The use of nuclear radiation to excite lasers is examined from the perspective of nuclear flashlamps. Nuclear driven flashlamps can also be used as photon sources for photochemical and photovoltaic events. This can lead to the large scale production of chemicals and electricity.

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.

Generation of large amplitude plasma waves using high-power lasers in either the wakefield or beat-wave scheme is considered. We show how the nonlinear behavior of the plasma wave may make it advantageous to split the total energy into more than one pulse in the wavefield scheme. When a beat wave is generated by a pulse of finite length, we show how the final wave amplitude may be enhanced if the frequency of one or both pulses is chirped in such a way that the wavelength of the beat increases from the front to the back of the pulse.

The time-dependent condition for population inversion in the X-ray 3 → 2 transition in hydrogen-like ions of a recombining plasma produced by a short laser pulse is studied. The population densities of the energy levels are theoretically obtained in a collisional-radiative plasma model; the reabsorption of the 2 → 1 resonance line is taken into account via the escape probability. A new feature is first that the escape probability is treated as an explicitly time-dependent function, E21(r,t). On the basis of a four-level model of the H-like ions, the rate differential equations governing the time development of the population densities are considered, including time-dependent pumping terms and coefficients. Furthermore, specially modeling the time dependence of E21 (r,t), and assuming the other rate coefficients to be approximately constant with respect to time, via the explicit closed-form solution of the corresponding rate equations, the Balmer-α inversion condition ΔN32(r,t) > 0 is given in terms containing confluent hypergeometric functions and depends on rate coefficients, pumping terms, and explicitly on the time. For the free-electron density Ne of the recombining plasma, this relation means a condition depending on atomic and plasma state parameters and qualitatively changing in the course of time.

Plasmas with solid-state density at temperatures of a few eV will be produced in the near future at GSI by high-energy heavy ions. To diagnose these plasmas, novel methods–based on hard X-ray diagnostics–have to be applied. An investigation of the hydrodynamic expansion of the target requires a space- and time-resolved measurement of the plasma density. The determination of the target density independently of its temperature is obtained by a special X-ray pinhole camera enabling a selective registration of the target K-shell emission in combination with space- and time-resolved beam intensity measurements.

The time-dependent soft X-ray emission of helium and nitrogen plasmas generated by optical-field ionization is reported. The experiments were carried out by focusing pulses of the high-power Ti:sapphire laser of the Lund Institute of Technology (λ = 796 nm, pulse duration 150 fs, pulse energy 150 mJ) to a 50-μm diameter spot close to a nozzle, using He and N2 as target gases. The emission on He+, N4+, and N3+ resonance lines was recorded by means of a flat-field grating spectrometer coupled to an X-ray streak camera. A pronounced difference in the temporal shape of the emission of the Lyman-α line of hydrogen-like helium and of the 2p−3d resonance lines of lithium-like and beryllium-like nitrogen was observed. The helium line exhibited an initial spike followed by a slow revival of the emission, whereas the nitrogen lines showed a slow decay after a fast initial rise. These observations are explained with the help of simulations.

The propagation of electron driven shock waves has been investigated by employing a one-dimensional, three-component fluid model. In the fluid model, the basic set of equations consists of equations of conservation of mass, momentum, and energy, plus Poisson's equation. The wave is assumed to be a shock front followed by a dynamical transition region. Following Fowler's (1976) categorization of breakdown waves, the waves propagating into a preionized medium will be referred to as Class II Waves. To describe the breakdown waves, Shelton and Fowler (1968) used the terms proforce and antiforce waves, depending on whether the applied electric field force on electrons was with or against the direction of wave propagation. Breakdown waves, i.e., return strokes of lightning flashes, therefore, will be referred to as Antiforce Class II waves. The shock boundary conditions and Poisson's equation for Antiforce Class II waves are different from those for Antiforce Waves. The use of a newly derived set of boundary conditions and Poisson's equation for Antiforce Class II waves allows for a successful integration of the set of fluid equations through the dynamical transition region. The wave structure, i.e., electric field, electron concentration, electron temperature, and electron velocity, are very sensitive to the ion concentration ahead of the wave.

