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Short current pulses are very diffuse and have also been used in many electronic devices for biological stress recently. In order to measure these current pulses, Rogowski coils are applied. In this work, we focus our efforts on the structure of the Rogowski box, which has a narrow slit, needed to correctly lead the current to be diagnosed. The attenuation coefficient depends mainly on the inductance values, the load resistance, and the virtual capacitance between coil and ground. Until now, the influence of the slit length and its width was never considered. We have studied, either theoretically or experimentally, the influence of the slit dimensions on calibration factor variations. The attenuation factor ranged from 11.3 to 16.3 A/V for s ranging from 0.8 to 0.2 mm, respectively. The device we realized is able to perform precise measurements of sub-nanosecond rise time pulses (∼100 ps).

Zebrafish (Danio rerio) embryos were subjected to different physical stresses, consisting of a static and two low frequency magnetic fields, and two radiofrequencies. Embryos were exposed to static (Bo, 0 Hz), very low frequency (VLF, 0.2 Hz), low frequency (LF, 270 kHz), very high frequency (VHF, 100 MHz), and ultra-high frequency (UHF, 900 MHz) magnetic field irradiation for up to 5 days. The field intensities were 40 mT, 40 mT, 470 µT, 240 nT and 240 nT, respectively. Untreated embryos were used as control.(n= 10 for each condition).

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.

It is known that exposure of a target to a focused laser beam results in the occurrence of a time-varying current between the target and the grounded vacuum chamber. This current is composed by three distinct phases, namely, the ignition phase, in which the laser pulse drives the electron emission, while electrons coming from the ground through the target holder balance the positive charge generated on the target. The active phase appears at post-pulse times and it is characterized by the presence of peaked structures in the time-resolved current, representing characteristics of the target composition. Finally, the afterglow phase is determined by a current of electrons flowing from the target to the ground. In the active phase of target current resulting from polymers ablation with an UV $${\mathrm {KrF}}$$ laser, negative target current peaks have been observed, whose origin is still unknown. We investigate the dependence of these current structures on the dimensions of the target, using ultra-high molecular weight polyethylene disks of different thickness. We provide evidence to explain the origin of such negative peaks. We found, indeed, that target initially charges positively under the action of the laser pulse, leading to a first negative target current peak. Then, a net charge unbalance is produced that further attracts free electrons on target surface. This behavior is enhanced if an opportune static electric field is imposed between the target and an opposite electrode.

The exposure of a target to a focused laser beam results in the occurrence of a time-varying current between the target itself and the grounded vacuum chamber. This current is composed by three distinct phases, namely the ignition phase, in which the laser pulse drives the electron emission, while electrons coming from the ground through the target holder balance the positive charge generated on the target. The active phase appears at post-pulse times and it is characterized by the presence of peaked structures in the time-resolved current, representing characteristics of the target composition. Lastly, the afterglow phase is determined by a current of electrons flowing from the target to the ground. During the active phase of the target current resulting from polymers ablation with an UV KrF laser, negative target current peaks are observed, whose origin is still unknown. We investigate the dependence of these current structures on the dimensions of the target, using ultra-high molecular weight polyethylene disks of different thickness.

In light of recent speculations on a potentially increased speed of the radioactive decay of $\ensuremath{\alpha}$-emitters embedded in a metallic matrix at very low temperature, four high-purity Cu disks deep-implanted with $^{209}\mathrm{Bi}$ were prepared. The disks were irradiated in a high-flux reactor to transmute the $^{209}\mathrm{Bi}$ into $^{210}\mathrm{Po}$. After the irradiation, the $^{210}\mathrm{Po}$ activity was measured for all four disks. While two of the disks were stored at room temperature, the other two disks were stored in a sealed container submerged in liquid helium ($T=4.2$ K) for approximately 200 days. After the storage time the $^{210}\mathrm{Po}$-activity measurements were repeated and the $^{210}\mathrm{Po}$ half-life was calculated for each sample. No difference between the half-lives for the four samples could be detected within the uncertainties of the measurements. In other words, the results of this study show no evidence for an increase of activity for $\ensuremath{\alpha}$ emitters embedded in a metallic matrix at very low temperature.

