Publications


Laser-wakefield acceleration of electron beams in a low density plasma channel

Physical Review Special Topics - Accelerators and Beams 13 (2010)

TPA Ibbotson, N Bourgeois, TP Rowlands-Rees, LS Caballero, SI Bajlekov, PA Walker, S Kneip, SPD Mangles, SR Nagel, CAJ Palmer, N Delerue, G Doucas, D Urner, O Chekhlov, RJ Clarke, E Divall, K Ertel, PS Foster, SJ Hawkes, CJ Hooker, B Parry, PP Rajeev, MJV Streeter, SM Hooker

The generation of quasimonoenergetic electron beams, with energies greater than 500 MeV, in a laser-plasma accelerator driven by 2.5 J, 80 fs laser pulses guided in a low density plasma channel, is investigated. The laser energy required to achieve electron injection is found to depend strongly on the quality of the input laser focal spot. Simulations show that, although the matched spot size of the plasma channel is greater than the self-focused spot size, the channel assists relativistic self-focusing and enables electron injection to occur at lower plasma densities and laser powers than would be possible without a waveguide. © 2010 The American Physical Society.


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.


X-ray polarization spectroscopy from ultra-intense interactions

Journal of Physics: Conference Series 244 (2010)

N Booth, R Clarke, P Gallegos, L Gizzi, G Gregori, P Koester, L Labate, T Levato, B Li, M Makita, J Pasley, PP Rajeev, D Riley, E Wagenaars, JN Waugh, NC Woolsey

Detailed knowledge of fast electron energy transport following the interaction of ultrashort intense laser pulses is a key subject for fast ignition. This is a problem relevant to many areas of laser-plasma physics with particular importance to fast ignition and X-ray secondary source development, necessary for the development of large-scale facilities such as HiPER and ELI. Operating two orthogonal crystal spectrometers set at Bragg angles close to 45° determines the X-ray s- and p- polarization ratio. From this ratio, it is possible to infer the velocity distribution function of the fast electron beam within the dense plasma. We report on results of polarization measurements at high density for sulphur and nickel buried layer targets in the high intensity range of 1019 - 1021 Wcm-2. We observe at 45° the Ly-α doublet using two sets of orthogonal highly-orientated pyrolytic graphite (HOPG) crystals set in 1st order for sulphur and 3rd order for nickel. © 2010 IOP Publishing Ltd.


Transport of laser accelerated proton beams and isochoric heating of matter

Journal of Physics: Conference Series 244 (2010)

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

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. 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 (XRTS) 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. © 2010 IOP Publishing Ltd.


Laser Physics

Oxford University Press, 2010
Part of a series from Oxford Master Series in Atomic, Optical, and Laser Physics

SM Hooker, CE Webb

In this book the interaction of radiation and matter, and the principles of laser operation are treated at a level suitable for fourth-year undergraduate ...


Phonon instabilities in uniaxially compressed fcc metals as seen in molecular dynamics simulations

PHYSICAL REVIEW B 81 (2010) ARTN 092102

G Kimminau, P Erhart, EM Bringa, B Remington, JS Wark


Electronic structure of an XUV photogenerated solid-density aluminum plasma.

Phys Rev Lett 104 (2010) 225001-

SM Vinko, U Zastrau, S Mazevet, J Andreasson, S Bajt, T Burian, J Chalupsky, HN Chapman, J Cihelka, D Doria, T Döppner, S Düsterer, T Dzelzainis, RR Fäustlin, C Fortmann, E Förster, E Galtier, SH Glenzer, S Göde, G Gregori, J Hajdu, V Hajkova, PA Heimann, R Irsig, L Juha, M Jurek, J Krzywinski, T Laarmann, HJ Lee, RW Lee, B Li, KH Meiwes-Broer, JP Mithen, B Nagler, AJ Nelson, A Przystawik, R Redmer, D Riley, F Rosmej, R Sobierajski, F Tavella, R Thiele, J Tiggesbäumker, S Toleikis, T Tschentscher, L Vysin, TJ Whitcher, S White, JS Wark

By use of high intensity XUV radiation from the FLASH free-electron laser at DESY, we have created highly excited exotic states of matter in solid-density aluminum samples. The XUV intensity is sufficiently high to excite an inner-shell electron from a large fraction of the atoms in the focal region. We show that soft-x-ray emission spectroscopy measurements reveal the electronic temperature and density of this highly excited system immediately after the excitation pulse, with detailed calculations of the electronic structure, based on finite-temperature density functional theory, in good agreement with the experimental results.


