Evidence of resonant surface wave excitation in the relativistic regime through measurements of proton acceleration from grating targets

The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, has been experimentally investigated. Ultrahigh contrast ($\sim 10^{12}$) pulses allowed to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultra-high intensity >10^{19} \mbox{W/cm}^{2}. A maximum increase by a factor of 2.5 of the cut-off energy of protons produced by Target Normal Sheath Acceleration has been observed with respect to plane targets, around the incidence angle expected for resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance.Comment: 5 pages, 5 figures, 2nd version implements final correction

Table-top water-window soft X-ray microscope using a Z-pinching capillary discharge source

The development and demonstration of a table-top transmission soft X-ray (SXR) microscope, using a laboratory incoherent capillary discharge source has been carried out. This Z-pinching capillary discharge water-window SXR source, is a first of its kind to be used for high spatial resolution microscopy at λ = 2.88 nm (430 eV) . A grazing incidence ellipsoidal condenser mirror is used for focusing of the SXR radiation at the sample plane. The Fresnel zone plate objective lens is used for imaging of the sample onto a back-illuminated (BI) CCD camera. The achieved half-pitch spatial resolution of the microscope approaches 100 nm, as demonstrated by the knife-edge test. Details about the source, and the construction of the microscope are presented and discussed. Additionally, the SXR images of various samples, proving applicability of such microscope for observation of objects in the nanoscale, are shown

Laser-driven high-energy proton beam with homogeneous spatial profile from a nanosphere target

A high-energy, high-yield proton beam with a good homogeneous profile has been generated from a nanosphere target irradiated by a short (30-fs), intense (7 x 10(20) W/cm(2)) laser pulse. A maximum proton energy of 30 MeV has been observed with a high proton number of 7 x 10(10) in the energy range 5-30 MeV. A homogeneous spatial profile with a uniformity (standard deviation from an average value within 85% beam area) of 15% is observed with the nanosphere dielectric target. Particle-in-cell simulations show the enhancement of proton cutoff energy and proton number with the nanosphere target and reveal that the homogeneous beam profile is related with a broadened angular distribution of hot electrons, which is initiated by the nanosphere structure. The homogeneous spatial properties obtained with the nanosphere target will be advantageous in developing laser-driven proton sources for practical applications in which high-quality beams are required120191sciescopu

Laser-driven high-energy proton beam with homogeneous spatial profile from a nanosphere target

A high-energy, high-yield proton beam with a good homogeneous profile has been generated from a nanosphere target irradiated by a short (30-fs), intense (7×10^{20}  W/cm^{2}) laser pulse. A maximum proton energy of 30 MeV has been observed with a high proton number of 7×10^{10} in the energy range 5–30 MeV. A homogeneous spatial profile with a uniformity (standard deviation from an average value within 85% beam area) of 15% is observed with the nanosphere dielectric target. Particle-in-cell simulations show the enhancement of proton cutoff energy and proton number with the nanosphere target and reveal that the homogeneous beam profile is related with a broadened angular distribution of hot electrons, which is initiated by the nanosphere structure. The homogeneous spatial properties obtained with the nanosphere target will be advantageous in developing laser-driven proton sources for practical applications in which high-quality beams are required

Laser plasma proton acceleration experiments using foam-covered and grating targets

Experimental results are reported for two different configurations of laser driven ion acceleration using solid targets with a structured layer on the irradiated side. Two experimental campaigns have been performed exploiting the 100TW 25fs Ti:Sa UHI-100 laser pulse at CEA Saclay. The use of a double plasma mirror allowed a contrast ratio of > 1012 so that the structures of the front surface withstanded the prepulse. ”Foam” targets have been manufactured by depositing a 10 μm nanostructured carbon foam with an average density of 1-5 mg/cm3 on a 1 μm thick aluminium foil. At maximum focalization, corresponding to an intensity of 1019 W/cm2. the foam targets gave a maximum proton energy similar to the case of bare aluminium target (about 6 MeV). Reducing the intensity by moving the target from the best focus plane, the presence of the foam enhanced the maximum proton energy, obtaining about 1.5MeV vs. 500KeV with a target 500 μm from the best focus, corresponding to an intensity of 5 · 1016 W/cm2. ”Grating” targets have been manufactured by engraving thin mylar foils (0.9, 20 and 40 μm) with a regular modulation having 1.6 μm period and 0.5 μm depth. The periodicity of the grating corresponds to a resonant incident angle of 30 degrees for the excitation of surface waves. Considering a target of 20 micron and changing the angle of incidence from 10 to 45 degrees, a broad maximum in the proton energy cut-off was observed around the resonant angle. The proton energy cut-off was up to 5 MeV for a laser intensity of 1019 W/cm2. As suggested by numerical simulation, radiochromic films placed 300 degrees around the target showed a very intense electron signal suggesting the presence of a peak emission tangent to the target only in presence of the grating. The experiments have been supported by the LaserLAB EU access scheme

Does pre-existing aortic regurgitation protect from death in patients who develop paravalvular leak after TAVI?

