Publications


Soft x-ray free electron laser microfocus for exploring matter under extreme conditions.

Opt Express 17 (2009) 18271-18278

AJ Nelson, S Toleikis, H Chapman, S Bajt, J Krzywinski, J Chalupsky, L Juha, J Cihelka, V Hajkova, L Vysin, T Burian, M Kozlova, RR Fäustlin, B Nagler, SM Vinko, T Whitcher, T Dzelzainis, O Renner, K Saksl, AR Khorsand, PA Heimann, R Sobierajski, D Klinger, M Jurek, J Pelka, B Iwan, J Andreasson, N Timneanu, M Fajardo, JS Wark, D Riley, T Tschentscher, J Hajdu, RW Lee

We have focused a beam (BL3) of FLASH (Free-electron LASer in Hamburg: lambda = 13.5 nm, pulse length 15 fs, pulse energy 10-40 microJ, 5 Hz) using a fine polished off-axis parabola having a focal length of 270 mm and coated with a Mo/Si multilayer with an initial reflectivity of 67% at 13.5 nm. The OAP was mounted and aligned with a picomotor controlled six-axis gimbal. Beam imprints on poly(methyl methacrylate) - PMMA were used to measure focus and the focused beam was used to create isochoric heating of various slab targets. Results show the focal spot has a diameter of < or =1 microm. Observations were correlated with simulations of best focus to provide further relevant information.


Measurement of short-range correlations in shock-compressed plastic by short-pulse x-ray scattering.

Phys Rev Lett 102 (2009) 165004-

B Barbrel, M Koenig, A Benuzzi-Mounaix, E Brambrink, CR Brown, DO Gericke, B Nagler, M Rabec le Gloahec, D Riley, C Spindloe, SM Vinko, J Vorberger, J Wark, K Wünsch, G Gregori

We have performed short-pulse x-ray scattering measurements on laser-driven shock-compressed plastic samples in the warm dense matter regime, providing instantaneous snapshots of the system evolution. Time-resolved and angularly resolved scattered spectra sensitive to the correlation effects in the plasma show the appearance of short-range order within a few interionic separations. Comparison with radiation-hydrodynamic simulations indicates that the shocked plastic is compressed with a temperature of a few electron volts. These results are important for the understanding of the thermodynamic behavior of strongly correlated matter for conditions relevant to both laboratory astrophysics and inertial confinement fusion research.


Hybrid Simulations for the Ion Structure and Dynamics in Dense Plasmas

ATOMIC PROCESSES IN PLASMAS 1161 (2009) 280-285

G Gregori, J Vorberger, DO Gericke


Making relativistic positrons using ultraintense short pulse lasers

Physics of Plasmas 16 (2009)

H Chen, SC Wilks, JD Bonlie, SN Chen, KV Cone, LN Elberson, DF Price, MB Schneider, R Shepherd, DC Stafford, R Tommasini, R Van Maren, P Beiersdorfer, G Gregori, DD Meyerhofer, J Myatt

This paper describes a new positron source using ultraintense short pulse lasers. Although it has been theoretically studied since the 1970s, the use of lasers as a valuable new positron source was not demonstrated experimentally until recent years, when the petawatt-class short pulse lasers were developed. In 2008 and 2009, in a series of experiments performed at the Lawrence Livermore National Laboratory, a large number of positrons were observed after shooting a millimeter thick solid gold target. Up to 2× positrons/s ejected at the back of approximately millimeter thick gold targets were detected. The targets were illuminated with short (∼1 ps) ultraintense (∼1× 10 W/ cm) laser pulses. These positrons are produced predominantly by the Bethe-Heitler process and have an effective temperature of 2-4 MeV, with the distribution peaking at 4-7 MeV. The angular distribution of the positrons is anisotropic. For a wide range of applications, this new laser-based positron source with its unique characteristics may complement the existing sources based on radioactive isotopes and accelerators. © 2009 American Institute of Physics.