The electromagnetic and geometric characteristics of electron beams generated by molybdenum cathodes illuminated by an excimer laser are reported. To determine the electromagnetic characteristics, a fast Rogowski coil was utilized, while the geometric characteristics were performed by a suitable slit–slit meter system. During the experiment the laser spot on the cathode was fixed to 4 mm2. The maximum output current (370 mA) was reached with 0.5 mJ laser energy and 50 kV accelerating voltage. In these conditions the electron beam normalized emittance was 6 (π mm mrad) calculated at 80% level current density. The laser used in this experiment was a singular excimer laser (KrCl) operating in the NUV range.

In this work, the generation and the characterization of high current electron beams from rough photocathodes induced by an ultraviolet excimer laser are reported. The cathodes were rough Cu disks. In order to study the influence of the cathode surface, the electron emission from different surface roughnesses was investigated. To establish the electromagnetic and geometric parameters a Rogowski coil and a new slit–slit emittance meter were used. The laser beam utilized was obtained by a mixture of Kr and Cl which generated coherent light at 222 nm. Fixing the laser energy at 0.5 mJ and the laser spot into 4 mm2, the maximum current as well as the maximum emittance value were obtained with the cathode that had the highest surface roughness which resulted in 1 A and 46 π mm mrad, respectively. A low current and a low emittance were obtained with the cathode that had the lowest roughness, namely, 410 mA and 19 π mm mrad, respectively. A quantum efficiency value of 1.2×10−4 was reached with the cathode with t...

This work reports on electron beam characteristics obtained from a Cu photocathode utilizing an UV excimer laser of 222 nm for the first time. The values of the current, emittance, and brightness of the electron beams generated are reported. A suitable slit–slit emittance meter was developed to assess the electron beam emittance. This instrument allowed us to determine the electron beam phase-space areas by slicing the beam in small beamlets and measuring the beamlet direction distributions. Small Faraday cups placed after the slits were utilized to this reason. The laser beam was focused in a 4 mm2 spot and the maximum energy laser was established to 0.5 mJ. The highest current was 410 mA and the corresponding normalized emittance value was 10 π mm mrad corresponding to 80% of the total points. From these data the beam quality, expressed as normalized beam brightness, resulted in 4.1×109 A[π m rad]−2 and the quantum efficiency was 4.6×10−5. By increasing the KrCl laser spot and its energy a very charge e...

The effects of the surface modification of diamond films with thin Ni layers and of the influence of the Ni/diamond structures, on photoelectron emission induced by KrCl excimer laser (222 nm wavelength) pulses of a nanosecond duration, were studied. The Ni/diamond structures were prepared by deposition of ultrathin nickel coatings (≈2 nm thick) onto 1 μm thick diamond films on Si. The photocurrent induced by the UV laser pulses from a Ni-coated diamond surface was found to increase as compared with the photocurrent from the original film surface. Using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) techniques, the electronic structure of the Ni-coated and as-grown surfaces, and the chemical state of nickel and surface band bending, were investigated. It is discussed that the formation of the downwards band bending and a lowering of the surface work function are responsible for the observed enhancement of laser-induced electron emission from the Ni-coated diamond films.

Stimulated rotational and vibrational Raman scattering in H/sub 2/ was investigated with a circularly and a linearly polarized XeCl laser beam and the influence of the focusing geometry on the threshold for rotational and vibrational scattering, respectively, was studied. It is shown that with a circularly polarized pump beam a high-angle focusing geometry allows to get only rotational Raman scattering, whereas a low-angle focusing geometry provides only vibrational Raman scattering for gain suppression effects.

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.

