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Applied Surface Science (v.272, #)
Proton driven acceleration by intense laser pulses irradiating thin hydrogenated targets by L. Torrisi; M. Cutroneo; S. Cavallaro; L. Giuffrida; L. Andò; P. Cirrone; G. Bertuccio; D. Puglisi; L. Calcagno; C. Verona; A. Picciotto; J. Krasa; D. Margarone; A. Velyhan; L. Laska; E. Krousky; M. Pfeiffer; J. Skala; J. Ullschmied; J. Wolowski; J. Badziak; M. Rosinski; L. Ryc; A. Szydlowski (pp. 2-5).
► Plasma proton acceleration. ► Hydrogenated thin targets. ► Thomson parabola spectrometry.The Asterix iodine laser of the PALS laboratory in Prague, operating at 1315nm fundamental frequency, 300ps pulse duration, 600J maximum pulse energy and 1016W/cm2 intensity, is employed to irradiate thin hydrogenated targets placed in high vacuum. Different metallic and polymeric targets allow to generate multi-energetic and multi-specie ion beams showing peculiar properties. The plasma obtained by the laser irradiation is monitored, in terms of properties of the emitted charge particles, by using time-of-flight techniques and Thomson parabola spectrometer (TPS). A particular attention is given to the proton beam production in terms of the maximum energy, emission yield and angular distribution as a function of the laser energy, focal position (FP), target thickness and composition.
Keywords: Laser-matter-interaction; Plasma; Proton-acceleration; Hydrogenated-target
Ionic and atomic characterization of laser-generated plasmas at 5×109W/cm2 pulse intensity by F. Caridi; L. Torrisi; M. Cutroneo (pp. 6-12).
► A non-equilibrium plasma was produced by ablating several different targets (silicon, titanium, copper and germanium) at 5×109W/cm2 laser pulse intensity. ► The ion emission from the plasma was monitored through time-of-flight (TOF) measurements, performed by using an ion collector (IC) placed along the normal to the target surface. ► A classical mass quadrupole spectrometer (MQS) was employed to detect ion charge states and plasma neutrals at various detection angles. ► The plasma fractional ionization, the ions and neutrals angular distribution and the ablation yield, as estimated through a MQS calibration process, were also evaluated.A Nd:YAG laser operating at 1064nm wavelength, 150mJ pulse energy and 3ns pulse width, was employed to produce a non-equilibrium plasma by ablating several different targets (silicon, titanium, copper and germanium) at 5×109W/cm2 pulse intensity.The ion emission from the plasma was monitored through time-of-flight (TOF) measurements, performed by using an ion collector (IC) placed along the normal to the target surface. The deconvolution of the IC experimental spectra with a Coulomb–Boltzmann-shifted function permitted to evaluate the equivalent ion temperature and acceleration voltage, and the mean ion charge state developed inside the non-equilibrium plasma.A classical mass quadrupole spectrometer (MQS) was employed to detect ion charge states and plasma neutrals at various detection angles.The plasma fractional ionization, the ions and neutrals angular distribution and the ablation yield, as estimated through a MQS calibration process, were also evaluated.
Keywords: Laser-generated plasma; Ion collector; Mass quadrupole spectrometer
Mitigation of ion and particulate emission from laser-produced plasmas used for extreme ultraviolet lithography by Paolo Di Lazzaro; Sarah Bollanti; Francesco Flora; Luca Mezi; Daniele Murra; Amalia Torre (pp. 13-18).
► We measured velocity, size, charge, momentum, spectral energy, space distribution of debris emitted by a laser-plasma source. ► Our debris mitigation systems allows reduction factors ∼800 for atoms and nm-size clusters and ∼1600 for particles >500nm. ► Our debris mitigation system consists of buffer gas and a mechanical device, the latter stops debris slowed-down by the gas. ► We note the formation of sub-micrometric clusters due to a homogeneous nucleation-like mechanism.While developing a laboratory-scale micro-exposure tool for extreme ultraviolet (EUV) projection lithography which uses a laser-produced plasma emitting EUV pulsed radiation, we faced the problem of suppressing the various debris (ions, neutrals, particulate, clusters, droplets) emitted by the plasma target. The suppression of debris is a crucial task in the frame of EUV projection lithography, mainly because debris seriously limit both lifetime and performance of the expensive optics and filters put close to the plasma source. In this paper we present the experimental measurements of main debris characteristics (velocity, size, charge, momentum, spectral energy, spatial distribution). Then, we present the operating results of a patented debris mitigation systems (DMS) specifically designed to suppress debris with the measured characteristics. We achieved reduction factors ∼800 for atoms and nm-size clusters, and ∼1600 for particles larger than 500nm. These results are at the forefront in this field. The excellent performance of our DMS was a breakthrough to achieve a 90-nm patterning on commercial resists by our micro-exposure tool EUV projection lithography.
Keywords: Extreme ultraviolet lithography; Laser-plasma sources; Excimer lasers; Debris mitigation systems
Evolution of β-SiC in laser-generated plasmas by L. Gemini; D. Margarone; T. Mocek; F. Neri; S. Trusso; P.M. Ossi (pp. 19-24).
