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The time-dependent graphene oxide (GO) reduction in medium vacuum under ultraviolet (UV) irradiation at 365 nm has been investigated. We found that GO exposed to UV at room temperature and at a vacuum of about 10−1 mbar shows a notable oxidation for irradiation times up to about 60 min followed by a successive reduction up to 210 min. Characterization measurements have been performed mainly using the Attenuated Total Reflectance (ATR) Fourier Transform Infrared (FTIR) and Raman spectroscopies. ATR-FTIR spectra, acquired in the (400–4000) cm−1 wavenumber range, have indicated an initial decrement of the IR transmission (oxidation process) with the exposure time up to about 60 min and a successive increase of the IR transmission (reduction process) for greater irradiation times up to 210 min. The IR transmission bands are attributed to the oxygen functional groups contained in GO which increase for low UV exposure times and gradually disappear during the UV-induced reduction process. Raman spectra confirm this interpretation showing a decrease of the AD/AG ratio value, with respect to the GO virgin value, for low UV exposure times and an increase for greater times. The GO oxidation and reduction processes, due to the UV GO treatment in medium vacuum conditions, have been also verified by energy dispersive X-ray fluorescence and surface wettability measurements. [ABSTRACT FROM AUTHOR]

A silicon carbide (SiC) plasma has been produced by a Q-switched laser at 1064 nm, 3 ns pulse and 1010 W/cm2 intensity, in high vacuum to investigate the fundamental mechanisms of laser-semiconductor interaction. Although the high hardness and chemical stability restrain the SiC micromachining, it is a valuable semiconductor for devices working under extreme conditions.The plasma has been characterized by using time-of-flight (TOF) measurements of ions detected by an ion collector ring (ICR) and an ion energy analyzer (IEA). Fast CCD camera, quadrupole mass spectroscopy (QMS) and surface profiler have been employed to provide deep insights into the laser-SiC interaction mechanisms.Ion kinetic energies, charge states, plasma expansion velocity, ablation yield per laser pulse, plasma temperature and density have been measured.Applications of the laser-generated plasma are presented and discussed. [ABSTRACT FROM AUTHOR]

Polymethylmethacrylate (PMMA) has been irradiated by 365 nm UV wavelength at different exposition times in air and room temperature. The macromolecular modifications induced in the polymer have been investigated using attenuated total reflectance (ATR) coupled to Fourier transform infrared (FTIR) spectroscopy, UV-Visible spectroscopy, surface profiler, wetting ability, and electronic microscopy. The observed chemical, optical and morphological changes occurred as a consequence of the UV irradiation suggest that chain scissions are induced by the UV radiations, with reduction of the IR and visible transmittance, wetting ability and surface roughness. The study of the degradation of PMMA by different times of exposure to UV radiation is investigated with the aim of understanding the effects produced over time on optical devices such as intraocular lenses, optical fibres, protective screens, and instrumental lenses. [ABSTRACT FROM AUTHOR]

A ns-pulsed laser operating at 532 nm wavelength has been employed to irradiate micrometric mylar films (1–100 μm) with an attached 0.1 μm Al film on its back face. Protons and light ions have been accelerated by the electric field developed in the non-equilibrium plasma generated by the laser pulse in a vacuum at an intensity of the order of 1010 W/cm2. The Time-of-flight (TOF) technique, using a Faraday cup (ion collector) coupled to a fast storage oscilloscope, has been employed to measure the ion velocity, energy and yield. The yield of plasma-emitted photons has been also evaluated. Two ion collectors have been used in opposite directions to measure the maximum ion acceleration by the TOF data acquired in backward and forward directions and the photon yield as a function of the target thickness. The evaluation of the ion energy distribution has been based on the Coulomb-Boltzmann-Shifted (CBS) distribution function. [ABSTRACT FROM AUTHOR]

Graphene nanoplatelets/polydimethylsiloxane (GNPs/PDMS) nanocomposites foils are obtained by dispersing nanoplatelets of graphene (GNPs) into polydimethylsiloxane (PDMS) at a given GNPs concentration but at different curing times to study the effects of curing time on some their bulk and surface properties. Their appearance and morphology have been examined by optical and scanning electron microscopies, their wettability and roughness by the sessile drop method and profilometry, their bonds by µRaman and ATR-FTIR spectroscopies, their dielectric response by dielectric spectroscopy. In particular, optical and SEM images and roughness measurements indicate a roughened and hydrophobic surface at the shortest curing time that becomes less roughened, more uniform and less hydrophobic as curing time increases. ATR-FTIR and µRaman spectra reveal the absence of chemical interaction between GNPs and PDMS. The behavior of the PDMS real and imaginary parts of dielectric permittivity without and with GNPs and at increasing curing times seems to define the obtained GNPs/PDMS nanocomposites as low-loss materials. The obtained results show that the curing time significantly affects the filler distribution in the PDMS matrix and consequently the properties of the final nanocomposites. [ABSTRACT FROM AUTHOR]

