Search

Boron carbide (B4C) has outstanding properties making it particularly interesting in the field of neutron detection. In this study we exploit nanosecond pulsed laser deposition (PLD) for the synthesis of B-enriched films with micrometer-scale thickness for future realization of a neutron converter layer. B-enriched B4C layers were deposited by PLD at room temperature under different wavelength conditions (λP = 266, 248,193 nm), fluence (from 2 to 10 J/cm2) and substrate (silica, Si (100), kapton (polyamide), PMMA and AZ 1512 resist). The measured elemental composition of boron (B), carbon (C) and oxygen (O) as well as the structural properties of the deposited films highlighted: i) wavelength- and fluence-dependent B sub-stoichiometry with respect to the ablated target, ii) formation of polycrystalline grains despite the room temperature growth in the case of λP = 266 nm, and iii) deposition rates higher for λP = 266 than for the other investigated wavelengths. The film deposited at a wavelength of λP = 266 nm and F = 2 J/cm2 yielded the best B/C ratio, negligible O-contaminations, and a very smooth surface with low density of surface particulates. Moreover, the possibility of depositing well adherent films on soft substrates with thicknesses > 1 μm is demonstrated, due to ability to accommodate tensile stress at the substrate-B4C film interface.

We report a design of photocathode, which combines the good photoemissive properties of lead (Pb) and the advantages of superconducting performance of niobium (Nb) when installed into a superconducting radio-frequency gun. The new configuration is obtained by a coating of Nb thin film grown on a disk of Pb via pulsed laser deposition. The central emitting area of Pb is masked by a shield to avoid the Nb deposition. The nanomechanical properties of the Nb film, obtained through nanoindentation measurements, reveal a hardness of 2.8±0.3 GPa, while the study of the electrical resistivity of the film shows the appearance of the superconducting transitions at 9.3 K and 7.3 K for Nb and Pb, respectively, very close to the bulk material values. Additionally, morphological, structural and contamination studies of Nb thin film expose a very low droplet density on the substrate surface, a small polycrystalline orientation of the films and a low contamination level. These results, together with the acceptable Pb quantum efficiency of 2×10−5 found at 266 nm, demonstrate the potentiality of the new concept photocathode. Funding agencies: Italian National Institute of Nuclear Physics (INFN); Italian MIUR through the Project FIRB Futuro in Ricerca [RBFR12NK5K]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]

Polyethylene oxide (PEO) films were grown by pulsed laser deposition using two different lasers: ArF (193 nm, 5 ns) and Nd:YAG (355 nm, 7 ns). Even though very similar experimental conditions have been applied to ablate identical targets, different surface morphologies and structures have been observed. Depending on laser fluence, labyrinthine patterns in PEO films have been formed when using 355 nm laser pulses at fluence values in the range 280–1000 mJ/cm2. The same material ablated by 193 nm excimer laser pulses at 200 mJ/cm2 fluence grows in dendritic morphologies. Both target and laser deposited materials have been thoroughly characterized using infrared spectroscopic, microscopic and X-ray analytical methods. Infrared spectroscopy demonstrated the close similarity of molecular chains for both target and film materials. X-ray diffraction analysis indicates polymer chain scissoring by ultraviolet irradiation, a fact also confirmed by size exclusion chromatography.

In this work yttrium and lead thin films have been deposited by pulsed laser deposition technique and characterized by ex situ different diagnostic methods. All the films were adherent to the substrates and revealed a polycrystalline structure. Y films were uniform with a very low roughness and droplet density, while Pb thin films were characterized by a grain morphology with a relatively high roughness and droplet density. Such metallic materials are studied because they are proposed as a good alternative to copper and niobium photocathodes which are generally used in radiofrequency and superconducting radiofrequency guns, respectively. The photoemission performances of the photocathodes based on Y and Pb thin films have been also studied and discussed. Funding agencies: Italian National Institute of Nuclear Physics (INFN); Italian Ministry of Research [RBFR12NK5 k]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

