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.

Fever can be elicited in the rabbit by the intravenous administration of relatively large doses of a synthetic immunoadjuvant, N-acetylmuramyl-L-alanyl-D-isoglutamine, or muramyl dipeptide (MDP). This response could be mediated by endogenous pyrogen because MDP has been shown to induce their production both in vivo and in vitro. The results reported here show that intracisternal injection of minute amounts of MDP could elevate fever without activating the release of endogenous pyrogen in the plasma or in the cerebrospinal fluid. Moreover, indomethacin inhibited hyperthermia produced by intracerebroventricular administration of MDP. Therefore, our findings argue in favor of a direct effect of the glycopeptide on the thermoregulatory centers besides its indirect effect through the production of leukocytic pyrogen. This molecule apparently represents the minimal requirement for the pyrogenicity of bacterial peptidoglycan because administration, even by the intracerebral route, of a mixture of muramic acid and of its dipeptide moiety did not elicit fever.

The results of investigations are presented that are connected with defocused laser beam–planar target interaction. Following the very large focus laser-plasma interaction experiments on the Nova [H. T. Powell, J. A. Caird, J. E. Murray, and C. E. Thompson, 1991 ICF Annual Report UCRL-LR-105820-91, p. 163 (1991)] and GEKKO-XII [C. Yamanaka, Y. Kato, Y. Izawa, K. Yoshida, T. Yamanaka, T. Sasaki, T. Nakatsuka, J. Kuroda, and S. Nakai, IEEE J. Quantum Electron. QE-17, 1639 (1981)] lasers, as well as on the National Ignition Facility (NIF) laser [W. J. Hogan, E. I. Moses, B. E. Warner, M. S. Sorem, and J. M. Soures, Nucl. Fusion 41, 567 (2001)] with generation of high Mach number jets, this paper is devoted to similar jet generation with very detailed measurements of density profiles by using high-power lasers at large focus conditions. The experiment was carried out with target materials of different mass densities (Al, Cu, Ag, Ta, and Pb) using the Prague Asterix Laser System (PALS) iodine laser [K. Jungwirth, A. Cejnarova, L. Juha, B. Kralikowa, J. Krasa, E. Krousky, P. Krupickova, L. Laska, K. Masek, A. Prag, O. Renner, K. Rohlena, B. Rus, J. Skala, P. Straka, and J. Ullschmied, Phys. Plasmas 8, 2495 (2001)]. The investigations were conducted for the laser radiation energy of 100J at two wavelengths of 1.315 and 0.438μm (the first and third harmonics of laser radiation), pulse duration of 0.4ns, and a focal spot radius of 300μm. Most of the experimental data were obtained by means of a three-frame laser interferometer and an x-ray streak camera; the crater parameters were obtained by using the crater replica technique. These investigations have shown that stable dense plasma jets can be produced in a simple configuration of laser beam–planar target interaction, provided that a proper target material is used.

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