1,356,803 research outputs found
Simulating the tail of the interference in a Poisson network model
No full textInterference among simultaneous transmissions represents the main limitation factor for the capacity and connectivity of dense wireless networks. In this paper we provide efficient simulation laws for the tail of the interference in a simple wireless ad hoc network model. Particularly, we consider node locations distributed according to a Poisson point process and various classes of light-tailed fading distribution
neutron source controlled by high‐intensity pulsed laser generating plasma
No full textA laptop neutron source suited for the most demanding field or laboratory applications is presented. It is based on laser ablation of CD2 primary targets, plasma acceleration of the D+ ions, and their irradiation of secondary CD2 targets. The deuterium–deuterium (D-D) fusion reaction is induced in the secondary target, according to the values of fusion cross-section versus deuteron energy, which show a significant probability also at relatively low ion energies. The experiments were completed in the PALS laboratory, Prague, detecting monoenergetic neutrons at 2.45 MeV with an emission flux of about 109 neutrons per laser shot. Other experiments demonstrating the possibility to induce D-D events were performed at IPPLM, Warsaw, and at INFN-LNS, Catania, where the deuterons were accelerated at about 4 MeV and 50 keV, respectively. In the last case, a low laser intensity and a post-ion acceleration system were employed. A special interaction chamber, under vacuum, is proposed to develop a new source of monochromatic neutrons or thermalized distribution of neutrons
SiC and Ion collectors as diagnostics of laser-generated plasma at intensity of 10 10 W/cm 2
No full textCharacterization of non-equilibrium plasma by 10(10) W/cm(2) IR pulsed laser irradiating metallic targets in a vacuum, has been performed employing a Faraday cup as an ion collector (IC) and a SiC interdigitated detector, connected in time-of-flight (TOF) configuration.Both detectors reveal the emitted fast UV and the slower plasma ions. The measure of energy of ions and photons has been evaluated using the TOF spectra and thin absorbers.The fast semiconductor response and its high detection efficiency give a good benchmark measurement of radiations at low energy emitted by plasma generated by ns laser pulses. Thanks to the IC detector response it is possible to evaluate the ion current emitted from the plasma. The simultaneous use of the two detectors allows to monitor and evaluate different plasma parameters, such as the time emission, the temperature, the maximum particle energy and charge state, and others
Laser ablation parameters influencing gold nanoparticle synthesis in water
No full textThe synthesis of gold nanoparticles using pulsed laser ablation in water has special interest in many scientific fields. The nanoparticle production in solution employing an Nd:YAG laser depends mainly on the laser parameters (i.e. by the wavelength, the pulse energy and duration), on the irradiation conditions (target depth in water, focal spot, repetition rate, irradiation time), and on the medium where the ablation occurs (water, solution concentration, presence of surfactants). Optimal conditions can be found in order to control the particle size, the size distribution, and the coalescence effect. A study of these characteristic factors is presented here and discussed
Aluminum ion plasma monitored by SiC detectors from low to high laser intensity and from ns up to fs pulse duration
No full textThick and thin films of Al targets were irradiated in vacuum with different IR lasers at intensities between 1010 W/cm 2 and 1019 W/cm2, with pulse duration ranging between 3 ns and 45 fs. The laser-generated plasma was monitored in forward and backward directions, from thin and thick targets, by using SiC detectors, ion collectors, ion energy analyzer, optical spectrometer, Thomson parabola spectrometer and X-ray streak camera. Ion emission shows a maximum ion acceleration proportional to the laser intensity, which reaches about 1 MeV per charge state at 1016 W/cm2. Using fs laser, Al ion acceleration occurs at energies up to about 26 MeV and protons are accelerated at energies up to about 2.0 MeV. In the used experimental conditions, the maximum ion acceleration can be controlled by the laser parameters, irradiation conditions, and target geometry, such as the pulse energy, the focal position and the target thickness. Although different lasers and irradiation conditions were employed, the produced ion charges per solid angle of detection remain comparable, as it will be discussed
Shockwave and spallation in silver and other materials by sub-ns laser pulse at 10^16 W/cm^2 intensity
No full textThe laser spallation effect due to intense shockwaves caused by a brief and intense laser pulse irradiating a target surface, 2 mm thick, has been investigated for silver and other materials. For 300 ps IR laser pulse, at intensities of the order of 10(16) W/cm(2), the shockwave may produce deformations of the back-face in ductile materials, such as Ag, Cu and Al. In heavy materials with high tensile strength, such as Ta, the shockwave produces cracks in the bottom of the laser crater but not deformation in the back-face, while in brittle materials, such as monocrystalline Ge, it produces only superficial cracks and flaking, but not deformation and spallation of the back-face. In thick polymeric materials, such as high-density polyethylene, the ablated crater shape is well defined and the shockwave is strongly damped, and no deformation has been observed in the back-face. The laser ablation yield and the ion acceleration in the backward direction have been measured by mass lost and time-of-flight measurements. SEM microscopy of the different irradiated targets, showing details of the crater size, edges, flaking and deformation in the back-face, useful for a discussion on the shockwave propagation and shock pressure calculation, is presented
Laser ablation of boron nitride in vacuum and in water
No full textThe laser ablation of boron-nitride (BN) ceramic was employed for the preparation of thin films in high vacuum and nanoparticles and nanocrystals generated in water. The obtained plasma was investigated using ion detectors to determine the ion velocity, the energy per charge state and the plasma temperature and describing the acceleration mechanism. The kinetics of laser ablation in water and the comparison of different ablation rates in the vacuum and in water, and the possible applications of the BN thin film and nanoparticles are presented and discussed
laser ablation in vacuum and in water to deposit thin films or to generate nanoparticles in solution
No full textAn ns Nd:YAG pulsed laser was used to deposit thin films in a vacuum and to generate nanoparticles in the water of Ni, Ti, and NiTi alloys. Laser ablation was measured in terms of removing mass per laser pulse. The laser-generated plasma in vacuum was characterized in terms of temperature and energy of emitted particles. The ablation in water produces nanoparticles with dimensions of the order of 25 nm and solutions with concentrations of the order of some mg/ml. The NiTi alloy stoichiometry is well reported in the deposited thin film and in the composition of the produced nanoparticles
Pulsed laser cleaning (PLC) applied to samples in cultural heritage field
No full textThe pulsed laser cleaning (PLC) technique employing different laser wavelengths, with a ns pulse duration, is presented. Such a technique can be applied to the preservation of cultural heritage artworks on different materials, like metals, ceramics and glasses to clean the surfaces of debris accumulated over the years, to remove the oxidation layers, the dust, the organic materials and other unwanted layers, restoring their original composition and shape. PLC should be preceded by surface analyses to control the state of the surface before and during the cleaning process, which has to be carefully controlled, in order to stop the cleaning before to damage the underlying original surface. PLC examples, applied to metals, terracotta and glazy ceramics, are presented and discussed using IR, visible and UV pulsed laser irradiations at low intensity
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