Due to the growing demand for high-current and long-duration electron-beam devices, laser electron sources were investigated in our laboratory. Experiments on electron-beam generation and propagation from aluminium and copper targets illuminated by XeCl (308 nm) and KrCl (222 nm) excimer lasers, were carried out under plasma ignition due to laser irradiation. This plasma supplied a spontaneous accelerating electric field of about 370kV/m without an external accelerating voltage. By applying the modified one-dimensional Poisson equation, we computed the expected current and we also estimated the plasma concentration during the accelerating process. At 40 kV of accelerating voltage, an output current pulse of about 80 A/cm(2) was detected from an Al target irradiated by the shorter wavelength laser.

Experiments on electron‐beam generation from an Al target illuminated by XeCl and KrCl excimer lasers were carried out under plasma ignition threshold intensities. Direct experimental evidence of such a plasma formation under ignition threshold is given for the first time. By Langmuir‐like probe measurements, positive potentials as large as 0.36 and 0.75 V at distances down to about 2 μm from the grounded target over the laser spot area were reproducibly observed during the XeCl and KrCl laser action, respectively. From this result and in absence of cathode voltage, an accelerating electric field on the target of about 375 kV/m was estimated. The highest positive charge density near the cathode that resulted was about 3.3 mC/m3. The strong electric field caused by the plasma formation modified the acceleration conditions for a space‐charge dominated electron beam and it should be the main cause of the discrepancies between the experimental current values and the calculated ones.

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.

We propose a method to estimate a precise value for the critical distance Lcr after which three-body recombination stops to produce charge losses in an expanding laser-induced plasma. We show in particular that the total charge collected has a ``reversed sigmoid'' shape as a function of the target-to-detector distance. Fitting the total charge data with a logistic related function, we could consider as Lcr the intercept of the tangent to this curve in its inflection point. Furthermore, this value scales well with theoretical predictions. From the application point of view, this could be of great practical interest, since it provide a reliable way to precisely determine the geometry of the extraction system in Laser Ion Sources.

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.

High energy excimer laser photons favour the generation of heavy ions as well as the generation of electrons from metal targets. This experimental work reports the generation of lead ions extracted from a hot laser-generated plasma and the generation of electrons from yttrium targets having a work function of 3.1 eV, both by an XeCl (4.02 eV) excimer laser. At laser fluences of 75 MW cm 2 , an output beam formed by Pb3+, Pb2+ and Pb1+ ions was extracted. With an acceleration voltage of 500 V between the Pb target and the collector, the peak current of the Pb3+ pulse was 1.4 A large. Besides, the application of a low value capacitance in the accelerating region, allowed the extraction only of the highest charge ions. Modifying the acceleration chamber and applying an accelerating voltage of 10 keV, an output electrons beam having 15.6 nC (3.6 A cm 2 peak current) was obtained from Y targets.

In this experimental work, the generation of electrons induced by an XeCl excimer laser of 4.02 eV photon energy, on a Zn target having a work function of 3.9 eV, has been studied. During the laser illumination the target temperature was time dependent and this behavior strongly influences the electron emission. In fact, if the laser pulse is long enough, the electron emission increases at the laser pulse tail. To explain the experimental results, numerical calculations of the generalized Richardson equation were performed. The maximum current density obtained was 5 A/cm 2 and the total charge extracted was 11.6 nC/bunch.

Presented are the results of an experimental study on the operation of a folded self-filtering unstable resonator having a beam splitter as output coupler, applied to an XeCl laser. The output energy, the near- and far-field performance, the pulse rise times and the pulse duration times were investigated and they were compared to those obtained by an equal magnification aligned self-filtering unstable resonator having a scraper as output coupler. As a result it comes out that the fold resonator gives uniform near-field distribution and low energy in contrast to the aligned resonator, which gives near-field distribution with strong diffraction effects and higher energy.

