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The Front Surface Acceleration (FSA) obtained in Laser Ion Source (LIS) systems is one of the most interesting methods to produce accelerated protons and ions. We implemented a LIS to study the electric field responsible for the ion acceleration mechanisms. A high impedance resistive probe was used to map the electric potential inside the chamber, near the target. We detected the time resolved profiles of the electric potential moving the probe from 4.7 cm to 6.2 cm with respect to the main target axis. The corresponding electric field depends on the distance x as 1 / x α with α ∼ 1.8 . We suggest that the electric field strength stems from the contribution of an electrostatic and an induced field.

We studied the electron beam generated from a metal cathode illuminated by XeCl and KrCl excimer lasers below plasma ignition threshold intensities. By Langmuir-like probe measurements, positive potentials of about 0.75 V at distances down to 2 μm from the grounded target above the laser spot area were observed during the laser action. From this result and in the absence of an accelerating voltage, a positive charge near the cathode of about 3.3 mC/m3 was estimated. The strong charge density modified the accelerating voltage and under space charge regime, the output current was higher than that theoretically calculated. Therefore, under these conditions we solved the 1-D Poisson equation including the influence of the small radial beam dimension. The maximum experimental current density was 80 A/cm2 with a normalised emittance of 43 (π mm mrad) for an Al target at 40 kV accelerating voltage. Further studies of the plasma influence were performed with a large cross-section laser beam (90 mm2) and with anode-cathode distances larger and shorter than 90 π (mm) and neglecting the beam enlargement.

Magnetic field effects are diffused among living organisms. They are mainly studied with static or extremely low frequency fields, while scarce information is available for pulsed fields. This work is devoted to the study of the interaction between Drosophila melanogaster, both adults and larvae, and pulsed magnetic fields. We exposed the organisms to a peak field of 0.4 T, lasting for about 2 μ s, within an ad hoc designed copper coil. Adult individuals didn't present any deregulation of repetitive sequences in the germ line of Drosophila. Instead, we noticed a marked magnetic field effect in larvae. Polytene chromosomes coming from treated individuals showed the presence of heat shock puffs; the same organisms revealed also an upregulation of the genes encoding for the Hsp70 protein. These observations suggest that the larvae underwent an oxidative stress caused by the modulation of free radicals' yield induced by the magnetic field through a radical pair mechanism.

The generation of photoelectrons by an incident XeCl laser beam of 4.02 eV photon energy on three different targets, Y, Zn, and Ge, having work functions of 2.9, 3.9, and 4.8 eV, respectively, has been studied. Considering that the laser pulse has a trapezoidal evolution time and a rectangular spatial dependence, the evolution of the target temperature at the laser spot has been calculated. Using the computer code egun, the output current picked up by the collector resulted only of 44%, 42%, and 37% of the effective current for Y, Zn, and Ge, respectively, at 3 kV charging voltage. By utilizing the generalized Richardson equation which governs the generated current density, the dominant process existing during the laser‐matter interaction has been determined. During the electron extraction, plasma was formed on the target surface particularly at high laser energies and high accelerating voltages. This plasma introduces an impedance into the cathode‐anode region which shifts the Child–Langmuir law.

We report on the behaviour of electron beams extracted from metal cathodes illuminated by a powerful XeCl-laser beam. The target materials used were Zn, Y and Ge. During the electron extraction a plasma was created on the target surface. At high laser energies and high accelerating voltages the plasma introduces an impedance into the cathode-anode region. Owing to the plasma formation short-circuits occur in the accelerating region thus limiting the maximum output current. Under our experimental conditions, a laser energy of 27 mJ and 3 mm of distance cathode-anode, a maximum output corrent density of about 4.9 A/cm2 was obtained with the Zn cathode. The yttrium target may provide a higher current density but so far it could not be demonstrated due to plasma formation which short-circuits the anode-cathode region. The experimental results obtained with Ge targets are interesting for obtaining short electron pulses.

Experimental results are reported, concerning the energy coupling of laser light to metal (copper) surfaces. It is shown that besides the ignition and the evolution of a surface plasma—of either erosion of optical breakdown type—the formation of surface chemical compounds and the condition of the sample surface play key roles in the determination of the interaction process, finally determining the energy coupling efficiency of laser radiation to metal samples.