Foils of graphene oxide (GO) prepared by micrometric graphene oxide platelets dispersed in water at low concentrations were physically investigated during their thermal reduction in a vacuum. The water, the carbon dioxide and the functional groups of oxygen, degassed during the thermal treatment, were monitored for the first time with a quadrupole mass spectrometer as a function of the foil temperature. Fourier transform infrared (FTIR) spectroscopy and energy dispersive X-rays (EDX) analyses were also presented to confirm the modality of reduction in vacuum. The thermal reduction process increases the C/O atomic ratio from the pristine value of about 2.0 to about 4.5 using a temperature of about 200°C. The reduced graphene oxide (rGO), depleted of water and some functional oxygen groups, shows a more compact structure with an increment of the density from the pristine value of about 1.36 g/cm3 to about 1.9 g/cm3, which determines a decreasing of the distance between the graphene layers. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) have been produced by laser ablation in chloroform and then embedded in polylactic acid (PLA) thus realizing PLA/Au nanocomposite films. Two initial volumes of chloroform of about 5 and 4 mL have been used, thus obtaining two different PLA/Au nanocomposite films. The effects of the embedded AuNPs into PLA films have been studied using Attenuated Total Reflectance Fourier Transform Infrared (ATR–FTIR) spectroscopy and ultraviolet/visible (UV–Vis) absorption spectroscopy. In the ATR-FTIR spectra, as AuNPs are embedded in PLA and their concentration grows up, the PLA characteristic vibrational features maintain their positions in wavenumber, but their IR absorption increases. This result confirms the presence of AuNPs in PLA and suggests that no strong chemical interaction occurs between PLA and AuNPs and no new bonds are formed. Concerning the UV–Vis optical properties an increase in the PLA optical absorption in the visible region has been also observed when AuNPs are embedded. The AuNPs presence is attested by the appearance of localized surface plasmon resonance (LSPR) absorption peak between 500 and 600 nm that shifts at longer wavelengths and broadens as the AuNPs concentration increases. The PLA absorption edge has been determined and its position in wavelength increases with increasing AuNPs concentrations. This observed absorption edge red shift indicates a decrease in the PLA band gap probably due to the electronic levels introduced by the embedded gold nanoparticles. [ABSTRACT FROM AUTHOR]

At present graphene is the most exciting star in the materials science but graphene oxide, GO, that is its low-cost precursor attracts researchers from various fields because it is very easily produced at low cost. GO is an electrical insulator than can be transformed into graphene through the 'reduction' process. The oxygen functional groups it contains can be removed by various ways, also using lasers, ion beams and the intercalation process. The intensive research on graphene has allowed the rediscovery of various graphite-like layered materials with composition other than carbon, but properties are not yet fully known and with interesting possible applications. Among them, manganese thiophosphate, MnPS3, is a layered inorganic host matrix for making, through the intercalation-exfoliation-restacking technique, multi-functional hybrid thin films that can find application as optical switches, transparent coatings, in catalysis and photocatalysis, as lubricants, to create new multilayer structures, as dielectric substrates for graphene-based electronics and so on. If exfoliated at few layers, MnPS3 allows to realize good ultraviolet photodetectors with a gate tunable photoresponsivity and high photo gain. Recent progress in these graphene-like materials will be presented and discussed together with measurements based on the use of lasers, ion beams and intercalation emphasizing their potential applications. [ABSTRACT FROM AUTHOR]

Graphene-based materials have peculiar optical, electrical, mechanical and chemical properties, which make them useful for making thin films and thick sheets suitable for different needs. Matter physics, nuclear physics, microelectronics, biomedicine, engineering, agriculture and cultural heritage just represent some of the sectors in which these materials can be successfully used. The advancements allow us to go from a given graphene-based material to another transforming, for example, the insulator graphene oxide to electrically and thermally conductive reduced graphene oxide. Thanks to the interesting properties possessed by graphene-based materials, it is possible to realize gas sensors, dosimeters for ionizing radiation, light detectors, electronic devices, membranes for gases and desalination, biocompatible surfaces, medical protheses and thin coating films to preserve underlying layers. Different analysis techniques are presented to control the physical modifications of reduced graphene oxide (rGO) due to the different treatments for the pristine one. The paper reports the possibility to realize GO micro-dosimeters for ionizing radiations, sensors for air humidity and other gases, field effect transistors as the detector of visible and UV radiations, GO and rGO membranes realization for different gases, source ion strippers to enhance the charge state of different ions to be accelerated. Some of these aspects and possible applications will be presented and discussed with measurements carried out in our laboratories. [ABSTRACT FROM AUTHOR]

Light trapping and luminescence have been observed in polydimethylsiloxane (PDMS) foils containing about 0.1–0.2 wt% gold nanoparticles (AuNPs). The so-prepared PDMSs have been physically characterized using SEM microscopy, UV–Vis, FTIR and Raman spectroscopies. The used AuNPs have been controlled by means of the surface plasmon resonance absorption spectra. In the AuNPs–PDMS foils, a luminescence peak at about 425 nm has been induced by an exciting light at 280 nm. The light injection with an optical fiber is trapped inside the polymer-containing NPs and illuminates all the polymer volume. The measurements of scattered light show an increment in the light intensity due to the presence of AuNPs and air bubbles inducing diffractions, reflections and Mie scattering. Further investigations have been conducted irradiating the PDMS with AuNPs in vacuum with 2.9 MeV proton beams producing luminescence in the blue region. The mechanisms of light trapping and luminescence and the possible applications of the prepared material are presented and discussed. [ABSTRACT FROM AUTHOR]

The pulsed laser cleaning (PLC) technique employing different laser wavelengths, with a ns pulse duration, is presented. Such a technique can be applied to the preservation of cultural heritage artworks on different materials, like metals, ceramics and glasses to clean the surfaces of debris accumulated over the years, to remove the oxidation layers, the dust, the organic materials and other unwanted layers, restoring their original composition and shape. PLC should be preceded by surface analyses to control the state of the surface before and during the cleaning process, which has to be carefully controlled, in order to stop the cleaning before to damage the underlying original surface. PLC examples, applied to metals, terracotta and glazy ceramics, are presented and discussed using IR, visible and UV pulsed laser irradiations at low intensity. [ABSTRACT FROM AUTHOR]