► Compact, homogeneous, crack-free β-SiC thin films were pulsed laser deposited. ► The films were characterised by SEM, TEM, FTIR, m-Raman spectroscopy. ► The films were directly irradiated with ns laser pulses and their morphology and nano-structure were investigated by FTIR, SEM, EDX, TEM, m-Raman. ► The films were irradiated by a plasma produced by irradiation with fs laser pulses a low-density polyethylene (LDPE) foil placed in front of the β-SiC. ► The indirect irradiation results in a laser-induced periodic surface structure on β-SiC. ► β-SiC shows meaningful chemical and structural stability in highly energetic, aggressive plasma ambient.A relevant issue in fusion reactors is to choose materials for plasma facing components such that an acceptable lifetime is guaranteed. Silicon carbide is among the very few materials that appear promising to resist harsh environmental conditions including high thermal loads, strong chemical erosion and severe energetic particle bombardment. Thin films, around 130nm thick, of cubic silicon carbide (β-SiC) were pulsed laser deposited on Si (100) substrates at 1173K, at fluences ranging from 3 to 9Jcm−2. The films deposited at 6Jcm−2 appear the most compact, homogeneous, crack free, with a reduced density of particulate and droplets at the surface. Such films were irradiated by different plasmas, generated by ns and fs laser pulses respectively, corresponding to deposited intensities between 108Wcm−2 and 1018Wcm−2. The compositional, morphological and microstructural evolution of irradiated β-SiC films were investigated by energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), vibrational spectroscopies (IR and Raman) and transmission electron microscopy (TEM). Under both irradiation conditions the films remain well adherent to the substrates, showing thermal and mechanical stability. The samples loose only a minor fraction of carbon. However, all irradiations induce meaningful changes of surface morphology, qualitatively different between the ns and fs pulses. In the former an evident columnar structure develops at the crater edges; in the latter, after a single pulse, a wavy structure was observed whose periodicity is nearly identical to the laser wavelength. Under both kinds of irradiation β-SiC shows meaningful chemical and structural stability in highly energetic, aggressive plasma ambient.
Keywords: Pulsed laser ablation; Silicon carbide; Nuclear fusion; Laser damage
Silver/oxygen depth profile in coins by using laser ablation, mass quadrupole spectrometer and X-rays fluorescence by M. Cutroneo; L. Torrisi; F. Caridi; R. Sayed; C. Gentile; G. Mondio; T. Serafino; E.D. Castrizio (pp. 25-29).
► Old silver coins. ► X-ray fluorescence. ► laser ablation coupled to mass quadrupole spectrometer.Silver coins belonging to different historical periods were investigated to determine the Ag/O atomic ratio depth profiles.Laser ablation has been employed to remove, in high vacuum, the first superficial layers of the coins. Mass quadrupole spectrometry has been used to detect the Ag and the O atomic elements vaporized from the coin surface. The depth profile allowed to determine the thickness of the oxidation layer indicating that, in general, it is high in old coins.A complementary technique, using scanning electron microscope and the associated XRF microprobe, have been devoted to confirm the measurements of Ag/O atomic ratio measured with the laser-coupled mass spectrometry.The oxidation layer thicknesses range between about 25 and 250microns.
Keywords: Laser ablation; Silver coins; SEM; LAMQS
ZnO nanostructures produced by laser ablation in water: Optical and structural properties by E. Fazio; A.M. Mezzasalma; G. Mondio; F. Neri; R. Saija (pp. 30-35).
► ZnO nanostructures have been synthesized by pulsed laser ablation. ► Structural and optical properties have been investigated by XPS, PL, TEM, REELS and XRD. ► Diffraction patterns and interplanar spacing agree with the ZnO wurtzite structure. ► Optical band gap has been found dependent on the nanoparticles size. ► A large number of Oxygen vacancies has been found in accordance with the measured sample densities.ZnO nanostructures have been prepared in distilled water by pulsed laser ablation, by varying the laser pulse energy between 20 and 150mJ and for an ablation time of 10min. The structural properties of the samples have been studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron (XPS), reflection electron energy loss (REELS), UV–vis and photoluminescence (PL) spectroscopies. The nanoparticles in colloidal suspension have shown a good degree of stoichiometry, as deduced by the analysis of the O 1s and Zn2p3/2 photoemission spectra. The diffraction pattern and the interplanar spacings well match to the standard diffraction pattern of wurtzite zinc oxide (ZnO). The optical band gap calculated by the absorption spectra is found to be size dependent showing an increase for a decreasing particle size. As estimated from the analysis of TEM images and confirmed by the XRD data, the diameter of the nanocrystals within the greater nanostructures is mainly in the range of 1–10nm. A large number of oxygen vacancies have been put in evidence by our PL measurements. This supports the lower density value of 6.12g/cm3, estimated by REELS in the free electron approximation, with respect to the one generally reported for thin film and crystal phases.