The backward stimulated Raman scattering in CH 4 has been investigated using a XeCl laser beam of narrow bandwidth and good optical quality and varying the Raman medium pressure. It has been found that increasing the CH 4 pressure the backscattered laser beam energy increases too, as predicted by theory, while the pulse temporal evolution suffers strong modifications due to the formation of relaxation oscillations. The experimental conditions in order to get a single and short pulse are given.

In this experimental work, the SBS and SRS processes were used in order to produce UV laser beams of good optical quality and short time duration. An XeCl oscillator and a double-pass amplifier with a phase-conjugate mirror via stimulated Brillouin scattering, generate the laser beam at 308 nm to pump a Raman cell. The oscillator pulse was 11 ns long, while the amplified phase-conjugate beam duration could vary from 3.3 to 1.5 ns, due to the compression operated by the Brillouin mirror. When this last laser beam was focused into a Raman cell containing methane at 30 atm, the shortest backward stimulated Raman scattering pulse at 338.4 nm was 170 ps long with 0.4 ml of energy. The 338.4-nm wavelength is interesting for the production of short bunches of cold electrons from Mg and Zn targets. >

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 changing its characteristics at a laser intensity threshold of 1014 W/cm2. 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 but it also shows irregular and intense outbursts of ions similar to a self pulsing instability leading to a chaos. The sequence of fast ion outbursts visible on time‐of‐flight spectra is sensitive to details of non‐linear interaction of the sub‐nanosecond laser beam with the generated plasma.

Multiple charge heavy ion pulses were extracted from a plasma produced by an XeCl excimer laser beam at a relatively low flux (∼ 30 MW/cm2) focused on Si, Ge, Mg and Zn targets. An output peak current of Si3− ions of 375 mA was recorded at an acceleration voltage of 200 V only. The insertion of a variable capacitance between the target holder and the acceleration electrode allows a self-bunching of the ion beam. When a W target was used, a higher incident laser flux (∼ 90 MW/cm2) was necessary in order to produce ions from it.

Confocal and non-confocal negative branch unstable resonators with an intracavity spatial filter have been applied to a high-gain short-pulse UV preionized XeCl laser. The near- and far-field radiation characteristics have been investigated in both configurations. Laser beams of larger brightness have been obtained with non-confocal schemes. A maximum beam brightness of 1.3×1014 Wcm−2Sr−1 has been achieved.

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 porous silicon based hydrogen filter has been designed in STMicroelectronics RD so a working temperature ranging between 200 and 500 O C is requested to obtain proper flow rates. Moreover, the cost of Pd alloy membranes as purifiers is quite high, due to the thickness of the Pd alloy foil able to withstand at high permeation pressure gradients. In order to improve the performance of a device like that described above, in the STMicroelectronics it has been proposed a new design in which a very thin Pd layer (500 nm) on a porous silicon substrate (200 pm thick) allows to obtain high flow rates using a very small amount of the precious metal (Pd), with no mechanical filter robustness degradation. The thickness of the porous substrate, as well as the design of the polymer sustain, will be evaluated.

In this paper, a compact XeCl laser system made up of an oscillator and an amplifier is described. By applying to the amplifier a stimulated Brillouin scattering mirror (SBSM), an output laser beam of optical and spectral characteristic very close to those of the oscillator has been obtained. By realizing a phase conjugate cavity, 1.6 m long, formed by a SBSM and a quartz flat window, a pulse train made of pulse separated by the cavity round trip time has been obtained. The first pulse was 8 ns long while the last pulse was shorter than 2 ns.

We present a very compact and very reliable laser system formed of two discharge sections both with lateral UV preionization. The discharge electrodes are contained in a single vessel and form an oscillator-amplifier system. A single spark gap switches on both circuits. By applying a generalized self-filtering unstable resonator to the oscillator and injecting the laser beam into the single pass amplifier, an output beam of 105 mJ, with a brightness of 5.5×1013 W cm−2Sr−1 has been obtained. Moreover, by applying a pulse-forming network in one discharging circuit, the duration of the discharge breakdown has been increased and output laser pulses of 40 ns FWHM, and 80 ns base width duration (at 10% points) and of energy 100 mJ are obtained.