The laser ablation is an established material processing for many applications in nanotechnology, materials science and biomedicine. The laser ablation can be carried out in vacuum, in air and in liquid. Laser ablation mechanisms and their products depend on laser fluence, wavelength, pulse duration, ablation environment as well as target composition, density, thickness, roughness. This contribution is addressed to laser ablation of solid targets with the aim of hot plasma generation and thin film deposition on substrates located in appropriate positions in vacuum and in air. In the first section is presented an example of forward and backward plasma accelerations using the sub-nanosecond laser at the PALS laboratory (Czech Republic) for pulsed laser deposition processing. In the second section is reported the use of a nanosecond laser coupled to a post-accelerating compact system employed at the INFN in Catania (Italy) to ablate germanium solid targets in vacuum and to deposit thin films on SiO2/Si substrates to modify their native features. The last section is focused on the use of the nanosecond laser at the Tandetron laboratory (Czech Republic) employed for pulsed laser deposition and laser-induced backward transfer processing in vacuum and in air. [ABSTRACT FROM AUTHOR]

The INFN-CIMA project deals with the employment of graphene, graphene oxide (GO) and reduced graphene oxide (rGO) for applications in Nuclear Physics. In particular, the project aim is that to use the special properties of GO, which can be synthesized as a thin foil with 0.1–100 µm thickness, to realize thin films for solid ion strippers employed in ion accelerator sources with lifetime advantages with respect to the traditional graphite foils. rGO thin foils can be employment to develop laser-generated plasma and to accelerate protons and carbon ions in target-normal-sheath-acceleration (TNSA) regime. The GO can be also employed for the realization of special sensors of temperature, air relative humidity and gas. Moreover, it can be used to realize water-equivalent, biocompatible and low dimensional, dosimeters based on the lecture of the reduction level produced by the absorbed dose. Finally, graphene and rGO films can be applied to investigate the implemantation ofsmall radiation detectors. Many applications and experimental results will be presented and discussed. [ABSTRACT FROM AUTHOR]

Pulsed IR lasers were employed to irradiate high boiling elements, such as C, Mo, Ta, W and Re, in high vacuum. The ablation yield, given in terms of removed mass per pulse, was investigated using a ns laser at intensities of the order of 1010 W/cm2 and a sub-ns laser operating at about 1015 W/cm2. The produced plasma in high vacuum was studied by the time-of-flight measurements of emitted ions. The plasma-accelerated particles can be deposited and implanted on a near substrate to form a very adherent thin film useful for applications involving high temperatures and hard materials. [ABSTRACT FROM AUTHOR]

2.0 MeV proton beam accelerated at Tandetron is extracted in air through a thin film and allowed to scatter to irradiate the cell culture attached to the polymeric base of a biological flask. The irradiated cells were human medulloblastoma cell line Daoy treated with and without 5 nm sized spherical gold nanoparticles. Proton doses from 0.5 to 1.5 Gy have been employed to irradiate the cultures and to investigate the role of the radiotherapy performed with and without the use of the gold nanoparticles. Results indicated that cell survival is significantly reduced to about 50% when the nanoparticles at a concentration of about 6 × 1013 particles/ml are employed. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) is a two-dimensional material, which is attracting increasing attention due to its special properties. It can be obtained by laser or ion beam irradiations of pristine graphene oxide (GO). It shows high mechanical resistance, considerable electric and thermal conductivity. All these rGO characteristics together with the high number of molecular species that can be embedded between its layers, make graphene oxide a potential material for electronic sensors or efficient support on which conductive strips, condensers, and micrometric electronic devices can be designed. In particular, as it is described in this paper, it is possible to carry out high spatial resolution lithography in GO by using a focused laser or micro ion beam in order to design macro, micro, and submicron geometrical structures. The use of the reduced graphene oxide for the laser and ion beam fabrication of electrical resistances and capacitances is presented. [ABSTRACT FROM AUTHOR]

Radiochromic films (RCF), also called GafChromic™ films, represent a performant material for accurate quantitative radiation dosimetry. Their compositions allow high dose sensitivity and fewer environmental dependence, giving a good feedback to the absorbed dose value and to the active media absorption, turning color upon being irradiated. The RCF take into account their reduced response near the Bragg peak due to a high linear energy transfer (LET). HD-810 GafChromic™ films are tissue-equivalent, have easy optical readings and can be employed for ion dosimetry in radio diagnostic and therapy and for industrial applications. Such dosimeters were employed at Tandetron-Nuclear Physics Institute (Řež, Czech Republic) to study the responses of helium, proton and carbon beams, commonly employed in radiotherapy and microelectronics. The sensitivity of the detector is low enough to measure multiple-beam exposures. The induced effects by the ions in the energy range of 600 keV to 2.0 MeV were investigated in terms of optical absorbance, measured in the irradiated active region of the polymer. The employed ion dose range was between 40 Gy and 2.5 kGy. The experimental results show that the absorbance increases with the irradiation time (i.e. with the absorbed dose). The absorbance induced in the radio chromic film was measured at 673 nm, at which is observed the highest sensitivity of the films. Such data, together with the dose linearity and the dependence on the ion stopping power will be presented and discussed. [ABSTRACT FROM AUTHOR]

