Publications by Simon Hooker


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.


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 × 10 17 W cm -2 were 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 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 2.7 ×10 18 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 × 10 16 W 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.


Inner-shell soft X-ray lasers in Ne-like ions driven by optical field ionization

Optics Communications 182 (2000) 209-219

SM Hooker

A novel short-wavelength laser based upon monopole excitation of inner-shell electrons in Ne-like ions following optical field ionization with circularly polarized radiation is discussed. Calculations of the small-signal gain are presented for one such ion, Ne-like Ar, for which a small-signal gain of 13.7 cm -1 is predicted on the 2s → 2p hole transition at 15.8 nm for an Ar pressure of 50 mbar. Extensions of this approach to other inner-shell transitions are suggested. © 2000 Elsevier Science B.V. All rights reserved.


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 10 16 W cm -2 are 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 × 10 17 Wcm -2 . © 2000 Optical Society of America.


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

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest (2000) 293-294

DJ Spence, SM Hooker

An overview is given on the results of numerical simulations of the propagation of high-intensity pules through discharge-ablated capillary waveguides. The numerical code solves the paraxial wave equation for a plasma undergoing optical field ionization, and so accounts for refractive defocusing due to further ionization by the propagating pulse.


Inner-shell soft x-ray lasers driven by optical field ionization

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest (2000) 515-516

SM Hooker

Presented is a novel approach for driving short-wavelength lasers, with good prospects for scaling to shorter wavelengths. Present investigations include analysis of extensions to other transitions such as the 3s → 3p and 3p → 3d hole transitions in Ni-like ions following monopole excitation of 3s and 3p holes in OFI plasmas. The results of those calculations are presented.


Measurement of the electron-density profile in a discharge-ablated capillary waveguide

Optics Letters 24 (1999) 993-995

DJ Spence, PDS Burnett, SM Hooker

Discharged-ablated capillary waveguides were investigated based on electron-density profile using time-resolved interferometric measurements. A pronounced axial minimum with a relative depth of as much as 60% of the axial electron density was developed in the electron density profile. Results showed that this profile can be used for high-intensity laser pulse tunneling.


Effects of a prepulse in the femtosecond-pulse-driven Xe IX laser

Journal of the Optical Society of America B: Optical Physics 14 (1997) 2735-2741

SM Hooker, PT Epp, GY Yin

We describe experiments that demonstrate the detrimental effect of a prepulse on the femtosecond-pulse-driven Xe IX laser. The mechanism of this effect is discussed in terms of the results of a hydrodynamic model of the preplasma formed by the prepulse. The benefit of inserting a simple electro-optic switch that allows full transmission of the main driving pulse, but reduces the prepulse to a level at which no preplasma is formed, is demonstrated experimentally. © 1997 Optical Society of America.


Vacuum ultraviolet gain measurements in optically pumped LiYF<inf>4</inf>:Nd<sup>3+</sup>

Applied Physics B: Lasers and Optics 64 (1997) 293-300

JS Cashmore, SM Hooker, CE Webb

We present measurements of the net-induced gain on the 5d-4f transition at 186 nm in LiYF 4 :Nd 3+ optically pumped by radiation from a molecular fluorine laser. It is found that for LiYF 4 : Nd 3+ one of a series of potential continuously tunable VUV lasers, relatively strong excited-state absorption results in net-induced loss. The prospects for VUV laser operation being realised in other rare-earth-doped fluorides is discussed.


Light at the end of the tunnel? Femtosecond pulses excite short-wavelength lasers

Optics and Photonics News 8 (1997) 21-25

SM Hooker

Hooker explores current work in the XUV and soft x-ray spectral region aimed at achieving "table-top" short-wavelength lasers.

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