In this work Magnesium (Mg) and Yttrium (Y) thin films have been deposited on Copper (Cu) polycrystalline substrates by the pulsed laser ablation technique for photocathode application. Such metallic materials are studied for their interesting photoemission properties and are proposed as a good alternative to the Cu photocathode, which is generally used in radio-frequency guns. Mg and Y films were uniform with no substantial differences in morphology; a polycrystalline structure was found for both of them. Photoemission measurements of such cathodes based on thin films were performed, revealing a quantum efficiency higher than Cu bulk. Photoemission theory according to the three-step model of Spicer is invoked to explain the superior photoemission performance of Mg with respect to Y.

This paper reports the fabrication of Nb thin films through pulsed laser deposition at different substrate temperatures, ranging from 300 to 660 K. While the variation of the substrate temperature does not affect significantly the excellent Nb thin film adhesion to the Si(100) substrate surface, the increase of the substrate temperature up to 570 K promotes an improvement of the grown film in terms of morphology and roughness. Such improvement is achieved through the formation of wider columnar structures with a reduced superficial roughness, around 5 nm, as shown by scanning electron microscopy (SEM) and atomic force microscopy. The use of temperatures over 570 K increases the substrate roughness due to the formation of irregular structures inside the film, as observed by SEM cross section analysis, and does not produce a relevant improvement on the crystalline structure of the material.

Silver artefacts and particularly ancient silver artefacts present the serious problem of the black look due to ambient contamination. The black colour is the consequence of the layer forming on the surface made of acanthite and jalpaite, both compounds are sulphur composts. Recently UV laser cleaning technique has demonstrated to be very promising in processing of cultural artefacts. To operate on artefacts without to contaminate the bulk, first we determined the laser fluence threshold of the bulk, second we controlled the surface compounds and at the end we operated the laser irradiation. In this work we utilised certified silver and silver/copper samples in order to perform preliminary studies. The threshold fluence we found were 780 and 510 mJ/cm2 for the Ag pure and for the Ag/Cu alloy, respectively. The jalpaite concentration on Ag/Cu sample increased after the laser dose of 25 J/cm2, while for higher laser dose its value lowered pointing out that complex processes take part during the laser application. As a successful of our studies we applied the technique on a Carlino coin made of silver coined in 1689 under King Carlo II. The analyses were performed by two different techniques able to find the percentage of elements and the chemical compounds; the EDXRF and the XRD. We found that the sulphur concentration decreased on laser dose. Operating on the coin up to a dose of 280 J/cm2 the sulphur concentration deceases up to 20 %, while the coin look becomes clear just after a 50 J/cm2.

In this work, two different techniques to modify polymeric surfaces are compared: laser irradiation and ion implantation. The treated polymers were samples of ultra high molecular weight polyethyle...

In the last years the ion component of a laser-produced plasma has been considered and studied as an object to provide high-density ion sources, which can be applied in many fields such as laser-induced implantation. In this work a KrF laser beam of 108 W/cm2 irradiance was focused onto single-crystalline Fe and single-crystalline Fe with 2% of Si targets and the characteristics of both free expanding laser-produced plasmas were compared. The time-of-flight (TOF) method was applied to determine the ion charge yield at various laser fluences and the ion angular spread. The analyses of TOF spectra showed a synergetic effect of the silicon admixture in target material on the Fe ions production. Besides, this admixture was also responsible of the increasing of the plasma temperature which corresponds in turn to the increasing of the average kinetic energy of the particles as well as of the more collimated ion distribution.