Keywords: Zinc oxide; Nanostructures; Pulsed laser ablation; Optical properties
Surface-enhanced Raman scattering study of organic pigments using silver and gold nanoparticles prepared by pulsed laser ablation by E. Fazio; S. Trusso; R.C. Ponterio (pp. 36-41).
The identification of pigments used in ancient times represents an interesting task in order to discriminate a production of a precise geographic area or to trace out the ancient commercial networks. Conventional micro-Raman spectroscopy (MRS), being a non-destructiveness technique, has been largely used for the analysis of dyes. Nevertheless several pigments, especially of organic origin, show weak Raman activity beside a strong a fluorescence that prevents their identification. Surface enhanced Raman scattering (SERS) can address such difficulties. The presence of noble metal nanoparticles induces a giant amplification of the Raman signal beside the fluorescence quenching. In this work we present the use of gold and silver nanoparticles to enhance the Raman signal of some commercial red organic dyes: bazilwood, dragon's blood, carmine and madder lake. The nanoparticles were prepared adopting two approaches: (1) ablating metallic targets in water using a pulsed Nd:YAG laser at 532nm and (2) depositing the nanoparticles on glass substrates by means of a KrF excimer laser ablation process, performed in a controlled argon atmosphere.
Keywords: Surface-enhanced Raman spectroscopy; Laser ablation; Cultural heritage; Nanoparticles; Pigments
Deuterium–deuterium nuclear reaction induced by high intensity laser pulses by L. Torrisi; S. Cavallaro; M. Cutroneo; L. Giuffrida; J. Krasa; D. Margarone; A. Velyhan; J. Kravarik; J. Ullschmied; J. Wolowski; A. Szydlowski; M. Rosinski (pp. 42-45).
A 1016W/cm2 Asterix laser pulse intensity, 1315nm wavelength, 300ps pulse duration, was employed at PALS laboratory of Prague, to irradiate thick and thin primary CD2 targets placed into the high vacuum chamber. The laser irradiation produces non-equilibrium plasma with deuterons and carbon ions emission with energy up to about 4MeV per charge state, as measured by time-of-flight (TOF) techniques by using ion collectors and silicon carbide detectors. Accelerated deuterium ions may induce high D–D cross section for fusion processes generating 3MeV protons and 2.5MeV neutrons, as measured by TOF analyses. In order to increase the mono-energetic proton yield, secondary CD2 targets can be availed to be irradiated by the plasma-accelerated deuterons. Experiments demonstrated that high intensity laser pulses can be employed to promote nuclear reactions from which characteristic ion streams may be developed. Results open new scenario for applications of laser-generated plasma to the fields of ion sources and ion accelerators.
Keywords: D–D fusion; Cross-section; Laser-plasma
Gaussian energy distribution of fast ions emitted by laser-produced plasmas by J. Krása (pp. 46-49).
► Ions emitted by laser-produced plasmas have shifted Maxwell–Boltzmann velocity distribution. ► Only almost monoenergetic fast ions have Gauss energy distribution. ► Linear relation between relative spreads in energy Δ E/ E and time-of-flight Δ t/ t of fast ions is valid only for Δ E<0.2 E. ► TOF energy-sensitive detector gives higher peak velocity than velocity- and density-sensitive ones. ► Bursts of fast ions emitted by laser-produced plasma consist of almost monoenergetic ion beams.The analysis of ion collector signals with the use of a time-of-fight signal function derived from a shifted Maxwell–Boltzmann velocity distribution is used to quantify the ion characteristics as the ion temperature and velocity of centre-of-mass motion of groups of ionized species constituting the ablated plasma. The analysis is also focused on velocity and energy distributions derived from the signal of a time-of-flight detector taking into account the underlying principle of sensor operation. The energy Maxwell spectra of ions are compared with the Gauss distribution with respect to the ratio of the centre-of-mass energy of ions to their temperature. The difference threshold between the Gauss and energy Maxwell spectra is determined via the limited validity of the basic relationship between spreads in energy and time-of-flight spectra ½Δ E/ E=Δ t/ t. The analysis of velocity spectrum of fast ions emitted by Ti plasma produced with 300ps, kJ-class iodine laser operating at PALS facility shows that ion bursts consist of almost monoenergetic ion beams.
Keywords: Laser-produced fast ions; Ion detector signal function; Velocity distribution of fast ions; Gauss energy distribution of fast ions; Spread in energy and time-of-flight of fast ions
Proton emission from resonant laser absorption and self-focusing effects from hydrogenated structures by M. Cutroneo; L. Torrisi; D. Margarone; A. Picciotto (pp. 50-54).
