Recently developed silicon carbide (SiC) detectors have been employed to study pulsed laser plasmas produced by irradiation of a double-stream gas puff target with nanosecond laser pulses. The plasma emitted by a gas-puff target source in the soft X-ray (SXR, λ = 0.1 - 10 nm) and extreme ultraviolet (EUV, λ = 10 - 120 nm) ranges was monitored with silicon carbide (SiC) detectors and compared with a commercial, calibrated silicon (Si) photodiode (AXUV-HS1). Different filters have been used to select the emission in different wavelength ranges from the broad-band emission of the plasma. This work shows the applicability of SiC detectors to measure the SXR and EUV ns pulses from the plasma, useful for monitoring and optimizing the gas-puff laser-plasma sources developed at IOE-MUT, in Warsaw (Poland). Some aspects relative to the plasma stability as well as characterization of the plasma source (i.e. the overall evaluation of the signal and the time trace profile) will be presented and discussed.
Laser accelerated proton beams have been proposed to be used in different research fields. A great interest has risen for the potential replacement of conventional accelerating machines with laser-based accelerators, and in particular for the development of new concepts of more compact and cheaper hadrontherapy centers. In this context the ELIMED (ELI MEDical applications) research project has been launched by INFN-LNS and ASCR-FZU researchers within the pan-European ELI-Beamlines facility framework. The ELIMED project aims to demonstrate the potential clinical applicability of optically accelerated proton beams and to realize a laser-accelerated ion transport beamline for multi-disciplinary user applications. In this framework the eye melanoma, as for instance the uveal melanoma normally treated with 62 MeV proton beams produced by standard accelerators, will be considered as a model system to demonstrate the potential clinical use of laser-driven protons in hadrontherapy, especially because of the limited constraints in terms of proton energy and irradiation geometry for this particular tumour treatment. Several challenges, starting from laser-target interaction and beam transport development up to dosimetry and radiobiology, need to be overcome in order to reach the ELIMED final goals. A crucial role will be played by the final design and realization of a transport beamline capable to provide ion beams with proper characteristics in terms of energy spectrum and angular distribution which will allow performing dosimetric tests and biological cell irradiation. A first prototype of the transport beamline has been already designed and other transport elements are under construction in order to perform a first experimental test with the TARANIS laser system by the end of 2013. A wide international collaboration among specialists of different disciplines like Physics, Biology, Chemistry, Medicine and medical doctors coming from Europe, Japan, and the US is growing up around the ELIMED project with the aim to work on the conceptual design, technical and experimental realization of this core beamline of the ELI Beamlines facility.
High intensity lasers produce hot plasmas when irradiating solid matter in vacuum. Properties of the generated plasmas depend strongly on the laser and target parameters and on the target irradiation geometry. Physical characterization of such non-equilibrium plasmas can be performed by using different fast diagnostic techniques based on the detection of energetic charge particles and photons. Thomson parabolas recorded in single laser shots, bring a lot of information about the plasma ion emission, such as the charge-to-mass ratio, ion energy and charge state distributions, furnishing the data necessary for understanding physical mechanisms involved in the plasma dynamics. The ion measurements performed at intensities of the order of 10<sup>16</sup> W/cm<sup>2</sup>, at which thin samples were irradiated by using the iodine laser at PALS laboratory in Prague in target normal sheath acceleration (TNSA) conditions, are presented and discussed.
A study of the laser ablation of a ZnO target has been carried out in vacuum, by using a Nd:Yag laser with a pulse
duration of 3 ns, a wavelength of 532 nm and a maximum pulse energy of 150 mJ. The measurements of ablation
yields, crater profiles and fast CCD plasma imaging allowed the evaluation of the plasma density. Time-of-flight
(TOF) measurements have been also utilized to monitor the ion emission by using a special ion collector placed
along the normal to the target surface. Coulomb-Boltzmann-shifted ion energy distributions have been obtained
depending on the ions charge states. The plasma temperature was evaluated by such ion energy distributions of the
experimental data. A special attention has been devoted to the ion acceleration processes due to the high electric
fields generated inside the non-equilibrium plasma. The characterization of the latter and the deposition of ZnO thin
films are correlated and discussed.
