A novel technique for ion implantation of electronics materials by means of a laser ion source emitting multi-energetic ion streams was investigated. A UV pulsed laser beam, at intensities of the order of 10<sup>8</sup> W/cm<sup>2</sup>, was employed to produce plasma in a vacuum from a Ge target. The apparatus utilized was very versatile and able to contain an expansion chamber in order to allow the plasma to be diluted before the application of an accelerating voltage. The mean ion energy increased with the laser pulse energy and the ion charge state, and ranged between about 100 eV and 1 keV. To increase the ion energy a post-acceleration up to 50 kV was employed, which resulted in ion energies from about 50 keV to about 150 keV, depending on the charge state. The multi-energetic ion beam, with current density of the order of 10 mA/cm<sup>2</sup>, was employed to irradiate silicon substrates and to obtain surface implantations up to a depth of about 150 nm. During the implantation process the ion beams were generated with a repetition rate of the laser pulse of 1 Hz. The depth profiles of the ion implants were investigated by Rutherford backscattering spectrometry and laser ablation - inductively coupled plasma - mass spectrometry.
A UV pulsed lasers was employed to produce C and Ti ions of different charge with current densities of the order of 10 mA/cm<sup>2</sup>. A post ion acceleration, up to 30 kV, was employed to increase the ion energy and to implant polyethylene biocompatible surfaces up to a depth of about 200 nm. Preliminary results about surface properties indicate that implanted surfaces have higher wetting and micro-hardness with respect to un-implanted ones.
In this work the mutagenic effect on <i>Escherichia coli</i> strains induced by UV radiation emitted by a XeCl laser (λ =
308 nm) has been analysed as a function of the exposure dose and compared with the effect induced by 254 nm
radiation emitted by a conventional germicidal lamp. <i>E. coli</i> strains, wild-type (<i>recA+</i>) and mutant (<i>recA1</i>, defective in
DNA damage repair systems), plated on LB agar, supplemented with rifampicin when requested, were irradiated by
means of a germicidal lamp in the dose range 0 - 9 mJ/cm<sup>2</sup>. Similar strains were exposed to 308 nm pulsed laser
radiation (τ = 20 ns FWHM; max. pulse energy: 100 mJ) in the dose range 0-1.0 x 10<sup>4</sup> mJ/cm<sup>2</sup>. The discrepancy
between the results obtained with the lamp and the laser on the mutation frequency, suggested that the biological
response to the two radiation sources involves distinct mechanisms. This hypothesis was supported by the evidence that
exposure to near-UV 308 nm induced mutagenesis in the recA-defective strain at an extent considerably higher than in
the recA-proficient strain.
In this work we report the preliminary experimental results on the selective ablation of sulphur in ancient stones. The sulphur concentration was reduced after laser action. For this goal an excimer laser operating at 308 nm wavelength and time duration of 20 ns was used. In order to estimate the sulphur concentration before and after laser cleaning, a portable apparatus for energy-dispersive X-ray fluorescence (EDXRF) was utilised. The processed sample were characterized by an initial sulphur concentration of 2.8% w/w. After the laser treatment, sulphur concentration decreased after a total deposited energy of about 30 J/cm<sup>2</sup> up to 1.2% w/w value. Due to the porosity of the stone, in fact, it is difficult to eliminate completely the S presence in the composition of the stones. It was also observed that after a few laser shots the initial black area of the stone became white showing in this way the great potential of the laser action on the cleaning process of the pietra leccese.
In this work an ion acceleration system based on a laser ion source was studied. It was able to generate ion beams utilizing as a source a laser plasma produced by a XeCl laser from a copper target. The focused laser beam provided a power density on the target surface of about 3.5x10<sup>8</sup> W/cm<sup>2</sup>. Laser wavelength and pulse duration were 308 nm and 20 ns, respectively. The experimental apparatus consisted substantially of a plasma generation chamber, a drift tube and an expansion chamber mounted on the target stem inside the generation chamber. The expansion chamber end formed the acceleration gap together with a grounded bored electrode, placed in front of it at a distance of 1.3 cm. A Faraday cup placed at the end of the drift tube was used to reveal the ion intensity.
Many attempts were done in order to accelerate plasma ions without the expansion chamber, but arcs were present. The maximum accelerating voltage applied to the extraction gap was 18 kV, resulting in an ion bunch of about 4.2 nC and a peak current of 220 μA.
We report here the results about the sulphur concentration in ancient stones and its removal after the application of UV laser action. A portable apparatus for energy-dispersive X-ray fluorescence (EDXRF) was utilised to measure the sulphur concentration before and after laser cleansing. After laser application the sulphur concentration decrased to 1.2% w/w whilst the initial value was 2.8% w/w. The laser energy density was about 1 J/cm<sup>2</sup> and the efficient shot number was approximately 30 with a rate of 1Hz.