (1968). 42. S. Guérin, P. Mora, J. C. Adam, A. Heron, and G. Laval, "Propagation of ultraintense laser pulses through overdense plasma layers," Phys. Plasmas 3(7), 2693-2701 (1996)