The Prague Asterix Laser System (PALS) is a new international laboratory where research teams are invited to compete for the beam time. The PALS Center runs an iodine photodissociation high-power laser system delivering up to 1.2 kJ of energy in ∼400 ps pulses at the wavelength of 1.315 μm. Optional doubling and tripling of the frequency is assured by large-diameter nonlinear crystals. The ASTERIX IV laser [H. Baumhacker et al., Appl. Phys. B 61, 325 (1995)], transferred from Garching into a new laser hall in Prague, was updated and put into operation on 8 June 2000. These upgrades include new beam delivery options and a twin interaction chamber, which is designed flexibly for a broad spectrum of applications. Results of the first series of experiments are presented and some planned upgrades are briefly described. These include implementation of adaptive optics, replacement of the iodine master oscillator by a more flexible solid state oscillator based on fiber optics, and a femtosecond extension of the laser output to reach the petawatt pulse power region.

Detailed measurements of the angular distribution of 3 ω0/2 radiation are presented in short scale length plasmas (0.8–7 μm) generated by laser radiation at intensities reaching the relativistic level (1016–6×1018 W/cm2). The experimental results are in very good agreement with theoretical predictions based on two-plasmon decay and stimulated Raman scattering instabilities. New three-halves harmonic generation mechanisms are an identified characteristic of femtosecond laser induced parametric instabilities. These are the joint interaction of incident and reflected laser beams as well as stimulated Raman scattering. It is shown both experimentally and theoretically that the three-halves harmonic radiation is a useful preplasma diagnostic tool.

The Lyman lines γ , δ and ε of hydrogenic aluminum emitted from a laser-generated plasma were recorded using a novel high-dispersion x-ray spectrometer. The shifts of the spatially resolved emission profiles were identified and correlated with the plasma densities inferred from numerical simulation of the experiment. The red shifts observed are consistent with the predictions of the plasma polarization shift based on the quantum-mechanical impact theory.