► Resonant absorption. ► Laser-generated plasma. ► Nanostructures enhancing absorption.Effects of resonant absorption and self-focusing are investigated by using fast and intense laser pulses. The ion emission and acceleration in the non-equilibrium laser-generated plasma are investigated at low and high intensities, from 1010 up to about 1016W/cm2.The properties of plasma are strongly dependent on the time and space, laser intensity and wavelength.A special interest concerns the energetic and intense proton generation for the multiplicity use that proton beams have in different scientific fields (Nuclear Physics, Astrophysics, Bio-Medicine, Microelecronics, etc.).Investigations have been performed at INFN-LNS of Catania and at PALS Laboratory of Prague, by using thick and thin targets and different technique of ion analysis.The mechanisms of resonant absorption of the laser light, produced in special targets containing nanostructures with dimensions comparable with the laser wavelength, enhances the proton energy. The mechanisms of self-focusing, obtained by changing the laser focal distance from the target surface, increase the local intensity and consequently the high directional ion acceleration.Real-time ion detections were performed through Thomson parabola spectrometer (TPS), ion collectors (IC), SiC detectors and ion energy analyzer (IEA) employed in time-of-flight configuration (TOF).The energy and the amount of ions increase significantly when the two non-linear phenomena occurs, as will be described.
Keywords: Resonant absorption; Self-focusing; Thomson parabola spectrometer; IC; SiC; IEA
Laser cleaning of a bronze bell by Giovanni Buccolieri; Vincenzo Nassisi; Alessandro Buccolieri; Fabrizio Vona; Alfredo Castellano (pp. 55-58).
► UV laser cleaning treatment was performed on a bronze bell outdoor. ► Laser is an effective tool to remove the common compounds of alteration of bronze. ► The laser ablation threshold and efficiency of laser cleaning were assessed. ► EDXRF analysis was performed before, during and after the cleaning treatment. ► Chemical composition of the constituents of both patina and alloy was determinated.In this paper we report the experimental results of the study of evaluation of an UV laser cleaning treatment on a bronze bell outdoor, dating from the second half of the 600.Energy dispersive X-ray fluorescence (EDXRF) non-destructive analysis was performed on the bell before, during and after the cleaning treatment in order to assess the laser ablation threshold, to define the efficiency of laser cleaning process, to avoid possible damage of laser on the bell, to determine the concentration of the constituents of both the patina and the alloy. In particular, an EDXRF portable apparatus was used in order to evaluate the variation of concentration of sulfur, chlorine, calcium, copper, lead and tin during the laser cleaning.
Keywords: Laser cleaning; Bronze; Patina; EDXRF
Ion acceleration in non-equilibrium plasmas driven by fast drifting electron by G. Castro; F. Di Bartolo; N. Gambino; D. Mascali; F.P. Romano; A. Anzalone; L. Celona; S. Gammino; R. Di Giugno; D. Lanaia; R. Miracoli; T. Serafino; S. Tudisco (pp. 59-64).
► Similarities in ion acceleration between microwave plasmas and laser plasmas exist. ► Electrostatic Bernstein Waves as mechanism of plasma heating. ► Generation of a vortex in a magnetized plasma and 107V/m electric field. ► Mechanisms of ion acceleration produce a Coulomb-like explosion. ► Multilayers plasma structure has been observed.We hereby present results on ion acceleration mechanisms in non equilibrium plasmas generated by microwaves or high intensity laser pulses. Experiments point out that in magnetized plasmas X–B conversion takes place for under resonance values of the magnetic field, i.e. an electromagnetic mode is converted into an electrostatic wave. The strong self-generated electric field, of the order of 107V/m, causes a E× B drift which accelerates both ions and electrons, as it is evident by localized sputtering in the plasma chamber. These fields are similar (in magnitude) to the ones obtainable in laser generated plasmas at intensity of 1012W/cm2. In this latter case, we observe that the acceleration mechanism is driven by electrons drifting much faster than plasma bulk, thus generating an extremely strong electric field ∼107V/m. The two experiments confirm that ions acceleration at low energy is possible with table-top devices and following complementary techniques: i.e. by using microwave-driven (producing CW beams) plasmas, or non-equilibrium laser-driven plasmas (producing pulsed beams). Possible applications involve ion implantation, materials surface modifications, ion beam assisted lithography, etc.
Keywords: Electrostatic Bernstein waves; Plasma heating; Plasma vortex; Langmuir probe measurements; Multilayer plasma structure; Laser plasma
Characterization of laser plasma by Cu, Cu/Be and Cu/Sn alloy targets by L. Velardi; J. Krása; A. Velyhan; V. Nassisi (pp. 65-68).
► The properties of plasma produced by laser ablation of pure and doped targets have been studied. ► The investigated targets were pure Cu, Cu with 2% of Be and Cu with 4% of Sn, in order to assess the influence of these admixture on the emission characteristics of plasma ions. ► The emission of Cu ions exhibited a higher gain from the Cu/Be and Cu/Sn plasmas with respect to the pure Cu one. ► We also performed studies of the temperature, ion velocity and charge angular distribution for the three plasmas.In this work, the properties of laser plasma produced by ablation of pure and doped targets have been studied. A KrF laser, λ0=248nm and 20ns of pulse duration, was used to induce ablation. Pure Cu, Cu with 2% of Be and Cu with 4% of Sn targets of 500μm thickness were ablated to assess the influence of these admixture on the emission characteristics of plasma ions. The utilized laser irradiance values were 0.6, 1.2 and 2.4×108W/cm2. It was observed that the emission of Cu ions exhibited a higher gain from the Cu/Be and Cu/Sn plasmas with respect to the pure Cu one. We also performed studies of the temperature, ion velocity and charge angular distribution for the three plasmas. Under the above conditions, the analyses of the experimental data demonstrated that the influence of these admixtures on the emission of Cu ions played a not negligible role which enhances the interest in plasmas by alloy targets.