Usually the synthesis of such structures is performed using ion implantation techniques or chemical reaction methods or ablating metal targets inside liquid solutions, while here we propose pulsed laser ablation in vacuum for the generation of these particles without any catalytic environment and annealing procedures for their activation. Silver targets were ablated in a vacuum chamber at
(10<sup>-7</sup> Torr) by Nd:YAG high power pulsed laser at room
temperature. The consequent deposition on Si-substrates covered by a ~50 nm thick SiO<sub>2</sub> results in the formation of well separated nanometric spheroidal particles of Ag with a diameter of
5-10 nanometers depending on the deposition time. The generation of silver nanoparticles was confirmed by scanning electron microscopy analysis (SEM). The kinetic energy (2 keV) of Ag ions of the non-equilibrium plasma produced by the high power pulse was measured by
the aid of Faraday's cup inserted in the interacting chamber. Monte Carlo simulations of ions tracks in solid targets (TRIM) reveal that silver ions are implanted in a region thinner than 10 nm just under the surface. Optical properties of the samples were studied by variable angle ellipsometric spectroscopy (VASE). The ellipsometric spectra were modeled with a 2-layer model. Layer-1 is modeled using the dielectric function of SiO<sub>2</sub> and a variable thickness, while Layer-2 is best modeled with a single Lorenztian-oscillator and a constant layer thickness of 7 nm. The imaginary part of the
refractive index for layer-2 reveals an absorption band in the energy range characteristic for surface plasmon resonances (SPR) of Ag nanoparticles. The maximum of SPR shifts 372 nm to 414 nm for longer deposition time indicating an increase of the average particle size . Interestingly, although silver nanoparticles are located within the SiO<sub>2</sub> layer, nanparticle formation occurs during PLD
and needs no additional forming or annealing step.
Results about the efficiency of the laser cleaning on the reduction of corrosion products from the surface of ancient coins are reported. In this work an ancient copper coin datable from 1500 to 1600 A.D. and a UV excimer laser were utilized. The goal of this work consists to study the potentiality of UV laser treatment in the reduction of the chlorine concentration on the coin surface which is the main responsible of the corrosion processes of the ancient coins. We used Energy Dispersive X-Ray Fluorescence (EDXRF) and X-Ray Diffraction (XRD) techniques to estimate the chemical composition of the coin surface, before and after UV excimer laser cleaning. In particular, we measured the chlorine, copper and calcium concentrations. We found that a radiation dose of about 19 J/cm<sup>2</sup> was able to reduce the chlorine concentration from 2.3 % w/w to 0.6 % w/w without damaging the metal bulk.
A UV pulsed lasers was employed to produce C and Ti ions of different charge with current densities of the order of 10 mA/cm<sup>2</sup>. A post ion acceleration, up to 30 kV, was employed to increase the ion energy and to implant polyethylene biocompatible surfaces up to a depth of about 200 nm. Preliminary results about surface properties indicate that implanted surfaces have higher wetting and micro-hardness with respect to un-implanted ones.
A novel technique for ion implantation of electronics materials by means of a laser ion source emitting multi-energetic ion streams was investigated. A UV pulsed laser beam, at intensities of the order of 10<sup>8</sup> W/cm<sup>2</sup>, was employed to produce plasma in a vacuum from a Ge target. The apparatus utilized was very versatile and able to contain an expansion chamber in order to allow the plasma to be diluted before the application of an accelerating voltage. The mean ion energy increased with the laser pulse energy and the ion charge state, and ranged between about 100 eV and 1 keV. To increase the ion energy a post-acceleration up to 50 kV was employed, which resulted in ion energies from about 50 keV to about 150 keV, depending on the charge state. The multi-energetic ion beam, with current density of the order of 10 mA/cm<sup>2</sup>, was employed to irradiate silicon substrates and to obtain surface implantations up to a depth of about 150 nm. During the implantation process the ion beams were generated with a repetition rate of the laser pulse of 1 Hz. The depth profiles of the ion implants were investigated by Rutherford backscattering spectrometry and laser ablation - inductively coupled plasma - mass spectrometry.