Two well-established electrical insulators, graphene oxide and poly(methylmethacrylate) (PMMA) have been selectively exposed to controlled energy and fluence of ions. Ion micro beam has been proposed for processing of both graphene-based material and polymeric foils for tailoring of their properties. In a single step, the mask-less production of pattern on graphene-oxide and poly(methylmethacrylate) was realized at the Tandetron Laboratory of the Nuclear Physics Institute (Czech Republic) using a stream of 2.2 MeV alpha particles. Elements of a circuit were written on GO and poly(methylmethacrylate) in a controlled way using a software written in LabVIEW code. The induced deoxygenation, and dehydrogenation change the compositional, structural and electrical properties in the exposed samples. The accuracy of the method has been investigated by Rutherford backscattering spectrometry, elastic recoil detection analysis, Raman microscopy and the electrical standard two points method. [ABSTRACT FROM AUTHOR]

Gold nanoparticles were prepared by laser ablation in water and then characterized through physical analyses, in the perspective to be employed for different applications in the fields of Physics and Bio-Medicine. Different parameters have to be taken into account, such as the surface wetting ability, the possibility to improve the contrast image in microscopic and macroscopic systems and the enhancement of deposited dose by radiotherapy and thermal therapy treatments. The presence of a high-Z element, in fact, allows to modify the chemical and physical properties of materials and to release energy from ionizing radiation or from light absorption in the matter in which Au nanoparticles are embedded. These factors enhance the energy released to diseased tissues increasing the radiation effects in cells, for instance, the DNA of cancer cells can be destroyed with more efficiency due to the higher released dose inside the cell. [ABSTRACT FROM AUTHOR]

A new type of ion dosimeter based on graphene oxide (GO) foils is presented and discussed. GO is biocompatible, stable, tissue equivalent and has special chemical and physical properties. The ion irradiation reduces the material thanks to the breaking of oxygen functional groups bonded to the carbon matrix and to the consequent their desorption. The reduction effect increases the carbon-to-oxygen atomic ratio and transforms the pristine insulator GO into the semiconductive reduced GO (rGO). The reduction increases with the ion dose making the material more electrically conductive, decreasing its band gap and making it denser. At high doses of 2 MeV helium beam irradiation, the electrical conductivity increases linearly with the ion fluence for values within 1011 and 5 × 1014 ions/cm2, corresponding to absorbed doses of 25.9 kGy and 129.55 MGy, respectively. The results indicate that this material reduction is controllable through the desorption of oxygen groups and absorbed hydrogen, by the increment of the electrical conductivity and by the surface roughness, all these parameters depending on the absorbed dose by the material, which can be a good candidate to realise small ion dosimeters, especially to be used in the small-field dosimetry. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) films can be employed as ion strippers in an accelerator. They show some advantages with respect to the graphite foils, due to their high thermal and electrical conductivity, low density, high mechanical resistance and high stability. Thin graphene oxide (GO) films with a sub-micron thickness have been synthesized and transformed into reduced GO (rGO) by ion beam irradiations. Physical characterizations of the pristine and ion irradiated GO films have been performed. Measurements of stripping efficiency have been carried out by using helium, lithium, carbon and oxygen ion beams. The rGO stripper films demonstrate a significantly high charge production, comparable to that of the graphite films but with the advantage of a longer lifetime. [ABSTRACT FROM AUTHOR]

Particle in cell simulation was applied to fit the measurements of protons and ions acceleration obtained using an fs laser pulse irradiating a thin foil in target-normal-sheath-acceleration regime. The simulation code calculates the maximum electrical field generated in the rear side of the target driving the forward ions acceleration. The electron density versus time and space, and the plasma temperatures are evaluated using a medium contrast laser at an intensity of about 1019 Wcm−2. Proton acceleration above 10 MeV was experimentally measured using SiC detectors connected in time-of-flight configuration. A comparison between theoretical aspects and experimental data is reported and discussed. [ABSTRACT FROM AUTHOR]

Gafchromic HD-V2 films are employed to study the response to light ions useful in radiotherapy, such as protons, helium and carbon beams. The effects induced by the ions at an energy within about 300 keV and 16 MeV were investigated in terms of optical absorbance measurements in the irradiated active region of the film. The employed ion doses range between 0.4 Gy and 12 kGy. The results show that the net optical density increases almost exponentially with the absorbed dose and that it becomes saturated after prolonged dose higher than 1 kGy. The optical density produced in the film was measured by light transmission measurements at 700 nm wavelength, at which is observed the highest gafchromic sensitivity. Calibration curves of optical density versus exposure dose and type of ion are given. The dependence on the ion stopping power was presented and discussed. [ABSTRACT FROM AUTHOR]

The laser ablation of boron-nitride (BN) ceramic was employed for the preparation of thin films in high vacuum and nanoparticles and nanocrystals generated in water. The obtained plasma was investigated using ion detectors to determine the ion velocity, the energy per charge state and the plasma temperature and describing the acceleration mechanism. The kinetics of laser ablation in water and the comparison of different ablation rates in the vacuum and in water, and the possible applications of the BN thin film and nanoparticles are presented and discussed. [ABSTRACT FROM AUTHOR]

