The X-ray emission from an ultrashort-pulse laser incident on a solid aluminum and a layered aluminum /silicon slab is investigated with a non-LTE radiation-hydrodynamics model coupled to a Helmholtz wave equation for P-wave polarization. A fraction of the absorbed energy is expended in the production of fast electrons, which are transported and deposited in the cold material. These electrons create K-shell vacancies that produce characteristic Kα line radiation. A time history of the emission spectra, including the Kα lines and continuum radiation, is presented for a laser intensity of 1017 W/cm2.

We report on multiphoton ionization experiments using picosecond (ps) and sub-ps UV-laser radiation at focused intensities up to 1018 W/cm2. The experiments are concerned with determining the electron temperature of optically ionized gases produced by intense KrF lasers. Thomson scattering, stimulated Raman scattering (SRS), and X-ray emission measurements have been made and compared with modeling calculations of heating. A particular objective is to identify the respective roles of above-threshold ionization, nonlinear inverse bremsstrahlung absorption, and SRS in determining the temperature of the electrons. Results for 350-fs pulses are compared with previous measurements for 12-ps pulses (for which strikingly different behavior is observed). The importance of using subps, short-wavelength lasers to minimize electron temperature is confirmed.

So-called “space junk” forced a change of plan for a recent Shuttle mission. However, ground-based lasers with atmospheric-turbulence-compensating beam directors represent a singularly effective method of de-orbiting space junk, because they use cheap Earth-based power, and because they lend themselves to rapid retargeting. Plasma physics and lasertarget interaction theory dictate the laser parameters for a particular mission. We will discuss a practical laser system and beam director with 20-kW average power at 0.5-µm wavelength that is capable of clearing most low-Earth-orbit objects with mass less than 100 kg in about 4 years. This is a special application of the Laser Impulse Space Propulsion (LISP) concept, by which objects are propelled in space by the ablation jet produced on their surface by a remote laser.

Cluster-driven inertial confinement fusion (ICF) is analyzed. A cluster is defined as a charged supermolecule with a charge of one (or of the order 1) and with a very high mass number A, so that Z/A « 1. The energy deposition range is shown to be very small (a few micrometers) for projectiles with a few tens of kev/a.m.u. A significant momentum transfer is therefore possible in its slowing down as it passes through matter. In this case, a high hydrodynamic efficiency seems evident. Three relevant models for cluster beam-target interactions are discussed: (1) the rocket model, where the ablation pressure (Pa) is much larger than the cluster beam direct pressure (II); (2) the hammer model, where Pa « II (in this case, two possibilities are discussed—an impact interaction between the beam and the target, and an impact interaction between one cluster and its absorption volume); (3) an intermediate model, where Pa ~II (in this regime, the hydrodynamic efficiency is maximum). Preliminary simulations were performed and the general features of the models were confirmed. Most relevant for ICF, it was found that approximately 75% of the beam energy is converted into X rays, so that the indirect drive is promising in this context.

It is expected (Hora & Handel 1987) that the energy spectra of electrons emitted from laserirradiated atoms in low-density gases would be fundamentally different for laser intensities above and below the threshold of a correspondence principle. Below such a threshold, the emission is a quantum mechanical interaction while, in contrast, above the threshold it is a classical process. Both of our earlier experiments (Boreham & Hora 1979; Boreham & Luther-Davies 1979) and those of several others, including some very recent results (Monot et al. 1993) confirm—after some controversy—the existence of such a correspondence principle. Details are discussed.

A new concept of hot plasma confinement in a miniature magnetic bottle induced by circularly polarized laser light is suggested. Magnetic fields generated by circularly polarized laser light may be of the order of megagauss. In this configuration the circularly polarized laser light is used to obtain confinement of a plasma contained in a good conductor vessel. The poloidal magnetic field induced by the circularly polarized laser and the efficiency of laser absorption by the plasma are calculated. The confinement in this scheme is supported by the magnetic forces. The Lawson criterion for a DT plasma might be achieved for number density n = 5.1021 cm-3 and confinement time τ = 20 ns. The laser and plasma parameters required to obtain an energetic gain are calculated.

An ICF plant is designed to use nuclear-driven flashlamp-pumped solid-state lasers as fusion drivers. It is proposed to use a separated fission reactor with aerosol fuel to drive alkali metal excimer flashlamps as the pumping source for solid-state lasers. The first observation of nuclear-excited sodium excimer emission at 436 nm in a TRIGA reactor with 815 Torr of He-3 and 60 Torr of sodium vapor (at T = 924 K) is reported. The experiment demonstrates the feasibility of a nuclear-driven alkali metal excimer lamp. The compatibility of alkali metal excimers with different laser crystals is evaluated for driver efficiency. High overall laser efficiency ensures large fractional output power extraction from nuclear fusion by this plant. The suitability of laser crystals for the ICF plant is also presented.

This paper presents the results of theoretical and experimental studies on high-pressure He-Cd and He-Zn lasers. It is shown that using the hard ionizer approximation makes it possible to readily and efficiently simulate the plasma chemical processes that occur in the active media of high-pressure lasers pumped by electron and ion beams as well as by nuclear reaction products in electron-beam experiments. Laser oscillation was achieved at λ = 325, 441.6, 533.7, and 537.8 nm for the cadmium ion and at λ = 610.3 nm for the zinc ion.

Some results of an experimental study of the hard X rays emitted from a 15-kV, 3-kJ plasma focus operated in argon are reported. The temporal evolution of the hard X rays detected by a plastic scintillator-photomultiplier detector and the voltage across the focus tube measured by a resistive voltage divider are simultaneously recorded on a two-channel digitizing oscilloscope. Metal absorbers of various thicknesses are used to provide some indications of the energies of the X rays. When the time delay of the detector system with respect to the anode voltage is taken into account, the hard X rays are observed to be emitted about 15 ns before the peak of the anode voltage and last for about 100 ns. There are two periods of emission, the X rays emitted in the first period being more intense, more energetic, and more directional than the X rays emitted in the second period. The X rays are attributed to the bombardment of the anode by energetic electrons generated in the pinch and the disruption phases of the focus.

The process of target ablation induced by pulsed ion beams is investigated. The beam power density of 0.01–0.1 GW/cm2 is around the sublimation energy of the target material. The thickness of the layer to be removed from the target is estimated from the temperature distribution calculated numerically with a diffusion equation. The emitted particles are collected with C collectors, which are later subjected to RBS and SEM/EPMA analyses. It is found that ablated particles forming a film on the collector amount to only 10% of the target atoms within the maximum range of the ions, while a significant amount of the ablated material is observed as macroscopic particles with equivalent diameters up to several tens of micrometers. TOF measurements of the ablation plume together with RBS measurements of thin-film targets after irradiation suggest that the formation of the film is predominated by vaporization from the surface of the ablated mass, which is recondensed on the collector before completing the vaporization.

Electron acceleration by relativistic electron plasma waves is studied by theory and particle simulations. The maximum acceleration that can be obtained from this process depends on many different factors. This paper presents a study of how these various factors impact on the acceleration mechanism. Although particular reference is made to the laser plasma beatwave concept, the study is equally relevant to the acceleration of particles in the plasma wakefield accelerator and the laser wakefield accelerator.