This work has the purpose to characterize the plasma produced by solid target ablation. The experiment was performed by using a KrF laser with an irradiance of 10(8) W/cm(2) and different solid targets, i.e., Si, Ge, Pd, and Pb. A very suitable Faraday cup has been utilized to study the angular distribution of the plasma plume as well as to perform measurements of the ion charge carried by the plasma during its free expansion into the vacuum. Particular attention was done to estimate the charge losses ascribed to the recombination processes during the plasma expansion. Different charge angular distributions have been found for the four laser-induced plasmas which suggest the dependence of the plasma characteristics with the different physics processes involved during the laser-target and laser-plasma interaction. These processes are responsible also of the duration of the recombination processes which results to be different according to the different plasma.

We demonstrate that chemical reactions leading to the formation of AlO radicals in plasmas produced by ablation of aluminum or Ti-sapphire with ultraviolet nanosecond laser pulses can be predicted by the model of local thermodynamic equilibrium. Therefore, emission spectra recorded with an echelle spectrometer and a gated detector were compared to the spectral radiance computed for uniform and nonuniform equilibrium plasmas. The calculations are based on analytical solutions of the radiation transfer equation. The simulations show that the plasmas produced in argon background gas are almost uniform, whereas temperature and density gradients are evidenced in air. Furthermore, chemical reactions exclusively occur in the cold plume periphery for ablation in air. The formation of AlO is negligible in argon as the plasma temperature is too large in the time interval of interest up to several microseconds. Finally, the validity of local thermodynamic equilibrium is shown to depend on time, space, and on the elemental composition. The presented conclusions are of interest for material analysis via laser-induced breakdown spectroscopy and for laser materials processing.

This study is devoted to characterizing a free expansion laser plasma produced by an excimer laser with respect to recombination phenomena. The plasma was ejected from a Cu target after the laser pulse. The diagnostic system was a Faraday cup located at different distances from the target in order to collect the ions carried by the plasma. Ion recombination effects were clearly observed at distances close to the target, due to the high density of the laser-produced plasma at the beginning of its expansion. The recombination range and critical distance were experimentally estimated measuring the ion charge variation on the distance from the target. Beyond it, the charge loss due to the recombination effects was negligible and the freezing of the charge states set in. In this region the plasma dilution, which was due to its free expansion into the vacuum, occurred, and the collected ion charge, Q, followed the law Q ∝ L−2 as a function of the distance from the target, L. The assessment of recombination processes is very important for the optimization of a laser ion source.

A charge density profile of ions emitted from a laser ion source is derived from a time-resolved current of ions collected with a time-of-flight detector. This relationship between the density profile over path of ions and an ion current observed far from the ion source is based on a similarity relationship for ion currents with "frozen" charges observed at different distances from the target. In this contribution, we present distance-of-flight spectra of the charge density of ions emitted from various plasmas driven by a Compex 205 KrF excimer laser (λ=248 nm, τFWHM=23ns) which works at laser irradiances between 108 and 1010 W/cm2.

Time-integrated and-resolved mass spectrometric investigations were carried out during the laser ablation of yttrium target in high vacuum. The main aim of these experiments was to study the implications of the target surface chemistry and of the residual gas on the deposition process quality. The effect of the laser energy density on the ionic species formation during the ablation process was investigated. It was found that at a moderate laser fluence of 4.5 J/cm2 none hydrides, oxides nor nitrides of yttrium were observed; on the contrary, at a higher laser fluence of 7.6 J/cm2, the above chemical species were observed. During and after the laser ablation process, a getter effect was observed due to the absorption of the residual gas by the Y layer deposited on the internal wall of the vacuum system. The results of these mass spectrometric analyses will be useful to improve the performances of photocathodes based on Y thin films grown by pulsed laser ablation technique.

The effects of laser fluence on the growth characteristics and surface morphology of yttrium films grown by pulsed laser deposition are investigated. The presence of droplets in the deposited films, which is the main drawback of pulsed laser deposition technique, was studied at different laser fluences. The morphology and the structure of the grown films were studied by scanning-electron microscopy and x-ray diffraction, respectively. Careful scanning-electron microscope investigations obtained by tilting the samples show that the droplets arrive to the substrate in the molten phase. The ablation rate measured at five different laser fluences (0.9–7.6 J/cm2) shows a nonlinear trend correlated with the presence of the plasma-shielding effect. The present interest in the deposition of yttrium thin films by laser ablation is due to the well-known photoemission characteristics of this metal. Depositing good-quality thin films with high adhension and low droplet density will improve the performance of photocat...