Hadron therapy is a very powerful technique for tumor treating; it can be used to irradiate tumor tissues with high doses and 3D spatial selectivity compared with traditional radiotherapy using electron and photon beams. The use of monoenergetic proton and carbon beams need of high energy accelerators, such as superconducting cyclotrons, adapt to generate protons at energies of the order of 100 MeV or more and suitable currents to extract the ion beam in the air and use it against the cancer cells. Recently rose a growing interest to generate proton and carbon beams using high-intensity lasers generating non-equilibrium plasma and high electric fields accelerating ions at the energies useful for hadron therapy. This equipment is less expensive with respect to huge accelerators and more versatile to be used in radiological clinics. Moreover, new technologies based on the use of biocompatible nanoparticles may improve the radiotherapy and defeat the tumor better. The present paper reports some data on the state of art and the current progress towards laser-driven hadron cancer therapy using advanced technologies. [ABSTRACT FROM AUTHOR]

The synthesis of gold nanoparticles using pulsed laser ablation in water has special interest in many scientific fields. The nanoparticle production in solution employing an Nd:YAG laser depends mainly on the laser parameters (i.e. by the wavelength, the pulse energy and duration), on the irradiation conditions (target depth in water, focal spot, repetition rate, irradiation time), and on the medium where the ablation occurs (water, solution concentration, presence of surfactants). Optimal conditions can be found in order to control the particle size, the size distribution, and the coalescence effect. A study of these characteristic factors is presented here and discussed. [ABSTRACT FROM AUTHOR]

In the present study, the effects of soft X-ray irradiation on graphene oxide (GO) films are discussed. In particular, by means of the XPS technique, it has been observed that even with a short exposure time GO is sensitive to the soft x-ray radiation. The X-ray radiation effects were investigated evaluating the C/O atomic ratio. Different irradiation times were applied ranging between 12 and 450 min. Significant modifications were detected in the C/O ratio and consequently in the C1s and O1s XPS profiles. At the highest soft X-ray exposure times, we disclosed the transformation of the C-OH groups to the phenol/aromatic diol ones. [ABSTRACT FROM AUTHOR]

The comparison between two different approaches based on the use of the laser ablation in medium to synthetise gold nanoparticles is presented and discussed. Deionised water as well as a graphene oxide (GO) suspension in deionised water have been employed as solution to produce gold nanoparticles by laser ablation. In the former case, the nanoparticles assembly has been stabilised by using surfactants, but in the latter case to avoid undesired effects the use of chemicals was not necessary and Au reduced graphene oxide (Au-rGO) nanocomposites have been obtained. The structure, size and composition of the gold nanoparticles and of the Au-rGO nanocomposites have been monitored by UV-Vis-NIR absorption spectroscopy and Raman spectroscopy, the transmission and scanning electron microscopies and the X-ray energy-dispersive spectroscopy. The presented methodology of Au rGO nanocomposites preparation could represent a green alternative on the production of metallic nanoparticles in biocompatible environment. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) foils were irradiated by using different fluences of an infrared nanosecond pulsed laser and characterized before and after the laser irradiation. The produced laser ablation was investigated as well as the generated plasma. Optical and AFM microscopies, mass quadrupole spectrometry, Rutherford backscattering analysis and X-ray photoelectron spectroscopy were used to analyze the irradiated GO foils. Results demonstrated that the GO loses oxygen with the laser irradiation becoming richer in sp2-hybridized carbon content. [ABSTRACT FROM AUTHOR]

High-intensity lasers interacting with solids in vacuum produce non-equilibrium plasma having high equivalent temperatures and high ion energies. In these conditions, depending on the laser parameters, irradiation conditions and target composition and geometry, different nuclear reactions can be induced due to both the high plasma temperature and the wide ion energy distribution of the accelerated species. By focusing the laser spot of very high laser intensities above 1015 W/cm2on solid targets it is possible to accelerate electrons and ions at relativistic energies above 1–10 MeV/nucleon, sufficient to penetrate into the nucleus of many light atoms. Thus laser–plasma may induce activation, transmutation, fission and fusion processes. The high plasma density and the non-isotropic plasma distribution enhance the number of nuclear events during the laser–plasma interaction along special directions. X and gamma rays, electrons, different ion species and neutrons can be produced mono-energetically or in wide energy distribution. The nuclear reactions2H(d,n)3He,2H(d,p)3H,7Li(d,n)8Be and11B(p,a)8Be are discussed in more detail with respect to many others when hydrogenated targets containing deuterium, lithium and boron are employed, respectively. The monitoring of the plasma pulse and of the products of the nuclear reactions using different detectors and techniques are also presented and discussed. [ABSTRACT FROM PUBLISHER]

A study of the electron emission from laser-generated plasma in target normal sheath acceleration regime is presented for different targets. The used laser has an intensity of about 1016 W/cm2and a pulse duration of 300 ps. Electrons were detected using SiC detectors and plastic scintillators employed in time-of-flight configuration and a Thomson parabola spectrometer (TPS). Measurements indicated the presence of hot electrons with a kinetic energy of the order of some MeVs. SiC and scintillators detect electrons up to about 400 keV while TPS electrons up to about 5 MeV energy. Electrons yield emitted in the forward direction is proportional to the effective atomic number of the target and is inversely proportional to the target thickness. [ABSTRACT FROM PUBLISHER]