Generation and control of chirped, ultrafast pulse trains

Journal of Optics A: Pure and Applied Optics 12 (2010)

K O'Keeffe, T Robinson, SM Hooker

A method for generating non-uniformly spaced (chirped) trains of high-energy, high-contrast, femtosecond pulses is described and demonstrated. In this method a temporally stretched laser pulse is passed through an acousto-optic programmable dispersive filter (AOPDF), a birefringent plate, and a linear polarizer. It is demonstrated that linear and nonlinear variation of the pulse separation within the train may be controlled by changing respectively the third-and fourth-order dispersion introduced by the AOPDF. Programmable, non-uniform pulse trains of this type may find applications in quasi-phase matching high-harmonic generation. © 2010 IOP Publishing Ltd.


All-optical steering of laser-wakefield-accelerated electron beams

Physical Review Letters 105 (2010)

A Popp, J Vieira, J Osterhoff, Z Major, R Hörlein, M Fuchs, R Weingartner, TP Rowlands-Rees, M Marti, RA Fonseca, SF Martins, LO Silva, SM Hooker, F Krausz, F Grüner, S Karsch

We investigate the influence of a tilted laser-pulse-intensity front on laser-wakefield acceleration. Such asymmetric light pulses may be exploited to obtain control over the electron-bunch-pointing direction and in our case allowed for reproducible electron-beam steering in an all-optical way within an 8 mrad opening window with respect to the initial laser axis. We also discovered evidence of collective electron-betatron oscillations due to off-axis electron injection into the wakefield induced by a pulse-front tilt. These findings are supported by 3D particle-in-cell simulations. © 2010 The American Physical Society.


Investigation of the role of plasma channels as waveguides for laser-wakefield accelerators

New Journal of Physics 12 (2010)

TPA Ibbotson, N Bourgeois, TP Rowlands-Rees, LS Caballero, SI Bajlekov, PA Walker, S Kneip, M Spd, SR Nagel, P Caj, N Delerue, G Doucas, D Urner, O Chekhlov, RJ Clarke, E Divall, K Ertel, P Foster, SJ Hawkes, CJ Hooker, B Parry, PP Rajeev, MJV Streeter, SM Hooker

The role of plasma channels as waveguides for laser-wakefield accelerators is discussed in terms of the results of experiments performed with the Astra-Gemini laser, numerical simulations using the code WAKE, and the theory of self-focusing and self-guiding of intense laser beams. It is found that at a given electron density, electron beams can be accelerated using lower laser powers in a waveguide structure than in a gas-jet or cell. The transition between relativistically self-guided and channel-assisted guiding is seen in the simulations and in the behaviour of the production of electron beams. We also show that by improving the quality of the driving laser beam the threshold laser energy required to produce electron beams can be reduced by a factor of almost 2. The use of an aperture allows the production of a quasi-monoenergetic electron beam of energy 520 MeV with an input laser power of only 30 TW. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Soft X-ray scattering using FEL radiation for probing near-solid density plasmas at few electron volt temperatures

High Energy Density Physics 6 (2010) 15-20

S Toleikis, RR Fäustlin, L Cao, T Döppner, S Düsterer, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, J Mithen, K-H Meiwes-Broer, A Przystawik, P Radcliffe, R Redmer, F Tavella, R Thiele, J Tiggesbäumker, NX Truong, I Uschmann, U Zastrau, T Tschentscher

We report on soft X-ray scattering experiments on cryogenic hydrogen and simple metal samples. As a source of intense, ultrashort soft X-ray pulses we have used free-electron laser radiation at 92 eV photon energy from FLASH at DESY, Hamburg. X-ray pulses with energies up to 150 μJ and durations 15-50 fs provide interaction with the sample leading simultaneously to plasma formation and scattering. Experiments exploiting both of these interactions have been carried out, using the same experimental setup. Firstly, recording of soft X-ray inelastic scattering from near-solid density hydrogen plasmas at few electron volt temperatures confirms the feasibility of this diagnostics technique. Secondly, the soft X-ray excitation of few electron volt solid-density plasmas in bulk metal samples could be studied by recording soft X-ray line and continuum emission integrated over emission times from fs to ns. © 2009 Elsevier B.V.