A dual-channel, curved-crystal spectrograph for petawatt laser, x-ray backlighter source studies

REVIEW OF SCIENTIFIC INSTRUMENTS 80 (2009) ARTN 083501

W Theobald, C Stoeckl, PA Jaanimagi, PM Nilson, M Storm, DD Meyerhofer, TC Sangster, D Hey, AJ MacKinnon, H-S Park, PK Patel, R Shepherd, RA Snavely, MH Key, JA King, B Zhang, RB Stephens, KU Akli, K Highbarger, RL Daskalova, L Van Woerkom, RR Freeman, JS Green, G Gregori, K Lancaster, PA Norreys


Predicting EXAFS signals from shock compressed iron by use of molecular dynamics simulations

High Energy Density Physics 5 (2009) 44-50

A Higginbotham, WJ Murphy, B Nagler, JS Wark, RC Albers, TC Germann, B Lee Holian, K Kadau, PS Lomdahl

Simulated EXAFS signals from ab initio models and configurational averaging of molecular dynamics (MD) data are compared for α-Fe, and configurationally averaged MD EXAFS signals are compared with experimental data for iron shock compressed to pressures above the α-ε{lunate} transition pressure. It is shown that molecular dynamics potentials and ab initio models capable of recreating similar vibrational density of states lead to EXAFS signals in good mutual agreement. The effects of the classical nature of the phonon distribution in the MD and the anharmonicity of the potential give rise to noticeable differences between ab initio models and configurational averaging of MD data. However, the greatest influence on the spectra is the form of the potential itself. We discuss the importance of these effects in simulating EXAFS spectra for shock compressed polycrystalline iron. It is shown that EXAFS is an insensitive probe for determining the nature of the close packed product phase in this system. © 2009 Elsevier B.V.


Measurements of ionic structure in shock compressed lithium hydride from ultrafast X-ray Thomson scattering

Physical Review Letters 103 (2009)

AL Kritcher, P Neumayer, P Davis, T Döppner, OL Landen, SH Glenzer, EC Morse, CRD Brown, RW Falcone, HJ Lee, DO Gericke, J Vorberger, K Wünsch, G Gregori, B Holst, R Redmer, A Pelka, M Roth

We present the first ultrafast temporally, spectrally, and angularly resolved x-ray scattering measurements from shock-compressed matter. The experimental spectra yield the absolute elastic and inelastic scattering intensities from the measured density of free electrons. Laser-compressed lithium-hydride samples are well characterized by inelastic Compton and plasmon scattering of a K-α x-ray probe providing independent measurements of temperature and density. The data show excellent agreement with the total intensity and structure when using the two-species form factor and accounting for the screening of ion-ion interactions. © 2009 The American Physical Society.


Turning solid aluminium transparent by intense soft X-ray photoionization

Nature Physics 5 (2009) 693-696

B Nagler, SM Vinko, T Whitcher, G Gregori, WJ Murphy, JS Wark, U Zastrau, E Förster, I Uschmann, RR Fäustlin, S Bajt, S Düsterer, T Laarmann, S Toleikis, AJ Nelson, T Döppner, SH Glenzer, RW Lee, HJ Vollmer, R Sobierajski, M Jurek, D Klinger, AR Khorsand, J Krzywinski, J Chalupsky, T Burian, J Cihelka, V Hajkova, L Juha, E Abreu, M Fajardo, M Kozlova, T Bornath, C Fortmann, S Göde, K-H Meiwes-Broer, A Przystawik, R Redmer, H Reinholz, G Röpke, R Thiele, J Tiggesbäumker, H Chapman, D Riley, F Rosmej, R Schott, T Dzelzainis, E Galtier, P Heimann, FY Khattak, HJ Lee, P Mercere, K Saksl, T Tschentscher

Saturable absorption is a phenomenon readily seen in the optical and infrared wavelengths. It has never been observed in core-electron transitions owing to the short lifetime of the excited states involved and the high intensities of the soft X-rays needed. We report saturable absorption of an L-shell transition in aluminium using record intensities over 10 16 W cm 2 at a photon energy of 92 eV. From a consideration of the relevant timescales, we infer that immediately after the X-rays have passed, the sample is in an exotic state where all of the aluminium atoms have an L-shell hole, and the valence band has approximately a 9 eV temperature, whereas the atoms are still on their crystallographic positions. Subsequently, Auger decay heats the material to the warm dense matter regime, at around 25 eV temperatures. The method is an ideal candidate to study homogeneous warm dense matter, highly relevant to planetary science, astrophysics and inertial confinement fusion. © 2009 Macmillan Publishers Limited. All rights reserved.


