A. Mezzasalma

The electron cyclotron resonance coupled to laser ion source for charge state enhancement experiment: Production of high intensity ion beams by means of a hybrid ion source

The experiment concerning the ECLISSE method (ECR ion source coupled to a laser ion source for charge state enhancement) has been carried out by coupling a laser ion source (LIS) to the superconducting electron cyclotron resonance source (SERSE) electron cyclotron resonance (ECR) ion source with the goal to obtain intense beams of highly charged ions (cw or pulsed mode) from metal samples, especially from refractory elements. The coupling efficiency of the ion beam produced by the LIS with the ECR plasma was remarkable and the measured beam intensities were quite high. The maximum charge states, obtained with a good reproducibility, were 38+ for Ta and 41+ for Au. The highest current was obtained for 25+ and 28+ for Ta and Au ions, respectively, and it was in both cases of the order of some tens of microampere, i.e., higher than the current obtained from SERSE with other methods (i.e., evaporation and sputtering). The ion beam stability and reproducibility were both acceptable. The possibility to get a fu...

Correlation of highly charged ion and X-ray emissions from the laser-produced plasma in the presence of non-linear phenomena

Flux of X-ray radiation emitted from the Ta plasma, produced by the fundamental (1ω) and the third harmonic (3ω) frequencies of the high-power iodine laser PALS, was studied in dependence on the laser focus position. One or two (three) maxima, corresponding to the hard or soft component of the emitted spectrum, can appear, according to the experimental conditions. These dependencies are compared with those published by other authors, and also with our results concerning the highly charged ion generation. At laser intensities above I L∼ 1014 W/cm2, the participation of non-linear processes in the pre-formed plasma was confirmed.

Diamond detectors for characterization of laser-generated plasma

Diamond monocrystalline detectors were used to characterize radiation and particle emission from laser-generated plasma obtained at Laboratori Nazionali del Sud (LNS) and Plasma Asterix Laser Systems (PALS) laboratories by using a high power pulsed laser intensity of 1010 W/cm2 and 1016 W/cm2, respectively. Al, Ta, Au and CF2 plasmas were obtained in different irradiation conditions. Diamond detectors permitted to measure UV, X-rays, electrons and ions. Time-of-flight technique was employed to separate in time the different contributions. Results indicate that this detector has some advantages with respect to the others, such as the high energy gap, the high energy resolution, the low background current and the possibility to detect simultaneously photons, electrons and ions.

Characteristic modification of UHMWPE by laser-assisted ion implantation

The purpose of this work is the characteristic modification by ion implantation of ultra high molecular weight polyethylene, and a preliminary study of its surface. This biomedical material has been chosen for its excellent chemical and physical properties. An ultraviolet-pulsed laser of 248 nm was employed to produce, by laser ablation, C and Ti ions of different charges with current densities of the order of 10 mA/cm2. The ions were accelerated by the application of a positive high voltage, 30 kV, on the target support to accelerate ions to implant the polyethylene surfaces up to a depth of about 200 nm. Preliminary results about surface properties indicate that implanted surfaces have higher wettability and micro-hardness values with respect to unimplanted ones.

The effect of high-Z dopant on laser-driven acceleration of a thin plastic target

Acceleration of a thin (10 or 20μm) plastic foil by 120J, 0.438μm, 0.3ns laser pulse of intensity up to 1015W∕cm2 has been investigated. It is shown that the introducing a high-Z dopant to the foil causes an increase in the ablating plasma density, velocity, and collimation which, in turn, results in a remarkably higher kinetic energy and energy fluence of the flyer foil.

The influence of pre-pulse plasma on ion and x-ray emission from Ta plasma produced by a high-energy laser pulse

The paper describes studies of ion and x-ray emissions from plasma produced by the PALS laser system at different parameters of pre-plasma generated by a laser pre-pulse. The plasma was produced by 0.4-ns laser pulses of about 140 J at 438 nm (3rd harmonic frequency) focused on a slab Ta target. The main laser pulse was preceded by a pre-pulse having either 0.7 main-pulse energy. The main pulse was delayed by 0.6 ns, 1.2 ns, 2.3 ns, or 4.6 ns with reference to the prepulse. The characteristics of the ion streams (energies, charge states and angular distributions of ion emission) were investigated using diagnostics based on the time-of-flight method. The x-rays were measured using various types of semiconductor detectors covered with different filters. It was found that, at small delay times, Δt<1 ns, the values of the fast ion parameters (e.g. mean ion energy, average charge state, and peak current density) as well as the soft and hard x-ray yields change slightly and that they distinctly decrease with the increasing Δt, excluding the peak ion current density, which, after attaining a shallow minimum at ∼2.5 ns, reaches its highest value at the longest Δt. At the longest delay times, we observed the generation of a high-current-density (>0.2 A cm−2 at 1 m) ion stream having angular divergence and ion energy spread significantly smaller than those for the case without the pre-pulse.

