Th. Löwer

Pressure amplification in thermal X-ray irradiated foam layered gold targets

We have studied the interaction of soft X-ray thermal radiation with foam-layered metal targets. The X-radiation was produced by focusing a high energy laser inside a small size hohlraum. An increment in shock pressure was observed with the foam layer as compared to bare metal targets.

The Asterix IV Iodine Laser: Performance and Applications

The layout and performance of the single beam Asterix IV high-power iodine laser operating either at the fundamental wavelength at 1315 nm or the second or third harmonic at 658 nm and 438 nm, respectively, is described. Every 20 minutes Asterix IV can provide output pulses with durations ranging from 0.4 ns to several ns with pulse energies of up to 2.1 kJ and pulse powers reaching 3 TW. Preliminary experiments and calculations reveal that by pumping Ti:S disks with the 3(omega) -radiation of Asterix IV much higher powers in the multi-100 TW region can be attained. Since 1988 the laser fired 6500 target shots as a reliable tool. As a selection among numerous experiments three highlights are dealt with: (1) uniform megabar shock waves in solids, (2) XUV opacities in hot dense Al, Fe, and Ho, and (3) lasing on the J equals 0 - 1 line of neon-like ions using the prepulse technique.

Uniform shock waves driven by thermal radiation from laser-heated cavities

The generation of uniform and preheat-free shock waves in solids by laser-generated thermal x-rays requires careful design of the configuration of the cavity, laser beams and sample. With a new cavity design high-quality shock waves with pressures up to 14 Mbar could be generated with a single laser beam of 280 J energy.

Experiments with ASTERIX and ATLAS

We report on measurements of the equation-of-state of copper and gold in the multi-ten Megabar range, opacity measurements based on K-shell absorption in aluminium, and X-ray laser studies on a large number of neon-like ions applying the prepulse technique. For these investigations, the one-beam iodine laser facility ASTERIX emitting pulses with energies of up to 1000 J at 1315 nm and of up to 420 J at 438 nm was used. We also give a brief account of experimental and theoretical results referring to the propagation of an ultrashort pulse through underdense hydrogen or nitrogen plasmas and X-ray spectra from an optically field-ionized nitrogen plasma generated either by linearly or elliptically polarized light. For these investigations, 150-fs/200-mJ/800-nm pulses emitted from our titanium:sapphire laser ATLAS were employed.

Thermal Soft X-Rays Interaction with foam Layered Gold Targets

The purpose of the experiment presented in this paper was to study the effect of low density foams on the generation of shocks driven by thermal soft X-rays because of their applications in Inertial Confinement Fusion (ICF)1-4. Experiments were performed at MPQ, Garching using Asterix laser energy up to 400 J at 0.44 μm (3ω of Iodine laser) in ≈ 450 ps (FWHM). A conical shaped shield was constructed inside the Labyrinth cavity5 so that the laser irradiated area and the shocked material are not in direct view of each other (Fig. 1). Cavity surface area was equivalent to a sphere surface area of radius 0.5 mm. Target specifications are, 1) Aluminium base of thickness 16.95 μm with Al step of thickness 6.23 μm. 2) gold base of thickness 4.96 μm with a 1.95 μm gold step. The front surface of the gold foil was layered with low density foam (TMPTA-trimethylol propane triacrylate, C15H20O6) of 50 μm thickness, ρ = 20 mg/cc, and also 50, 100 and 150 μm thick with ρ = 50 mg/cc). The areal densities were d = 0.1, 0.25, 0.5 and 0.75 mg/cm2 respectively. A visible streak camera recorded the shock breakout signal.

High quality shocks produced by lasers: Application to equations of state measurements

High quality shock waves with direct and indirect laser drive were generated. We used Phase Zone Plate smoothing technique in the case of direct drive and thermal X-rays from laser heated cavities in the case of indirect drive. The possibility of producing homogeneous, steady shock waves without significant preheating effects with both methods has been proved. Such shocks have been used to test a new method for EOS experiments. Indeed the first simultaneous measurement of colour temperature and shock velocity in laser driven shocks is presented. The two parameters have been measured on each laser shot respectively from the target rear side emissivity in two spectral channels and by using stepped targets. A very good planarity of the shock has been ensured by using the Phase Zone Plate smoothing technique. A simple model describing the shock luminosity has been developed in order to estimate the shock temperature from the experimental rear side emissivities. Results have been compared to temperatures determined from shock velocity for materials of known equation of state.