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.

Numerical analyses show that a 40% mixing inhomogeneity of the deuterium (D) and tritium (T) concentrations in a DT pellet still gives a sufficient fusion energy output in DT inertial confinement fusion (ICF), as long as the D and T total amounts are equal. This new result means that fusion energy output is rather insensitive to the inhomogeneous fuel mixing in the DT ICF pellet.

The effect of multiple ionization on Kα spectra is investigated for aluminum targets irradiated by intense lithium beams. Multiple ionization cross sections have been calculated using a formulation incorporating single-electron ionization probability in the binomial distribution. In contrast to conventional binary-encounter approximation (BEA) theory, the single-electron ionization probabilities for each atomic shell have been calculated using a combination of modified plane-wave Born approximation (MPWBA) and an empirical effective interaction radius which is dependent on both the target ion and the projectile. Our calculations show that the effect of multiple inner-shell ionization on aluminum Kα spectra observed in intense lithium beam experiments is important. Multiple ionization effects become less important as the target ionization state increases. Nevertheless, even for highly ionized species up through Be-like Al multiple ionization effects can be significant and must be considered in the analysis of spectra obtained in intense Li beam-plasma interaction experiments.

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.

Far-field images produced using different random phase plates on a pulsed laser beam focused with variousf/numbers were recorded by a charge-coupled device (CCD) camera and then analyzed. Envelope spot sizes agree with diffraction theory while mean sizes of the pattern structures have been found to be larger than the diffraction limit. The probability density distribution of intensity in the focal plane is not the expected exponential. A central symmetry of the pattern has also been seen after suitably aperturing the beam. Some consequences for the use of powerful RPP-treated laser beams in laser-plasma interactions are discussed.

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.

In this paper, we present the results of our theoretical studies on the angular dependence of M and N band peaks emitted from a laser irradiated gold foil. The M band peak is seen to be nearly isotropic, while the magnitude of the N band peak decreases as we move away from normal to the foil. The trend is similar to that reported in the experiments of Chase et al.: (1977) for aluminium foil. It is also observed that the N band peak shifts towards longer wavelength as the angle φ relative to the normal to the target increases. We also present the effect of angular anisotropy on time and frequency integrated total conversion efficiency of laser light into X rays using a high Z target. As compared with the diffusion approximation, a significant reduction in conversion efficiency is observed for a wide range of laser powers, and wavelengths.

The plasma produced during pulsed-laser deposition of thin carbon films is studied in the presence of ambient gases (Air, He, Ar) at low and moderate irradiances of Nd:YAG laser. The presence of ambient gas shows a pronounced effect on the dynamics of the plasma plume. At moderate intensity, we report an appearance of a peculiar double-peak structure in the temporal profile of the C II transition in laser-produced carbon plasma as it expands into a background gas. We believe that the structure originates mainly due to stratification of the plasma into fast and slow ion components at the interface where Rayleigh-Taylor instability occurs. Thin carbon films deposited on silicon in the presence of argon gas have shown the characteristic features of diamond-like carbon in X-ray diffraction and Raman Spectroscopy. The X-ray diffraction pattern of carbon film deposited at 1 torr of argon gas pressure shows the dominance of (111), (220), (311), and (400) crystalline plane of cubic diamond.

Basic characteristics of an ablation plasma produced by an intense, pulsed, ion beam have been evaluated from the measurement of ion-flux density by a biased ion collector. The target mass loss is detected by the measurement of the weight of the target in the comparison before and after the shot. A one-dimensional hydrodynamic model is introduced with the assumption of a high-power, light-ion beam-driven expansion and the following adiabatic expansion into vacuum. With this model, it is possible for us to deduce the temperature and the pressure from the data of the ion flux and the mass loss of the target, respectively. This method is also applicable to other intense pulsed energy sources such as lasers or electron beams.