Silicon Carbide (SiC) semiconductor detectors are increasingly employed in Nuclear Physics for their advantages with respect to traditional silicon (Si). Such detectors show an energy resolution, charge mobility, response velocity and detection efficiency similar to Si detectors. However, the higher band gap (3.26 eV), the lower leakage current (∼10 pA) maintained also at room temperature, the higher radiation hardness and the higher density with respect to Si represent some indisputable advantages characterizing such detectors. The devices can be employed at high temperatures, at high absorbed doses and in the case of high visible light intensities, for example, in plasma, for limited exposition times without damage. Generally SiC Schottky diodes are employed in reverse polarization with an active region depth of the order of 100 µm, purity below 1014 cm−3and an active area lower than 1 cm2. Measurements in the regime of proportionality with the radiation energy released in the active region and measurements in time-of-flight configuration are employed for nuclear emission events produced at both low and high fluences. Alpha spectra demonstrated an energy resolution of about 1.3% at 5.8 MeV. Radiation emission from laser-generated plasma can be monitored in terms of detected photons, electrons and ions, using the laser pulse as a start signal and the radiation detection as a stop signal, enabling to measure the ion velocity by knowing the target-detector flight distance. SiC spectra acquired in the Messina University laboratories using radioactive ion sources and at the PALS laboratory facility in Prague (Czech Republic) are presented. A preliminary study of the use of SiC detectors, embedded in a water equivalent polymer, as a dosimeter is presented and discussed. [ABSTRACT FROM PUBLISHER]

The charge production from laser-generated plasmas generates not isotropically ion acceleration in vacuum and with mean kinetic energy proportional to the ion charge state. The ion velocity depends on many factors of which the most important are the plasma temperature, the adiabatic gas expansion in vacuum and the Coulomb acceleration. The ion energy distributions of the emitted ions from the plasma can be well explained by the Coulomb–Boltzmann-Shifted function, with a cut-off limitation at high energy for a wide range of laser intensities. It can be applied for intensities of 1010 W/cm2, when plasma is produced only in the backward direction from thick targets (backward plasma acceleration regime), as well as at intensities of the order of 1019 W/cm2, when plasma is produced in the forward direction from thin targets in target-normal sheath acceleration regime. It loses of validity in radiation pressure acceleration regime, at which ions are emitted near mono-energetically. [ABSTRACT FROM AUTHOR]

Single-lap and double-lap polymeric joints of ultrahigh molecular weight polyethylene (UHMWPE) sheets, opportunely overlapped, were realized and studied. One of the polymer sheets was doped with carbon nanomaterials as a laser-absorbent filler. The joints were irradiated by a diode laser operating at 970 nm with maximum pulse energy of 200 mJ. Four types of weld seam geometries were realized in the overlapped area. Optical microscopy observations and mechanical shear and hardness tests were performed in order to characterize all the prepared joints. The maximum shear load was ≈210 N, reached generally in the double-lap joints. High loads in the single-lap joints were reached if high surface area of the welding and high filler amount in the polymer were present. Three parameters influenced the joint resistance: the joint configuration (single or double lap), the welding geometry, and the filler amount. The absorption of diode laser energy at the sheet interface induces a melting process that softens the polymeric sheets in the laser contact area. Finally, a comparison between the welding ability of the diode laser and of the Nd:Yag laser upon the polyethylene sheets is presented. [ABSTRACT FROM AUTHOR]

High-intensity sub-nanosecond-pulsed lasers irradiating thin targets in vacuum permit generation of electrons and ion acceleration and high photon yield emission in non-equilibrium plasmas. At intensities higher than 1015 W/cm2thin foils can be irradiated in the target-normal sheath acceleration regime driving ion acceleration in the forward direction above 1 MeV per charge state. The distributions of emitted ions in terms of energy, charge state and angular emission are controlled by laser parameters, irradiation conditions, target geometry and composition. Advanced targets can be employed to increase the laser absorption in thin foils and to enhance the energy and the yield of the ion acceleration process. Semiconductor detectors, Thomson parabola spectrometer and streak camera can be employed asonlineplasma diagnostics to monitor the plasma parameters, shot by shot. Some applications in the field of the multiple ion implantation, hadrontherapy and nuclear physics are reported. [ABSTRACT FROM PUBLISHER]

Single-lap polymeric joints can be obtained using laser welding overlapping two polymeric sheets, with one laser transparent and the other laser adsorbent. In this study we employed crystalline carbon nanomaterials (in amounts of 0.2, 0.5, and 1.0 wt.%) as filler to enhance the absorption of polyethylene (UHMWPE type). A Nd:YAG laser operating at 1064 nm was used as a power source to make the welded joints. Morphological, mechanical, and calorimetrical tests were carried out to study the strength of the joints made. Serious attention was paid to find the best compromise between exposure time to laser light and filler amount. We found that in the optimal conditions (with 0.2 wt.% filler and 60 s exposure time) the joint exhibits a good shear strength with a regular welded area. In fact, the best conditions guarantee proper absorption power of the laser light and deep interpenetration of the chains between the two polymeric sheets without any damage. [ABSTRACT FROM AUTHOR]

Poly(methyl methacrylate) (PMMA) was irradiated using a medical UV-ArF excimer laser operating at the fundamental wavelength of 193 nm. Characterized by a beam diameter of 1.8 mm and energy of 180 mJ with a Gaussian energy profile, it operates in a single mode or at 30 Hz repetition rate. Mechanical profilometry was carried out on ablation craters in order to study the rugosity and the ablation yield in the various operative conditions. Optical transmission and reflection measurements at six wavelengths were conducted in order to characterize the optical properties of the irradiated surfaces. Measured crater depths in PMMA were lower with respect to the forecasted ones in corneal tissue, while the lateral crater aperture was maintained. The rugosity produced at the crater bottom after irradiation was about 0.3 μm, and the ablation yield was about 1015 molecules/laser pulse, while etching depth and diameter show a roughly linear dependence on the number of laser shots. These experiments constitute a base for deeper clinical investigations. [ABSTRACT FROM AUTHOR]

