Extreme Ultraviolet Beam Enhancement by Relativistic Surface Plasmons

The emission of high-order harmonics in the extreme ultraviolet range from the interaction of a short, intense laser pulse with a grating target is investigated experimentally. When resonantly exciting a surface plasmon, both the intensity and the highest order observed for the harmonic emission along the grating surface increase with respect to a flat target. Harmonics are obtained when a suitable density gradient is preformed at the target surface, demonstrating the possibility to manipulate the grating profile on a nanometric scale without preventing the surface plasmon excitation. In support of this, the harmonic emission is spatiotemporally correlated to the acceleration of multi-MeV electron bunches along the grating surface. Particle-in-cell simulations reproduce the experimental results and give insight on the mechanism of high harmonic generation in the presence of surface plasmons

Extensive study of electron acceleration by relativistic surface plasmons

The excitation of surface plasmons with ultra-intense (I ∼ 5 × 1019W/cm2), high contrast (∼1012) laser pulses on periodically modulated solid targets has been recently demonstrated to produce collimated bunches of energetic electrons along the target surface [Fedeli et al., Phys. Rev. Lett. 116, 015001 (2016)]. Here, we report an extensive experimental and numerical study aimed to a complete characterization of the acceleration mechanism, demonstrating its robustness and promising characteristics for an electron source. By comparing different grating structures, we identify the relevant parameters to optimize the acceleration and obtain bunches of ∼650 pC of charge at several MeV of energy with blazed gratings

Non-adiabatic cluster expansion after ultrashort laser interaction

AbstractWe used X-ray spectroscopy as a diagnostic tool for investigating the properties of laser-cluster interactions at the stage in which non-adiabatic cluster expansion takes place and a quasi-homogeneous plasma is produced. The experiment was carried out with a 10 TW, 65 fs Ti:Sa laser focused on CO2 cluster jets. The effect of different laser-pulse contrast ratios and cluster concentrations was investigated. The X-ray emission associated to the Rydberg transitions allowed us to retrieve, through the density and temperature of the emitting plasma, the time after the beginning of the interaction at which the emission occurred. The comparison of this value with the estimated time for the "homogeneous" plasma formation shows that the degree of adiabaticity depends on both the cluster concentration and the pulse contrast. Interferometric measurements support the X-ray data concerning the plasma electron density

Probing several structures of Fe(H2O)n+ and Co(H2O)n+ (n=1,...,10) cluster ions

International audienceCo(H2O)n≤10+ and Fe(H2O)n≤10+ cluster ions were generated in a source combining laser ablation and a supersonic expansion. The clusters were fragmented to get insight into their structure. Two questions were addressed: first, the arrangement of the water molecules about the metal ion, and second, the electronic properties of the solvated metal ion. Collision induced dissociation by helium was used to answer the first question, especially for the smallest clusters with n=2 and 3. This revealed the existence of filament structures where one water molecule lies in the second solvation shell about the metal ion although the first shell is not filled. The binding energies of second shell water in Co(H2O)2+ and Fe(H2O)2+ are 0.45±0.1 and 0.5±0.1 eV, respectively. The answer to the second question was provided by photofragmentation experiments where the cluster ions are illuminated at 532, 355 and 266 nm. The most striking effect is seen with cobalt ions where increasing the number n of water molecules above n=7 allows one to built up an absorption band that is known when Co+ is solvated in liquid water. The two fragmentation techniques appear as complementary

Binding energies of first and second shell water molecules in the Fe(H

The fragmentation cross-section of the Fe(H2O)$_{1,2}^+$, Co(H2O)$_{1,2}^+$ and Au(H2O)$_{1,2}^+$ ions were measured, as a function of the collision energy. Threshold energies of $1.4\pm0.2$ eV, $1.4\pm0.2$ eVand $1.7\pm0.1$ eVwere measured for the monohydrated $\rm Fe^+$, $\rm Co^+$ and $\rm Au^+$ ions respectively, in fair agreement with the existing literature. Small threshold energies of $0.7\pm0.2$ eV, $0.7\pm0.2$ eVand $0.5\pm0.1$ eV were found for the Fe(H2O)$_{2}^+$, Co(H2O)$_{2}^+$ and Au(H2O)$_{2}^+$ clusters respectively. Secondary thresholds were observed on the cross-section, respectively at $1.7\pm0.3$ eV and $2.0\pm0.2$ eV for the Co(H2O)$_{2}^+$ and Au(H2O)$_{2}^+$ clusters. This double threshold behavior could be attributed to the presence of two kinds of isomers in the beam. The upper threshold is associated with clusters where both water molecules are linked to the metal ion (first solvation shell), whereas the lower threshold corresponds to clusters with one water molecule in the first solvation shell and the other in the second shell. Such an analysis documents the binding energy of either a first shell or a second shell water molecule in the M(H2O)$_{2}^+$ cluster ions

Storia del turismo. Annale 9

Questo numero dell'Annale di Storia del turismo raccoglie una serie di saggi che riguardano in gran parte la storia del turismo balneare. Questi i temi: il disegno degli spazi costieri sull'Adriatico nel secondo Ottocento e nel primo Novecento (per rispondere a pratiche diverse: da quelle terapeutiche a quelle ludiche); le dinamiche sociali, culturali e politiche che portano alla nascita dei primi villaggi turistici; i piani di investimento degli anni '60 progettati dalla grande industria italiana e mai realizzati; i programmi pubblici di intervento straordinario e di sviluppo, anch'essi non attuati, per le aree costiere meridionali