Publications by Simon Hooker


Generation of stable, low-divergence electron beams by laser-wakefield acceleration in a steady-state-flow gas cell

Physical Review Letters 101 (2008)

J Osterhoff, A Popp, Z Major, B Marx, TP Rowlands-Rees, M Fuchs, M Geissler, R Hörlein, B Hidding, S Becker, EA Peralta, U Schramm, F Grüner, D Habs, F Krausz, SM Hooker, S Karsch

Laser-driven, quasimonoenergetic electron beams of up to ∼200MeV in energy have been observed from steady-state-flow gas cells. These beams emitted within a low-divergence cone of 2.1±0.5mrad FWHM display unprecedented shot-to-shot stability in energy (2.5% rms), pointing (1.4 mrad rms), and charge (16% rms) owing to a highly reproducible gas-density profile within the interaction volume. Laser-wakefield acceleration in gas cells of this type provides a simple and reliable source of relativistic electrons suitable for applications such as the production of extreme-ultraviolet undulator radiation. © 2008 The American Physical Society.


OPALS: The Oxford plasma accelerator light source project

30th International Free Electron Laser Conference, FEL 2008 (2008) 163-166

S Bajlekov, R Bartolini, N Delerue, G Doucas, SM Hooker, K Peach, D Urner, JS Wark

Recent progress in Laser Plasma Accelerators has demonstrated the possibility of generating GeV electron bunches with very interesting beam qualities. It is now conceivable that the further development of such devices could generate beams with emittance, energy spread and peak current suitable for FEL operation in the XUV range with relatively short undulator trains. In this context the OPALS project aims at the construction of a XUV radiation source, driven by a Laser Plasma Accelerator, capable of generating ultrashort fs XUV pulses. Such a source is small enough to be hosted in an academic or industrial institution and could therefore have a major impact on time-resolved science.


Bright quasi-phase-matched soft-X-ray harmonic radiation from argon ions

Physical Review Letters 99 (2007)

M Zepf, B Dromey, M Landreman, P Foster, SM Hooker

Selective enhancement ( > 103) of harmonics extending to the water window (∼4nm) generated in an argon gas filled straight bore capillary waveguide is demonstrated. This enhancement is in good agreement with modeling which indicates that multimode quasi-phase-matching is achieved by rapid axial intensity modulations caused by beating between the fundamental and higher-order capillary modes. Substantial pulse energies ( > 10nJ per pulse per harmonic order) at wavelengths beyond the carbon K edge (∼4.37nm, ∼284eV) up to ∼360eV are observed from argon ions for the first time. © 2007 The American Physical Society.


Modeling of a square pulsed capillary discharge waveguide for interferometry measurements

Physics of Plasmas 14 (2007)

BHP Broks, W Van Dijk, JJAW Van Der Mullen, AJ Gonsalves, TP Rowlands-Rees, SM Hooker

Slow pulsed capillary discharges in round capillaries are currently under investigation for use as plasma channel laser waveguides in laser-wakefield acceleration, x-ray lasers, and higher-harmonic generation. In this study, a capillary discharge with a square cross section is presented. The electron density, which determines the laser guiding properties, can be measured by means of transverse interferometry in this device. Using a numerical model of the plasma and the capillary wall, an analysis of the discharge is made. The results predict that the square channel is capable of guiding circular laser pulses. The guiding properties are quite similar to those of a round channel with nearly the same diameter as the channel width. This suggests the results obtained by measuring the square capillary discharge are applicable for round channels as well. It was found that the wall heating was inhomogeneous, which makes the wall more susceptible to ablation. The heating of the wall changes the transverse optical pathlength in the interferometry experiments. © 2007 American Institute of Physics.


Transverse interferometry of a hydrogen-filled capillary discharge waveguide.

Phys Rev Lett 98 (2007) 025002-

AJ Gonsalves, TP Rowlands-Rees, BHP Broks, JJAM van der Mullen, SM Hooker

Transverse interferometric measurements are presented of the plasma channel formed in a hydrogen-filled capillary discharge waveguide recently used to generate 1 GeV electrons in a laser-driven plasma accelerator for the first time. The measurements were found to be in good agreement with nonlocal thermal equilibrium simulations, but showed significant differences with the results of a quasistatic model developed by Bobrova et al. [Phys. Rev. E. 65, 016407 (2001)]. The measurements are used to determine scaling laws for the axial electron density and matched spot size of the plasma channel, enabling optimization of the channel to specific applications.


