Search

A 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.

High intensity ion beams can be obtained by laser plasma or applying high electric fields or utilising large acceleration gaps. We get it developing a double acceleration gap system supplied by two power generators of different bias voltages. In this way we realized a new LIS accelerator configuration in order to produce and to accelerate ions of different elements. The LIS consists of a laser-induced plasma from solid targets, where the plume freely expands before the action of the accelerating fields. Our system provides ion beams of maximum energy up to 160 keV per charge state. We extracted charge from a Cu plasma as a function of the accelerating voltage at laser fluence values of 1.8, 2.2 and 3.4 J/cm 2 . At 60 kV of total accelerating voltage, the peak currents were 3.9 and 5.3 mA corresponding to 1.8 and 2.2 J/cm 2 laser fluences, respectively. At the highest laser fluence, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV and a corresponding ion flux of 10 12 ions/cm 2 . Under the condition of 60 kV accelerating voltage and 5.3 mA output current (ion flux 3.4×10 11 ions/cm 2 ) the normalized emittance of the beam measured by pepper pot method resulted of 0.22π mm mrad. Under the condition of 160 kV accelerating voltage the ion flux was higher than 1.0×10 11 ions/cm 2 .

New photo-injector sources having fast response time, long lifetime and relatively high-quantum efficiency (QE) are very needed for many applications. Metallic cathodes are promising candidates to supply high-intensity and good quality electron beams. We carried out measurements utilising thin films and a smooth bulk made of yttrium (Y). The Y thin films were produced by pulsed laser deposition (PLD, using a XeCl excimer laser) in high vacuum. It was covered, in situ, by a gold film to avoid oxidation. The Y smooth bulk was mechanically processed in air. The laser used to get experimental values of photoemission was a KrF excimer laser of 5 eV photon energy and 23 ns pulse duration. The maximum accelerating voltage applied to the photodiode (the anode) was+25 kV. The measurements of photocurrent were performed at different laser energies. We found that the output current was depended on the cathode surface. The higher QE values were obtained for the smooth cathode. It provided a maximum output current of 8.4 A, at 25 kV and 12 mJ laser energy. The maximum QE was 7.0x(10)^-5.

In this work, the photoemission performance of rough and smooth cathodes is presented. The cathodes were made up of pure yttrium metal bulk. For evaluation of the photocathodes, a KrF excimer laser, operating at 248 nm wavelength, 5 eV photon energy and 23 ns full width at half maximum (FWHM) was used. The targets were tested in a vacuum photodiode cell at 10^(-7) mbar; they were irradiated at normal incidence and the anode-cathode distance was set to 5 mm. The measurements were performed after a series of electric breakdowns between anode and cathode, induced under high laser energy and high accelerating voltage. This operation was performed in order to restore/increase the surface roughness. For the rough cathode, the maximum output current was 10.5 A, reached at 25 kV and 12 mJ laser energy; the maximum quantum efficiency (QE) value was 1.3 x 10^(-4), whereas for the smooth cathode, the maximum output current was 8.4 A and the maximum QE value was 7.0 x 10^(-5), calculated in the same experimental conditions. The temporal behavior of photoemission from these cathodes was studied. Plasma production and Schottky effect played a fundamental role in this process.

X-ray radiation is generated by laser induced plasma also at very low laser fluence. In this work the diagnostic of a pulsed X-ray source utilizing as detector a very sensitive fast polarized Faraday cup is described. The plasma was generated by a pulsed KrF excimer laser focused on a pure copper target. The X-ray energy was studied at 30 and 102 mJ laser energy focused by a convergent lens of 15 cm focal length which provided an intensity of 1.3x108 and 4.5x108 Wcm-2, respectively. The maximum X-ray energy was approximately 1 keV for the both laser energies, whereas the energy peak value was of about 140 eV for the lower laser energy and about 160 eV for the higher. This behavior was compared with the calculation of plasma temperature performed by the Faraday cup at long time. The plasma temperature was determined by the best fit of the modified Maxwell-Boltzmann equation which resulted of about 600 kK (57 eV) and 970 kK (84 eV) for the lower and higher applied laser energy. Such a source is useful for studying on living cells and on sequencing of DNA.

In this work we present the experimental study and a theoretical approach of the photoemission of rough and smooth photocathodes. The cathode bulk was made of pure yttrium while its surface was morphologically modified. The cathode surface was irradiated by a KrF excimer at normal incidence with the anode-cathode distance set to 5mm. The measurements were performed after electric breakdowns between anode and cathode, induced under high laser energy and high accelerating voltage. This operation was made in order to increase the surface roughness. For the rough cathode the maximum output current was 10.5 A, reached at 25 kV and 12 mJ, with a maximum quantum efficiency value of 1.3×10-4. Instead, under the same experimental conditions the smooth cathode provided an output current of 8.4 A with a maximum quantum efficiency value of 7.0×10-5. We can conclude that in this process the plasma production and the Schottky effect play a fundamental role.