Keywords: Laser ablation; Ion source; Doped target
Dynamics of colliding aluminium plasmas produced by laser ablation by N. Gambino; P. Hayden; D. Mascali; J. Costello; C. Fallon; P. Hough; P. Yeates; A. Anzalone; F. Musumeci; S. Tudisco (pp. 69-75).
The collision of two aluminium plasmas was investigated by combining both time and space resolved spectroscopy and Langmuir probe measurements. Plasma plumes were produced by a Continuum™ Surelite Nd:YAG Laser System with pulse duration of FWHM of 6ns and wavelength of 1064nm, at a laser irradiance of 1011W/cm2 on slab Al targets. By analyzing the emission spectra, the temporally and spatially resolved electron density and electron temperature at the stagnation layer were extracted, with a time resolution of 10ns. Data analysis confirms that the electron density of the stagnation layer evolves over a longer timescale than in the single plume case. On the other hand, the temperature trends show that the electron temperature decreases much more rapidly at the stagnation layer than in the case for the single expanding plasma. In addition, a Langmuir probe was used to investigate the properties of the collisional front evolution. The overall experimental results show that colliding laser produced plasmas could be useful in the design of experiments devoted to fusion reaction rate measurements in a low energy domain by including the effect of the electron screening (ES).
Keywords: Laser plasma; Colliding plasmas; Stagnation; Spectroscopy; Langmuir probe
The effects of liquid environments on the optical properties of linear carbon chains prepared by laser ablation generated plasmas by G. Forte; L. D’Urso; E. Fazio; S. Patanè; F. Neri; O. Puglisi; G. Compagnini (pp. 76-81).
► Linear carbon chains are produced by laser ablation in different solvents. ► UV–vis spectra show that solvent effects are negligible for these species. ► DFT calculations indicate that polyynes are the main species produced. ► Solvent's polarity and chain length play a driving role in nonlinear optical response. ► A change from RSA to SA is observed as function of both solvent polarity and acidity.Linear carbon chains (LCCs) were successfully produced by laser generated plasmas in different solvents starting from graphite rods. An identification of the prepared carbon structures was carried out from the analysis of the UV–vis spectra. Moreover, a systematic analysis of the DFT computed structural and electronic response of both polyynic and cumulenic model molecules, as a function of the solvents with different polarity, was carried out. The comparison between the calculated UV–vis spectra of polyynes series with the experimental ones clearly indicates that polyynes are the dominant species produced by the ablation process. The optical limiting properties were investigated by the Z-scan method, using a nanosecond pulsed laser. Both the different solvents and the carbon chain length distribution have a driving role in the nonlinear optical response. Hence, the effect of the solvent polarity and acidity was taken into account to explain the nature of the optical limiting behaviour.
Keywords: Polyynes; Laser ablation; Z-scan analysis; Solvent polarity; DFT
XPS and XRF depth patina profiles of ancient silver coins by F. Caridi; L. Torrisi; M. Cutroneo; F. Barreca; C. Gentile; T. Serafino; D. Castrizio (pp. 82-87).
Ancient silver coins of different historical periods going from IV cent. B.C. up to recent XIX century, coming from different Mediterranean countries have been investigated with different surface physical analyses. X-ray photoelectron spectroscopy (XPS) analysis has been performed by using electron emission induced by 1.4keV X-rays. X-ray fluorescence (XRF) analysis has been devoted by using 30keV electron beam. Scanning electron microscopy (SEM) has been employed to analyze the surface morphology and the X-ray map distribution by using a 30keV microbeam.Techniques were used to investigate about the patina composition and trace elements as a function of the sample depth obtained coupling XPS to 3keV argon ion sputtering technique.
Keywords: X-ray photoelectron spectroscopy; X-ray fluorescence; Silver coins
Nonlinear optical effects from Au nanoparticles prepared by laser plasmas in water by E. Fazio; F. Neri (pp. 88-93).
► Au nanoparticles were synthesized by pulsed laser ablation in liquid. ► Nonlinear optical properties were investigated. ► Nonlinear optical mechanism is sensitive to sample's morphology.The optical limiting properties of Au nanoparticles prepared by laser generated plasmas in water were investigated. The ablation processes were carried out irradiating an Au target with the second harmonic (532nm) output of a Nd:YAG laser, changing the water level above the target, the lens position and the laser pulse energy. Different surface morphologies, from isolated nearly spherical nanoparticles to elongated structures, were observed by TEM imaging. A significant nonlinear optical response was probed by the Z-scan technique. The efficiency and the nature of the nonlinear response are found to be strongly dependent on the morphological properties of the nanostructures. The third order optical susceptibility χ(3) assumes the values of 1.83×10−6esu and 6.34×10−6esu for the smaller nanoparticles size obtained at the lower ablation energies (10–20mJ), 8.25×10−6esu and 2.13×10−5esu for the particles agglomerations obtained at the higher ablation energies (50–100mJ). The high value of χ(3) and the possibility to tailor the nonlinear optical response by changing the morphological properties of the Au nanostructures make them interesting materials for potential applications in the nonlinear optics field.
