Investigation on the origin of hot electrons in laser plasma interaction at shock ignition intensities.

Shock Ignition is a two-step scheme to reach Inertial Confinement Fusion, where the precompressed fuel capsule is ignited by a strong shock driven by a laser pulse at an intensity in the order of [Formula: see text] W/cm[Formula: see text]. In this report we describe the results of an experiment carried out at PALS laser facility designed to investigate the origin of hot electrons in laser-plasma interaction at intensities and plasma temperatures expected for Shock Ignition. A detailed time- and spectrally-resolved characterization of Stimulated Raman Scattering and Two Plasmon Decay instabilities, as well as of the generated hot electrons, suggest that Stimulated Raman Scattering is the dominant source of hot electrons via the damping of daughter plasma waves. The temperature dependence of laser plasma instabilities was also investigated, enabled by the use of different ablator materials, suggesting that Two Plasmon Decay is damped at earlier times for higher plasma temperatures, accompanied by an earlier ignition of SRS. The identification of the predominant hot electron source and the effect of plasma temperature on laser plasma interaction, here investigated, are extremely useful for developing the mitigation strategies for reducing the impact of hot electrons on the fuel ignition.

Full aperture backscatter diagnostics for characterization of laser plasma instabilities at the extreme light infrastructure (ELI) beamlines.

We report on the commissioning of a full aperture backscatter diagnostics station for the kilojoule, nanosecond high repetition rate L4n laser operating at a wavelength of 527 nm at the Extreme Light Infrastructure (ELI) - Beamlines, Dolni Brezany, Czech Republic. Light scattered back from laser-plasma interaction into the cone of the final focusing lens is captured and split into different channels to measure the signatures of laser plasma instabilities from stimulated Brillouin scattering, stimulated Raman scattering, and two plasmon decay with respect to back scattered energy, its spectrum, and its temporal profile. The performance was confirmed in a commissioning experiment with more than 800 shots at laser intensities ranging from 0.5 × 1013 to 1.1 × 1015 W cm-2. These diagnostics are permanently installed at ELI Beamlines, and can be used to understand the details of laser-plasma interactions in experiments with kJ and 527 nm light. The large number of shots that can be collected in an experimental campaign will allow us to study the details of the laser-plasma interaction with a high level of confidence.

Development of an experimental platform for the investigation of laser-plasma interaction in conditions relevant to shock ignition regime.

The shock ignition (SI) approach to inertial confinement fusion is a promising scheme for achieving energy production by nuclear fusion. SI relies on using a high intensity laser pulse (≈1016 W/cm2, with a duration of several hundred ps) at the end of the fuel compression stage. However, during laser-plasma interaction (LPI), several parametric instabilities, such as stimulated Raman scattering and two plasmon decay, nonlinearly generate hot electrons (HEs). The whole behavior of HE under SI conditions, including their generation, transport, and final absorption, is still unclear and needs further experimental investigation. This paper focuses on the development of an experimental platform for SI-related experiments, which simultaneously makes use of multiple diagnostics to characterize LPI and HE generation, transport, and energy deposition. Such diagnostics include optical spectrometers, streaked optical shadowgraph, an x-ray pinhole camera, a two-dimensional x-ray imager, a Cu Kα line spectrometer, two hot-electron spectrometers, a hard x-ray (bremsstrahlung) detector, and a streaked optical pyrometer. Diagnostics successfully operated simultaneously in single-shot mode, revealing the features of HEs under SI-relevant conditions.

Bremsstrahlung cannon design for shock ignition relevant regime.

We report on the optimization of a BremsStrahlung Cannon (BSC) design for the investigation of laser-driven fast electron populations in a shock ignition relevant experimental campaign at the Laser Megajoule-PETawatt Aquitaine Laser facility. In this regime with laser intensities of 1015 W/cm2-1016 W/cm2, fast electrons with energies ≤100 keV are expected to be generated through Stimulated Raman Scattering (SRS) and Two Plasmon Decay (TPD) instabilities. The main purpose of the BSC in our experiment is to identify the contribution to x-ray emission from bremsstrahlung of fast electrons originating from SRS and TPD, with expected temperatures of 40 keV and 95 keV, respectively. Data analysis and reconstruction of the distributions of x-ray photons incident on the BSC are described.

Resolving surface details with reflection and fluorescence video-confocal profilometry.

Video-confocal profilometry has been exploited to characterize reflecting and non-reflecting surfaces in materials with tilted and corrugated areas. An alternative method based on fluorescence detection has been developed and tested to characterize metal surfaces modified by intense laser irradiation. Combined representations of surface topography have been obtained on the basis of both reflectance and fluorescence signals. A discussion of results and problems encountered in reflection and fluorescence based techniques is provided.

Transition from Coherent to Stochastic electron heating in ultrashort relativistic laser interaction with structured targets.

Relativistic laser interaction with micro- and nano-scale surface structures enhances energy transfer to solid targets and yields matter in extreme conditions. We report on the comparative study of laser-target interaction mechanisms with wire-structures of different size, revealing a transition from a coherent particle heating to a stochastic plasma heating regime which occurs when migrating from micro-scale to nano-scale wires. Experiments and kinetic simulations show that large gaps between the wires favour the generation of high-energy electrons via laser acceleration into the channels while gaps smaller than the amplitude of electron quivering in the laser field lead to less energetic electrons and multi-keV plasma generation, in agreement with previously published experiments. Plasma filling of nano-sized gaps due to picosecond pedestal typical of ultrashort pulses strongly affects the interaction with this class of targets reducing the laser penetration depth to approximately one hundred nanometers. The two heating regimes appear potentially suitable for laser-driven ion/electron acceleration schemes and warm dense matter investigation respectively.