Objective The aim of this study was to investigate interactions among pre-procedural aortic regurgitation (AR), post-procedural paravalvular leak (PVL) and long-term clinical outcomes. Methods and results We analyzed data prospectively collected in the Italian Transcatheter balloon-Expandable Registry (ITER) on aortic stenosis (AS) patients. The degree of pre-procedural AR and post-procedural PVL was stratified as: absent/trivial, mild, and moderate/severe. VARC definitions were applied to outcomes. Of 1708 patients, preoperatively, AR was absent/trivial in 40% of the patients, mild in 42%, and moderate in 18%. Postoperatively, PVL was moderate\u2013severe in 5%, mild in 32% of patients, and absent/trivial in 63%. Clinical follow-up, median 821 days (IQR 585.75), was performed in 99.7% of patients. PVL, but not preoperative AR, was a major predictor of adverse outcome (HR 1.33, CI 95% 0.9\u20132.05, p = 0.012 for mild PVL, HR 1.36, CI 95% 0.9\u20132.05, p < 0.001 for PVL  65 moderate and OR 1.04, p = 0.97 respectively). Patients with moderate\u2013severe PVL and preoperative left ventricle (LV) dilatation (LVEDVi > 75 ml/m2) showed better survival than those without dilatation (HR 8.63, p = 0.001). Conclusions In patients with severe AS treated with balloon-expandable TAVI, the presence of PVL, but not pre-procedural AR, was a major predictor of adverse outcome. Preoperative LV dilatation seemed to offer some clinical advantages

Predictive ability of the CHADS2 and CHA2DS2-VASc scores for stroke after transcatheter aortic balloon-expandable valve implantation: An Italian Transcatheter Balloon-Expandable Valve Implantation Registry (ITER) sub-analysis

OBJECTIVES: Stroke incidence after transcatheter aortic valve implantation (TAVI) still represents a concern. This multicentre study aimed at investigating the hypothesis that CHADS2 and CHA2DS2-VASc scores may be used to predict perioperative stroke after TAVI. METHODS: The Italian Transcatheter Balloon-Expandable Valve Implantation Registry (ITER) is a multicentre, prospective registry of patients undergoing balloon-expandable TAVI using Edwards Sapien and Sapien XT prosthesis between 2007 and 2012. The primary endpoint of this study was the 30-day stroke rate. Secondary safety end-points were all the major adverse events based on Valve Academic Research Consortium (VARC-2) criteria. RESULTS: One thousand nine hundred and four patients were enrolled in the registry. Mean age was 81.6 \ub1 6.2 years and 1147 (60.2%) patients were female; mean CHADS2 and CHA2DS2-VASc scores were 2.2 \ub1 0.8 and 4.4 \ub1 1.1, respectively. Fifty-four (2.8%) patients had a stroke within 30 days. At multivariable logistic regression analysis, CHA2DS2-VASc (OR: 1.35, 95% CI: 1.03-1.78; P = 0.031) and previous cardiac surgery (OR: 1.96, 95% CI: 1.06-3.6; P = 0.033) but not CHADS2 (OR: 1.05, 95% CI: 0.76-1.44; P = 0.77) were found to be independent predictors of in-hospital stroke. A CHA2DS2-VASc score 655 was strongly related to the occurrence of in-hospital stroke (OR: 2.51, 95% CI: 1.38-4.57; P= 0.001). However, CHA2DS2-VASc score showed only poor accuracy for in-hospital stroke with a trend for better accuracy when compared with CHADS2 score (area under the curve: 0.61, 95% CI: 0.59-0.63 vs 0.51; 95% CI: 0.49-0.54, respectively, P = 0.092). CONCLUSIONS: In TAVI patients, CHA2DS2-VASc provided a strong correlation for in-hospital stroke but with low accuracy. Dedicated scores to properly tailor procedures and preventive strategies are needed