Direct implantation of Ge ions produced by high-energy low-intensity laser pulses into SiO2 films prepared on Si substrates

Due to the development and growing demands for implantation techniques, the laser plasma as a source of multiply charged ions has been investigated. With focusing the laser beam on the solid target it is possible to produce higher current densities of ions than with other currently available ion sources. Kinetic energy and the charge state of ions depend on the properties of the irradiated target material and the parameters of the laser radiation used. Selection of proper laser beam characteristics is very important for efficiency of the ion implantation technology. Several experiments on the implantation of different kinds of laser-produced ions have been performed at the Institute of Physics ASCR and at the PALS Research Center, ASCR in Prague. During these experiments 0.4 ns iodine laser pulses of energies up to 750 J at a wavelength of 1315 nm or up to 250 J at a wavelength of 438 nm have been used for generation of ions. The significant part of these experiments concerned the characterization and optimization of laser-produced Ge ion fluxes as well as the analysis of the direct implantation of these ions into SiO2 films prepared on the surface of a Si single crystal. In this paper we present the results, analysis and conclusions of these experiments which include ion collector and ion analyser measurements and the bulk profiles of Ge ion implantation with maximum depth of ~450 nm.

Temperature measurements in plasmas generated by using lasers at different intensities

The temperature of laser-generated pulsed plasmas is an important property that depends on many parameters, such as the particle species and the time elapsed from the laser interaction with the matter and the surface characteristics. Laser-generated plasmas with low intensity (<1010 W/cm2) at INFN-LNS of Catania and with high intensity (>1014 W/cm2) in PALS laboratory in Prague have been investigated in terms of temperatures relative to ions, electrons, and neutral species. Time-of-flight (ToF) measurements have been performed with an electrostatic ion energy analyzer (IEA) and with different Faraday cups, in order to measure the ion and electron average velocities. The IEA was also used to measure the ion energy, the ion charge state, and the ion energy distribution. The Maxwell–Boltzmann function permitted to fit the experimental data and to extrapolate the ion temperature of the plasma core. The velocity of the neutrals was measured with a special mass quadrupole spectrometer. The Nd:Yag laser operating at low intensity produced an ion temperature core of the order of 400 eV and a neutral temperature of the order of 100 eV for many ablated materials. The ToF of electrons indicates the presence of hot electron emission with an energy of ∼1 keV.

Ion energy enhancement in laser-generated plasma of metallic-doped polymers

Laser-generated plasma in vacuum are obtained ablating hydrogenated polymers at the Physics Department of Messina University and Prague Asterix Laser System laboratory of Prague. In the first case, a 3-ns, 532-nm Nd:Yag laser at 5×109 W/cm2 intensity was employed. In the second case, a 300-ps, 438-nm iodine laser at 5×1014 W/cm2 intensity was employed. Different ion collectors are used in time-of-flight configuration to monitor ‘on line’ the ejected ions from the plasma at different angles with respect to the normal direction to the target surface. Measurements demonstrated that the mean ion velocity, directed orthogonally to the target, increases for ablation of polymers doped with metallic elements (Br, Cu, Au and W) with respect to that obtained with no-doped polymers. The possible mechanism explaining the results can be found in the different electron density of the plasma, due to the higher number of electrons coming from the metallic doping elements. This charge enhancement increases the equivalent ion voltage acceleration, i.e. the electric field generated in the non-equilibrium plasma placed in front of the ablated target surface.

Characteristics of laser-produced Ge ion fluxes used for modification of semiconductor materials

This paper describes the laser generation of Ge ion fluxes and their application to the modification of semiconductor materials by ion implantation. The Ge ions were produced by ablating solid targets using the PALS high-power iodine laser system at the PALS Research Centre in Prague, operating at its third harmonic frequency (438 nm wavelength) and producing 0.4 ns pulses with energy up to 0.25 kJ (intensity≤1015 W/cm2). The goal of these investigations was optimisation of the implantation of low and medium energy laser-generated Ge ion fluxes and they were carried out as part of the project PALS000929. Recently, a new repetitive pulse laser system at IPPLM in Warsaw, with a wavelength of 1.06 μm, energy of ∼0.8 J in a 3.5 ns-pulse, repetition rate of up to 10 Hz, and intensity on target of up to 1011 W/cm2, has also been employed to produce Ge ions by irradiating solid targets. The laser-generated ions were investigated with diagnostics based on the time-of-flight method: various ion collectors and an electrostatic ion-energy analyzer. The Ge ion fluxes were implanted into Si and SiO2 substrates located at distances of 10–30 cm from the target. The SiO2 films were prepared on single crystal Si substrates and were implanted with Ge ions with different properties. The properties of the Ge-implanted layers, in particular, the depth distributions of implanted Ge ions, were characterised using Rutherford backscattering and other material surface diagnostic methods.