A positive and a negative branch confocal unstable resonator with magnification |M| = 10 and with an intracavity spatial filter have been applied to a high-gain short-pulse u.v. pre-ionized XeCl laser. The performance of both resonators has been investigated and compared.

Plasma bursts were produced by focusing excimer-laser (XeCl, 308 nm) pulses on Ge and Si targets. At moderate laser fluences (∼30 MW/cm2) high-intensity Ge3+ and Si3+ ion pulses were extracted from the laser-produced plasma. A peculiar electrical circuit allows a self-bunching of the beam. By time-of-flight method, the currents produced by the ions of different charge number were measured. Peak currents of 620 mA and 800 mA were recorded for Ge3+ and Si3+ ions, respectively, with an extraction voltage of only 400 V.

We report the details of a technique for the production of proton beams with very low energy spread exploiting the short soft X-rays obtained by laser ablation. These beams have been generated by the dissociation and ionization of an hydrogen buffer gas induced by the laser-plasma X-rays and then accelerated by means of an electrostatic accelerator. Their properties have been analyzed through the time-of-flight method applying different accelerating voltages. The resulting energetic spread ranges between 6 and 11%, as a function of the applied voltage. Such a system could be extremely useful for producing quasi-monoenergetic proton beams.

The direct synthesis of silicon oxinitride films by multipulse excimer (λ=308 nm) laser irradiation in a nitrogen‐containing ambient gas is reported featuring characteristics consistent with potential application in microelectronics.

A Monte-Carlo electron transport algorithm is described for transmission and energy loss calculation in the 10–1000 keV energy range. The results obtained considering homogeneous targets are in good agreement with experimental results and with computation with different Monte-Carlo and semi-empirical models. Our Monte-Carlo program (VALE) allows energy loss calculations in a non-homogeneous in-depth target, like layered materials. It produces good results for the energy loss calculation in metal/silicon systems, allowing confident computations of the thermal effects produced by electron pulses in layered samples (electron beam annealing).

The authors present the output characteristics of an excimer laser (XeCl and KrCl) with delayed double UV preionisation. He- and Ne-based mixtures were used for the XeCl laser and Ne-based mixtures for the KrCl laser, at pressures up to 7*105 Pa. For both lasers, maximum output energies (1.1 J/pulse at 308 nm and 0.3 J/pulse at 222 nm) were obtained for a delay time of about 290 ns between the onset of the preionisation and the breakdown of the laser gas. At a charging voltage of 50 kV, by varying the delay time from 140 ns to 290 ns, an improvement in the output energy of 16% for the XeCl laser and 22% for the KrCl laser was obtained. The improvement in respect of a single preionisation is about 18% for the XeCl laser with the He-based mixture, and about 14% for the XeCl laser with the Ne-based mixture.

The unsaturated losses α, and the saturation intensityIs, were measured in an uv-preionized KrCl laser for optimized He and Ne based laser gas mixtures. The measurements were made as a function of the specific power loading and of the total pressure of the laser mixtures. Higher values for α andI s were found for the Ne-based laser mixture than for the He-based mixture. At 45 kV charging voltage and at 355 kPa of total pressure we measured α=0.053 cm−1 andI s =9.4MW/cm2 for the Ne based mixture, and α=0.035 cm−1 andI s =5.1MW/cm2 for the He based mixture.

Atomic krypton was excited in presence of SF 6 by an intense electron beam. The radiation emitted by the Kr 2 F ∗ ( 2 B 2 → A 1 ) transition was studied at 430 nm using time resolved spectroscopic techniques. The radiative lifetimes of Kr 2 F ∗ and of Kr ∗ 2 were found to be 200 ns and 270 ns respectively.

An XeCl laser beam has been used to investigate stimulated Raman scattering in H2 and in various H2-foreign gas mixtures. Helium, neon, argon, and nitrogen have been tested as foreign gases. In all the investigated mixtures with 50% of H2, the energy conversion efficiency to the first Stokes (353 nm) was more than 70% higher than that obtained in H2 at the same total pressure (40 bar) and pump energy (60 mJ). The dependence of the energy conversion efficiency on pump beam divergence has also been investigated.

