Publications


Observation of K-Shell Soft X Ray Emission of Nitrogen Irradiated by XUV-Free Electron Laser FLASH at Intensities Greater than 1016 W/cm2

Contributions to Plasma Physics 51 (2011) 284-287

E Galtier, E Galtier, FB Rosmej, FB Rosmej, O Renner, L Juha, J Chalupsky, JC Gauthier, S White, D Riley, S Vinko, T Witcher, J Wark, B Nagler, RW Lee, AJ Nelson, S Toleikis

In the past few years, the development of light sources of the 4th generation, namely XUV/X-ray Free Electron Lasers provides to the scientific community outstanding tools to investigate matter under extreme conditions never obtained in laboratories so far. As theory is at its infancy, the analysis of matter via the self-emission of the target is of central importance. The characterization of such dense matter is possible if photons can escape the medium. As the absorption of K-shell X-ray transitions is minimal, it plays a key role in this study. We report here the first successful observation of K-shell emission of Nitrogen at 430 eV using an XUV-Free Electron Laser to irradiate solid Boron Nitride targets under exceptional conditions: photon energy of 92 eV, pulse duration of ∼20 fs, micro focusing leading to intensities larger than 1016 W/cm2. Using a Bragg crystal of THM coupled to a CCD, we resolved K-shell line emission from different charge states. We demonstrate that the spectroscopic data allow characterization of electron heating processes when X-ray radiation is interacting with solid matter. As energy transport is non-trivial because the light source is monochromatic, these results have an important impact on the theory. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Measuring fast electron distribution functions at intensities up to 1021 W cm-2

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (2011)

N Booth, RJ Clarke, D Doria, LA Gizzi, G Gregori, P Hakel, P Koester, L Labate, T Levato, B Li, M Makita, RC Mancini, J Pasley, PP Rajeev, D Riley, APL Robinson, E Wagenaars, JN Waugh, NC Woolsey


Towards laboratory produced relativistic electron-positron pair plasmas

High Energy Density Physics 7 (2011) 225-229

H Chen, DD Meyerhofer, SC Wilks, R Cauble, F Dollar, K Falk, G Gregori, A Hazi, EI Moses, CD Murphy, J Myatt, J Park, J Seely, R Shepherd, A Spitkovsky, C Stoeckl, CI Szabo, R Tommasini, C Zulick, P Beiersdorfer

We review recent experimental results on the path to producing electron-positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 1016 cm-3 and 1013 cm-3, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 1018 cm-3, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter. © 2011 Elsevier B.V.


Simulations of efficient Raman amplification into the multipetawatt regime

Nature Physics 7 (2011) 87-92

RMGM Trines, RMGM Trines, F Fiúza, R Bingham, R Bingham, RA Fonseca, RA Fonseca, LO Silva, RA Cairns, PA Norreys, PA Norreys

Contemporary high-power laser systems make use of solid-state laser technology to reach petawatt pulse powers. The breakdown threshold for optical components in these systems, however, demands metre-scale beams. Raman amplification of laser beams promises a breakthrough by the use of much smaller amplifying media, that is, millimetre-diameter plasmas, but so far only 60 GW peak powers have been obtained in the laboratory, far short of the desired multipetawatt regime. Here we show, through the first large-scale multidimensional particle-in-cell simulations of this process, that multipetawatt peak powers can be reached, but only in a narrow parameter window dictated by the growth of plasma instabilities. Raman amplification promises reduced cost and complexity of intense lasers, enabling much greater access to higher-intensity regimes for scientific and industrial applications. Furthermore, we show that this process scales to short wavelengths, enabling compression of X-ray free-electron laser pulses to attosecond duration. © 2011 Macmillan Publishers Limited. All rights reserved.


Decay of cystalline order and equilibration during the solid-to-plasma transition induced by 20-fs microfocused 92-eV free-electron-laser pulses.

