A 9 μm thick aluminium foil is accelerated to a velocity of about 160 km/s by a laser of 0.26 μm wavelength and intensity of 1015 W/cm2 and collides with an aluminium impact foil. The measurement of the velocity of the induced shock wave in the impact foil, using a step method at the rear of the impact foil, gives pressures in the multi-hundred megabar range. The dynamics and constraints of this shock wave are presented and the effect of X-ray preheating, which can be important at this laser wavelength, is discussed.

Wavelength dependent absorption in laser-plasma interactions was investigated by measuring the energy spectra of freely expanding plasmas in their asymptotic stage of expansion. The experiments were performed with both 1·06- and 0·53-μm-wavelength light incident on flat tantalum targets. The experimental conditions were chosen adequately to ensure that inverse bremsstrahlung was the dominating absorption mechanism. As a result it is found that the absorption is enhanced at the shorter wavelength by a factor of 1·3. Primarily this leads to a higher ionisation state of the plasma and higher kinetic ion energies and temperatures, respectively, while the amount of ablated mass is approximately the same.

The spectra of laser-produced plasmas of various materials of Z>70 have been interpreted as spin-orbit-split arrays of the 3d – 4f and 3d – 5f transitions for Ni-like to Ge-like ions. The excellent agreement between the model and the experiments indicated the possibility of their use for plasma diagnostics. First results from targets of Gold alloyed with Aluminium give an alternative diagnostic.

Using radial plasma acceleration in a laser beam, an alternative type of free electron laser has been developed by radial injection of electrons. Its properties have been elaborated for a laser amplifier of 400 μtm wavelength. To overcome the difficulties of this FEL, a basically new laser amplifier concept has been developed where a laser pulse is amplified by nearly lateral injection of solid particles (clusters, pellets etc.) whose kinetic energy (at appropriate adjustment and synchronisation) is converted into 80% optical energy of the laser pulse. The mechanism of energy transfer is the radial slowing down by nonlinear ponderomotive forces of the plasma made from the cluster reaching the beam axis, and the switching-off process of the beam with regard to the transient nonlinear force processes. It is an inversion of the plasma ejection with ponderomotive self-focussing. Apart from the unusually high efficiency, a relatively high gain is expected even for such small laser wavelengths as 10 nm. Furthermore, the difficult problem of modification of phase fronts and convergence (focussing, directing of X-ray beams) should be solved by the optical plasma properties at injection.

A simple model in two dimensions is developed and solved analytically taking into account the electric and magnetic fields in laser produced plasmas. The electric potential in this model is described by the non-linear differential equation

ψ = eφ/T, where eφ is the electric potential energy and T is the temperature in energy units. The physical branch ψ < 1, defined by the electron density n = no exp ψ, boundary conditions n (x = 0) = const and n (x = +∞) = 0, introduces a typical electrostatic double layer. The stationary solution of this model is consistent for − 3 ≲ ψ < 1, with electron temperatures in the KeV region and a ratio of the electric (E) to magnetic (B) fields of [E/106 v/cm]/[B/MGauss] ∼ 1.

This paper discusses the general requirements for inertial confinement fusion, technology requirements and choices, overall efficiencies, and laser system costs for scaling krypton fluoride amplifiers to high energy, and describes the design of a 100 kilojoule double-pass KrF power amplifier.

First experimental results with a pulsed iodine photodissociation laser controlled by target plasma reflectivity are reported. One of the laser mirrors is substituted for a focusing lens and a solid tilted target is located in its focal region. The laser dynamics depends on the geometry of the set-up. Laser pulse durations from 200 to 5 ns were observed if the resonator length was changed from 2 to 5 meters. Simultaneous mode-locking and Q-switching took place if the resonators were longer than 3 meters. Peak power densities of up to 1011 W/cm2 on the target and about a 1 per cent plasma reflectivity, increasing with increasing power density, were measured. A theoretical explanation of the laser behaviour and a comparison of our observations with previous results obtained with TEA-CO2 and Nd-glass amplifiers are presented.

We describe here a new oscillator that performs the three functions of aligning, mode-locking, and Q-switching.

The interaction of a laser beam (1·06 μm) with an underdense plasma produced by optical breakdown of helium was experimentally studied. Evidence for whole beam self-focusing is reported and discussed.