Investigation on target normal sheath acceleration through measurements of ions energy distribution.

An experimental campaign aiming at investigating the ion acceleration mechanisms through laser-matter interaction in femtosecond domain has been carried out at the Intense Laser Irradiation Laboratory facility with a laser intensity of up to 2 × 10(19) W/cm(2). A Thomson parabola spectrometer was used to obtain the spectra of the ions of the different species accelerated. Here, we show the energy spectra of light-ions and we discuss their dependence on structural characteristics of the target and the role of surface and target bulk in the acceleration process.

Selective PF4 release in vitro induced by heparin and related glycosaminoglycans (GAGs)--correlation with beta-TG release and platelet aggregation.

We studied human platelet aggregation and beta-TG/PF4 release induced by heparin and related GAGs in vitro both in normal PRP and in PRP after aspirin. In our experimental conditions, heparin and related GAGs always caused PF4 release in vitro from normal platelets, whether or not there was measurable platelet aggregation in the aggregometer. Significant beta-TG release was induced only by the mucosal heparin preparation (which also induced platelet aggregation in some citrated PRP). Therefore, while beta-TG release in vitro seems to correlate with platelet aggregating activity of heparin, the selective PF4 release, caused by heparin and related GAGs also in conditions in which neither platelet aggregation nor beta-TG are measurable, is probably associated with the high affinity of PF4 for heparin. The degree of affinity of GAGs for PF4 (heparin greater than DeS greater than HS) seems to correlate with PF4 release. Moreover, the significant reduction in PF4 release in vitro after aspirin suggests that GAGs-induced PF4 release is related to a cyclooxygenase-dependent activation process.

Low-dose heparin in thoracic surgery: effect on blood coagulation and fibrinolysis system.

Plasma kallikrein, antithrombin III and antiplasmin were determined with chromogenic methods in 29 patients pre-, per- and post-operatively in a controlled, randomized study. 16 patients received calcium heparin, 5000 IU s. c. every 8 hr for 7 days, the first administration given 2 hr before surgical procedure. 13 control patients received saline. A significant reduction of kallikrein and antiplasmin in per- and post-operative periods was observed in the control patients compared with the heparin-treated patients, while there was a significant reduction of anti-thrombin III in the control patients compared with the treated patients only in the per-operative period. The results obtained suggest that activation of the coagulation and fibrinolysis system occurs in patients undergoing thoracic surgery, and that it is inhibited significantly by calcium heparin prophylaxis.

Temporal and spatial evolution of a laser-induced plasma from a steel target.

The space and time evolution of a laser-induced plasma from a steel target has been studied using optical time-of-flight and shadowgraphic techniques. The results, obtained for two distinct laser energy regimes, allow us to individuate two different regions in the plume, one characterized by air and continuum emissions produced by the shock wave ionization and the other characterized by emissions from ablated material. Moreover, it was shown that a sufficiently high laser fluence and short delay time of acquisition are needed to avoid inhomogeneous effects in the plasma, as required in analytical applications such as laser-induced breakdown spectroscopy.

Spatially resolved analysis of Kα x-ray emission from plasmas induced by a femtosecond weakly relativistic laser pulse at various polarizations.

Spatially resolved K-shell spectroscopy is used here to investigate the interaction of an ultrashort laser pulse (λ=800 nm, τ=40 fs) with a Ti foil under intense irradiation (Iλ(2)=2×10(18)Wµm(2)cm(-2)) and the following fast electron generation and transport into the target. The effect of laser pulse polarization (p, s, and circular) on the Kα yield and line shape is probed. The radial structure of intensity and width of the lines, obtained by a discretized Abel deconvolution algorithm, suggests an annular distribution of both the hot electron propagation into the target and the target temperature. An accurate modeling of Kα line shapes was performed, revealing temperature gradients, going from a few eV up to 15-20 eV, depending on the pulse polarization. Results are discussed in terms of mechanisms of hot electron generation and of their transport through the preplasma in front of the target.

Modì: a new mobile instrument for in situ double-pulse LIBS analysis.

Laser-induced breakdown spectroscopy (LIBS) is a promising technique for in situ elemental analysis. A new mobile instrument for LIBS analysis, developed in a collaboration between Marwan Technology s.r.l. and the Applied Laser Spectroscopy Laboratory in Pisa, is presented, and some applications of it and results from it are outlined. The innovative experimental set-up, based on the use of two suitably retarded laser pulses and a standardless analysis procedure, which overcomes problems related to matrix effects, greatly improves the potential of this technique for accurate quantitative analysis.

Value of CT scanning in the diagnosis of CNS mycotic involvement: report of 3 cases.

Fungal infections of the CNS are becoming an increasingly serious problem in immunosuppressed patients. We describe three patients with malignant blood disease who in the course of systemic fungal infection presented cerebral involvement. The nature, site and extent of the cerebral involvement were defined by computed tomography (CT). Further, in one patient it was possible to follow the course of the lesion and assess the effectiveness of antimycotic therapy by CT because of its noninvasiveness and repeatability.

Beta-thromboglobulin and platelet factor 4 plasma levels during haemodialysis: effect of indobufen.

The effect of a single dose of indobufen (100 mg i.v.) on the release of beta-thromboglobulin and of the platelet factor 4 was investigated during dialysis in 20 uraemic subjects by a within-subjects, single-blind, indobufen versus placebo study. Plasma levels were measured in baseline conditions and 15, 30, 60, 120 and 240 minutes after the beginning of dialysis. Pre-treatment with indobufen clearly inhibited beta-TG and PF 4 output. The difference from placebo was highly significant (p less than 0.01) from the 30-minute control up to the end of dialysis. No changes in platelet count before and after dialysis were observed.