Stimulated Brillouin and Raman scattering for the generation ofshort excimer laser pulses

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     

Rogowski coils: theory and experimental results

The theory is given of the voltage output of a Rogowski coil excited by a current pulse flowing along the axis of the coil. In this theory the Rogowski coil is considered as a delay line. The results do not differ from those obtained usually by considering the coil as a voltage source dphi/dt with an inductive output impedance. Details are also given of the design of two Rogowski coils and their working modes are fully analyzed.     

Gain measurements in the KrCl excimer laser

The single-pass/double-pass amplified spontaneous emission technique has been used to measure the net gain at 222.4 nm in a discharge-pumped UV-preionized KrCl laser. The net gain has been measured as a function of pump rate and total pressure in He- and Ne-based gas mixtures. A maximum net gain of 0.15 cm(-1) has been obtained in a 0.09% HC1/10.1% Kr/1.5% He/88.3% Ne mixture at a total pressure of 355 kPa and at a specific power loading of approximately 21 MW/cc. The data presented are compared with previous net gain measurements performed using the passive absorption cell method.     

Production and acceleration of ion beams by laser ablation

In this work, we present a new pulsed laser ablation technique to obtain energetic ion beams. The accelerator we made is a compact device able to extract and accelerate the ionic components of plasma up to 160 keV per charge state. It is composed by a generating chamber containing an expansion chamber used like first electrode. Next, a second electrode connected to ground and a third electrode connected to negative voltage are used. The third electrode is used also as Faraday cup. By the analysis of the ion signals we studied the plume parameters such as TOF accelerated signals, charge state, and divergence.     

Fast capacitive probe for electromagnetic pulse diagnostic

In this work, we report the study and the development of a capacitive probe which is suitable for getting fast and high voltage/current measurements. Due to the fact that fast pulses propagate generally in coaxial structures, the probe realized in this work was a capacitive divider with the divider electrode properly designed to assure the same characteristic impedance of the coaxial structure and the recombination time of the split signals during the propagation. It was a folded cylindrical ring of 1.4 cm long and 0.8 cm thick, which introduce a theoretical delay time of about 100 ps. Analyzing the behavior of the probe closed on 520 Omega, the voltage amplification resulted to be of (3.6+/-0.1) x 10(-4) and, as a consequence, the current attenuation factor of 56+/-1 AV. The response rise time was less than 320 ps, which was limited by oscilloscope bandwave. The capacitor probe can operate voltage measurements of the order of 100 kV.     

INDIGO-DataCloud: a Platform to Facilitate Seamless Access to E-Infrastructures

This paper describes the achievements of the H2020 project INDIGO-DataCloud. The project has provided e-infrastructures with tools, applications and cloud framework enhancements to manage the demanding requirements of scientific communities, either locally or through enhanced interfaces. The middleware developed allows to federate hybrid resources, to easily write, port and run scientific applications to the cloud. In particular, we have extended existing PaaS (Platform as a Service) solutions, allowing public and private e-infrastructures, including those provided by EGI, EUDAT, and Helix Nebula, to integrate their existing services and make them available through AAI services compliant with GEANT interfederation policies, thus guaranteeing transparency and trust in the provisioning of such services. Our middleware facilitates the execution of applications using containers on Cloud and Grid based infrastructures, as well as on HPC clusters. Our developments are freely downloadable as open source components, and are already being integrated into many scientific applications.     

Experimental study of a generalized self-filtering unstableresonator applied to an XeCl laser

A diffraction-limited laser beam of 3.5 mJ with a pulse width of 11 ns and a brightness of 4.8×10¹³ W-cm^-2-Sr ^-1 has been obtained by applying a generalized self-filtering unstable resonator (SFUR) scheme to a short-pulse XeCl laser. In accordance with the theory, the generalized SFUR maintains the excellent properties of the SFUR, such as high transverse-mode discrimination, fast establishment of steady-state condition, and diffraction-limited output beam, but offers the possibility of having high magnification and higher mode volumes with shorter resonator lengths. It is possible to demonstrate that with the generalized SFUR, one can increase, by a factor more than two, the mode volume with respect to the confocal case by leaving the cavity length unaltered. These properties make the nonfocal SFUR particularly suitable for short-pulse excimer lasers     

Emission characteristics and stability of laser ion sources

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 and 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 during the expansion but it also shows outbursts of ions similar to a self-pulsing instability leading to a chaos. The sequence of fast ion outbursts visible on the time-resolved ion currents is sensitive to the details of non-linear interaction of the laser beam with the generated plasma.Analysis of ion sources based on a time-of-flight signal function is applied to quantify their emission characteristics as the hidden partial currents of the ionized species constituting, the total measured current, the centre-of-mass velocity of individual charge states, their abundance and the ion temperature.