Since the early 1970s ablative laser propulsion (ALP) has promised to revolutionize space travel by reducing the 30:1 propellant/payload ratio needed for near-earth orbit by up to a factor of 50, by leaving the power source on the ground. But the necessary sub-ns high average power lasers were not available. Dramatic recent progress in laser diodes for pumping solid-state lasers is changing that. Recent results from military laser weapons R&D programs, combined with progress on ceramic disk lasers, suddenly promise lasers powerful enough for automobile-size, if not space shuttle-size payloads, not only the 4 - 10 kg "microsatellites" foreseen just a few years ago. For ALP, the 1.6-μm Er:YAG laser resonantly pumped by InP diode lasers is especially promising. Prior coupling experiments have demonstrated adequate coupling coefficients and specific impulses, but were done with too long pulses and too low pulse energies. The properties of ions produced and the ablated surface were generally not measured but are necessary for understanding and modeling propulsion properties. ALP-PALS will realistically measure ALP parameters using the Prague Asterix Laser System (PALS) high power photodissociation iodine laser (λ = 1.315 μm, E<sub>L</sub> ≤1 kJ, τ ~ 400 ps, beam diameter ~29 cm, flat beam profile) whose parameters match those required for application. PALS' 1.3-μm λ is a little short (vs. 1.53-1.72 μm) but is the closest available and PALS' 2ω / 3ω capability allows wavelength dependence to be studied.
In this work an ion acceleration system based on a laser ion source was studied. It was able to generate ion beams utilizing as a source a laser plasma produced by a XeCl laser from a copper target. The focused laser beam provided a power density on the target surface of about 3.5x10<sup>8</sup> W/cm<sup>2</sup>. Laser wavelength and pulse duration were 308 nm and 20 ns, respectively. The experimental apparatus consisted substantially of a plasma generation chamber, a drift tube and an expansion chamber mounted on the target stem inside the generation chamber. The expansion chamber end formed the acceleration gap together with a grounded bored electrode, placed in front of it at a distance of 1.3 cm. A Faraday cup placed at the end of the drift tube was used to reveal the ion intensity.
Many attempts were done in order to accelerate plasma ions without the expansion chamber, but arcs were present. The maximum accelerating voltage applied to the extraction gap was 18 kV, resulting in an ion bunch of about 4.2 nC and a peak current of 220 μA.
The investigations of nonthermal processes in laser-produced plasmas are not yet complete, especially with regard to the ion acceleration in the plasma generated by high-energy short-wavelengths lasers. This contribution presents the results of studies of fast ion emission from plasma generated using a short wavelength (438 nm), high-energy (up to 250 J in 400 p5 pulse) iodine laser PALS at the Joint Research Laboratory PALS ASCR in Prague, Czech Republic. The properties of highly charged ion streams were investigated by ion diagnostic methods: ion collectors and solid state track detectors as well as a cylindrical electrostatic energy analyzer. Attention was paid to the determination of ion energy and comparison of the energies and abundance of different ion groups. The presented results shown the existence of highly charged ions with z <40 (measured z, =57 forTa) and with energies higher then 20 MeV in a far expansion zone. Ion current densities up to tens of mA/cm2 at a distance of 1 m from the target were obtained. On the basis of the ion diagnostic investigations the existence of nonthermal and nonlinear accelerating processes was demonstrated for the plasma produced by a high-energy short-wavelength laser pulse.
The experimental results of investigations on influence of external magnetic and electric fields on characteristics of ion stream emitted from a plasma produced by the Nd:glass performed at IPPLM, Warsaw are presented. A negatively biased target up to -15 kV and a magnetic field up to 0.45 T were used in the experiment. A set of ion collectors and an electrostatic cylindrical ion energy analyzer located at small angles with respect to the laser beam axis and at large distances from the target were applied for ion measurements. The effect of an external magnetic field is essential to plasma expansion but the effect of the retarding potential of the target is very weak in our experimental conditions. The presented results relate only to tungsten plasma. The aim of the studies was to prove a possibility of optimization of ion beam parameters from laser-produced plasma for particular application as a Laser Ion Source coupled with the Electron Cyclotron Resonance ion source for particle accelerators.