Study of the conditions for the effective energy transfer in a process of acceleration and collision of the thin metal disks with the massive target

Efficiency studies of laser driven thin metal disks acceleration using the first harmonic (λ₁=1.315 μm) of the Prague Asterix Laser System (PALS) and subsequent craters creation produced by collisions of these disks with massive targets are presented. Several different disks made of aluminium and copper foils with diameters of 300 μm and 600 μm and thicknesses of 11 μm (Al) and 3.6 μ m (Cu) were employed. Disks were placed at the distance of either 100 μ m or 300 μm in front of aluminium massive targets. The following irradiation conditions were used: the laser beam energy of 120 J, the focal spot diameter of 200 μm, and the pulse duration of 0.4 ns (FWHM). A three-frame interferometric system was employed to determine electron density distributions in plasma corona. Shape and volume of craters were obtained by crater replica technology and microscopy measurements. The aim of these investigations was to analyse conditions leading to the most effective energy transfer in the process of collision of the accelerated disks with solid targets. The overall efficiency of these processes was characterized by the volume of craters produced in such targets.     

Investigation of Shock Wave Loading and Crater Creation by Means of Single and Double Targets in the PALS-Laser Experiment

The efficiency of crater creation for different types of Al targets, namely, single massive targets and double targets consisting of a foil or a disk placed before the massive target at a chosen distance (300 and 500 µm), is studied. Targets were irradiated by the PALS facility laser beam with E _L = 100 – 400 J at the first harmonic λ = 1315 nm, a focal spot radius of 125 µm, and pulse duration of 400 ps. Velocities of the accelerated foil’s fragments or disks and electron density distributions of the plasma streams are determined by means of three-frame interferometry. Shapes and volumes of craters are obtained using the crater replica technology and microscopy measurements. It is shown that direct laser action is the most efficient way of energy transfer to the massive target and the most efficient method of crater creation. Somewhat lower efficiencies of shock wave loading and crater creation in comparison with direct laser action are found in the case of double targets where the energy is transferred to the massive target by colliding laser-driven foils or disks. The efficiencies of such a colliding energy transfer are close to 60% for foils and 40% for disks. The experimental results are in a good agreement with two-dimensional hydrodynamic models of shock wave generation under direct laser action and laser-driven macroparticle impact.     

Interferometric investigation of an early stage of plasma expansion with the high-power laser system PALS

The results of interferometric investigation of early stage of plasma expansion carried out in the high-power laser system PALS are presented. The plasma was generated on planar solid Al and Mo targets, irradiated by iodine laser pulses with energies of 100 and 600 J in 0.4 ns at a wavelength of 1.315 μm. The interferometric investigation allowed to determine electron density distributions at chosen moments of the plasma expansion. On the basis of these distributions, information about dynamics and properties of expanding plasma was obtained. The effects of laser-target interaction, i.e., the diameter and the depth of craters as well as the crater shape, were investigated. This research was carried out within the framework of the project PALS/013 (reg. no. HPRI-CT-1999-00053).     

Application of Laser Simulation Method for the Analysis of Crater Formation Experiment on PALS Laser

The crater formation process is studied in the laser - Al solid target interactions on the PALS iodine laser facility. A great variety of laser beam parameters are used to irradiate massive aluminium targets. Large laser energies available (up to 600 J) open a possibility to investigate the process of crater formation for physical conditions different from the earlier studies for the lower laser energies. Comparison with the earlier results is presented.A simple theory, LSM (laser simulation method), has been applied for the analysis of the experimental results. This model leads to a universal relation (scaling law) for the crater relative volume. Our work extends the study of crater formation to the virtual macroparticle velocities exceeding 100 km/s. The scaling law is derived here for this previously unexplored region. An alternative method of studying crater formation is also proposed.     

Plastic plasma interaction with plasmas with growing atomic number

This paper describes the investigation of the influence of target material atomic number (Z) on the laser-produced plasma pressure. For this reason, several target materials representing a wide range of atomic numbers (Z = 3.5 - 73), i.e. plastic (CH), Al, Cu, Ag, and Ta, were used. The results presented show that the plasma pressure decreases with growing atomic number but in a limited range of Z only. For higher Z, starting approximately from Z = 47 (Ag), the plasma pressure becomes constant, as confirmed by interferometric measurements and x-ray plasma imaging.     

A Note on the Integrability of Hamiltonian Systems

We consider a family of Hamiltonian systems

Energy of a shock wave generated in different metals under irradiation by a high-power laser pulse

The energies of a shock wave generated in different metals under irradiation by a high-power laser beam were determined experimentally. The experiments were performed with the use of targets prepared from a number of metals, such as aluminum, copper, silver and lead (which belong to different periods of the periodic table) under irradiation by pulses of the first and third harmonics of the PALS iodine laser at a radiation intensity of approximately 10¹⁴ W/cm². It was found that, for heavy metals, like for light solid materials, the fraction of laser radiation energy converted into the energy of a shock wave under irradiation by a laser pulse of the third harmonic considerably (by a factor of 2–3) exceeds the fraction of laser radiation energy converted under irradiation by a laser pulse of the first harmonic. The influence of radiation processes on the efficiency of conversion of the laser energy into the energy of the shock wave was analyzed.