Keywords: Gold nanoparticles; Laser ablation in liquid; Optical properties; Morphology; Z-scan
Studies of intense-laser plasma instabilities by L. Láska; J. Krása; J. Badziak; K. Jungwirth; E. Krouský; D. Margarone; P. Parys; M. Pfeifer; K. Rohlena; M. Rosiński; L. Ryć; J. Skála; L. Torrisi; J. Ullschmied; A. Velyhan; J. Wołowski (pp. 94-98).
► Pinching of laser-produced plasma. ► Focus position dependence of partial ion group velocities. ► Oscillation dependence of ion peak current on laser focus position.The PALS high power iodine laser system in Prague ( λ=1.315μm) was used to study non-linear processes in a laser-produced plasma at intense laser beam interactions with planar targets. The focus setting allows to alter the non-linear interaction of the main laser pulse with the ablated plasma produced by the front edge of a nanosecond laser pulse (300ps FWHM). The arisen non-linear effects significantly influence the behavior of electrons, which accelerate fully striped or highly charged fast ions. Variations in time of the expanding plasma, recorded at the target surface by the use of Kentech low-magnification soft X-ray streak camera on ∼2ns time scale, are presented and discussed. Narrowing, arching and even splitting of expansion paths in the target-normal space-time diagram are shown. These phenomena are ascribed to the magnetic field, self-generated at high laser intensities, which may become strong enough to cause pinching of the expanding plasma.
Keywords: Laser plasma instabilities; Self-generated magnetic field; Longitudinal structure of the expanding plasma
Modification in polyethylene–iron oxide joints induced by laser irradiation by A.M. Visco; V. Brancato; N. Campo; L. Torrisi; F. Caridi; M. Cutroneo (pp. 99-103).
► The laser irradiation modifies the UH/UH–Fe2O3 joint at its interface for the filler presence. ► The filler amount controls the deepness of the modified material. ► Low filler amounts (<1wt%) produce joints with high mechanical strength and vice versa. ► The deepness of the seal can be regulated and applied to disparate geometries.The laser welding is a thermal bonding technique with high localized heating that produces a strong adhesion between polymers. The plastic is able to absorb the laser energy with the use of embedded fillers in itself. In this work we studied blends made by polyethylene and different amount of fillers (iron oxide, red color). Mechanical and physical analyses were performed with the aim to study the effect of filler percentage on the welding features.Experimental results showed that the filler amount influences the optical properties of the polyethylene since it regulates the amount of adsorbed energy and the depth of the material layers involved in the welding. A high concentration of filler improves the absorption laser energy, decreasing the layers involved in the welding and worsening the mechanical strength of the joint. Vice versa, a low filler amount involves deeper layers of the material so that the sealing action improves. The efficiency of the joint can be regulated by the filler concentration. Some applications of thermoplastic polymeric joints with different geometries are proposed and discussed.
Keywords: Laser irradiation; Polyethylene joints; Modification deepness; Mechanical performance
Analysis of laser-generated plasma ionizing radiation by synthetic single crystal diamond detectors by M. Marinelli; E. Milani; G. Prestopino; C. Verona; G. Verona-Rinati; M. Cutroneo; L. Torrisi; D. Margarone; A. Velyhan; J. Krasa; E. Krousky (pp. 104-108).
► Single crystal CVD diamond detectors were fabricated and employed to monitor the products of laser generated plasmas. ► Both the forward and backward expanding plasma was characterized by TOF technique. ► The proposed diamond detectors are able to measure UV, X-rays, electrons and ions simultaneously. ► The detectors showed fast response and good sensitivity to ions and electrons which are well separated from the photopeak.Diamond based detectors have been used in order to analyze the ionizing radiation emitted from the laser-generated plasma. High energy proton/ion beams were generated at Prague Asterix Laser System (PALS) Centre by the sub-nanosecond kJ-class laser at intensities above 1016W/cm2.The tested detectors consisted of a photoconductive device based on high quality chemical vapor deposition (CVD) single crystal diamond, produced at Rome “Tor Vergata” University. They have been operated in planar configuration, having inter-digitized electrodes.The proposed diamond detectors were able to measure UV, X-rays, electrons and ions. They have been employed in time-of-flight (TOF) configuration and their reliability was checked by comparison with standard ion collectors (mostly used at PALS). Both the forward and backward expanding plasma was characterized in the experiment. The results indicate that diamond detectors are very promising for the characterization of fast proton and ion beams produced by high power laser systems.
Keywords: Single crystal diamond; Diamond detector; Laser-generated plasma; Ionizing radiation; Time-of-fight spectrometer
Laser generated Ge ions accelerated by additional electrostatic field for implantation technology by M. Rosinski; P. Gasior; E. Fazio; L. Ando; L. Giuffrida; L. Torrisi; P. Parys; A.M. Mezzasalma; J. Wolowski (pp. 109-113).