The effects of liquid chlorine donors (BCl 3 and CCl 4 ) on the output energy and the efficiency of a KrCl laser (222 nm) are investigated. Maximum laser energies of 230 mJ (3.3 J/l) in pulses of 16 ns duration were obtained from a 0.035% BCl 3 /10.1% Kr/89.8% Ne mixture at a total pressure of 2600 Torr, and at a specific power loading of about 24 MW/cm 3 , a power conversion efficiency of 0.86% was obtained. These figures are reduced by a factor of two when He is used as buffer gas. Much weaker laser emissions were obtained when CCl 4 was used as a chlorine donor.

Etude du chauffage d'une puce de silicium avec un revetement de 300 nm de platine, irradiee par un faisceau d'electrons pulses. Calcul des temperatures obtenu en fonction de la densite d'energie du faisceau et etude des couches de diffusion formees

Polycrystalline SiC layers were synthesized through nanosecond pulse heating of thin carbon films deposited on single-crystalline silicon wafers. The samples were submitted to electron beam irradiation (25 keV, 50 ns) at various current densities in vacuum (∼10−4mbar) and to XeCl excimer laser pulses (308 nm, 15ns) in air. Rutherford backscattering spectrometry (RBS) showed that in the e-beam annealed samples mixing of the elements at the interface starts at current densities of about 1200 A/cm2. The mixed layer thickness increases almost linearly with current density. From the RBS spectra a composition of the intermixed layers close to the SiC compound was deduced. Transmission electron microscopy (TEM) and electron diffraction studies clearly evidenced the formation of SiC polycrystals. Using the XeCl excimer laser, intermixing of the deposited C film with the Si substrate was observed after a single 0.3 J/cm2 pulse. Further analysis evidenced the formation of SiC nanocrystals, embedded in a diamond film.

The characteristics of electron beam pulses used for the annealing of ion implanted semiconductors and for silicon/metal reactions are given. Methods for the attainment of large area currents using different field-emission cathodes are discussed. Qualitative and quantitative systems for the evaluation of beam homogeneity (graphite films, thermoluminescent LiF crystal arrays, radiochromic films) are described together with results obtained by pulsed electron beam induced reaction in silicon/platinum systems.

Poly-crystalline silicon carbide layers were obtained through nanosecond pulse heating of thin carbon films deposited on silicon wafers. The samples were submitted to electron beam pulses (25 kev, 50 ns) at various current densities in vacuum (~10 −4 mbar) and to XeCl excimer laser pulses (308 nm, 15 ns) in air. Rutherford backscattering spectrometry (RBS) evidenced that in the electron beam annealed samples mixing of elements at the C Si interface starts at current densities of about 1200 A/cm 2 . The mixed layer thickness increases almost linearly with current density. From the RBS spectra a composition of the intermixed layers close to the SiC compound was deduced. Transmission electron microscopy (TEM) and electron diffraction studies clearly evidenced the formation of SiC poly-crystals. Using the XeCl laser, intermixing of the deposited C film with the Si substrate was observed after a single 0.3 J/cm 2 pulse. Further analysis evidenced the formation of SiC crystals, embedded in a diamond film.