Electron acceleration in a gas-discharge capillary

34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts 31 (2007) 57-60

A Popp, J Osterhoff, TP Rowlands-Rees, Z Major, M Fuchs, B Marx, R Hörlein, K Schmid, B Hidding, L Veisz, F Grüner, U Schramm, F Krausz, SM Hooker, S Karsch


Quasi-phasematching of harmonic generation via multimode beating in waveguides

Optics Express 15 (2007) 7894-7900

B Dromey, M Zepf, M Landreman, SM Hooker

A new scheme for quasi-phasematching high harmonic generation (HHG) in gases is proposed. In this, the rapid variation of the axial intensity resulting from excitation of more than one mode of a waveguide is used to achieve quasi phasematching. Numerical modeling demonstrates enhancement of the harmonic signal over that achieved for a single coherence length by factors > 10 4 . © 2007 Optical Society of America.


GeV electron beams from a centimeter-scale channel guided laser wakefield accelerator - art. no. 056708

PHYS PLASMAS 14 (2007) 56708-56708

K Nakamura, B Nagler, C Toth, CGR Geddes, CB Schroeder, E Esarey, WP Leemans, AJ Gonsalves, SM Hooker

Laser wakefield accelerators can produce electric fields of order 10-100 GV/m, suitable for acceleration of electrons to relativistic energies. The wakefields are excited by a relativistically intense laser pulse propagating through a plasma and have a phase velocity determined by the group velocity of the light pulse. Two important effects that can limit the acceleration distance and hence the net energy gain obtained by an electron are diffraction of the drive laser pulse and particle-wake dephasing. Diffraction of a focused ultrashort laser pulse can be overcome by using preformed plasma channels. The dephasing limit can be increased by operating at a lower plasma density, since this results in an increase in the laser group velocity. Here we present detailed results on the generation of GeV-class electron beams using an intense femtosecond laser beam and a 3.3 cm long preformed discharge-based plasma channel [W. P. Leemans et al., Nature Physics 2, 696 (2006)]. The use of a discharge-based waveguide permitted operation at an order of magnitude lower density and 15 times longer distance than in previous experiments that relied on laser preformed plasma channels. Laser pulses with peak power ranging from 10-40 TW were guided over more than 20 Rayleigh ranges and high quality electron beams with energy up to 1 GeV were obtained by channeling a 40 TW peak power laser pulse. The dependence of the electron beam characteristics on capillary properties, plasma density, and laser parameters are discussed. (C) 2007 American Institute of Physics.


Generation of a train of ultrashort pulses from a compact birefringent crystal array.

Appl Opt 46 (2007) 5142-5146

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

A linear array of n calcite crystals is shown to allow the generation of a high contrast (>10:1) train of 2(n) high energy (>100 microJ) pulses from a single ultrafast laser pulse. Advantage is taken of the pulse-splitting properties of a single birefringent crystal, where an incident laser pulse can be split into two pulses with orthogonal polarizations and equal intensity, separated temporally in proportion to the thickness of the crystal traversed and the difference in refractive indices of the two optic axes. In the work presented here an array of seven calcite crystals of sequentially doubled thickness is used to produce a train of 128 pulses, each of femtosecond duration. Readily versatile properties such as the number of pulses in the train and variable mark-space ratio are realized from such a setup.


GeV plasma accelerators driven in waveguides

PLASMA PHYS CONTR F 49 (2007) B403-B410

SM Hooker, E Brunetti, E Esarey, JG Gallacher, CGR Geddes, AJ Gonsalves, DA Jaroszynski, C Kamperidis, S Kneip, K Krushelnick, WP Leemans, SPD Mangles, CD Murphy, B Nagler, Z Najmudin, K Nakamura, PA Norreys, D Panasenko, TP Rowlands-Rees, CB Schroeder, CS Toth, R Trines

During the last few years laser-driven plasma accelerators have been shown to generate quasi-monoenergetic electron beams with energies up to several hundred MeV. Extending the output energy of laser-driven plasma accelerators to the GeV range requires operation at plasma densities an order of magnitude lower, i.e. 10(18) cm(-3), and increasing the distance over which acceleration is maintained from a few millimetres to a few tens of millimetres. One approach for achieving this is to guide the driving laser pulse in the plasma channel formed in a gas-filled capillary discharge waveguide. We present transverse interferometric measurements of the evolution of the plasma channel formed and compare these measurements with models of the capillary discharge. We describe in detail experiments performed at Lawrence Berkeley National Laboratory and at Rutherford Appleton Laboratory in which plasma accelerators were driven within this type of waveguide to generate quasi-monoenergetic electron beams with energies up to I GeV.