High purity yttrium was ablated by using frequency quadrupled ultra-violet pulses of a Nd:YAG laser ( λ = 266 nm, τ FWHM = 7 ns) with power density of about 1 GW/cm 2 . Laser ablation process was studied using in-situ mass spectrometry of the ablated species in combination with ex-situ analyses of both target surface and deposited films. An increase on the Y ablation rate was found at the beginning, followed by a significant drop with increasing of the number of laser pulses per site until it reaches a constant value after 40 pulses per site. Initial topographic changes on the target surface, observed by scanning electron microscope investigations, and plasma shielding effect could be the origin of these changes on the ablation rate. Careful time-integrated and -resolved mass spectrometric studies of the laser ablated material indicate evident hydridation and oxidation processes in gas phase of ablated yttrium. These results clearly suggest that high purity metallic thin films can be deposited only after a deep and prolonged laser cleaning treatment of the target surface. The present parametric studies are aimed and tailored to prepare photocathodes based on Y thin films to be used in RF photoinjectors.

The effects of laser fluence on the morphology of Y films in the regime characteristic of multiple-pulse laser deposition were investigated. Y thin films were deposited on silicon and copper substrates. The samples deposited on silicon substrate were used to deduce the morphology and the thickness of the deposited films. On the contrary, the samples deposited on copper were tested as photocathodes in a DC photodiode cell. The interest to produce Y-based photocathodes is due to the low work function of this metal with the possibility to drive such photocathodes with a visible radiation in the radio-frequency photo-injector. In this way it is possible to reduce the thermal emittance of the photoelectron beam and to increase the photocurrent intensity by utilizing the second harmonic of Ti:Sa driver laser. The quantum efficiency was measured for the first time by using a visible CW laser diode emitting at 406 nm.

A new classification of laser ion sources concerning their pulse-to-pulse reproducibility in the ion emission is proposed. In particular, we distinguish between plasmas according to the electron distribution and changing its characteristics at a laser intensity threshold of 10 14 W/cm 2 . Well reproducible continuous pulsed ion currents are typical for the intensity below the threshold. In contrast to this plasma the “two-temperature” plasma arising for the intensity above this threshold shows not only a separation of charges in space and time during the expansion but it also shows outbursts of ions similar to a self-pulsing instability leading to a chaos. The sequence of fast ion outbursts visible on the time-resolved ion currents is sensitive to the details of non-linear interaction of the laser beam with the generated plasma. Analysis of ion sources based on a time-of-flight signal function is applied to quantify their emission characteristics as the hidden partial currents of the ionized species constituting, the total measured current, the centre-of-mass velocity of individual charge states, their abundance and the ion temperature.

The requirement of a short response time of a cathode with respect to the laser beam for the generation of the photoelectrons limits, in the case of SPARC photoinjectors, the choice of the cathode materials to metals that usually present response time on the order of a few tens of femtoseconds. While copper and magnesium have been extensively studied, new research activities were devoted to study the photoemission properties of yttrium and to explore the feasibility of a photocathode based on this metal. Nevertheless, to date little data has been reported in literature. We present, in this work, the results of our investigation of Y films as suitable materials for the production of bright electron beams. Bulk and thin films of Y, prepared by pulsed laser deposition on Si substrates, have been tested as photocathodes in an ultra-high vacuum photodiode chamber at 10−7 Pa. Systematic laser cleaning treatments improved the film quantum efficiency (QE) from 10−6 to 4.5×10−4 at 266 nm, comparable to those of th...

