[en] Recently, five quasi-polynomial-time algorithms solving parity games were proposed. We elaborate on one of the algorithms, by Lehtinen (2018). Czerwiński et al. (2019) observe that four of the algorithms can be expressed as constructions of separating automata (of quasi-polynomial size), that is, automata that accept all plays decisively won by one of the players, and rejecting all plays decisively won by the other player. The separating automata corresponding to three of the algorithms are deterministic, and it is clear that deterministic separating automata can be used to solve parity games. The separating automaton corresponding to the algorithm of Lehtinen is nondeterministic, though. While this particular automaton can be used to solve parity games, this is not true for every nondeterministic separating automaton. As a first (more conceptual) contribution, we specify when a nondeterministic separating automaton can be used to solve parity games. We also repeat the correctness proof of the Lehtinen’s algorithm, using separating automata. In this part, we prove that her construction actually leads to a faster algorithm than originally claimed in her paper: its complexity is n O(log n) rather than n O(log d·log n) (where n is the number of nodes, and d the number of priorities of a considered parity game), which is similar to complexities of the other quasi-polynomial-time algorithms.

[en] A new method of generation of nanosecond soft x-ray pulsed with a photon energy around 1 keV is presented. X-rays are generated in a high-temperature plasma, which is created as a result of interaction of Nd:glass laser radiation with a gas puff target. The target was obtained by puffing a small amount of gas, through the nozzle, into the vacuum chamber, by means of a pressure electromagnetic valve. The pulses of laser radiation with the pulse duration of 1 ns and energy up to 15 J, generated in the system of a high-power Nd:glass laser, were for the target heating. Spatial, spectral and temporal measurements of X-ray emission have shown that the high-intensity soft X-ray are generated as a result of the interaction of nanosecond pulses of Nd:glass laser radiation with the gas puff target. High efficiency of X-ray generation is suggested to be related to the effect of condensation of the gas, outflowing from the valve nozzle and, in effect, to the interaction of laser radiation with matter in a form of aerosol. (author). 55 refs, 5 figs

[en] This work presents results of the first stage of investigations of ion emission from the plasma produced with the PALS laser system at the PALS Research Centre in Prague, Czech Rep. Using an aspherical lens the laser beam was focused onto solid targets. The ion measurements, based on the time-of-flight method, were performed with the use of ion collectors located at various angles with respect to the laser beam axis. Ion collector signals show different groups of ions (slow, thermal and fast ions). The charge velocity distribution, ion current density and angular distribution of ion charge emission, as well as the total charge and the average energy of ions were obtained from these signals. Using an electrostatic ion-energy analyzer the emission of highly-charged heavy ions (Ta⁵²⁺, Ag³⁸⁺) with energies up to 7 MeV is demonstrated. The dependencies of ion stream parameters on the experimental conditions are discussed. Preliminary experiments on direct implantation of laser-produced ions into different materials have already started. (author)

[en] Results of experimental investigations of characteristics of ion streams generated from laser plasma after focusing the laser beam either with an aspheric lens or with a parabolic mirror (allowing an observation of the ion emission in the direction of the target normal) are presented. The photodissociation iodine laser PERUN operating with λ = 1.315μm and delivering energy up to 50J was exploited in the experiment. In this contribution we restricted ourselves to the results of ion emission measurements from Ta-, Pb- and Bi- plasma. (author)

[en] The Polish commercial photodiodes BPYP35, BPYP41, BPYP44 have been used for X-ray diagnostics of laser produced plasmas. Short nanosecond pulses of soft (1-10 keV) X-ray in time-integrated as well as in time-resolved (for BPYP41) modes of operation have been registered. The paper presents experimental arrangements with single photodiodes and their arrays. Such features of the photodiodes as X-ray energy response function, dynamic range of amplitudes of pulses and temporal response are most important in this application. Results are presented of numerical evaluation of the photodiode X ray response function and a method is described for photodiode examinations in which α - particle source have been used

[en] Essential differences in properties of fast ion fluxes from the interaction of 1 ps and 0.5 ns laser pulses with Au target have been observed. In the short-pulse case, only a single fast ion group with a small angular divergence is generated and ions are likely to be accelerated by an axial ponderomotive force from the skin-layer interaction. In the long-pulse case, at least two groups of fast ions are emitted into a wide solid angle and the ion flux properties seem to be determined by self-focussing of the laser beam in plasma

[en] The results of measurements of microablation from a silver target irradiated by the high-power PALS laser system in Prague are presented. in this experiment the laser beam energy 110 J in a 400 ps pulse was focused perpendicularly to the massive silver target. The target surface position was changed with respect to the focal spot of the laser beam in the range from -2.5 to 2.5 mm. A set of four ion collectors was used for plasma ion emission measurements. The effect of the laser pulse irradiation with the target, i.e. craters and damages formed in the vicinity of the craters, were investigated with the use of scanning electron microscopy (SEM) and optical microscopy methods. The characteristics of the crater were compared with the essential parameters of ion streams emitted from the plasma produced in the same laser shot. (author)

[en] The experimental results of measurements of microablation from a silver target irradiated by the high-power PALS laser system in Prague are presented. In this experiment the laser beam energy of about 110 J in a 400 ps pulse was focused normally on the massive silver target surface. The target surface position was changed with respect to the focal spot of the laser beam in the range from -2.5 to 2.5 mm. A set of four ion collectors was used for ion emission measurements. The effect of laser pulse interaction with the target, i.e., the diameter and the depth of the craters as well as of damages formed in the vicinity of the craters, were investigated with the use of scanning electron microscopy (SEM) and optical microscopy methods. The characteristics of the crater were compared with the essential parameters of ion streams emitted from the plasma produced in the same laser shot. (author)

[en] First results of a novel experiment with magnetically confined laser-plasma are presented. The laser plasma is created by irradiating solid target with a focused Nd-glass laser. The target was placed on the axis of the two, single-turn magnetic coils which provided a magnetic field up to 500 kGs in the target region. The expanding laser plasma is confined by the magnetic field and an elongated plasma column is formed along the axis. The plasma column emits strong soft X-radiation. The pinhole photographs show that the plasma column is at least 5 mm long. To study the interaction of the expanding laser plasma with a magnetic field the laser interferometry was used. (author) 4 figs

[en] The high power pulsed laser Prague asterix laser system (PALS), operating at the fundamental (1ω) and third (3ω) harmonics (1315 and 438 nm wavelengths, respectively), is employed in a single-shot mode to irradiate tantalum targets in vacuum. The laser pulse width is 400 ps and the laser pulse energy ranges between 43 and 736 J at 1ω and between 12 and 230 J at 3ω. High ablation yields (0.1-0.6 mg per pulse) are measured as a function of the laser pulse energy at both wavelengths; at 438 nm higher etching rates are observed. The produced craters are analysed by the scanning electron microscope (SEM) and by the high sensitivity surface profiler system. They are investigated in dimension, shape and angle aperture as a function of the incident laser energy. Different possible mechanisms responsible for the different crater shapes are presented and discussed