GeV-scale electron acceleration in a gas-filled capillary discharge waveguide

New Journal of Physics 9 (2007)

S Karsch, J Osterhoff, A Popp, TP Rowlands-Rees, Z Major, M Fuchs, B Marx, R Hörlein, K Schmid, L Veisz, S Becker, U Schramm, B Hidding, G Pretzler, D Habs, F Grüner, F Krausz, SM Hooker

We report experimental results on laser-driven electron acceleration with low divergence. The electron beam was generated by focussing 750 mJ, 42 fs laser pulses into a gas-filled capillary discharge waveguide at electron densities in the range between 10 18 and 10 19 cm -3 . Quasi-monoenergetic electron bunches with energies as high as 500MeV have been detected, with features reaching up to 1 GeV, albeit with large shot-to-shot fluctuations. A more stable regime with higher bunch charge (20-45 pC) and less energy (200-300 MeV) could also be observed. The beam divergence and the pointing stability are around or below 1 mrad and 8 mrad, respectively. These findings are consistent with self-injection of electrons into a breaking plasma wave. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Simple technique for generating trains of ultrashort pulses.

Opt Lett 32 (2007) 2203-2205

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

A simple method for generating trains of high-contrast femtosecond pulses is proposed and demonstrated: a linearly polarized, frequency-chirped laser pulse is passed through a multiple-order wave plate and a linear polarizer. It is shown theoretically that this arrangement forms a train of laser pulses, and in experiments the production of a train of approximately 100 pulses, each of 200 fs duration, is demonstrated. In combination with an acousto-optic programmable dispersive filter this technique could be used to generate and control pulse trains with chirped spacing. Pulse trains of this type have widespread applications in ultrafast optics.


GeV electron beams from a centimeter-scale laser-driven plasma accelerator

Proceedings of the IEEE Particle Accelerator Conference (2007) 1911-1915

AJ Gonsalves, K Nakamura, C Tóth, CGR Geddes, CB Schroeder, E Esarey, E Cormier-Michel, WP Leemans, D Bruhwiler, JR Cary, SM Hooker

Results are presented on the generation of quasimonoenergetic electron beams with energy up to 1GeV using a 40TW laser and a 3.3 cm-long hydrogen-filled capillary discharge waveguide [1, 2]. Electron beams were not observed without a plasma channel, indicating that self-focusing alone could not be relied upon for effective guiding of the laser pulse. Results are presented of the electron beam spectra, and the dependence of the reliability of producing electron beams as a function of laser and plasma parameters. ©2007 IEEE.


Performance of capillary discharge guided laser plasma wakefield accelerator

Proceedings of the IEEE Particle Accelerator Conference (2007) 2978-2980

K Nakamura, E Esarey, CGR Geddes, AJ Gonsalves, WP Leemans, D Panasenko, CB Schroeder, C Toth, SM Hooker

A GeV-class laser-driven plasma-based wakefield accelerator has been realized at the Lawrence Berkeley National Laboratory (LBNL). The device consists of the 40 TW high repetition rate Ti:sapphire LOASIS laser system at LBNL and a gas-filled capillary discharge waveguide developed at Oxford University. The operation of the capillary discharge guided laser plasma wakefield accelerator with a capillary of 225 μm diameter and 33 mm in length was analyzed in detail. The input intensity dependence suggests that excessive self-injection causes increased beam loading leading to broadband lower energy electron beam generation. The trigger versus laser arrival timing dependence suggests that the plasma channel parameters can be tuned to reduce beam divergence. ©2007 IEEE.