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.

High brightness electron beam (e-beam) injectors are necessary for seeding the new accelerators. The RF photocathode guns have confirmed the possibility of getting emittances much lower than those provide by thermionic source.1 In particular, metal photocathodes seem to be very promising for their capability to work in degraded vacuum and to work with excimer lasers. They seem also very promising in getting emittances much lower than those provide by thermionic source.2

In this work a new circuit to compress a pulse current utilizing transmission lines and transistor switches is proposed. It demonstrated a time compression factor of 2 on a low load impedance. A 12 m, 50Ω coaxial transmission line provided a current pulse of 3 A, 120 ns. A 6 m, 50Ω storage line connected to main line was able to store the 50% of the initial pulse. A fast switch was used in order to close both lines on a halved load impedance with respect to the transmission line characteristic one. We obtained a current pulse compression recording an output current of 6 A, 60 ns.

An new concept to get high current pulses by transmission lines has been developed. Utilizing two 50 W transmission lines and a fast transistor to switch on the circuit, a rectangular current pulse without the reduction to a half of its intensity has been obtained. 8 m long transmission lines were charged up to 1 kV. They yielded a current pulse of 20 A, 500 V of maximum voltage. Similar set up opens applications in the field of high current short pulse generators.

In this work we present the experimental results concerning the study of the plasma produced by pulsed laser irradiation of a copper target. The analysis of the generated plasma plume was performed for three different laser spot sizes determining the threshold conditions of the ablation process. A diagnostic system with a Faraday cup was developed in order to detect the ion current along the propagation tube. Time-of-flight (TOF) measurements were performed, and an adjustable voltage electrostatic barrier was employed in order to analyse the kinetic energy of the produced ions. To study the plasma characteristics we evaluated the total etched material per pulse, 1.8x1016 atoms/cm 2 , and the fractional ionisation, 36%. A modified Maxwell-Boltzmann distribution was applied to provide a consistent description of the velocity distributions in the plume. The ablated material was spatially monitored by optical transmission analysis of a deposited film.

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.

We report on the photoemission of electrons from a GaAs cathode illuminated by a circular polarised laser beam. The maximum output current intensity was 28 mA with 8.8 mJ laser energy. The quantum yield was 1.5x10^{-7}. This value was limited either to the GaAs work function or the optical transitions involved during the polarised light interaction. Measurements with a no-polarised laser beam were also performed.

In this work we studied an electron beam source using an KrCl excimer laser and three Cu cathodes having three different roughness values: 0, 3.5 and 9 µm. The experimental apparatus is shown in Fig.1. The laser beam illuminated the cathodes by a convergent lens accelerating the electrons generated from cathode. The electron beam total current was monitored by a fast Rogowski coil while the beam quality was estimed determining the beam emittance. For this last measurements a slit-slit method was used1. Namely, the electron beam was selected in small beamlets by the first slit array and the beamlet direction spread was monitored moving the second slit arrays and measuring the current by the small Faraday cups, see Fig. 1.

This work reports on the experimental results concerning electron beam emittance and current photo-extracted from aluminium, zinc and copper targets utilising two excimer lasers of different wavelengths, 308 nm (XeCl) and 222 nm (KrCl). The maximum laser energies utilised were limited by the high plasma density on the cathode that short-circuited the diode gap. The output current was higher with the KrCl laser than with the XeCl laser for the three metals used. The maximum extracted current, 1.03 A, was obtained with Cu targets at 20 kV of accelerating voltage, while at the same acceleration voltage a computer simulation of a space-charge limited electron beam resulted in a total current of only 200 mA and a normalised emittance of 22π mm mrad. The output current for large anode-cathode distance was higher than that predicted by the Child-Langmuir law while for small distances the current was lower than that theoretically calculated. This behaviour was attributed to plasma formation on the cathode during the laser action.