Publications by Simon Hooker


Collisional lasers at 41.8 nm in a guided regime

J PHYS IV 127 (2005) 33-37

I Bettaibi, S Sebban, T Mocek, CM McKenna, B Cros, A Butler, DJ Spence, G Maynard, AJ Gonsavles, SM Hooker


Effects of polarization on inverse Bremsstrahlung heating of a plasma.

Phys Rev E Stat Nonlin Soft Matter Phys 72 (2005) 036402-

N David, SM Hooker

A molecular dynamic (MD) code is used to compare the rates of heating by inverse Bremsstrahlung (IB) for circularly and linearly polarized radiation. For low intensities the heating rate is found to be independent of polarization. However, at higher intensities the variation of the heating rate with the radiation intensity is found to exhibit a sharper peak for circularly polarized than linearly polarized radiation. This difference is explained in terms of differences in the variation of the electron quiver speed during the optical cycle for linearly and circularly polarized radiation. An analytical expression--which includes a term which is nonlinear in the density of the plasma--for the rate of IB heating is fitted to the rates calculated by the MD code.


Application of the gas-filled capillary discharge waveguide to laser-plasma acceleration

AIP CONF PROC 737 (2004) 825-831

DJ Spence, AJ Gonsalves, CM McKenna, SM Hooker

The application of the gas-filled capillary discharge waveguide to laser-plasma accelerators is reviewed. The results of experiments to guide high-intensity laser pulses in capillaries with circular or square cross-sections are described. The relation between capillary diameter, guided spot size, and plasma density are explored, and a possible new hybrid regime of guiding is identified.


Molecular-dynamic calculation of the inverse-bremsstrahlung heating of non-weakly-coupled plasmas.

Phys Rev E Stat Nonlin Soft Matter Phys 70 (2004) 056411-

N David, DJ Spence, SM Hooker

A molecular dynamic (MD) code is used to calculate the inverse bremsstrahlung (IB) heating rates of a plasma as a function of density and laser intensity. The code belongs to the class of particle-particle-particle-mesh codes. Since the equations solved by the MD code are fundamental, this approach avoids several assumptions which are inherent to alternative methods, for example those which employ a Coulomb logarithm, and is not restricted to weakly coupled plasmas. The results of the MD code are compared to previously published results for plasmas of low coupling. The results of calculations for dense, moderately coupled plasmas are also presented. An analytic expression for the IB heating rate, based on a fit to the rates calculated by the MD code, is suggested. This expression includes terms nonlinear in the plasma density.


A review of laser guiding experiments

AIP CONF PROC 737 (2004) 125-136

SM Hooker

In many cases the length over which particles can be accelerated in a laser-driven plasma accelerator is limited by refraction or diffraction of the driving laser pulse. In order to overcome this limitation the driving pulse must be guided or channeled through the plasma, In this paper we briefly review of the techniques used to guide laser pulses with peak intensities up to 10(19) W cm(-2), and describe recent experimental results.


41.8-nm Xe<sup>8+</sup>laser driven in a plasma waveguide

Physical Review A - Atomic, Molecular, and Optical Physics 70 (2004)

A Butler, AJ Gonsalves, CM McKenna, DJ Spence, SM Hooker, S Sebban, T Mocek, I Betttaibi, B Cros

The results of the first experimental demonstration of a short-wavelength laser driven within a gas-filled capillary-discharge waveguide were described. The xenon gas was mixed with the hydrogen and strong lasing on the 4d95d-4d95p transition in Xe8+at 41.8 nm was observed. Analysis shows that lasing was strongly correlated with good guiding of the pump pulse and numerical simulations indicate that gain is likely to have been achieved over a significant fraction of the 30 mm length of the capillary. The success of this proof-of-principle experiment suggests that this and other short-wavelength lasers could be driven within waveguides of this type, leading to increased energy output and reduced beam divergence.


Progress on collisionally pumped optical-field-ionization soft X-ray lasers

IEEE Journal on Selected Topics in Quantum Electronics 10 (2004) 1351-1362

S Sebban, T Mocek, I Bettaibi, B Cros, G Maynard, A Butler, AJ Gonzalves, GM McKenna, DJ Spence, SM Hooker, LM Upcraft, P Breger, P Agostini, S Le Pape, P Zeitoun, C Valentin, P Balcou, D Ros, S Kazamias, A Klisnick, G Jamelot, B Rus, JF Wyart

We present the status of optical field ionization soft X-ray lasers. The amplifying medium is generated by focusing a high-energy circularly polarized 30-fs 10-Hz Ti: sapphire laser system in a gaseous medium. Using xenon or krypton, strong laser emission at 41.8 and 32.8 nm, respectively, has been observed. After presenting the basis of the physics, we present recent characterization of the sources as well as dramatic improvement of their performances using the waveguiding technique.