Laser wakefield simulations towards development of compact particle accelerators

Journal of Physics: Conference Series 78 (2007)

CGR Geddes, D Bruhwiler, JR Cary, E Cormier-Michel, E Esarey, CB Schroeder, WA Isaacs, N Stinus, P Messmer, A Hakim, K Nakamura, AJ Gonsalves, D Panasenko, GR Plateau, C Toth, B Nagler, J Van Tilborg, T Cowan, SM Hooker, WP Leemans

Laser driven wakefield accelerators produce accelerating fields thousands of times those achievable in conventional radio-frequency accelerators, offering compactness and ultrafast bunches to potentially extend the frontiers of high energy physics and enable laboratory scale ultrafast radiation sources. Realization of this potential requires understanding of accelerator physics to advance beam performance and stability, and particle simulations model the highly nonlinear, kinetic physics required. One-to-one simulations of experiments provide new insight for optimization and development of 100 MeV to GeV and beyond laser accelerator stages, and on production of reproducible and controllable low energy spread beams with improved emittance (focusability) and energy through control of injection. © 2007 IOP Publishing Ltd.


Performance of capillary discharge guided laser plasma wakefield accelerator

2007 IEEE PARTICLE ACCELERATOR CONFERENCE, VOLS 1-11 (2007) 2222-+

K Nakamura, E Esarey, CGR Geddes, AJ Gonsalves, WP Leernans, D Panasenko, CB Schroeder, C Toth, SM Hooker, IEEE


GeV electron beams from a centimeter-scale laser-driven plasma accelerator

2007 IEEE PARTICLE ACCELERATOR CONFERENCE, VOLS 1-11 (2007) 4367-+

AJ Gonsalves, K Nakamura, C Toth, CGR Geddes, CB Schroeder, E Esarey, E Cormier-Michel, WP Leemans, D Brahwiler, JR Cary, SM Hooker, IEEE


Comparison of parallel and perpendicular polarized counterpropagating light for suppressing high harmonic generation

Journal of the Optical Society of America B: Optical Physics 24 (2007) 2421-2427

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

The use of counterpropagating laser pulses to suppress high harmonic generation (HHG) is investigated experimentally for pulses polarized parallel or perpendicular to the driving laser pulse. It is shown for the first time that perpendicularly polarized pulses can suppress HHG. The intensity of the counterpropagating pulse required for harmonic suppression is found to be much larger for perpendicular polarization than for parallel polarization, in good agreement with simple models of the harmonic suppression. These results have applications to quasi-phase-matching of HHG with trains of counterpropagating pulses. © 2007 Optical Society of America.


Energy extraction from pulsed amplified stimulated emission lasers operating under conditions of strong saturation

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 23 (2006) 1057-1067

SM Hooker, DJ Spence


Inverse free electron lasers and laser wakefield acceleration driven by CO<inf>2</inf>lasers

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 364 (2006) 611-622

WD Kimura, NE Andreev, M Babzien, I Ben-Zvi, DB Cline, CE Dilley, SC Gottschalk, SM Hooker, KP Kusche, SV Kuznetsov, IV Pavlishin, IV Pogorelsky, AA Pogosova, LC Steinhauer, A Ting, V Yakimenko, A Zigler, F Zhou

The staged electron laser acceleration (STELLA) experiment demonstrated staging between two laser-driven devices, high trapping efficiency of microbunches within the accelerating field and narrow energy spread during laser acceleration. These are important for practical laser-driven accelerators. STELLA used inverse free electron lasers, which were chosen primarily for convenience. Nevertheless, the STELLA approach can be applied to other laser acceleration methods, in particular, laser-driven plasma accelerators. STELLA is now conducting experiments on laser wakefield acceleration (LWFA). Two novel LWFA approaches are being investigated. In the first one, called pseudo-resonant LWFA, a laser pulse enters a low-density plasma where nonlinear laser/plasma interactions cause the laser pulse shape to steepen, thereby creating strong wakefields. A witness e-beam pulse probes the wakefields. The second one, called seeded self-modulated LWFA, involves sending a seed e-beam pulse into the plasma to initiate wakefield formation. These wakefields are amplified by a laser pulse following shortly after the seed pulse. A second e-beam pulse (witness) follows the seed pulse to probe the wakefields. These LWFA experiments will also be the first ones driven by a CO 2 laser beam. © 2006 The Royal Society.

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