A pulsed KrF excimer laser of irradiance of about 10 8 W/cm 2 was utilized to synthesize Si nanocrystals on SiO 2 /Si substrates. The results were compared with that ones obtained by applying low bias voltage to Si(1 0 0) target in order to control the kinetic energy of plasma ions. Glancing incidence X-ray diffraction spectra indicate the presence of silicon crystalline phases, i.e. (1 1 1) and (2 2 0), on SiO 2 /Si substrates. The average Si nanocrystal size was estimated to be about 45 nm by using the Debye–Scherrer formula. Scanning electron microscopy and atomic force microscopy images showed the presence of nanoparticles of different size and shape. Their distribution exhibits a maximum concentration at 49 nm and a fraction of 14% at 15 nm.

In this work we report on the characterization of pulsed soft x-rays emitted from laser-produced plasma. The plasma was generated by a pulsed KrF excimer laser focused on pure Si, Cu and Ta targets by 40, 80 and 120 mJ laser energies. The utilized detector was a very sensitive Faraday cup which opportunely biased was able to record time-resolved signals of x-rays and to estimate their energy. The found x-rays energy values were compared with the ion temperature of the plasma obtained by fitting the time-resolved ion current signals with a shifted Maxwell-Boltzmann velocity distribution. The results showed that the laser-produced Ta plasma induced bunches of x-rays having in average the highest energy values and it was also characterized by ion temperature higher than the ones of the laser-produced Si and Cu plasmas.

Ultra-high-molecular-weight polyethylene (UHMWPE) is a versatile polymer employed in many fields for its good chemical-physics characteristics. In particular, it is widely utilized in biomedical fields due to its high degree of biocompatibility and its easy control on wettability of the surface. In this work, the laser radiation has been utilized to effect different degrees of change to the wettability characteristics of the UHMWPE depending on the laser used. The wettability modification was investigated by measuring the contact angles using the sessile drop method. It was observed that the interaction with laser wavelengths at 1064 and 532 nm effected very little change in the wettability characteristics of UHMWPE. On the contrary, the interaction of UHMWPE with 248 and 308 nm laser wavelengths resulted in a marked improvement in the wettability characteristics of the polymer; in particular, the UHMWPE irradiated by 308 nm, after 10 laser shots, reported a linearly increasing of the polymer wettability.

A novel analysis of ion currents, which is based on the use of shifted Maxwell–Boltzmann velocity distribution, is applied to quantify the properties of expanding laser-produced plasmas into the vacuum. The ion currents were measured outside the critical zone where the recombination and collisional excitation processes are not important and the charge-states of ions are frozen. The deconvolution of single-shot ion currents is applied for recovering the partial currents of participating ion species in the measured ion currents in carbon, copper and polyethylene plasmas created by various pulsed laser beams. This method allows determining the plasma temperature, the centre-of-mass velocities of individual charge-states and their abundance. The obtained charge-state dependencies of the centre-of-mass velocities render important details in establishing the mechanisms responsible for the ion emission, which has fundamental importance in applications of laser ion sources.

(UV) lamps are widely used in mutagenesis-selection protocols. Nevertheless, since the eighties, due to the development of excimer lasers, new frontiers in the study of UV applications have been opened. It has been established that the presence of an intact SOS response system is required for the mutagenic effect of UV254 nm. The exposure to UV254 nm radiation is not mutagenic for Escherichia coli mutants lacking the RecA protein, the regulator of the SOS response.We have recently demonstrated that at variance with the UV254 nm mutagenesis, the UV308 nm mutagenesis by XeCl308 nm excimer laser is RecA-independent. This suggests that the UV308 nm might be mutagenic also in microorganisms naturally lacking the SOS response. In this study, we have developed an innovative mutagenesis protocol based on a homemade XeCl308 nm excimer laser and have demonstrated its efficiency on mutagenesis of Nonomuraea American type culture collection 39727, an industrial strain producing an antibiotic, which is relatively refractory to UV254 nm radiation-induced mutagenesis

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 2 . 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.

