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Fast ignition of inertial fusion targets is one of the promising ways for future energy production. Recent studies of ignition with fast electrons have shown only little progress - mainly caused by the unresolved problem of controlled electron transport in dense plasmas. Ion-assisted ignition schemes are less sensitive in this regard and laser energies in the range of 50 - 100 kJ are required for fuel ignition. Picosecond laser pulses with intensities exceeding 10 22 Wcm -2 and a high intensity contrast of better than 10 -10 are needed thereby. The cone-guided target proves to be the most efficient scheme, although targets without a cone are more appropriate for high repetition rate operation.

High-order harmonics generated by weakly relativistic femtosecond laser pulses interacting with solid and thin foil targets were studied. It was found that the conversion efficiency is one or two orders of magnitude larger than that of gas-harmonics and thus due to the high laser intensity also the harmonics are very intense. In addition, anomalies and complex interference structures have been observed in the harmonic spectra of the solid targets. They are explained by simulations. Furthermore, for the first time intense harmonics were observed from thin foil targets and, in particular, from the target rear side. This type of studies provides a promising tool for obtaining information about the laser plasma interaction itself, e.g., on the presence of large fields and oscillations inside the foil up to a penetration depth comparable to the laser wavelength.

We have studied the influence of the target properties on laser-accelerated proton and ion beams generated by the LULI multi-terawatt laser. A strong dependence of the ion emission on the surface conditions, conductivity, shape and material of the thin foil targets were observed. We have performed a full characterization of the ion beam using magnetic spectrometers, Thompson parabolas, radiochromic film and nuclear activation techniques. The strong dependence of the ion beam acceleration on the conditions on the target back surface was found in agreement with theoretical predictions based on the target normal sheath acceleration (TNSA) mechanism. Proton kinetic energies up to 25 MeV have been observed.

Laser energy requirements for the creation of active plasma media with Ne- and Ni-like ions with a `long' subnanosecond prepulse (100 - 1000 ps) and a `short' picosecond main pulse (0.1 - 10 ps) have been determined for foil and low density targets (foams, gases, vapors, etc.). RADEX hydrodynamics and atomic kinetics calculations show that X-ray laser action in the 200 - 400 A can be obtained with 1 - 2 J in 100 - 1000 ps prepulse followed of an approximately 1 ps pulse of similar energy. Transient gains of approximately 100 cm-1 level have been calculated. For the wavelengths 38 - 46 A (`red' edge of `water window' spectral band) a short pulse of only approximately 5 - 10 J is required.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.