Generation and control of ultrafast pulse trains for quasi-phase-matching high-harmonic generation

Journal of the Optical Society of America B: Optical Physics 27 (2010) 763-772

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

Two techniques are demonstrated to produce ultrashort pulse trains capable of quasi-phase-matching highharmonic generation. The first technique makes use of an array of birefringent crystals and is shown to generate high-contrast pulse trains with constant pulse spacing. The second technique employs a grating-pair stretcher, a multiple-order wave plate, and a linear polarizer. Trains of up to 100 pulses are demonstrated with this technique, with almost constant inter-pulse separation. It is shown that arbitrary pulse separation can be achieved by introducing the appropriate dispersion. This principle is demonstrated by using an acousto-optic programmable dispersive filter to introduce third- and fourth-order dispersions leading to a linear and quadratic variation of the separation of pulses through the train. Chirped-pulse trains of this type may be used to quasi-phase-match high-harmonic generation in situations where the coherence length varies through the medium. © 2010 Optical Society of America.


Ultrafast melting of carbon induced by intense proton beams

Physical Review Letters 105 (2010)

A Pelka, G Gregori, DO Gericke, J Vorberger, SH Glenzer, MM Günther, K Harres, R Heathcote, AL Kritcher, NL Kugland, B Li, M Makita, J Mithen, D Neely, C Niemann, A Otten, D Riley, G Schaumann, M Schollmeier, A Tauschwitz, M Roth

Laser-produced proton beams have been used to achieve ultrafast volumetric heating of carbon samples at solid density. The isochoric melting of carbon was probed by a scattering of x rays from a secondary laser-produced plasma. From the scattering signal, we have deduced the fraction of the material that was melted by the inhomogeneous heating. The results are compared to different theoretical approaches for the equation of state which suggests modifications from standard models. © 2010 The American Physical Society.


Bragg diffraction using a 100 ps 17.5 keV x-ray backlighter and the Bragg diffraction imager

REVIEW OF SCIENTIFIC INSTRUMENTS 81 (2010)

BR Maddox, H-S Park, J Hawreliak, A Elsholz, R Van Maren, BA Remington, A Comley, JS Wark


First milestone on the path toward a table-top free-electron laser (FEL)

AIP Conference Proceedings 1228 (2010) 295-300

M Fuchs, R Weingartner, A Popp, Z Major, S Becker, J Osterhoff, T Seggebrock, R Hörlein, GD Tsakiris, U Schramm, TP Rowlands-Rees, SM Hooker, D Habs, F Krausz, S Karsch, F Grüner

Latest developments in the field of laser-wakefield accelerators (LWFAs) have led to relatively stable electron beams in terms of peak energy, charge, pointing and divergence from mmsized accelerators. Simulations and LWFA theory indicate that these beams have low transverse emittances and ultrashort bunch durations on the order of ∼ 10 fs. These features make LWFAs perfectly suitable for driving high-brightness X-ray undulator sources and free-electron lasers (FELs) on a university-laboratory scale.With the detection of soft-X-ray radiation from an undulator source driven by laser-wakefield accelerated electrons, we succeeded in achieving a first milestone on this path. The source delivers remarkably stable photon beams which is mainly due to the stable electron beam and our miniature magnetic quadrupole lenses, which significantly reduce its divergence and angular shot-to-shot variation. An increase in electron energy allows for compact, tunable, hard-Xray undulator sources. Improvements of the electron beams in terms of charge and energy spread will put table-top FELs within reach. © 2010 American Institute of Physids.


Observation of ultrafast nonequilibrium collective dynamics in warm dense hydrogen.

Phys Rev Lett 104 (2010) 125002-

RR Fäustlin, T Bornath, T Döppner, S Düsterer, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, KH Meiwes-Broer, J Mithen, B Nagler, A Przystawik, H Redlin, R Redmer, H Reinholz, G Röpke, F Tavella, R Thiele, J Tiggesbäumker, S Toleikis, I Uschmann, SM Vinko, T Whitcher, U Zastrau, B Ziaja, T Tschentscher

We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state. Thomson scattering measurements using 91.8 eV photons from the free-electron laser in Hamburg (FLASH at DESY) show that the hydrogen plasma has been driven to a nonthermal state with an electron temperature of 13 eV and an ion temperature below 0.1 eV, while the free-electron density is 2.8x10{20} cm{-3}. For dense plasmas, our experimental data strongly support a nonequilibrium kinetics model that uses impact ionization cross sections based on classical free-electron collisions.