Hydrogenated targets have been irradiated in vacuum with the pulsed Nd:YAg laser at intensities of the order of 1010 W/cm2. The laser-generated plasma, produced by the interaction with the solid, emits protons and other ions along the normal to the target surface. Ion collectors and ion energy analyzer were used to measure the current, the angular emission and the energy distributions of the emitted protons. Time-of-flight measurements, Coulomb–Boltzmann-distributions and the fits of experimental data were also used in order to evaluate the equivalent ion plasma temperature and the ion acceleration developed in the non-equilibrium-pulsed plasma. [ABSTRACT FROM PUBLISHER]

Laser ion sources are employed with success to generate, in vacuum, any ion species with high current, ion energy, charge states and directivity. Nanosecond infrared laser pulses, with intensities of the order of 1010 W/cm2, induce ablation in metals. Ions are produced in vacuum with energy distribution following the Coulomb-Boltzmann-shifted distribution and are ejected mainly along the normal to the target surface. The free ion expansion process occurs in a constant potential chamber placed at high positive voltage variable between 0 and 30 kV, by means of nose along the normal to the target surface. The electric field reaches 5 kV/cm and is used to accelerate Ti ions emitted from the plasma at the INFN-LNS laser facility. The time-of-flight technique is employed to measure the mean ion energies of the post-accelerated particles. Ion charge states and energy distributions were measured through an ion energy spectrometer. Ion energies, charges per pulse, ion currents and beam directivity of Ti beams were measured, and the results were compared with those coming from simulation programs. [ABSTRACT FROM AUTHOR]

Surface ion implantation induced by laser-generated plasmas was investigated using the PALS Prague laser facilities. Cu, Ge, Ag and Ta ions were obtained through the ablation of solid targets in vacuum by means of 1015 W/cm2 laser pulses. Energetic ions (∼ 0.1-1 MeV) were implanted on different substrate surfaces (Si, C, Al, Ti and polyethylene) placed at different distances from the target and angles from the normal to the target surface. In order to increase the ion dose, implantation was performed by using more laser shots in the same experimental conditions. An ion energy analyzer was employed for online measurements of the ion energies and charge states produced by the laser plasma. Off-line Rutherford backscattering spectroscopy (RBS) of alpha particles allowed us to determine the ion depth profiles, the ion energies and the ion amount implanted on the substrate surfaces. RBS spectra have shown typical implanted deep profiles only for substrates placed along the normal to the target surface at which the ion energy is maximum. At large angles, no implantation occurs and ions are only deposited. At a high dose, the multi-energetic ion implantation can be used to modify the physical and chemical properties of the implanted layer surfaces. [ABSTRACT FROM AUTHOR]

Physical analyses by laser ablation coupled to a mass quadrupole spectrometry technique on different metallic samples (standards of calibration, minerals and old bronze coins) have been undertaken. Laser ablation induces controllable surface layer removal in high vacuum. Contemporary mass spectrometry analyzes mass elements, mass compounds and isotopic relative content. A comparison between the experimental isotopic ratios and the expected values from the natural abundance is presented. The differences are discussed in terms of the technique's limitations and of the fluctuations due to geographic areas of the material's provenience. Measurements of stable isotopic ratios in copper, lead and tin have been performed in old Egyptian coins. Results confirm that the minerals contained in the coins come from different geographical locations and mines. Results are presented and discussed from the point of view of the physical technique, geological areas and archaeological aspects of peculiar investigated samples. [ABSTRACT FROM AUTHOR]

A set of Egyptian bronze coins, dating back to the sixth or seventh century AD, has been studied by different experimental techniques in order to compare their composition and surface morphology, the process of coinage and, possibly, to also identify the place of production. The measurements have been performed by laser ablation with mass quadrupole spectrometry and energy dispersed X-ray fluorescence. Both analyses are non-invasive and can be safely used according to the integrity requirements of the analyzed pieces. Owing to the poor number of available samples, this work, more than to solve a numismatic question, has been carried out in order to test the validity of the above experimental techniques in view of further analyses on the same coins, based on better quality statistics. The preliminary results, presented in this paper, indicate significant differences in the chemistry of the coins' patina, i.e. composition and isotopic species content. This seems to support, in agreement with the archaeological expectations, the hypothesis of the existence of a local mint in Antinoopolis, never before considered in Egyptian numismatics. [ABSTRACT FROM AUTHOR]

Silver nanoparticles were synthesized in vacuum (10-7) by using a Nd:YAG high-power pulsed laser without any catalytic gas and/or thermal annealing processes. The ablated material was collected on several SiO2/Si substrates (with 50 nm thickness) deposited before the laser ablation with a plasma-enhanced chemical vapor deposition system. The substrates were analyzed with the aid of a variable angle spectra ellipsometer at different angles. The analysis revealed the presence of a surface plasmon resonance at about 3 eV, which is in good agreement with results in the literature. A deconvolution method utilizing the Lorentz model was applied to fit the experimental optical absorption peaks in order to recognize different groups of nanoclusters with different sizes varying from 2 to 10 nm in radius. Electronic elaborations of scanning electron microscopy of the embedded particles in the SiO2 matrix were also carried out to measure their densities as a function of the deposition time and dimension distributions. The experimental measurements were performed at the INFN-LNS laboratory of Catania and at the MT laboratory of the FBK-IRST foundation of Trento. [ABSTRACT FROM AUTHOR]