A dual-channel, curved-crystal spectrograph for petawatt laser, x-ray backlighter source studies

Review of Scientific Instruments 80 (2009)

W Theobald, C Stoeckl, PA Jaanimagi, PM Nilson, M Storm, DD Meyerhofer, TC Sangster, D Hey, AJ MacKinnon, H-S Park, PK Patel, R Shepherd, RA Snavely, MH Key, JA King, B Zhang, RB Stephens, KU Akli, K Highbarger, RL Daskalova, L Van Woerkom, RR Freeman, JS Green, G Gregori, K Lancaster, PA Norreys

A dual-channel, curved-crystal spectrograph was designed to measure time-integrated x-ray spectra in the ∼1.5 to 2 keV range (6.2-8.2 Å wavelength) from small-mass, thin-foil targets irradiated by the VULCAN petawatt laser focused up to 4× 10 W/ cm . The spectrograph consists of two cylindrically curved potassium-acid-phthalate crystals bent in the meridional plane to increase the spectral range by a factor of ∼10 compared to a flat crystal. The device acquires single-shot x-ray spectra with good signal-to-background ratios in the hard x-ray background environment of petawatt laser-plasma interactions. The peak spectral energies of the aluminum He and Ly resonance lines were ∼1.8 and ∼1.0 mJ/eV sr (∼0.4 and 0.25 J/Å sr), respectively, for 220 J, 10 ps laser irradiation. © 2009 American Institute of Physics.


Perspective for high energy density studies on X-ray FELs

Proceedings of SPIE - The International Society for Optical Engineering 7451 (2009)

RW Lee, SM Vinko, T Whitcher, AJ Nelson, K Budil, RC Cauble, T Döppner, SH Glenzer, R Shepherd, B Nagler, J Chalupsky, G Gregori, WJ Murphy, JS Wark, U Zastrau, E Förster, I Uschmann, R Fäustlin, S Bajt, H Chapman, S Düsterer, T Laarmann, S Toleikis, T Tschentscher, R Sobierajski, M Jurek, D Klinger, J Krzywinski, JB Hastings, WE White, L Juha, T Burian, J Cihelka, V Hajkova, T Bornath, C Fortmann, S Göde, K-H Meiwes-Broer, A Przystawik, R Redmer, H Reinholz, G Röpke, R Thiele, J Tiggesbäumker, T Dzelzainis, D Riley, M Ajardo, M Kozlova, P Heimann, RW Falcone, FY Khattak, AR Khorsand, H-J Lee, P Mercere, K Saksl

We report on the x-ray absorption of Warm Dense Matter experiment at the FLASH Free Electron Laser (FEL) facility at DESY. The FEL beam is used to produce Warm Dense Matter with soft x-ray absorption as the probe of electronic structure. A multilayer-coated parabolic mirror focuses the FEL radiation, to spot sizes as small as 0.3μm in a ∼15fs pulse of containing >10 photons at 13.5 nm wavelength, onto a thin sample. Silicon photodiodes measure the transmitted and reflected beams, while spectroscopy provides detailed measurement of the temperature of the sample. The goal is to measure over a range of intensities approaching 10 W/cm . Experimental results will be presented along with theoretical calculations. A brief report on future FEL efforts will be given. © 2009 SPIE.