► Electrostatic acceleration and deflection can enhance the quality of laser ion implantation. ► Performance of the electrostatic acceleration and deflection set-up was simulated and optimized with the Opera 3D code. ► The optimized system was tested in experiments with the ion time of flight ion measurements. ► Ion time of flight measurements confirmed the improvements due to the application of the electrostatic system. ► Results of the material research methods confirmed he improvements due to the application of the electrostatic system.The paper presents research on the optimization of the laser ion implantation method with electrostatic acceleration/deflection including numerical simulations by the means of the Opera 3D code and experimental tests at the IPPLM, Warsaw. To introduce the ablation process an Nd:YAG laser system with repetition rate of 10Hz, pulse duration of 3.5ns and pulse energy of 0.5J has been applied. Ion time of flight diagnostics has been used in situ to characterize concentration and energy distribution in the obtained ion streams while the postmortem analysis of the implanted samples was conducted by the means of XRD, FTIR and Raman Spectroscopy. In the paper the predictions of the Opera 3D code are compared with the results of the ion diagnostics in the real experiment. To give the whole picture of the method, the postmortem results of the XRD, FTIR and Raman characterization techniques are discussed. Experimental results show that it is possible to achieve the development of a micrometer-sized crystalline Ge phase and/or an amorphous one only after a thermal annealing treatment.
Keywords: Ion implantation; Germanium; Ions diagnostic; Structural properties
Electromagnetic and geometric characterization of accelerated ion beams by laser ablation by V. Nassisi; L. Velardi; D. Delle Side (pp. 114-118).
► Pulsed lasers at intensities of the order of 108W/cm2 and of ns pulse duration, interacting with solid matter in vacuum produce plasma of high temperature and density. ► A post-acceleration system, up to 160kV of accelerating voltage, can be employed to increase the energy of the extracted ions from the plasma plume. ► A study of the electromagnetic and geometric properties, like emittance, of the beams delivered by pure Cu, Y and Ag solid targets has been performed. ► The electromagnetic characterization of the plasma was performed by a Faraday cup, whereas the geometric one by a pepper pot system.Laser ion sources offer the possibility to get ion beam useful to improve particle accelerators. Pulsed lasers at intensities of the order of 108W/cm2 and of ns pulse duration, interacting with solid matter in vacuum, produce plasma of high temperature and density. The charge state distribution of the plasma generates high electric fields which accelerate ions along the normal to the target surface. The energy of emitted ions has a Maxwell–Boltzmann distribution which depends on the ion charge state. To increase the ion energy, a post-acceleration system can be employed by means of high voltage power supplies of about 100kV. The post acceleration system results to be a good method to obtain high ion currents by a not expensive system and the final ion beams find interesting applications in the field of the ion implantation, scientific applications and industrial use. In this work we compare the electromagnetic and geometric properties, like emittance, of the beams delivered by pure Cu, Y and Ag targets. The characterization of the plasma was performed by a Faraday cup for the electromagnetic characteristics, whereas a pepper pot system was used for the geometric ones. At 60kV accelerating voltage the three examined ion bunches get a current peak of 5.5, 7.3 and 15mA, with a normalized beam emittance of 0.22, 0.12 and 0.09πmmmrad for the targets of Cu, Y, and Ag, respectively.
Keywords: Ion beams; Cu, Y and Ag targets; Pulsed laser ablation (PLA)
X-ray emission analysis of a plasma source using an yttrium and a mylar target for the generation of 2.48nm wavelength microbeam by Libero Palladino; Ramon Gimenez De Lorenzo; Maurizio Di Paolo Emilio; Tania Limongi (pp. 119-123).
► The X-ray beam is generated from a plasma produced focusing a Nd-Yag/glass laser beam on mylar or yttrium target. ► At the wavelength of 2.48nm, a monochromatic soft X-rays beam was collected by multilayer spherical mirrors. ► In the Water Window region, Yttrium represents a good X-ray emitter.In this work, the characteristics of X-ray beam generated from a plasma produced by focusing a Nd-Yag/glass laser beam on mylar or yttrium target were presented.For each target material, the conversion efficiencies of the soft X-ray emission in two different energy ranges, (i) 300–510eV (almost coincident with the Water Window), (ii) 450–850eV were measured. The experimental results of the conversion efficiencies will be utilized at the PLASMA-X laboratory of L’Aquila University for the realization of an intense monochromatic X-ray microbeam to be used in radiobiological and in transmission X-ray microscopy applications. In the presented experimental set-up, at the wavelength of 2.48nm, a monochromatic soft X-rays beam was collected by multilayer spherical mirrors reflecting at an incidence angle close to the normal of the surface.The optical system geometry, the monochromatic beam intensity and the measures of efficiency of conversion of X-ray were described in this paper [5].
Keywords: X-ray microbeam; Plasma source
Production and acceleration of protons by Titanium Hydride solid disks via excimer laser ablation by D. Delle Side; L. Velardi; V. Nassisi (pp. 124-127).
