Efforts to demonstrate the feasibility of a gamma-ray laser scored major advances in 1987. Culminating with the successes in optically pumping the first of the 29 actual candidate isomers, priority issues were brought into better focus by the lessons learned from a wealth of new results. Perceptions were advanced so greatly that we must reassess the critical issues for 1988. Only the bottom line remains the same. A gamma-ray laser is feasible if the right combination of energy levels occurs in some real material. The likelihood of this favorable arrangement has been markedly increased by the experimental results to date.

A large, high density, high temperature plasma has been produced by using a high power laser with a capillary electrical discharge. The laser beam is synchronized with the discharge to reach the plasma after it emerges several hundred microns from the capillary.

The physics and technology for e-beam generation, large volume excitation and the ultra-violet optics for high power KrF lasers is presented. The potential, due to the charge deposition, induces a return current in the plasma which balances the e-beam current. The local equilibrium mechanism stabilizes the large volume excitation using intense electron beams. The spatial and temporal characteristics of large aperture diodes are analyzed. Substantial progress in ultra violet optics in Japan has been achieved. The damage threshold of HR dielectric coating increases up to 11 J/cm2 by using low absorption materials.

The present status of the development of a high-power KrF laser system, Ashura, is described. The main amplifier has generated 710 J (95 ns) at the pumping density of 1·lMW/cm3 with the wall plug efficiency of 2·0%. Maximum power of 9·0 GW (200 J/22 ns) per beam has been obtained from the beam lines of six-time pulse multiplexing. Power density of 1 × 1014 W/cm2 has been achieved on target with a 10−6 pre-pulse.

KrF and other short wavelength lasers are ideal candidates for producing hot dense plasmas since the laser energy can be absorbed with high efficiency by classical mechanisms, thereby virtually eliminating anomalous absorption and the production of non-thermal electrons. A high power KrF laser system employing optical beam multiplexing and stimulated Brillouin scattering to produce pulses as short as 1 ns and focused intensities on target of 1011−1014 W/cm2 has been developed for producing such plasmas and studying laser/plasma interaction phenomena. A variety of studies on absorption, transport, ablation, X-ray conversion and stimulated scattering instabilities have been pursued with this ¼ μm laser on single atomic number and multi-layer targets. This paper briefly describes some of the features of the KrF laser system and highlights some of the characteristics of the hot dense plasmas produced.

Progress in high-brightness excimer lasers and in optical angular multiplexing of excimer lasers presents an opportunity to provide very intense pumping of X-ray sources, both in favorable geometry and in traveling waves, all at low cost. The traveling-wave strategy can be tailored to the parameters of the system to be pumped. This design option can be of great importance for systems lasing at wavelengths in the kilovolt regime where upper level lifetimes are short, and where mirror technology is presently tenuous. Features of several design strategies are explored.

The Laboratory Microfusion Facility (LMF) has been proposed to study Inertial Confinement Fusion (ICF) targets with reactor-grade gains. An advanced solid-state laser is the prime candidate as the driver for the LMF. However, here we present a conceptual design for an alternate approach using a Nuclear Pumped Laser (NPL).

A pulsed fission reactor is used to excite an oxygen-iodine laser in this design, based on preliminary data on nuclear pumping of O2(1δ). Although a working NPL of this specific type has not yet been assembled, we believe this concept holds great potential, both as a test facility driver and as a future power reactor.

Periodical short pulse trains were observed in the oscillation of the waveguide mode free electron laser, which could be explained as a self mode-lock oscillation of the free electron laser.

The spectra of the spontaneous emission and the induced absorption were observed, which were in good agreement with theoretical calculations.

The energy spread of the relativistic electron beam was measured using Thomson back scattering from a high power CO2, laser.

Pulsed laser induced damage of optical thin films is, in general, initiated by the absorption of laser radiation by imperfections in the films or at interfaces between film layers and/or the substrate. A heat flow analysis of this process stresses the importance that the thermal conductivity of both the thin film host and that of the substrate play in establishing the laser-induced damage threshold. Unfortunately, recent work, which will be reviewed in this presentation, indicates that the thermal conductivity of thin films can be several orders of magnitude lower than that of the corresponding material in bulk form. This situation arises as a consequence of the film structure resulting principally from the deposition process. The importance of thermal conductivity will be compared to parameters such as absorption mechanisms, film materials, composition, and other variables. Its implication for the ultimate optical strength of materials and the direction in which thin film research and processing should proceed will be highlighted.

A novel concept is described which utilizes a liquified rare gas as both an energy converter and high-density lasing media. The concept allows the advantage of the large mean-free path of high energy fusion neutrons together with a highly-efficient mechanism for volumetric production of 1 MeV electrons which causes ionization and excitation throughout the medium. This scheme coupled together with the high efficiency for light production of liquid excimers may provide the possibilities for a new dimension in high power lasers.

The products of fusion reactions have unique properties which can be used for direct energy conversion. These products are neutrons and ions. Neutrons can be transported very long distances through solid materials and can interact with certain elements which have a very high absorption cross section. Ions on the other hand have a very short transport length even in a gaseous medium. It is possible to utilize these products in an inertial confinement fusion reactor with two different direct energy conversion devices: a nuclear-pumped laser using neutrons from the fusion reaction; a photon generator material combined with a photovoltaic converter using the ionic fusion products.

It will be argued that a nuclear-pumped laser can be more efficient than a conventional laser. It will also be shown that an advanced energy conversion concept based on photon production and photovoltaics can produce ICF system efficiencies of 56%.