Phys Rev Lett 106 (2011) 164801-

E Galtier, FB Rosmej, T Dzelzainis, D Riley, FY Khattak, P Heimann, RW Lee, AJ Nelson, SM Vinko, T Whitcher, JS Wark, T Tschentscher, S Toleikis, RR Fäustlin, R Sobierajski, M Jurek, L Juha, J Chalupsky, V Hajkova, M Kozlova, J Krzywinski, B Nagler

We have studied a solid-to-plasma transition by irradiating Al foils with the FLASH free electron laser at intensities up to 10(16)  W/cm(2). Intense XUV self-emission shows spectral features that are consistent with emission from regions of high density, which go beyond single inner-shell photoionization of solids. Characteristic features of intrashell transitions allowed us to identify Auger heating of the electrons in the conduction band occurring immediately after the absorption of the XUV laser energy as the dominant mechanism. A simple model of a multicharge state inverse Auger effect is proposed to explain the target emission when the conduction band at solid density becomes more atomiclike as energy is transferred from the electrons to the ions. This allows one to determine, independent of plasma simulations, the electron temperature and density just after the decay of crystalline order and to characterize the early time evolution.


X-ray laser-induced ablation of lead compounds

Proceedings of SPIE - The International Society for Optical Engineering 8077 (2011)

V Hájková, L Juha, P Boháček, T Burian, J Chalupský, L Vyŝín, J Gaudin, PA Heimann, SP Hau-Riege, M Jurek, D Klinger, J Pelka, R Sobierajski, J Krzywinski, M Messerschmidt, SP Moeller, B Nagler, M Rowen, WF Schlotter, ML Swiggers, JJ Turner, SM Vinko, T Whitcher, J Wark, M Matuchová, S Bajt, H Chapman, T Dzelzainis, D Riley, J Andreasson, J Hajdu, B Iwan, N Timneanu, K Saksl, R Fäustlin, A Singer, K Tiedtke, S Toleikis, I Vartaniants, H Wabnitz

The recent commissioning of a X-ray free-electron laser triggered an extensive research in the area of X-ray ablation of high-Z, high-density materials. Such compounds should be used to shorten an effective attenuation length for obtaining clean ablation imprints required for the focused beam analysis. Compounds of lead (Z=82) represent the materials of first choice. In this contribution, single-shot ablation thresholds are reported for PbWO4 and PbI2 exposed to ultra-short pulses of extreme ultraviolet radiation and X-rays at FLASH and LCLS facilities, respectively. Interestingly, the threshold reaches only 0.11 J/cm2 at 1.55 nm in lead tungstate although a value of 0.4 J/cm2 is expected according to the wavelength dependence of an attenuation length and the threshold value determined in the XUV spectral region, i.e., 79 mJ/cm2 at a FEL wavelength of 13.5 nm. Mechanisms of ablation processes are discussed to explain this discrepancy. Lead iodide shows at 1.55 nm significantly lower ablation threshold than tungstate although an attenuation length of the radiation is in both materials quite the same. Lower thermal and radiation stability of PbI2 is responsible for this finding. © 2011 SPIE.


In-situ determination of dispersion and resolving power in simultaneous multiple-angle XUV spectroscopy

Journal of Instrumentation 6 (2011)

U Zastrau, V Hilbert, C Brown, T Döppner, S Dziarzhytski, E Förster, E Förster, H Glenzer, S Göde, G Gregori, M Harmand, D Hochhaus, T Laarmann, J Lee, KH Meiwes-Broer, P Neumayer, A Przystawik, P Radcliffe, M Schulz, S Skruszewicz, F Tavella, J Tiggesbäumker, S Toleikis, S Toleikis, T White

We report on the simultaneous determination of non-linear dispersion functions and resolving power of three flat-field XUV grating spectrometers. A moderate-intense short-pulse infrared laser is focused onto technical aluminum which is commonly present as part of the experimental setup. In the XUV wavelength range of 10-19 nm, the spectrometers are calibrated using Al-Mg plasma emission lines. This cross-calibration is performed in-situ in the very same setup as the actual main experiment. The results are in excellent agreement with ray-tracing simulations. We show that our method allows for precise relative and absolute calibration of three different XUV spectrometers. © 2011 IOP Publishing Ltd and SISSA.


