Publications by Simon Hooker


Transverse beam profile measurements of laser accelerated electrons using coherent optical radiation

AIP Conference Proceedings 1507 (2012) 258-261

N Bourgeois, M Heigoldt, W Rittershofer, A Popp, K Khrennikov, SI Bajlekov, S Karsh, SM Hooker

We use coherent optical transition radiation (COTR) to measure the transverse profile of laser-accelerated electron bunches. The retrieved electron beam profiles are compared to scintillator-based beam profile measurements. © 2012 American Institute of Physics.


Multiple pulse resonantly enhanced laser plasma wakefield acceleration

AIP Conference Proceedings 1507 (2012) 872-873

L Corner, R Walczak, LJ Nevay, S Dann, SM Hooker, N Bourgeois, J Cowley

We present an outline of experiments being conducted at Oxford University on multiple-pulse, resonantly-enhanced laser plasma wakefield acceleration. This method of laser plasma acceleration uses trains of optimally spaced low energy short pulses to drive plasma oscillations and may enable laser plasma accelerators to be driven by compact and efficient fibre laser sources operating at high repetition rates. © 2012 American Institute of Physics.


Optical rotation quasi-phase-matching for circularly polarized high harmonic generation

Optics Letters 37 (2012) 167066

LZ Liu, K O'Keeffe, SM Hooker


Quasi-phase-matched high harmonic generation using trains of uniformly-spaced ultrafast pulses

Optics InfoBase Conference Papers (2011)

K O'Keeffe, T Robinson, SM Hooker

We investigate quasi-phase-matching of high harmonic generation over a range of harmonic orders using trains of up to 8 uniformly-spaced counter-propagating pulses, produced using an array of birefringent crystals. © 2012 OSA.


High Harmonic Optical Generator (Polarization Beating 1/2)

(2011) UK Patent Application GB1117355.6

LZ Liu, K O'Keeffe, SM Hooker


Time-resolved plasma temperature measurements in a laser-triggered hydrogen-filled capillary discharge waveguide

Plasma Sources Science and Technology 20 (2011)

CJ Woolley, K O'Keeffe, HK Chung, SM Hooker

Temporally resolved, spatially integrated measurements of the temperature of the plasma channel formed by a hydrogen-filled discharge capillary waveguide are presented. Plasma temperatures of 4-7 eV are measured for peak discharge currents between 80 and 150 A. It is demonstrated that laser-triggering the capillary discharge enables capillary discharges with a peak current as low as 23 A to be driven, reducing the plasma temperature to approximately 3 eV. This plasma temperature meets the requirements of a recently proposed soft x-ray recombination laser. © 2011 IOP Publishing Ltd.


Simulation of free-electron lasers seeded with broadband radiation

Physical Review Special Topics - Accelerators and Beams 14 (2011)

SI Bajlekov, WM Fawley, CB Schroeder, R Bartolini, SM Hooker

The longitudinal coherence of free-electron laser (FEL) radiation can be enhanced by seeding the FEL with high harmonics of an optical laser pulse. The radiation produced by high-harmonic generation (HHG), however, has a fast-varying temporal profile that can violate the slowly varying envelope approximation and limited frequency window that is employed in conventional free-electron laser simulation codes. Here we investigate the implications of violating this approximation on the accuracy of simulations. On the basis of both analytical considerations and 1D numerical studies, it is concluded that, for most realistic scenarios, conventional FEL codes are capable of accurately simulating the FEL process even when the seed radiation violates the slowly varying envelope approximation. We additionally discuss the significance of filtering the harmonic content of broadband HHG seeds. © 2011 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.


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.


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.


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.


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.


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.


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 ...


Laser-driven soft-X-ray undulator source

Nature Physics 5 (2009) 826-829

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

Synchrotrons and free-electron lasers are the most powerful sources of X-ray radiation. They constitute invaluable tools for a broad range of research 1 ; however, their dependence on large-scale radiofrequency electron accelerators means that only a few of these sources exist worldwide. Laser-driven plasma-wave ccelerators 2-10 provide markedly increased accelerating fields and hence offer the potential to shrink the size and cost of these X-ray sources to the niversity-laboratory scale. Here, we demonstrate the generation of soft-X-ray undulator radiation with laser-plasma-accelerated electron beams. The well-collimated beams deliver soft-X-ray pulses with an expected pulse duration of ∼ 10 fs (inferred from plasma-accelerator physics). Our source draws on a 30-cm-long undulator and a 1.5-cm-long accelerator delivering stable electron beams with energies of ∼ 210 MeV. The spectrum of the generated undulator radiation typically consists of a main peak centred at a wavelength of ∼ 18 nm (fundamental), a second peak near ∼ 9 nm (second harmonic) and a high-energy cutoff at ∼ 7 nm. Magnetic quadrupole lenses ensure efficient electron-beam transport and demonstrate an enabling technology for reproducible generation of tunable undulator radiation. The source is scalable to shorter wavelengths by increasing the electron energy. Our results open the prospect of tunable, brilliant, ultrashort-pulsed X-ray sources for small-scale laboratories. © 2009 Macmillan Publishers Limited. All rights reserved.


Chirped pulse trains for quasi-phase-matching high harmonic generation

Optics InfoBase Conference Papers (2009)

T Robinson, K O'Keeffe, SM Hooker

A method for producing non-uniformly spaced (chirped) trains of ultrafast pulses is demonstrated, using an acousto-optic programmable dispersive filter (AOPDF). Programmable pulse trains of this type may find applications in quasi-phase matching of high-harmonic generation. © 2009 Optical Society of America.


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.


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

ULTRAFAST PHENOMENA XVI 92 (2009) 15-+

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


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, TP Rowlands-Rees, M Fuchs, R Hörlein, F Grüner, D Habs, F Krausz, SM Hooker, S Karsch

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.


Laser-driven acceleration of electrons in a partially ionized plasma channel.

Phys Rev Lett 100 (2008) 105005-

TP Rowlands-Rees, C Kamperidis, S Kneip, AJ Gonsalves, SPD Mangles, JG Gallacher, E Brunetti, T Ibbotson, CD Murphy, PS Foster, MJV Streeter, F Budde, PA Norreys, DA Jaroszynski, K Krushelnick, Z Najmudin, SM Hooker

The generation of quasimonoenergetic electron beams, with energies up to 200 MeV, by a laser-plasma accelerator driven in a hydrogen-filled capillary discharge waveguide is investigated. Injection and acceleration of electrons is found to depend sensitively on the delay between the onset of the discharge current and the arrival of the laser pulse. A comparison of spectroscopic and interferometric measurements suggests that injection is assisted by laser ionization of atoms or ions within the channel.

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