A key issue in the design of an HIF reactor cavity is the transport of the heavy ion beam from final focusing, across the cavity, to the target. Previous estimates have indicated that streaming instabilities will disrupt the beam transport for a background chamber gas pressure of 10−4 to 10−1 torr. The most attractive liquid lithium first wall reactor cavity designs produce a background gas density in just this pressure range. A detailed analysis of the streaming instabilities has now demonstrated that the beam can be transported through this background. The important fact that had been neglected is that a mode with a given wave number will grow for only a small fraction of the transport time, due to the changing beam and electron densities during transport. This analysis opens wide an attractive window for reactor cavity design.

Application of Fourier theory to heat conduction due to laser irradiation at high power intensities (i.e. 1010 W/m2) gives errors of the order of 30 per cent at the upper end of the temperature rise time. This is caused by the assumptions made in the Fourier theory, since the heat flux through a given plane depends on the electron energy distribution through the material. On the scale of distance required to examine the problem, the material can no longer be considered as being a homogeneous continuum and when the power intensities of interest are concerned, the higher order terms in the heat transfer equation become important. Therefore, the problem requires to be examined in the quantum field. Application of electron kinetic theory to the problem enhances the solution within an accuracy greater than 90 per cent. The present theory introduces a new model for the conduction mechanism.

The acceleration of test electrons by a resonant, one—dimensional electric structure is studied in the convective regime with the Zakharov equations. Depending on the nonlinearity level the particle acceleration is due to diffusion or trapping by the plasma wave. Electron distributions are obtained and compared with 1-D particle code results. Influence of Landau damping formulation is discussed.

This paper presents the design of the four-channel Nd: glass high power laser system in the Kaliski Institute of Plasma Physics and Laser Microfusion (IPPLM) in its optimized version, based on a theoretical analysis of propagation of radiation in the real laser channel.

The effects of microscopic energy deposition in hot, dense plasmas and radiation transport in plasmas, on the interaction of ion beams with plane metal targets are investigated in this paper. In order to do this we analyze the plasma dynamics of ablatively accelerated plane metal foils. The physical analysis of these results is achieved by the derivation of solutions of the non-linear radiation conduction equation with boundary temperatures which increase in time. We illustrate, by means of numerical simulations, how range shortening due to plasma effects such as increased energy loss to excited electrons and an increased effective charge due to a reduction in the recombination rate, may be compensated for by radiation transport. The effect of radiation transport and detailed microscopic energy deposition on ion beam implosions, including hydrodynamic instability, is discussed.

We have compensated for gain saturation in the Nova amplifiers by producing shaped input optical pulses. A silicon switch device generates kilovolt electrical pulses for driving pockels cells. The pulse shape is easily controllable with subnanosecond resolution.

The coherence of the laser radiation limits the average beam fluence in high power laser installations. The disadvantages of present optical schemes are analysed. A new optical scheme with controlled spatial coherence is described and its consequences are shown.

The laser and plasma conditions at the onset of Raman scattering have been measured in plasmas formed from thin-foil targets. The targets were Al disks 50 to 250 nm thick and 200 to 500 μm in diameter mounted on 100 nm polymer films. The incident wavelength was 526 nm. Raman scattering was observed for nominal intensities from 1014 W/cm2 to 5 × 1014 W/cm2. The most important observation of the experiment is that the density-gradient scale-length at onset is independent of intensity. One would expect the scalelength at onset to be inversely related to the intensity, since the convective gain for stimulated Raman scattering (SRS) is proportional to the product of intensity and scalelength.

The paper reviews a number of X-ray streak cameras developed at AWRE. These cameras are used to provide temporal and one-dimensional spatial or spectral information on X-rays emitted from laser produced plasmas. Two of these cameras have been designed to be combined with other diagnostic instrumentation; one with a Wolter X-ray microscope (×22 magnification) and the other with a Bragg diffraction crystal spectrometer. This latter instrument provides a few eV spectral resolution and ∼15 ps temporal resolution; a typical experimental application at the AWRE HELEN laser facility will be described. The paper describes the circuitry of the bipolar avalanche transistor ramp generator used to drive the streak plates of the cameras. Improvements to this include: (a) increasing the fastest streak rate to ∼10 ps mm−1 by a distributed capacitance network across each of the bipolar stacks of transistors, and (b) reducing the trigger jitter to approximately ±10 ps by the use of a new mix of transistors in the stack and a Raytheon RS 3500 avalanche transistor. Additional improvements have now been added. These include a ‘half-scan’ user facility to aid initial camera timing and direct switching to select the sweep rate of the camera.