Molecular-dynamic calculation of the inverse-bremsstrahlung heating of non-weakly-coupled plasmas

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 70 (2004)

N David, DJ Spence, SM Hooker

The inverse bremsstrahlung (IB) heating rates of a plasma as a function of density and laser intensity were calculated using a molecular dynamic (MD) code. The code belonged to the class of particle-particle-particle-mesh codes. The equations solved by the MD code avoided several assumptions which were inherent to alternative methods. The results of the MD code were compared to previous results for plasmas of low coupling. The results of the calculations for dense, moderately coupled plasmas were also presented. An analytic expression for the IB heating rate, based on a fit to the rates calculated by MD code, was also presented.


Molecular-dynamic calculation of the relaxation of the electron energy distribution function in a plasma.

Phys Rev E Stat Nonlin Soft Matter Phys 68 (2003) 056401-

N David, SM Hooker

A molecular-dynamic (MD) code is used to calculate the temporal evolution of nonequilibrium electron distribution functions in plasmas. To the authors' knowledge, this is the first time that a molecular-dynamic code has been used to treat this problem using a macroscopic number of particles. The code belongs to the class of P3M (particle-particle-particle-mesh) codes. Since the equations solved by the MD code are fundamental, this approach avoids several assumptions that are inherent to alternative methods. For example, the initial energy distribution can be arbitrary, and there is no need to assume a value for the Coulomb logarithm. The advantages of the MD code are illustrated by comparing its results with those of Monte Carlo and Fokker-Planck codes with a set of plasma parameters for which the Fokker-Planck calculation is shown to give incorrect results. As an example, we calculate the relaxation of the electron energy distribution produced by optical field ionization of a mixed plasma containing argon and hydrogen.


Demonstration of lasing at 41.8 nm in Xe8+ driven in a plasma waveguide

P SOC PHOTO-OPT INS 5197 (2003) 105-118

A Butler, AJ Gonsalves, CM McKenna, DJ Spence, SM Hooker, S Sebban, T Mocek, I Bettaibi, B Cros

We describe the first demonstration of a collisionally-excited optical field ionisation laser driven within a gas-filled capillary waveguide. Lasing on the 4d(9)5d-4d(9)5p transition at 41.8 nm in Xe8+ was observed to be closely-correlated to conditions under which the pump laser pulses were guided well by the waveguide. Simulations of the propagation of the pump laser radiation show that gain was achieved over essentially the whole 30 mm length of the waveguide.


Gas-filled capillary discharge waveguides

Journal of the Optical Society of America B: Optical Physics 20 (2003) 138-151

DJ Spence, A Butler, SM Hooker

We describe in detail the operation of the gas-filled capillary discharge waveguide for high-intensity laser pulses and discuss measurements and magnetohydrodynamic simulations that show that the plasma channel produced is parabolic and essentially fully ionized. We present the results of experiments in which laser pulses with a peak input intensity of 1.2 × 1017W cm-2were guided through hydrogen-filled capillary discharges with lengths of 30 and 50 mm. The pulse energy coupling and transmission losses were determined to be <4% and (7 ± 1) m-1, respectively. We discuss the application of waveguides of this type to driving short-wavelength lasers and laser wakefield accelerators. © 2003 Optical Society of America.


Demonstration of a collisionally excited optical-field-ionization XUV laser driven in a plasma waveguide

Physical Review Letters 91 (2003) article 205001 4 pages-

SM Hooker, Arthur Butler, Anthony J. Gonsalves, Claire M. McKenna


Molecular-dynamic calculation of the relaxation of the electron energy distribution function in a plasma

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 68 (2003) 564011-564018

N David, SM Hooker

A molecular-dynamic (MD) code for calculating the relaxation of an arbitrary electron energy distribution in a plasma was described. The MD approach provided a more fundamental set of equations, with fewer assumptions. The accuracy of the MD approach was proved by comparing its results with the Monte Carlo and Fokker-Planck codes using a set of plasma parameters for which the Fokker-Planck calculation gave incorrect results. Calculating energy relaxation in plasmas proved important for the understanding of the operation of new types of short-wavelength lasers based on optical field ionization.


Guiding of high-intensity laser pulses with a hydrogen-filled capillary discharge waveguide.