Probing near-solid density plasmas using soft x-ray scattering

Journal of Physics B: Atomic, Molecular and Optical Physics 43 (2010)

S Toleikis, T Bornath, T Döppner, S Düsterer, RR Fäustlin, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, K-H Meiwes-Broer, J Mithen, B Nagler, A Przystawik, P Radcliffe, H Redlin, R Redmer, H Reinholz, G Röpke, F Tavella, R Thiele, J Tiggesbäumker, I Uschmann, SM Vinko, T Whitcher, U Zastrau, B Ziaja, T Tschentscher

X-ray scattering using highly brilliant x-ray free-electron laser (FEL) radiation provides new access to probe free-electron density, temperature and ionization in near-solid density plasmas. First experiments at the soft x-ray FEL FLASH at DESY, Hamburg, show the capabilities of this technique. The ultrashort FEL pulses in particular can probe equilibration phenomena occurring after excitation of the plasma using ultrashort optical laser pumping. We have investigated liquid hydrogen and find that the interaction of very intense soft x-ray FEL radiation alone heats the sample volume. As the plasma establishes, photons from the same pulse undergo scattering, thus probing the transient, warm dense matter state. We find a free-electron density of (2.6 ± 0.2) × 1020 cm-3 and an electron temperature of 14 ± 3.5 eV. In pump-probe experiments, using intense optical laser pulses to generate more extreme states of matter, this interaction of the probe pulse has to be considered in the interpretation of scattering data. In this paper, we present details of the experimental setup at FLASH and the diagnostic methods used to quantitatively analyse the data. © 2010 IOP Publishing Ltd.


Screening of ionic cores in partially ionized plasmas within linear response

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 81 (2010)

DO Gericke, J Vorberger, K Wünsch, G Gregori

We employ a pseudopotential approach to investigate the screening of ionic cores in partially ionized plasmas. Here, the effect of the tightly bound electrons is condensed into an effective potential between the (free) valence electrons and the ionic cores. Even for weak electron-ion coupling, the corresponding screening clouds show strong modifications from the Debye result for elements heavier than helium. Modifications of the theoretically predicted x-ray scattering signal and implications on measurements are discussed. © 2010 The American Physical Society.


Relativistic quasimonoenergetic positron jets from intense laser-solid interactions.

Phys Rev Lett 105 (2010) 015003-

H Chen, SC Wilks, DD Meyerhofer, J Bonlie, CD Chen, SN Chen, C Courtois, L Elberson, G Gregori, W Kruer, O Landoas, J Mithen, J Myatt, CD Murphy, P Nilson, D Price, M Schneider, R Shepherd, C Stoeckl, M Tabak, R Tommasini, P Beiersdorfer

Detailed angle and energy resolved measurements of positrons ejected from the back of a gold target that was irradiated with an intense picosecond duration laser pulse reveal that the positrons are ejected in a collimated relativistic jet. The laser-positron energy conversion efficiency is ∼2×10{-4}. The jets have ∼20 degree angular divergence and the energy distributions are quasimonoenergetic with energy of 4 to 20 MeV and a beam temperature of ∼1  MeV. The sheath electric field on the surface of the target is shown to determine the positron energy. The positron angular and energy distribution is controlled by varying the sheath field, through the laser conditions and target geometry.


X-ray polarization measurements of dense plasmas heated by fast electrons

AIP Conference Proceedings 1228 (2010) 79-85

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

The detailed knowledge of fast electron energy transport following interaction with high-intensity, ultra-short laser pulses is a key area for secondary source generation for ELI. We demonstrate polarization spectroscopy at laser intensities up to 1021 Wcm-2. This is significant as it suggests that in situ emission spectroscopy may be used as an effective probe of fast electron velocity distributions in regimes relevant to electron transport in solid targets. Ly-α doublet emission of nickel (Z = 28) and sulphur (Z = 16) is observed to measure the degree of polarization from the Ly-α1 emission. Ly-α2 emission is unpolarized, and as such acts as a calibration source between spectrometers. The measured ratio of the X-ray σ-and π-polarization allows the possibility to infer the velocity distribution function of the fast electron beam. © 2010 American Institute of Physics.