Experimental Studies of the Stimulated Raman Scattering in H2 -Ar MixturesA.Luches, V.Nassisi and M.R.PerroneDipartimento di Fisica, Universita di Lecce, 73100 Lecce, ItalyAbstractStimulated Raman scattering experiments have been performed in H2 and H2 -Ar mixtures with an UV- preionizeddischarge laser (308 nm) as the pump. The energy conversion efficiency from the pump laser beam to Stokes be-ams has been investigated as a function of Ar concentration and pumping energy. It has been found that in theH2 -Ar mixture with 50% of Ar, the energy conversion efficiency to the first Stokes was more than 80% higherthan that obtained in H2 at the same total pressure (40 atm) and pump energy (60 mJ).IntroductionAt present there is a great interest in improving the performance of excimer lasers. Because of their highefficiency and short wavelength, excimer lasers are the most important drivers for high power laser - matterinteraction studies. Frequency shifting is widely investigated to improve the beam quality and to extend therange of application.Stimulated Raman scattering (SRS) in compressed molecular gases is one of the most efficient methods forshifting the output of high -power excimer lasers into the blue -green spectral region1 -3. which is of greatinterest for signal transmission through water. Hydrogen is expecially suited for this purpose, since it pre-sents both the largest Raman shift (4155 cm-1) and the largest gain4.When an intense laser beam is focused into a cell of a compressed molecular gas, the weak spontaneouslyscattered Stokes light is amplified by SRS at the expense of the pump field. As the first Stokes (S1) beamintensity becomes sufficiently high, it stimulates a second Stokes (S2) beam, and so on this process may rep-eat to produce higher Stokes beams5. Clearly, these last processes limit the energy conversion efficiencyfrom the pump laser beam to Sl, since they drain energy from the Si beam. Moreover, four wave mixing proces-ses of the pump beam and S1 can also produce S2 and higher order Stokes beams and so they limit the energyconversion efficiency to S1 still more. The four wave processes, like all parametric processes, have no thre-shold but require phase matching6. Then, this process can be minimized by the use of high pressure gas toincrease its linear dispersion, and also by utilizing a low -angle pumping geometry to reduce the angles whichlead to phase matching1-3.In the present work a XeC1 excimer laser (308 nm) was used to study SRS in H2 and H2-Ar mixtures. Our pri-mary goal was to investigate how the SRS and the four wave mixing processes in H2 are affected by the presence

Stimulated Raman scattering has been investigated in H2 and in different H 2 - foreing gas mixtures with a UV - preionized XeCl discharge laser (308 nm) as the pump. Helium, neon and nitrogen have been tested as foreing gases.The energy conversion efficiency of the pump laser beam to Stokes beams has been investigated as a function of the foreing gas concentration and of the pump beam energy. In all the investigated mixtures with 50 percent of H2, the energy conversion efficiency to the first Stokes was more than 70% higher than that obtained in pure H 2 at the same total pressure (40 bar) and pump energy (60 mJ).

Different mixtures containing atomic krypton and fluorinated compounds (Kr-NF 3 , Kr-SF 6 ) and atomic krypton, argon and fluorinated compounds (Ar-Kr-NF 3 , Ar-Kr-SF 6 , Ar-Kr-F 2 ) were excited with intense e-beam pulses. The fluorescence produced by Kr 2 F ∗ was studied using time resolved spectroscopic techniques. Rate constants for the production and quenching of Kr 2 F ∗ were deduced from the measurements. In all the mixtures used, at krypton partial pressure higher than about 100 mbar, direct production from Kr ∗ 2 is considered as the most important formation channel of Kr 2 F ∗ .

Diamond films with a thickness from submicron to a few microns were the choice to study the electron emission induced by UV laser pulses and by electric fields. One of the goals of the research was to compare photoelectron emission behaviour under irradiation with XeCl (λ=308 nm) and KrCl (λ=222 nm) laser pulses, i.e. with a photon energy being respectively smaller (4.02 eV) and larger (5.58 eV) than the diamond band gap. The effects of the film thickness (grain size) and post-growth plasma treatments on the photoelectron yield were also studied. In addition, the results on the field electron emission from these diamond films are presented. A correlation between the photoemission and field electron emission is discussed based on an analysis of deep level distribution in the films examined with a charge-based deep level transient spectroscopy (Q-DLTS). The role of defect states in the gap is shown to be important in the processes of electron emission from thin diamond films. It is pronounced in the wavelength-dependent photoemission behaviour and, especially, in the negative effect on photocurrent of the plasma treatments. The reduction of the photocurrent signals from both the H and Ar plasma-treated films was interpreted with the help of Q-DLTS spectra which give information on the parameters of electrically active defects (concentration, activation energy, capture cross-section). The field electron emission behaviour is shown to depend on the film thickness, and the lowest turn-on field of 25 V μm −1 was obtained for the thinnest diamond film.