Perspective for high energy density studies using x-ray free electron lasers

IEEE International Conference on Plasma Science (2009)

RW Lee, S Vinko, T Whitcher, A Nelson, H Chapman, T Döppner, SH Glenzer, B Nagler, J Chalupsky, G Gregori, WJ Murphy, JS Wark, U Zastrau, E Förster, I Uschmann, R Fäustlin, S Bajt, S Düsterer, T Laarmann, S Toleikis, T Tschentscher, R Sobierajski, M Jurek, D Klinger, J Krzywinski, L Juha, T Burian, J Cihelka, V Hajkova, T Bornath, C Fortmann, S Göde, K Meiwes-Broer, A Przystawik, R Redmer, H Reinholz, G Röpke, R Thiele, J Tiggesbäumker, T Dzelzainis, D Riley, M Fajardo, M Kozlova, P Heimann, F Khattak, AR Khorsand, H Lee, P Mercere, K Saksl


Stable laser-driven electron beams from a steady-state-flow gas cell

AIP Conference Proceedings 1086 (2009) 125-130

J Osterhoff, A Popp, Z Major, B Marx, M Fuchs, R Hörlein, F Grüner, D Habs, F Krausz, S Karsch, TP Rowlands-Rees, SM Hooker

Quasi-monoenergetic, laser-driven electron beams of up to ∼ 200 MeV in energy have been generated from steady-state-flow gas cells [1], These beams are emitted within a low-divergence cone of 2.1 ± 0.5 mrad FWHM and feature unparalleled shot-to-shot stability in energy (2.5% rms), pointing direction (1.4 mrad rms) and charge (16% rms) owing to a highly reproducible plasma-density profile within the laser-plasma-interaction volume. Laser-wakefield acceleration (LWFA) in gas cells of this type constitutes a simple and reliable source of relativistic electrons with well defined properties, which should allow for applications such as the production of extreme-ultraviolet undulator radiation in the near future. © 2009 American Institute of Physics.


Femtosecond X-ray Diffraction: Applications for Laser-Irradiated Materials

ATOMIC PROCESSES IN PLASMAS 1161 (2009) 253-253

JS Wark


Simulating sub-wavelength temporal effects in a seeded FEL driven by laser-accelerated electrons

FEL 2009 - 31st International Free Electron Laser Conference (2009) 119-122

SI Bajlekov, SM Hooker, R Bartolini

Ultrashort electron bunches from laser-driven plasma accelerators hold promise as drivers for short-wavelength free electron lasers. While FEL simulation techniques have been successful in simulating lasing at present-day facilities, the novel sources investigated here are likely to violate a number of widely-held assumptions. For instance the HHG seed radiation, as well as the radiation generated by the bunch, may not conform to the slowly-varying envelope approximation (SVEA) on which the majority of codes rely. Additionally, the longitudinal macroparticle binning precludes the modeling of the full physics of the system. In order to more completely simulate the sub-wavelength effects which arise, we have developed an unaveraged 1-D time-dependent code without the SVEA. We use this to perform numerical analyses and highlight some of the additional features that these new systems present. We conclude that while coherent spontaneous emission from ultra-short bunches may significantly affect start-up, the sub-wavelength structure of HHG seeds has little effect.


Proton acceleration experiments and warm dense matter research using high power lasers

Plasma Physics and Controlled Fusion 51 (2009)

M Roth, I Alber, M Günther, K Harres, F Nürnberg, A Otten, A Pelka, G Schaumann, M Schollmeier, J Schütrumpf, V Bagnoud, A Tauschwitz, CRD Brown, R Clarke, R Heathcote, B Li, H Daido, M Tampo, J Fernandez, K Flippo, S Gaillard, C Gauthier, D Offermann, M Geissel, S Glenzer, A Kritcher, N Kugland, S Lepape, G Gregori, J Mithen, M Makita, D Riley, C Niemann

The acceleration of intense proton and ion beams by ultra-intense lasers has matured to a point where applications in basic research and technology are being developed. Crucial for harvesting the unmatched beam parameters driven by the relativistic electron sheath is the precise control of the beam. In this paper we report on recent experiments using the PHELIX laser at GSI, the VULCAN laser at RAL and the TRIDENT laser at LANL to control and use laser accelerated proton beams for applications in high energy density research. We demonstrate efficient collimation of the proton beam using high field pulsed solenoid magnets, a prerequisite to capture and transport the beam for applications. Furthermore, we report on two campaigns to use intense, short proton bunches to isochorically heat solid targets up to the warm dense matter state. The temporal profile of the proton beam allows for rapid heating of the target, much faster than the hydrodynamic response time thereby creating a strongly coupled plasma at solid density. The target parameters are then probed by x-ray Thomson scattering to reveal the density and temperature of the heated volume. This combination of two powerful techniques developed during the past few years allows for the generation and investigation of macroscopic samples of matter in states present in giant planets or the interior of the earth. © 2009 IOP Publishing Ltd.