Measuring fast electron distribution functions at intensities up to 10 21 W cm-2

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 653 (2011) 137-139

N Booth, N Booth, RJ Clarke, D Doria, LA Gizzi, G Gregori, P Hakel, P Koester, L Labate, T Levato, B Li, M Makita, RC Mancini, J Pasley, J Pasley, PP Rajeev, D Riley, APL Robinson, E Wagenaars, JN Waugh, NC Woolsey

Here we present results from ultra-intense experiments demonstrating the viability of polarization spectroscopy as a diagnostic of the electron return current and spatial anisotropy and distribution function of the fast electron beam. The measurements extend to ultra-relativistic intensities of 10 21 W cm-2, including laserplasma interaction regimes important for fast ignition studies, for example HiPER, and the development of secondary sources from next generation ultra-short pulse, ultra-intense laser facilities such as Astra-Gemini and ELI. As an in situ diagnostic, spectroscopic measurements are vital to understanding fast electron beams, enabling extrapolation of results to define fast ignition inertial confinement fusion and secondary source facilities. © 2011 Elsevier B.V.


The zero vector potential mechanism of attosecond absorption

Physics of Plasmas 18 (2011)

T Baeva, S Gordienko, APL Robinson, PA Norreys

A new mechanism for the absorption of energy during the interaction between an ultra-intense laser pulse and a sharp-edged overdense plasma, which we term the zero vector potential (ZVP) mechanism, is presented. The ZVP-mechanism is a nonponderomotive absorption mechanism that should dominate in the interaction of very strong short laser pulses (a 0≫1) with overdense plasmas in the case of sharp density gradients. In the ZVP-mechanism the existence of moving zeroes in the vector potential of the relativistic skin layer is crucial to the generation of both fast electron bunches and coherent x-rays. We demonstrate that the laser energy is absorbed from the plasma on the attosecond timescale in the form of electron bunches with unprecedentedly short duration. The numerical simulations are able to validate all qualitative and quantitative aspects of the ZVP-mechanism. © 2011 American Institute of Physics.


Vibrational excitation induced by electron beam and cosmic rays in normal and superconductive aluminum bars

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (2011)

M Bassan, B Buonomo, G Cavallari, E Coccia, S D'Antonio, V Fafone, LG Foggetta, C Ligi, A Marini, G Mazzitelli, G Modestino, G Pizzella, L Quintieri, F Ronga, P Valente, SM Vinko


Precision X-ray spectroscopy of intense laser-plasma interactions

High Energy Density Physics 7 (2011) 105-109

NC Woolsey, RJ Clarke, D Doria, LA Gizzi, G Gregori, P Hakel, SB Hansen, P Koester, L Labate, T Levato, B Li, M Makita, RC Mancini, J Pasley, J Pasley, PP Rajeev, APL Robinson, E Wagenaars, JN Waugh, N Booth, N Booth

Polarisation sensitive emission spectroscopy measurements are reported for a petawatt laser-solid target interaction at intensities up to 5 × 1020 W cm-2. These measurements were single-shot and used pairs of highly-orientated graphite spectrometers to resolve the sulphur Ly-α doublet. The sulphur Ly-α1 component shows a large positive polarisation indicative of a low energy electron beam in the plasma, the Ly-α2 component acts as a cross-spectrometer calibration. The measurements show a significant anisotropic or beam-like component to a cold return current. © 2011 Elsevier B.V.


Decay of Cystalline Order and Equilibration during the Solid-to-Plasma Transition Induced by 20-fs Microfocused 92-eV Free-Electron-Laser Pulses

PHYSICAL REVIEW SPECIAL TOPICS-ACCELERATORS AND BEAMS 14 (2011) ARTN 164801

E Galtier, FB Rosmej, T Dzelzainis, D Riley, FY Khattak, P Heimann, RW Lee, AJ Nelson, SM Vinko, T Whitcher, JS Wark, T Tschentscher, S Toleikis, RR Faeustlin, R Sobierajski, M Jurek, L Juha, J Chalupsky, V Hajkova, M Kozlova, J Krzywinski, B Nagler


Investigation of fast electron energy coupling in a counter-propagating scheme

38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts 35 2 (2011) 1484-1487

P Koester, P Koester, N Booth, CA Cecchetti, CA Cecchetti, H Chen, RG Evans, G Gregori, L Labate, L Labate, T Levato, B Li, M Makita, J Mithen, C Murphy, M Notley, R Pattathil, D Riley, N Woolsey, LA Gizzi, LA Gizzi

