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The two-dimensional distribution of self-generated magnetic fields near the laser-plasma interaction region is observed for the first time by the very simple method of laser irradiation of audio magnetic tape. The lobe structure is a maximum at the incident angle of 10/sup 0/ to 15/sup 0/ for p-polarized laser light. The direction of the fields is perpendicular to the density gradient and to the incident p-polarization plane. These observations support resonance absorption as the field-generation mechanism.

The spectrum-resolved radiant energies in the 0.1--1.6 keV range from various plane targets irradiated by a 0.53-\ensuremath{\mu}m laser at 0.1--1.0-nsec pulses with intensities of ${10}^{13}$--2\ifmmode\times\else\texttimes\fi{}${10}^{15}$ W/${\mathrm{cm}}^{2}$ are obtained. The conversion efficiency increases with the laser-pulse duration. The physical meaning of the obtained spectrum, such as the correspondence between the emitted photons and the responsible plasma density and temperature region, is clarified from the computational studies by using the one-dimensional hydrodynamic Lagrangian code which is coupled with a nonlocal thermodynamic equilibrium average ion model and multigroup radiation transport. The energy transport of the absorbed laser energy is discussed. Atomic-number dependences of the obtained spectrum and x-ray conversion efficiency show an undulatory structure. This is well reproduced qualitatively and to some extent quantitatively by the code calculation and the contributions of the electronic transitions in different orbital shells are approximately estimated.

The coupling mechanism of CO/sub 2/ laser with a plasma has been investigated. The parametric decay instability, stimulated Brillouin backscattering, and the modulational instability were observed at theoretically predicted laser power thresholds. The modulational instability seems to be responsible for the generation of magnetic fields and fast ions.

The fifteen spectral lines between 3 and 4 keV from a laser-irradiated Au plasma were identified by the relativistic Hartree-Fock-Slater method and were attributed to multiple inner-shell vacancies: one in the $3{p}_{\frac{1}{2}}$ or $3{p}_{\frac{3}{2}}$ shell and one or two more in the $M$ or $N$ shell. The splitting of two groups of lines was about 400 eV, the same as the spin-orbit splitting in the $3p$ shell.

A double-shell target implosion was studied with the GEKKO IV glass laser system. The inner-shell trajectory, recorded for the first time by a newly developed two-frame x-ray shadowgraphy technique, was analyzed by a self-similar flow model, implying more than 20% outer-inner kinetic-energy conversion. The trajectory also agreed with a one-dimensional code result including a vacuum insulation effect. A two-dimensional particle-in-cell simulation analyzed the illumination nonuniformity printed on the inner shell.

Density profile of the glass-microballoon plasma irradiated by Nd laser with intensity of 10/sup 16/ W/cm/sup 2/ was measured by newly developed microscopic interferography. The existence of strong density modification by intense radiation pressure was clearly indicated.

Radiative energy transport in hot dense matter has been investigated in the sub-keV region. In a medium-Z element (aluminum), ionization burn-through has been observed. Burn-through speed is estimated to be 6 x 10/sup 5/ g/cm/sup 2/ sec or more at an x-ray intensity of 7.4 x 10/sup 12/ W/cm/sup 2/. At a high Z (gold), the spectral structure of transmitted x rays indicates the formation of an x-ray heat conduction band via absorption resonance. Penetration depth (rho ..delta..R) of radiative energy transport in Au is found to be 3--4 times larger than that in aluminum.

By converting a coherent wave to a random-phased wave, the intensity profile on a target becomes easily controllable. Planar as well as spherical targets were irradiated for the first time by the random-phased wave. The targets were uniformly accelerated without being affected by the small-scale intensity nonuniformities. The $\frac{3}{2}$-harmonic emission shows that the plasma waves at $\frac{{n}_{c}}{4}$ are only weakly excited in a spherical plasma. Irradiation with short-wavelength, random-phased beams will be suitable for compression.

A spectrum broadening due to the self phase modulation of a laser light was observed in the laser produced deuterium and hydrogen plasmas. Qualitative treatments of the density modulation due to the self focusing process and the modulational instability were discussed. The theoretical estimation of spectrum broadening fairly accorded with experimental results. (Author) (GRA)

The dynamic behavior of the plasma produced from a thin foil target irradiated by a focused intense electron beam is observed optically by the shadowgraphy and interferometry. Evidence of anomalous stopping of intense electron beam on the surface of the low-Z target is shown experimentally.

Brillouin backscattering from laser-produced plasmas of hydrogen and deuterium has shown an isotope effect in the red-side region of the generated second-harmonic light. This isotope shift is explained by the parametric instability at the cutoff region using the phase-matching condition of the waves. The decrease of the reflectivity appeared when the laser intensity increased up to 1 order of magnitude larger than the threshold of the parametric instability. A broad-band laser showed more effective heating of the plasma than a narrow-band laser.