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 2 was able to reduce the chlorine concentration from 2.3 % w/w to 0.6 % w/w without damaging the metal bulk. Keywords: ancient coins; patina ; copper chlorides; laser cleaning; EDXRF portable apparatus

The present work has the purpose to evaluate experimentally the ablation threshold fluences of copper, silver, and their alloys in order to induce a safety laser cleaning of the metal artifacts avoiding damages to the bulk. We used two different pulsed lasers: a KrF excimer laser operating at 248 nm, 23 ns pulse duration and a Nd:YAG laser operating at 532 nm (second harmonic), 3 ns pulse. Preliminary experimental results about the laser cleaning of bronze coins will be reported. The laser cleaning consists on the reduction of the chlorine concentration from the surface of the coins. The laser cleaning, carried out by the KrF laser, provides a safe way of removing the chlorine concentration as the Energy Dispersive X-Ray Fluorescence analyses will demonstrate.

In this work the mutagenic effect on Escherichia coli strains induced by UV radiation emitted by a XeCl laser (λ = 308 nm) has been analysed as a function of the exposure dose and compared with the effect induced by 254 nm radiation emitted by a conventional germicidal lamp. E. coli strains, wild-type (recA+ ) and mutant (recA1 , defective in DNA damage repair systems), plated on LB agar, supplemented with rifampicin when requested, were irradiated by means of a germicidal lamp in the dose range 0 - 9 mJ/cm2. Similar strains were exposed to 308 nm pulsed laser radiation (τ = 20 ns FWHM; max. pulse energy: 100 mJ) in the dose range 0-1.0 x 104 mJ/cm2. The discrepancy between the results obtained with the lamp and the laser on the mutation frequency, suggested that the biological response to the two radiation sources involves distinct mechanisms. This hypothesis was supported by the evidence that exposure to near-UV 308 nm induced mutagenesis in the recA-defective strain at an extent considerably higher than in the recA-proficient strain.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work we report the preliminary experimental results on the selective ablation of sulphur in ancient stones. The sulphur concentration was reduced after laser action. For this goal an excimer laser operating at 308 nm wavelength and time duration of 20 ns was used. In order to estimate the sulphur concentration before and after laser cleaning, a portable apparatus for energy-dispersive X-ray fluorescence (EDXRF) was utilised. The processed sample were characterized by an initial sulphur concentration of 2.8% w/w. After the laser treatment, sulphur concentration decreased after a total deposited energy of about 30 J/cm 2 up to 1.2% w/w value. Due to the porosity of the stone, in fact, it is difficult to eliminate completely the S presence in the composition of the stones. It was also observed that after a few laser shots the initial black area of the stone became white showing in this way the great potential of the laser action on the cleaning process of the pietra leccese.

We report on the ion implantation by a new laser ion source (LIS). It is able to accelerate plasma ions towards substrates by means of a polarized accelerating gap. A pulsed excimer laser, KrF, was utilized in producing plasma by target ablation. A laser pulse energy of 70 mJ was focused onto different solid targets by a 15 cm focal length lens, obtaining an irradiance of about 3.5 × 10 8 W/cm 2 . To overcome plasma effects, such as arcs, usually occurring during the extraction phase, an expanding chamber with a hole in its end, was developed. To realize implantations, Si substrates were placed in front of the ions extracted by the plasma. The implanted samples were characterized by Rutherford backscattering spectroscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and laser ablation combined to inductively coupled plasma mass spectrometry. Implantations of Al, Cu and Ge were achieved up to 80 nm at a relatively low accelerating voltage, 40 kV.

