1,721,024 research outputs found
Recombination processes during laser-plasma expansion of metal targets
No full textThis work has the purpose to characterize the plasma produced by solid target ablation. The experiment was performed by using a KrF laser with an irradiance of 108 W/cm2 and different solid targets, i. e., Si, Ge, Pd, and Pb. A very suitable Faraday cup has been utilized to study the angular distribution of the plasma plume as well as to perform measurements of the ion charge carried by the plasma during its free expansion into the vacuum. Particular attention was done to estimate the charge losses ascribed to the recombination processes during the plasma expansion
Si nanocrystals formation by a new ion implantation device
No full textMetallic and non-metallic ion beams can be used to modify the properties of wafer surfaces if accelerated at a moderate energy. We developed a new “implantation machine” able to generate ions and to accelerate them up to 80 kV. The ion generation is achieved by a laser-plasma source which creates plasma in expansion. The device consists of a KrF excimer laser and a generating vacuum chamber made of stainless steel. The laser energy was 45 mJ/pulse, providing a laser fluence of about 4.5 J/cm2 and a power density of 2.25x108W/cm2 by means a convergent lens. The target support was a stem mounted on an insulating flange and kept to positive voltage to accelerate the produced ions. The ion dose was estimated by a fast Faraday cup polarised at negative voltage. This machine was utilised to try synthesizing silicon nanocrystals in SiO2 matrix. In this work we present the preliminary results of Si ions implanted onto SiO2 films and the glancing-angle X-ray diffraction analyses
Low energy ion beams by laser interaction
No full textWe developed an ion accelerator with a double accelerating gap system supplied by two power generators of different polarity.-The ions were generated by laser ion source technique. The laser plasma induced by an excimer KrF laser, freely expanded before the action of accelerating fields. After the first gap action, the ions were again accelerated by a second gap. The total acceleration can imprint a maximum ion energy up to 160 keV per charge state. We analyzed the extracted charge from a Cu target as a function of the accelerating voltage at laser energy of 9, 11 and 17 mJ deposited on a spot of 0.005 cm2. The peak of current density was 3.9, 5.3 mA for the lower and medium laser energy at 60 kV. At the highest laser energy, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV. The maximum ion dose was estimated to be of 1012 ions/cm2. Under the condition of 60 kV accelerating voltage and 5.3 mA output current the normalized emittance of the beam measured by pepper pot method was 0.22 π mm mrad
Comparing of Soft X-Ray Pulses Induced by Different Metallic Plasmas
No full textIn this work, we report on the characterization of pulsed soft X-rays emitted from laser-produced plasma by different targets. The measurements were performed in a vacuum stainless-steel chamber at 10-7 mbar .The plasma was generated by a pulsed KrF excimer laser of 248 nm laser wavelength, operating at single shot and having a pulses of 23 ns FWHM. The beam was focused on pure Si, Cu and Ta targets. The laser energies were 40, 80 and 120 mJ, concentrated onto a spot of about 0.01 cm2, with a resulting irradiance of 1.7, 3.5 and 5.2x108 Wcm-2. The utilized detector was a very sensitive Faraday cup which opportunely biased was able to record time resolved signals of X-rays and to estimate their energy. The found X-rays energy values were compared to the ion temperature of the target plasma fitting the time resolved ion current signals by the shifted Maxwell-Boltzmann velocity distribution
Multi-Mode Velocity Distribution of Ions in UV Laser-Induced Plasma Plume
No full textWe study the velocity distribution of ions delivered by plasma whihs is induced by UV Laser
Short Soft X-Ray Sources
No full textIn this work we report on the characterization of pulsed soft X-rays emitted from laser-produced plasma. The plasma was generated by a pulsed KrF excimer laser focused on pure Si, Cu and Ta targets by 40, 80 and 120 mJ laser energies. The utilized detector was a very sensitive Faraday cup which opportunely biased was able to record time resolved signals of X-rays and to estimate their energy. The found X-rays energy values were compared with the ion temperature of the plasma obtained by fitting the time resolved ion current signals with a shifted Maxwell-Boltzmann velocity distribution. The results showed that the laser produced Ta plasma induced bunch of X-rays having in average the highest energy values and it was also characterized by ion temperature higher than the ones of the laser produced Si and Cu plasmas
Ion acceleration by a double stage accelerating device for laser-induced plasma ions
No full textA new LIS configuration was studied and realized in order to generate and accelerate ions of different elements. This ion source consisted of a laser-induced plasma from solid targets where the plume was made to expand before the action of the accelerating field. The accelerating field was reached by the application of two high voltage power supplies of different polarity. Therefore, the ions were undergone to double acceleration which can imprint a maximum ion energy up to 160keV per charge state. We analyzed the extracted charge from a Cu target as a function of the accelerating voltage at the laser fluence of 1.7 and 2.3 J/cm^2. At 60kV of total accelerating voltage and higher laser fluence, the maximum ion dose was of 10^12 ions/cm^2. Under this last conditions the maximum output current was 5 mA and the emittance measured by pepper pot method resulted of 0.22 π mm mrad. By this machine biomedical materials as UHMWPE were implanted with carbon and titanium ions. At doses of 6x10^15 ions/cm^2 the polyethylene surface increased its micro hardness of about 3-hold measured by the scratch test
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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