We studied the influence of foams on laser produced shocks. Experiments were performed at LULI using a Nd laser converted to second harmonic, and at MPQ (Max Planck Institut für Quantenoptik) using the iodine Asterix laser converted to third harmonic. In both cases, sub-ns lasers with pulse energies of several tens of joules were focused on large focal spots (hundreds of microns) to reduce 2D effects. The laser beams were optically smoothed with phase zone plates (PZP) and directly focused on layered targets made of a foam layer on the laser side and a stepped Al layer on the other side. A visible streak camera was used to detect shock breakthrough at the base and at the step of the Al target, allowing shock velocity to be determined. Using the well known SESAME Al equation of state, we determined shock pressure. A stronger pressure increase was measured when foam was present, compared to what was obtained by focusing the laser beam directly on the Al target. This was due to the impedance mismatch effect at the Al-foam interface.

The paper presents results of investigations of the process of the creation of a diamagnetic cavity by a laser-produced plasma in a strong transverse magnetic field of 10 T in induction. The plasma was produced from a flat, teflon target by an Nd laser of 5 J in energy and about 1 ns in pulse duration. The investigations were carried on by means of a three-frame interferometry and a non-contact magnetic probe, a so called remote magnetic probe (RMP). For the needs of this work, we developed a methodology for the measurement of the dimensions of the cavity during its expansion by means of the RMP, taking into account the plasma expansion geometry that is specific to flat targets. The dynamics of the process of creation of the diamagnetic cavity, its shape and dimensions have been determined. A very good consistency of dimensions of the diamagnetic cavity and plasma boundary in their quasisteady state, obtained with both diagnostics, allows us to apply the RMP method not only for the investigation of diamagnetic properties of various laser-produced plasmas, but also for the evaluation of their initial kinetic energy and its transformation in magnetic field.

When a high power laser (1012 W/cm2) irradiates a target, it induces a shock wave, which reaches the (free) rear surface. The free surface is accelerated and the shock wave is back-reflected as a rarefaction wave. In the shock wave pressure regime involved here, melting of the target during the shock or during the rarefaction may occur. An optically recording velocity interferometric system (ORVIS) has been developed to measure the time evolution of the change in the reflectivity of the free surface. Shock waves of the order of hundreds of kilobars are produced in 50–125 μm thick Sn and Al foils, by a Nd:YAG laser system with a wavelength of 1.06 μm, pulse width of 7 ns (FWHM), and irradiance in the range (1.4–2.4)·1013 W/cm2. The changes in the reflectivity occur along two time scales: a slow one, more than 17 ns in Al and more than 30 ns in Sn, and a rapid one, less than 2.5 ns, in both materials. A possible explanation for the sharp decreases in the time scale is that melting occurs during the release of the free surface.

The results of the experiments at the installation “PICO,” with thin foils heating by laser radiation pulses of nanosecond duration are reported. The Al foils with thickness in the range from 3 μ up to 40 μ were used as targets. The flux density was varied from 1013 W/cm2 to 1014 W/cm2. The sharp dependence of the portion of laser energy that passed through the target on foil thickness was observed. This phenomena was accompanied by a relatively small decrease of the passed radiation pulse duration. The anomalously high speed burning through of thin foil was observed in these experiments and the conclusion on the possible mechanism of this phenomena has been done on the base of comparison of experimental data with theoretical calculations. The observed phenomena can be interpreted with a conjecture about the local burning through of a target, in the small areas of the target surface, with many more values of flux density than the average one following laser radiation self-focusing and formation of “hot spots.”

With a Petawatt class CPA laser of the LLNL Livermore or the proposed GSI (Darmstadt) type laser, interactions with matter can be studied in the upper 1020 W/cm2 regime. With such a laser focused into an underdense plasma, strong electron bursts with energies up to several 100 MeV are ejected in a forward direction. This leads to a comparable burst of bremsstrahlung radiation in the presence of high-Z material. Here, we discuss the corresponding γ-induced nuclear reactions including secondary particle production, including pions. Due to the threshold behavior in the production, and the advantage of delayed detection, we propose to employ these reactions for probing the initial plasma conditions.

Interaction of relativistically strong laser pulses with under- and overdense plasmas is studied by 3D particle-in-cell simulations. We show that electrons in the underdense plasmas can be accelerated not only by the plasma wake field, but also by direct laser push in self-generated magnetic and electrostatic fields. These two mechanisms of acceleration manifest themselves in the electron energy spectra as two effective “temperatures.” We show that the fast electrons transport a significant part of the laser pulse power through the overdense plasma in the form of magnetized jets. We also find high collective stopping because of an anomalous resistivity of the plasma.

The calculations of 1014–1015 W/cm2 laser interaction with volume-structured agar-agar and Cu targets were performed. The influence of intrinsic X-ray plasma radiation on the propagation of thermal waves in such targets was investigated. It is shown that the velocity of heat transfer in agar-agar foam targets is increased due to X-ray preheating when a thin Cu layer is added.