Professor Simon Hooker

Abstract:

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.

Abstract:

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.

Abstract:

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.

Abstract:

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 × 1017 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.