This paper is concerned with broad-scale studies of self-generated magnetic fields by use of the magnetic-tape method. A refined technique which enables a sensible and fine-structure observation is described. In a large-cone-angle experiment parity existence is verified by using convergent and divergent laser beams. In a small-cone-angle experiment it is shown that negative and positive magnetic fields cross the resonance region; the existence of parity is demonstrated by reversing the sign of the incident angle. These observations strongly support resonance absorption as the mechanism of field generation.

With use of a large green laser system (5 kJ, 500 psec, ten beams), scattered light from cavity and cannonball targets (1500 \ensuremath{\mu}m diam) is investigated. Strong suppression of stimulated Brillouin scattering is observed for the cavity target, while weak to modest suppression of stimulated Brillouin scattering is measured for the cannonball targets. The observed damping is attributed to sudden temperature rise due to collisions of two plasmas in the cavity.

Experimental studies of the wavelength dependence of the following laser-plasma coupling processes were performed: (1) laser-light absorption, (2) energy transport, and (3) ablation and target-acceleration behavior. At a fixed intensity around ${10}^{14}$ W/${\mathrm{cm}}^{2}$, the ablation process was dominated by heat transport by cold electrons for 0.53-and 1.06-\ensuremath{\mu} m lasers and by hot electrons for a 10.6-\ensuremath{\mu} m laser.

The stability of ablatively accelerated single-layer and multilayer thin foil targets has been studied by x-ray shadowgraphy and x-ray spectral analysis of the rear target surface. Results show the single-layer foil acceleration to be essentially stable with the disassembly being thermally dominated. An upper limit to Rayleigh-Taylor growth of 1.8 is determined compared to a classical value of 11. Evidence, though, of internal layer mixing in the multilayer target is seen.

A strong magnetic field of 600 kG (60 T) is generated at the center of a 2-mm-diam one-turn coil in which the current is driven by a ${\mathrm{CO}}_{2}$ laser. The magnetic field, current, and voltage are measured as functions of the separation distance of the gap where the high voltage is induced by the laser irradiation in the coil loop at a fixed intensity of 1.3\ifmmode\times\else\texttimes\fi{}${10}^{14}$ W/${\mathrm{cm}}^{2}$. These results are analyzed on the basis of hot-electron E\ifmmode\times\else\texttimes\fi{}B drift and plasma expansion inside the gap. The analysis indicates how to design the target and the laser pulse for generation of a magnetic field of a few megagauss.

The fast-ion-velocity distributions for polyethylene plasmas produced by spherical laser illumination were observed by a Thomson parabola spectrometer. It has been found that the velocity distributions have undulations, sharp truncations, and broad shelf structure because of multi-ion-species effects. The spherical symmetric plasma expansions including multi-ion-species and two-electron temperature effects have been simulated by a newly developed computer code. The simulation results indicate that protons are accelerated near the front edge of carbon ions, and the maximum velocity is determined predominantly by the ions which run in the region ahead of the carbon-ion front. Consequently, the proton-expansion front has a structure slipped out from the carbon-ion front towards vacuum. Since such protons compensate the accelerating electric field, the maximum velocities of proton and carbon ions become higher and lower, respectively, than in the case of single-ion species. These expansion dynamics reduced by the simulation can explain well the detailed structure of the observed velocity distribution.

The first experimental observation of ablation-pressure distribution on spherical targets was made at several focusing conditions by using flash x-ray radiography. The results indicate that lateral smoothing of the ablation pressure is dominated by the magnetic field generation due to hot-electron streams and/or local-heating--induced deln x delT at an intensity near 10/sup 15/ W/cm/sup 2/ from a 1.053-..mu..m laser.

As lasers have an ability to deliver a large amount of energy very rapidly to matter, one can produce a plasma of thermonuclear temperature by laser bombardment of matter. We observed a neutron yield from a solid deuterium target irradiated by the beam of a glass laser, which had a power of 20 GW for 2 nsec. The theoretically estimated threshold laser power for anomalous heating owing to the parametric instability was in agreement with the experimental result. Above this threshold, an increase in the electron temperature, the appearance of a fast-ion group, and an anomaly in the reflection of light from the plasma were observed. These phenomena were closely correlated with the neutron yield. At the high-temperature region above a few hundred electron volts, the anomalous heating plays an essential role in reaching the fusion-reaction temperature.

A mechanism of long-scale magnetic field generation from rippled surface irregularities is given and compared with the thermoelectric effect. Criteria are given for the former dominating over the latter. These criteria are accessible in present-day experiments. An experiment is done to show an implication of the above mechanism.