The proton beam production from high-energy laser-generated plasma is increasingly becoming of special interest for investigations in the field of new techniques of ion acceleration, nuclear physics, astrophysics and radiotherapy. The evolution of short-pulsed lasers, from the nanosecond to the femtosecond pulse scale, has allowed for an increase in intensity from about 1010 W/cm2 to about 1020 W/cm2 with a consequent increase of the kinetic energy of the plasma-generated ions. Thus proton energy has increased from about 100 eV at low intensity to about 100 MeV at the actual femtosecond-terawatt lasers. Although the emitted ions are multi-energetic, the use of thin hydrogenated targets and a high repetition rate can be employed to obtain high proton energy, narrow energy spread, high ion directivity and high current. Literature data indicate that the proton energy, the equivalent plasma temperature and the Coulomb acceleration increase with the pulse intensity. The use of femtosecond-terawatt lasers may produce very intense electric fields in the non-equilibrium plasma, which accelerate ions up to tens of MeV/amu. Ponderomotive forces, supersonic plasma expansion in vacuum, self-focusing effects and the high plasma temperature influence the ion plasma acceleration. Literature data can be fitted by Coulomb-Boltzmann-shifted functions which permit a separation of the thermal contribution from the Coulomb one. The latter increases at very high laser intensities to a greater extent than its thermal counterpart. [ABSTRACT FROM AUTHOR]

In this work, indium tin oxide (ITO) thin films have been prepared by pulsed laser deposition (PLD) on quartz and silicon substrates at room temperature, starting from an ITO target with a Sn/In concentration ratio of 0.18. Structural, optical, and electronic properties of these films have been analyzed by means of X-ray photoemission and optical spectroscopy. By the analysis of the X-ray photoemission spectroscopy spectra in the In 3d5/2, Sn 3d5/2, and O 1s binding energy regions, carried out both for films and target, evidence of structural changes after the ablation process was found. It was deduced that the deposited films have an Sn/In ratio equal to 0.10, and are characterized by a predominantly amorphous structure. The optical properties in the visible and the near ultraviolet regions have been deduced by near normal incidence optical reflectivity and absorption measurements. A value of 3.7 eV for the optical band gap and an average refraction index of about 3.0 in the visible photon energy range have been obtained, in agreement with the results of other authors. [ABSTRACT FROM AUTHOR]

The high-power iodine laser PALS was used to generate highly charged Ta ions and to study non-linear processes in laser-produced plasma. Longitudinal structures of the expanding plasma, obtained by using an X-ray streak camera on a time scale ∼ 2 ns, are presented. Various bright spots (moon-like, half-moon-like), expansion-path curvature and even their splitting were recorded. These phenomena are ascribed to the effect of the magnetic field that is self-generated at high laser intensities. [ABSTRACT FROM AUTHOR]

The most effective devices able to feed modern accelerators with heavy ions (either in terms of reliability or performance) are electron cyclotron resonance ion sources (ECRIS), which are able to generate intense currents of multiply charged ions. One of the disadvantages of the ECRIS consists of the limitation in the production of metallic ions (usually obtained by means of ovens and sputtering techniques), especially in the case of refractory elements. Laser ablation is an effective method for such elements. The coupling between a laser ion source (LIS) and an ECRIS has been studied at some facilities (INFN-LNS, RIKEN, University of Frankfurt, ANL): the experiments were successful but an adequate modeling and additional experimental activities are mandatory. Preliminary calculations have shown that the ion energy from the LIS should be lower than a few hundreds of eV in order to permit an effective coupling of LIS ions with the ECRIS plasma. A detailed investigation of the ion capture by the ECRIS plasma has now been carried out by means of numerical simulations based on the Monte Carlo method. The energy distribution function of the LIS plasma has been taken into account, as well as the density and temperature distribution of the ECRIS plasmas and the pattern of the magnetic field in the resonance region. The captured fraction of LIS ions strongly depends on the temperature (the lower energy component of the ion energy distribution function is easily absorbed by the ECRIS plasma). The effect of negatively biased targets has been also investigated: simulations demonstrate that for negative potentials of the order of 0.4 kV the captured fraction abruptly increases, and in some particular cases it exceeds 50% of the total ion current. [ABSTRACT FROM AUTHOR]

The modeling of laser-generated plasmas can be carried out by means of different theoretical approaches. Hydrodynamic simulations have the advantage of treating the plasma as a continuous fluid that expands in vacuum with a high Mach number. We used the analytical Anisimov model for the numerical simulations of a plasma expanding at supersonic velocities. The model describes the plume by means of a special solution of the gas dynamical equations on the hypothesis that the flow expands adiabatically. Here, we carry out a comparative analysis between experimental and numerical results: the model fits the experimental data for monoatomic plumes quite well. More specifically, the numerical data have been tested by comparing the time-of-flight signals obtained at the INFN-LNS in Catania from a pure metallic target. A Coulomb drift velocity was added to the expansion velocity, and only in this way was it possible to explain the experimental results, thus confirming the presence of self-generated electrostatic fields inside the expanding plasma plume. [ABSTRACT FROM AUTHOR]

A plasma produced by a Nd:YAG laser beam has been characterized by means of a Langmuir probe. The diagnostics method has been applied in the region of ion saturation current of the I-V curve, because for probe potentials lower than the floating potential the electron current cannot be measured. The ion current was redefined by considering the ion sound velocity (according to the Bohm criterion) and the drift velocity due to the adiabatic expansion and Coulomb acceleration. The ion signal has been used to determine the plasma parameters. A comparison with the conventional analysis will be carried out, in order to describe the advantages and disadvantages. [ABSTRACT FROM AUTHOR]