► Titanium Hydride powder represents a widely available and cheap material. ► It is easy to obtain solid disks by compression of this powder. ► UV laser ablation of these disks represents a valid source of low energy protons.In this work we present the preliminary investigations about the production of proton beams by pulsed laser ablation of solid disks produced by compressed Titanium Hydride (TiH) powder. The laser we used was an excimer KrF, operating at low intensity and ns pulse duration. The ion emission was analyzed by the time-of-flight technique using a Faraday cup as ion collector. We performed initial studies on the produced plasma for different laser fluence values. In free expansion mode we obtained protons and titanium ions having kinetic energy of some hundred of eV; by applying a post-accelerating voltage we analyzed the beams up to 15keV.
Keywords: Laser ions sources; Protons; Pulsed laser ablation
Silicon carbide detector for laser-generated plasma radiation by Giuseppe Bertuccio; Donatella Puglisi; Lorenzo Torrisi; Claudio Lanzieri (pp. 128-131).
► Silicon carbide ionizing radiation detectors with 10fA and 0.2pA/cm2 at 30kV/cm. ► Acquisition and spectroscopy of radiation emitted by intense laser generated plasmas with a semiconductor detector. ► High amplitude signals (over 80V) from semiconductor radiation detectors with excellent signal to noise ratios. ► Nanosecond response and time resolution in particle time of flight measurements.We present the performance of a Silicon Carbide (SiC) detector in the acquisition of the radiation emitted by laser generated plasmas. The detector has been employed in time of flight (TOF) configuration within an experiment performed at the Prague Asterix Laser System (PALS). The detector is a 5mm2 area 100nm thick circular NiSiC Schottky junction on a high purity 4HSiC epitaxial layer 115μm thick. Current signals from the detector with amplitudes up to 1.6A have been measured, achieving voltage signals over 80V on a 50Ω load resistance with excellent signal to noise ratios. Resolution of few nanoseconds has been experimentally demonstrated in TOF measurements. The detector has operated at 250V DC bias under extreme operating conditions with no observable performance degradation.
Keywords: Semiconductor radiation detectors; Silicon carbide; Laser; Plasma; Radiation spectroscopy
Influence of the ablation threshold fluence on laser-driven acceleration by D. Margarone; A. Velyhan; L. Torrisi; M. Cutroneo; L. Giuffrida; A. Picciotto; J. Krasa; S. Cavallaro; J. Limpouch; O. Klimo; J. Psikal; J. Proska; F. Novotny (pp. 132-137).
Laser ablation threshold measurements has been carried out by the nanosecond-class Nd:YAG laser at LNS-INFN in Catania. Advanced targets, such as hydrogen-enriched silicon slabs and sub-micro structured polymeric samples, have been investigated. The estimated ablation fluences are correlated to recent experimental and theoretical results on high intensity laser driven ion acceleration. Characteristics of H-atoms/protons and heavier atoms/ions coming out from the bulk of the irradiated target or from surface contaminants have been determined by optical and time-of-flight spectroscopy as well as mass quadrupole spectrometry.
Keywords: Nanosecond lasers; Ablation threshold; Laser-driven acceleration
Radiation field characterization and shielding studies for the ELI Beamlines facility by A. Ferrari; E. Amato; D. Margarone; T. Cowan; G. Korn (pp. 138-144).
► Source term characterization of a laser-accelerated electron beam produced by an ultra-short pulse laser in the ultra-relativistic regime. ► 3-material shielding solution for the electron beam dump: particle fluence rates, H*(10) rates and deposited energy. ► Source term characterization of a high energy laser-accelerated proton beam. ► Optimization of a 3-material shielding structure for the proton beam dump.The ELI (Extreme Light Infrastructure) Beamlines facility in the Czech Republic, which is planned to complete the installation in 2015, is one of the four pillars of the ELI European project. Several laser beamlines with ultrahigh intensities and ultrashort pulses are foreseen, offering versatile radiation sources in an unprecedented energy range: laser-driven particle beams are expected to range between 1 and 50GeV for electrons and from 100MeV up to 3GeV for protons. The number of particles delivered per laser shot is estimated to be 109–1010 for the electron beams and 1010–1012 for the proton beams.The high energy and current values of the produced particles, together with the potentiality to operate at 10Hz laser repetition rate, require an accurate study of the primary and secondary radiation fields to optimize appropriate shielding solutions: this is a key issue to minimize prompt and residual doses in order to protect the personnel, reduce the radiation damage of electronic devices and avoid strong limitations in the operational time.A general shielding study for the 10PW (0.016Hz) and 2PW (10Hz) laser beamlines is presented here. Starting from analytical calculations, as well as from dedicated simulations, the main electron and proton fields produced in the laser-matter interaction have been described and used to characterize the “source terms” in full simulations with the Monte Carlo code FLUKA. The secondary radiation fields have been then analyzed to assess a proper shielding. The results of this study and the proposed solutions for the beam dumps of the high energy beamlines, together with a cross-check analysis performed with the Monte Carlo code GEANT4, are presented.
Keywords: Particle acceleration from laser-matter interaction; Shielding; Monte Carlo; Radiation protection