We report here the results about the sulphur concentration in ancient stones and its removal after the application of UV laser action. A portable apparatus for energy-dispersive X-ray fluorescence (EDXRF) was utilised to measure the sulphur concentration before and after laser cleansing. After laser application the sulphur concentration decrased to 1.2% w/w whilst the initial value was 2.8% w/w. The laser energy density was about 1 J/cm2 and the efficient shot number was approximately 30 with a rate of 1Hz.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Experimental results concerning the extraction of Cu ions from laser-produced plasma are reported in this work. An XeCl excimer laser was used, providing a power density on the target surface of about 3.5 × 108 W/cm2. Laser wavelength and pulse duration were 308 nm and 20 ns, respectively. The experimental apparatus consisted substantially of a plasma generation chamber and a drift tube. An expansion chamber was mounted on the target stem inside the generation chamber. Its end together with a bored electrode connected to ground formed the acceleration gap, which was 1.3 cm large. A Faraday cup was used to reveal ions. The highest accelerating voltage applied to the extraction gap was 18 kV, resulting in extraction of an ion bunch of about 4.2 nC, with a peak current of 220 μA.

The high-power iodine laser of the Prague Asterix Laser System (PALS), emitting radiation at 438 nm wavelength, 400 ps pulse duration and about 250 J maximum pulse energy, was employed to irradiate in vacuum a germanium target. The amount, the energy and the charge state of the ions emitted from the laser-produced plasma are analyzed by time-of-flight measurements performed with the use of ion collectors (ICs) and an electrostatic ion energy analyzer (IEA). Energetic Ge ions emitted from the laser-produced plasma were directly implanted into C substrates placed at 30 cm distance from the target and 30 degrees angle with respect to the normal to the target surface. The implantation depths and implanted doses were analyzed by two different techniques: the Rutherford backscattering spectrometry (RBS) and the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

In this work the mutagenic effect on Escherichia coli strains of UV radiation emitted by a XeCI laser (lambda=308 nm, tau=20 ns, 100 mJ pulse energy) has been analyzed as a function of the exposure dose and compared with the effect induced by 254 nm radiation emitted by a conventional germicidal lamp. Mutations can involve any genome site and therefore can give rise to various phenotypes, which then can be suitably selected. As a consequence, the impact of the induced mutagenesis is outstanding, both in scientific and industrial fields. In particular suitable doses of UV radiation can induce mutations, while higher doses can cause cell death, due to the induction of manifold damages to DNA

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 3.5x108 W/cm2. 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.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Plasmas induced by UV laser ablation have been studied and analysed using timeof- flight measurements. A KrF laser beam of 23 ns FWHM time duration was focused into Si and Nb targets with a moderate laser fluence of 2 J/cm2. A suitable theoretical expressions were derived for fitting the recorded ion current under the assumption of a “shifted” Maxwell- Boltzmann velocity distribution. The deconvolution of time resolved ion current signals, taking into account a multi-mode velocity distribution has revealed that the contribution of the different charge states of ions in the plasma induces electric field which accelerate the expanding plasma along the target normal.

In this work we determined experimentally the threshold fluence of the most common metals found in cultural heritage, e.g. copper, silver and their alloys. We carried out the ablation process in air at atmospheric pressure with 8 ns pulsed Nd:YAG and 23 ns pulsed KrF lasers, at 532 and 248 nm, respectively. We irradiated every target by a fixed number of laser shots (repetition rate of 1 Hz) at several laser fluence values. Then, the resulting craters were characterized by a stylus surface profiler in order to obtain the dependence of ablation rate on laser fluence F. Here, we defined the ablation raate as ablated matter thickness for single laser pulse, x. Therefore, we identified the ablation threshold fluence, Fth, as the fluence value below which no ablation process would occur.

The physical modifications induced by ion implantation of ultra-high-molecular-weight-polyethylene (UHMWPE) by using a laser ion source (LIS) emitting multi-energy ion streams are investigated. A UV pulsed laser was employed to produce the plasma of the implanting material. The surface mechanical properties of UHMWPE depend on the implanted dose, which can enhance the surface micro-hardness and decrease the surface wetting, roughness and wear.