A detailed knowledge of the physical phenomena underlying the transport of fast electrons generated in high-intensity laser-matter interactions is of fundamental importance for the fast ignition scheme for inertial confinement fusion. The fast electron currents largely exceed the Alfven limit, therefore a balancing return current is required to support the propagation of the fast electron beam in the target medium. An experimental study aimed at investigating the role of the return current on the dynamics of the fast electron beam was carried out with the Vulcan Petawatt beam. Two counter-propagating electron beams were generated by double-sided irradiation of a layered target containing a 5 micron thick Ti layer. Information on the energy coupling of the fast electron beam to the Ti layer was retrieved through X-ray measurements. In particular, high-resolution X-ray spectroscopy of the Ti emission lines was performed in the spectral range from 4.4 to 5.1 keV including the Lyα, the Heα and the Kα line. Spectra were acquired for double-sided irradiation with different timings between the two laser beams as well as for single-sided irradiation. The recorded spectra indicate a higher target temperature for a precise timing between the two beams in agreement with simulation results.


In-situ determination of dispersion and resolving power in simultaneous multiple-angle XUV spectroscopy

JOURNAL OF INSTRUMENTATION 6 (2011) ARTN P10001

U Zastrau, V Hilbert, C Brown, T Doeppner, S Dziarzhytski, E Foerster, SH Glenzer, S Goede, G Gregori, M Harmand, D Hochhaus, T Laarmann, HJ Lee, K-H Meiwes-Broer, P Neumayer, A Przystawik, P Radcliffe, M Schulz, S Skruszewicz, F Tavella, J Tiggesbaeumker, S Toleikis, T White


Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser.

Phys Rev E Stat Nonlin Soft Matter Phys 83 (2011) 016403-

J Andreasson, B Iwan, A Andrejczuk, E Abreu, M Bergh, C Caleman, AJ Nelson, S Bajt, J Chalupsky, HN Chapman, RR Fäustlin, V Hajkova, PA Heimann, B Hjörvarsson, L Juha, D Klinger, J Krzywinski, B Nagler, GK Pálsson, W Singer, MM Seibert, R Sobierajski, S Toleikis, T Tschentscher, SM Vinko, RW Lee, J Hajdu, N Tîmneanu

Studies of materials under extreme conditions have relevance to a broad area of research, including planetary physics, fusion research, materials science, and structural biology with x-ray lasers. We study such extreme conditions and experimentally probe the interaction between ultrashort soft x-ray pulses and solid targets (metals and their deuterides) at the FLASH free-electron laser where power densities exceeding 10(17) W/cm(2) were reached. Time-of-flight ion spectrometry and crater analysis were used to characterize the interaction. The results show the onset of saturation in the ablation process at power densities above 10(16) W/cm(2). This effect can be linked to a transiently induced x-ray transparency in the solid by the femtosecond x-ray pulse at high power densities. The measured kinetic energies of protons and deuterons ejected from the surface reach several keV and concur with predictions from plasma-expansion models. Simulations of the interactions were performed with a nonlocal thermodynamic equilibrium code with radiation transfer. These calculations return critical depths similar to the observed crater depths and capture the transient surface transparency at higher power densities.


Numerical simulation of plasma-based raman amplification of laser pulses to petawatt powers

IEEE Transactions on Plasma Science 39 (2011) 2622-2623

RMGM Trines, F Fiuza, RA Fonseca, RA Fonseca, LO Silva, R Bingham, RA Cairns, PA Norreys

Contemporary high-power laser systems make use of solid-state laser technology to reach petawatt pulse powers. The breakdown threshold for optical components in these systems, however, demands beam diameters up to 1 m. Raman amplification of laser beams promises a breakthrough by the use of much smaller amplifying media, i.e., millimeter-diameter-wide plasmas. Through the first large-scale multidimensional particle-in-cell simulations of this process, we have identified the parameter regime where multipetawatt peak laser powers can be reached, while the influence of damaging laser-plasma instabilities is only minor. Snapshots of the probe laser pulse being amplified, generated using state-of-the-art visualization techniques, are presented. © 2006 IEEE.