Phys Rev Lett 89 (2002) 185003-

A Butler, DJ Spence, SM Hooker

We report guiding of laser pulses with peak input intensities greater than 10(17) W cm(-2) in 30 mm and 50 mm long H2-filled capillary discharge waveguides. Under conditions producing good guiding the coupling and propagation losses of the waveguide were <4% and (7+/-1) m(-1), respectively. The spectra of the transmitted pulses were not broadened significantly, but were shifted to shorter wavelength. It is concluded that this shift is not associated with significant temporal distortion of the laser pulse.


Simulations of a hydrogen-filled capillary discharge waveguide

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 65 (2002)

NA Bobrova, AA Esaulov, JI Sakai, PV Sasorov, DJ Spence, A Butler, SM Hooker, SV Bulanov

A one-dimensional dissipative magnetohydrodynamics code is used to investigate the discharge dynamics of a waveguide for high-intensity laser pulses: the gas-filled capillary discharge waveguide. Simulations are performed for the conditions of a recent experimental measurement of the electron density profile in hydrogen-filled capillaries [D. J. Spence et al., Phys. Rev. E 63, 015401 (R) (2001)], and are found to be in good agreement with those results. The evolution of the discharge in this device is found to be substantially different to that found in Z-pinch capillary discharges, owing to the fact that the plasma pressure is always much higher than the magnetic pressure. Three stages of the capillary discharge are identified. During the last of these the distribution of plasma inside the capillary is determined by the balance between ohmic heating, and cooling due to electron heat conduction. A simple analytical model of the discharge during the final stage is presented, and shown to be in good agreement with the magnetohydrodynamic simulations. © 2001 The American Physical Society.


First demonstration of guiding of high-intensity laser pulses in a hydrogen-filled capillary discharge waveguide

Journal of Physics G: Atomic, Molecular and Optical Physics 34 (2001) 4103-4112

SM Hooker, Butler, A, Spence, DJ


Investigation of a hydrogen plasma waveguide.

Phys Rev E Stat Nonlin Soft Matter Phys 63 (2001) 015401-

DJ Spence, SM Hooker

A hydrogen plasma waveguide for high-intensity laser pulses is described. The guiding channel is formed by a small-scale discharge in a hydrogen-filled capillary. The measured lifetime of the capillary is inferred to be greater than 10(6) shots. The results of interferometric measurements of the electron density in the capillary are presented. The guiding channel is found to be highly ionized with an axial electron density of 2.7x10(18) cm(-3), and parabolic, the curvature corresponding to a matched spot-size of 37.5 microm.


Investigation of a hydrogen plasma waveguide

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 63 (2001) 1-4

DJ Spence, SM Hooker

A hydrogen plasma waveguide for high-intensity laser pulses is described. The guiding channel is formed by a small-scale discharge in a hydrogen-filled capillary. The measured lifetime of the capillary is inferred to be greater than 106 shots. The results of interferometric measurements of the electron density in the capillary are presented. The guiding channel is found to be highly ionized with an axial electron density of 2.7 ×1018 cm-3, and parabolic, the curvature corresponding to a matched spot-size of 37.5 μm. ©2000 The American Physical Society.


Guiding of high-intensity picosecond laser pulses in a discharge-ablated capillary waveguide

Journal of the Optical Society of America B: Optical Physics 17 (2000) 90-98

SM Hooker, DJ Spence, RA Smith

The results of a study of the channeling of intense picosecond laser pulses by a discharge-ablated capillary waveguide are presented. The peak-energy transmission for a 10-mm-long waveguide is measured to be 65% for an input intensity of 1 × 1016W cm-2. The importance of inverse bremsstrahlung, stimulated Raman scattering, stimulated Brillouin scattering, atomic modulation instabilities, and ionization of the discharge plasma as loss mechanisms for both intense femtosecond and picosecond pulses are considered. © 2000 Optical Society of America.


Simulations of the propagation of high-intensity laser pulses in discharge-ablated capillary waveguides

Journal of the Optical Society of America B: Optical Physics 17 (2000) 1565-1570

DJ Spence, SM Hooker

We present the results of simulations of the propagation of high-intensity laser pulses in discharge-ablated capillary waveguides. The limitations of this type of waveguide for pulse intensities of the order of 1016W cm-2are discussed. However, for higher intensities we describe a new regime of quasi-matched guiding, that results in significant improvements in guiding performance. The effect on quasi-matched guiding of changing the atomic numbers of the atoms that compose the plasma waveguide is discussed. Calculations are presented for boron capillaries that show quasi-matched guiding over lengths of 32 mm for an input intensity of 5 × 1017Wcm-2. © 2000 Optical Society of America.

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