Comparison of Parallel and Perpendicular Polarized Counterpropagating Light for Quasi-Phase-Matching High Harmonic Generation

ULTRAFAST PHENOMENA XVI 92 (2009) 15-17

T Robinson, K O'Keeffe, M Landreman, B Dromey, M Zepf, SM Hooker, RW Schoenlein


Radiation and hot electron temperature measurements of short-pulselaser driven hohlraums

High Energy Density Physics 5 (2009) 212-215

CRD Brown, SF James, R Edwards, JW Morton, BR Thomas, DJ Hoarty, SJ Rose, FN Beg, DP Higginson, C Constantin, C Niemann, RL Daskalova, RR Freeman, L van Woerkom, D Riley, G Gregori

We have performed measurements of the radiation and the hot electron temperature in sub-millimetre size hohlraums driven by a high intensity short-pulse laser. The results indicate that radiation temperatures ∼80 eV can be obtained with ∼20 J of laser energy delivered on target. Radiation-hydrodynamics simulations indicate an absorption into thermal X-rays of ≲1-2%, with peak temperatures similar to those measured experimentally. Crown Copyright © 2009.


Control of 2ω (527 nm) stimulated raman scattering in a steep density gradient plasma

Physics of Plasmas 16 (2009)

JD Moody, L Divol, DH Froula, SH Glenzer, G Gregori, RK Kirkwood, A MacKinnon, N Meezan, C Niemann, LJ Suter, R Bahr, W Seka

Experiments show that application of laser smoothing schemes including smoothing by spectral dispersion and polarization smoothing effectively suppresses stimulated Raman scattering from a 2ω (527 nm) laser beam in a low average-gain plasma with a steep density gradient. Full-wave simulations reproduce the observed trends in the data and show that the scattering reduction is an indirect result of suppressing active filamentation. © 2009 American Institute of Physics.


Low frequency structural dynamics of warm dense matter

Physics of Plasmas 16 (2009)

G Gregori, DO Gericke

Measurements of the microscopic response of warm dense matter have been demonstrated by multi-keV inelastic x-ray scattering using laser-based sources. These techniques have been used to study the high frequency electron correlations (plasmons) in low to mid- Z plasmas. The advent of fourth generation light sources will provide high fluxes of narrowband and coherent x rays that will allow to look at the low frequency correlations (the ion-acoustic waves). In this paper we present an analysis of such low frequency modes by calculating the frequency dependent ion-ion structure factor. Our model includes all the relevant multibody contributions arising from strong coupling and nonideal plasma effects. In particular, the ion-ion structure factor is obtained within the memory function formalism by satisfying a finite number of sum rules. This work could be used as a basis to a direct experimental test of dense plasma model as soon as keV free electron laser sources will become available. © 2009 American Institute of Physics.


Measurements of ionic structure in shock compressed lithium hydride from ultrafast x-ray Thomson scattering.

Phys Rev Lett 103 (2009) 245004-

AL Kritcher, P Neumayer, CR Brown, P Davis, T Döppner, RW Falcone, DO Gericke, G Gregori, B Holst, OL Landen, HJ Lee, EC Morse, A Pelka, R Redmer, M Roth, J Vorberger, K Wünsch, SH Glenzer

We present the first ultrafast temporally, spectrally, and angularly resolved x-ray scattering measurements from shock-compressed matter. The experimental spectra yield the absolute elastic and inelastic scattering intensities from the measured density of free electrons. Laser-compressed lithium-hydride samples are well characterized by inelastic Compton and plasmon scattering of a K-alpha x-ray probe providing independent measurements of temperature and density. The data show excellent agreement with the total intensity and structure when using the two-species form factor and accounting for the screening of ion-ion interactions.