Studying ignition schemes on European laser facilities

Nuclear Fusion 51 (2011)

S Jacquemot, S Jacquemot, F Amiranoff, SD Baton, JC Chanteloup, C Labaune, M Koenig, DT Michel, F Perez, HP Schlenvoigt, B Canaud, C Cherfils Clérouin, G Debras, S Depierreux, J Ebrardt, D Juraszek, S Lafitte, P Loiseau, JL Miquel, F Philippe, C Rousseaux, N Blanchot, CB Edwards, P Norreys, S Atzeni, A Schiavi, J Breil, JL Feugeas, L Hallo, M Lafon, X Ribeyre, JJ Santos, G Schurtz, V Tikhonchuk, A Debayle, JJ Honrubia, M Temporal, D Batani, JR Davies, F Fiuza, RA Fonseca, LO Silva, LA Gizzi, P Koester, L Labate, J Badziak, O Klimo

Demonstrating ignition and net energy gain in the near future on MJ-class laser facilities will be a major step towards determining the feasibility of Inertial Fusion Energy (IFE), in Europe as in the United States. The current status of the French Laser MégaJoule (LMJ) programme, from the laser facility construction to the indirectly driven central ignition target design, is presented, as well as validating experimental campaigns, conducted, as part of this programme, on various laser facilities. However, the viability of the IFE approach strongly depends on our ability to address the salient questions related to efficiency of the target design and laser driver performances. In the overall framework of the European HiPER project, two alternative schemes both relying on decoupling target compression and fuel heating - fast ignition (FI) and shock ignition (SI) - are currently considered. After a brief presentation of the HiPER project's objectives, FI and SI target designs are discussed. Theoretical analysis and 2D simulations will help to understand the unresolved key issues of the two schemes. Finally, the on-going European experimental effort to demonstrate their viability on currently operated laser facilities is described. © 2011 IAEA, Vienna.


Plasma emission spectroscopy of solids irradiated by intense XUV pulses from a free electron laser

High Energy Density Physics 6 (2010) 109-112

TWJ Dzelzainis, J Chalupsky, M Fajardo, R Fäustlin, PA Heimann, V Hajkova, L Juha, M Jurek, FY Khattak, M Kozlova, J Krzywinski, RW Lee, B Nagler, AJ Nelson, FB Rosmej, R Soberierski, S Toleikis, T Tschentscher, SM Vinko, JS Wark, T Whitcher, D Riley

The FLASH XUV-free electron laser has been used to irradiate solid samples at intensities of the order 1016 W cm-2 at a wavelength of 13.5 nm. The subsequent time integrated XUV emission was observed with a grating spectrometer. The electron temperature inferred from plasma line ratios was in the range 5-8 eV with electron density in the range 1021-1022 cm-3. These results are consistent with the saturation of absorption through bleaching of the L-edge by intense photo-absorption reported in an earlier publication. © 2009 Elsevier B.V. All rights reserved.


Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions

New Journal of Physics 12 (2010)

C Bellei, SR Nagel, S Kar, A Henig, A Henig, S Kneip, C Palmer, A Sävert, L Willingale, L Willingale, D Carroll, B Dromey, JS Green, JS Green, K Markey, P Simpson, RJ Clarke, H Lowe, D Neely, C Spindloe, M Tolley, MC Kaluza, MC Kaluza, SPD Mangles, P McKenna, PA Norreys, PA Norreys, J Schreiber, J Schreiber, J Schreiber, M Zepf, JR Davies, K Krushelnick, K Krushelnick, Z Najmudin

The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the second harmonic optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation (TR). A halo that surrounds the main region of emission is also polarized and is attributed to the effect of electron recirculation. The variation of the polarization state and intensity of radiation with the angle of observation indicates that the emission of TR is highly directional and provides evidence for the presence of μm-size filaments. A brief discussion on the possible causes of such a fine electron beam structure is given. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Measurement of the dynamic response of compressed hydrogen by inelastic X-ray scattering

Journal of Physics: Conference Series 244 (2010)

K Falk, AP Jephcoat, AP Jephcoat, BJB Crowley, BJB Crowley, RR Fäustlin, C Fortmann, FY Khattak, AK Kleppe, D Riley, D Riley, S Toleikis, J Wark, H Wilhelm, G Gregori

Measurement of the dynamic properties of hydrogen and helium under extreme pressures is a key to understanding the physics of planetary interiors. The inelastic scattering signal from statically compressed hydrogen inside diamond anvil cells at 2.8 GPa and 6.4 GPa was measured at the Diamond Light Source synchrotron facility in the UK. The first direct measurement of the local field correction to the Coulomb interactions in degenerate plasmas was obtained from spectral shifts in the scattering data and compared to predictions by the Utsumi-Ichimaru theory for degenerate electron liquids. © 2010 IOP Publishing Ltd.