The recent progress of laser fusion research has been remarkable in obtaining the high density of more than 100 times solid density (Nakai et al. 1988) and high temperature plasma producing thermonuclear neutrons of 1013 per shot (pellet gain of 0·2%) (Yamanaka et al. 1986a) and in the understanding of the implosion physics. The data bases of the laser fusion are rapidly being accumulated and the technologies for the advanced experiments have been developed, both of which enable us to proceed toward the fusion ignition experiment and the achievement of the breakeven conditions.

The key issues of laser fusion are to achieve highly efficient implosion by the ablation and to reach the high gain of a fuel pellet. Measures of the success are the neutron yield and the areal density of the fuel. Recent results show the neutron yield per laser shot to be 1013, and the ρR is 0·2g/cm2. These data seem to be approaching the breakeven condition.

We have developed medium and high resolution X-ray crystal spectrometers for measurements of charge state distributions of impurity ions, density of suprathermal electrons and ion temperature in magnetically confined plasmas. The techniques utilizing these spectrometers are, in principle, applicable to laser produced plasmas, especially in their expanding phase. The role of X-ray spectroscopy to produce useful data for atomic physics as well as for plasma diagnostics is emphasized. A beam-line has been designed and installed to the Ultraviolet Synchrotron Radiation Facility (UVSOR) at IMS, Okazaki, for the purpose of establishing calibration techniques for optical components, detectors and spectrometers in the range from ultraviolet to soft X ray for plasma diagnostics. Characteristics of the beam and its application to the study of interaction between synchrotron radiation and hot dense plasmas are described. Synchrotron radiation can replace the dye laser which has so far been used as a light source in the laser-induced fluorescence method to obtain population density of specified levels in a plasma.

In order to enhance the coupling efficiency, a low Z ablator is generally used for ICF targets. The ablator thickness is appropriately chosen so it is burned out by the end of a laser pulse. Then all of the implosion kinetic energy is contained in the DT fuel. However, a small amount of preheating degrades the compression in a hollow shell, DT fueled target implosion. In this paper, we investigate the preheating level of the fuel shell by Fokker–Planck simulations of the electron heat transport.

From the analysis, it is found that a thick surface layer of a laser irradiated low-Z target is preheated by Maxwellian tail electrons which have a long mean free path. Hence, we propose that the target be precompressed by a tailored pulse, in order to increase the shell ρΔR at the laser peak.

Emissions from the rear side of the targets were temporally resolved by irradiating an ultraviolet (UV) laser on Al and Au thin targets. A difference was clearly observed between the above two targets. Given the fact that absorbed laser energy is converted with a very high efficiency to soft x-rays in a high Z plasma, a characteristic emission peak only observed for Au targets was attributed to the effect of soft x-ray energy transport. The ablation pressures estimated from the emissions indicate that the pressure scaling for Au is close to the one by x-ray radiation rather than by a UV laser. With soft x-ray irradiation, energy transport in A1 foils was also studied. An ablation pressure was estimated by the shock speed.

When a one-shell three-layer cryogenic target is irradiated by a driver beam of total energy 10 MJ and pulse width 30 ns, the pusher pressure increases to 1013 Pa, accelerating fuel toward target center, and the fuel implosion velocity reaches 3 × 105 m/s. A spherical hollow target plays the role of a supersonic converging nozzle, and the fuel is compressed to 269 times the solid density in the supersonic region and to 3·51 × 104 times in subsonic region. Nonuniform beam-energy-deposition in pusher layer causes nonuniform pusher pressure and hence nonuniform implosion, which reduces fuel compression significantly. The smoothing of pusher pressure by radiative energy transfer, or gas-filled target instead of cryogenic hollow target can be used to reduce the defect of nonuniform implosion. At last, the structure of an indirect driven target is proposed to smooth out pusher pressure in spite of nonuniform beam irradiation.

Volume compression and volume ignition of laser compressed pellets has an enormous advantage against spark ignition since the alpha self-heat substantially contributes as an additional stimulation of nuclear fusion reactions. We present here improved computations of volume ignition in agreement with the classical fact that the generated fusion energy is larger than the bremsstrahlung energy in DT only at temperatures above 4·5 keV. This result is in very close agreement with Kidder's (1974) values, and in agreement with recent computations of Mima et al. (1987). The extension of these calculations to higher densities and input energies results in the self-absorption of bremsstrahlung at an initial temperature of about 1 keV only, much below the classical 4·5 keV. A fuel burnup fraction above 80% is shown to be possible.

The main tool for the laser plasma work at MPQ (Max-Planck-Institut für Quantenoptik) is the ASTERIX iodine laser delivering 300 J/300 ps pulses at 1·3 m, operational also at 2ω and 3ω. A fifth 30-cm diameter am lifier is under construction to increase the pulse energy up to 2 kJ.

Soft X-ray radiation emitted by laser plasmas and its influence on energy transport and hydrodynamics is studied. Time and space resolved spectroscopic measurements of soft X-radiation from a variety of targets are compared with analytical models and computer results. Planck radiation is produced in gold cavities to study radiation hydrodynamics. Theoretical work comprises shock waves in solids, the electronic structure of very high density matter, radiation pumped X-ray laser and development of the appropriate computer codes.

Estimates indicate that dense plasmas with temperatures of several ten keV can be produced with the heavy ion accelerator now under construction at GSI-Darmstadt. Experiments are being prepared to be started in 1991. Measurements at the present UNILAC-accelerator confirm the theoretical prediction that the energy loss of heavy ions in a plasma is much higher than in cold matter.