[Show abstract][Hide abstract] ABSTRACT: The excellent physical and chemical properties and the radiation hardness of silicon carbide (SiC) render this material particularly suitable for the realization of radiation detectors. In this paper we describe the main properties of SiC and the processes needed to realize good performance detectors. To this purpose, we made SiC Schottky diodes that were electrical characterized by using different techniques. In order to test the radiation hardness, the diodes were irradiated with different ion beams and the analysis of the electrical measurements allowed to identify the defects responsible of the device degradation. These detectors have been used to monitor the multi-MeV ions of the plasma emitted by irradiation of various targets with 300-ps laser at high intensity (1016 W/cm2). These measurements highlighted that the use of SiC detectors enhances the sensitivity to ions detection due to the cutting of the visible and soft ultraviolet radiation emitted from plasma. The small rise time and the proportionality to ion energy evidence that these detectors are a powerful tool for the characterization of ion generated by high-intensity pulsed laser.
Radiation Effects and Defects in Solids 04/2015; 170(4). DOI:10.1080/10420150.2015.1036429 · 0.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Stereoselective amino acid analysis is still a challenging task. In this work, we report a study on the chiral recognition of d,l-Trp and d,l-His using l-Cys capped silver nanoparticles (AgNPs) and copper(II) ion. The AgNPs have been characterized by TEM, UV–Vis spectra and dynamic light scattering (DLS) measurements and used for chiral discrimination. In the l-Cys capped AgNPs, the α-amino and α-carboxyl groups of the surface-confined amino acid, besides showing either a negative or a neutral charge as a function of the pH, can coordinate the copper(II) ion, which in turn, binds the l- or d-amino acid present in solution forming diastereoisomeric complexes. The resulting systems have been characterized by UV–Vis spectroscopy, exploiting the zwitterionic nature of the cysteine to obtain enantiodiscrimination by a fine tuning of the pH. The analysis of the UV–Vis data by using a multiwavelength approach allows us to determine the kinetic constants ruling the processes.
Journal of Colloid and Interface Science 04/2015; 443. DOI:10.1016/j.jcis.2014.11.067 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we discuss the velocity compression in a short rf linac of an electron bunch from a rf photoinjector operated in the blowout regime. Particle tracking simulations shows that with a beam charge of 2 pC an ultrashort bunch duration of 16 fs can be obtained at a tight longitudinal focus downstream of the linac. A simplified coherent transition radiation (CTR) spectrum method is developed to enable the measurement of ultrashort (sub-50 fs) bunches at low bunch energy (5 MeV) and low bunch charges (<10 pC). In this method, the ratio of the radiation energy selected by two narrow bandwidth filters is used to estimate the bunch length. The contribution to the coherent form factor of the large transverse size of the bunch suppresses the radiation signal significantly and is included in the analysis. The experiment was performed at the UCLA Pegasus photoinjector laboratory. The measurement results show bunches of sub-40 fs with 2 pC of charge well consistent with the simulation using actual experimental conditions. These results open the way to the generation of ultrashort bunches with time-duration below 10 fs once some of the limitations of the setup (rf phase jitter, amplitude instability and low field in the gun limited by breakdown) are corrected.
Physical Review Special Topics - Accelerators and Beams 03/2015; 18(3). DOI:10.1103/PhysRevSTAB.18.032802 · 1.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Plasma acceleration is the new frontier in particle beam accelerators. Using the strong electric fields inside a plasma it is possible to achieve accelerating gradients orders of magnitude larger with respect to current technologies. Different schemes, using completely different approaches, have been proposed and several already tested, producing beams of energy up to several GeV. Regardless of the technique used for acceleration a precise determination of the output beam parameters is mandatory for the fine tuning of the process. The measurement of these parameters, in particular the beam distribution in transverse and longitudinal phase space, is not trivial, mainly due to the large energy spread and to the tight focusing of these beams or to the background noise produced in the plasma channel. We illustrate the main problems related to the diagnostic of this kind of beams and some of the proposed or already realized solutions
[Show abstract][Hide abstract] ABSTRACT: UCLA/INFN-LNF/Univ. Rome has been developing the hybrid gun which has an RF gun and a short linac for velocity bunching in one structure. After the cavity was manufactured at INFN-LNF in 2012, tests of the gun was carried out at UCLA. The field in the standing wave part was 20% smaller than the simulation but the phase advance was fine. The cavity was commissioned successfully up to 13 MW. The beam test was performed at 11.5 MW and demonstrated the bunch compression.
[Show abstract][Hide abstract] ABSTRACT: We discuss a new method for the production of trains of FEL radiation pulses based on the FEL emission driven by a comb-like electron beam. In addition, we present recent experimental results on the two color FEL emission as generated at the SPARC_LAB facility: a train of two short (<200 fs) electron bunches, almost overlapped in time, with a comb-like energy distribution, has been injected in the undulator, giving rise to FEL pulses at two characteristic frequencies with multi-peaked time structure. This scheme shows also the versatility of the SPARC photo-injector to generate and manipulate such energy and time distributions.
[Show abstract][Hide abstract] ABSTRACT: We have developed, at the SPARC test facility, a procedure for a real time self-amplified spontaneous emission free electron laser (FEL) device performance control. We describe an actual FEL, including electron and optical beam transport, through a set of analytical formulas, allowing a fast and reliable on-line “simulation” of the experiment. The system is designed in such a way that the characteristics of the transport elements and the laser intensity are measured and adjusted, via a real time computation, during the experimental run, to obtain an on-line feedback of the laser performances. The detail of the procedure and the relevant experimental results are discussed.
Physical Review Special Topics - Accelerators and Beams 11/2014; 17(11):110706 (6). DOI:10.1103/PhysRevSTAB.17.110706 · 1.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Compact, table-top sized accelerators are key to improving access to high-quality beams for use in industry, medicine and academic research. Among laser-based accelerating schemes, the inverse free-electron laser (IFEL) enjoys unique advantages. By using an undulator magnetic field in combination with a laser, GeV m(-1) gradients may be sustained over metre-scale distances using laser intensities several orders of magnitude less than those used in laser wake-field accelerators. Here we show for the first time the capture and high-gradient acceleration of monoenergetic electron beams from a helical IFEL. Using a modest intensity (~10(13) W cm(-2)) laser pulse and strongly tapered 0.5 m long undulator, we demonstrate >100 MV m(-1) accelerating gradient, >50 MeV energy gain and excellent output beam quality. Our results pave the way towards compact, tunable GeV IFEL accelerators for applications such as driving soft X-ray free-electron lasers and producing γ-rays by inverse Compton scattering.
[Show abstract][Hide abstract] ABSTRACT: In this paper we review the present status of MeV electron sources for ultrafast diffraction and microscopy applications
and trace the path forward to improve the spatio-temporal resolution of electron scattering probes.
[Show abstract][Hide abstract] ABSTRACT: Recent advances in ultrafast technology enable both the study and the control of materials properties thanks to the ability to record high temporal resolution movies of their transformations, or the ability to generate new states of matter by selecting ad hoc an excitation to drive the system out of equilibrium. The holy grail of this type of experiments is to combine a high tuneability of the excitation with a wide observation window. For example, this is achieved in multidimensional optical spectroscopy where the response to several excitation energies is monitored in a broad energy range by a large bandwidth optical pulse. In this article, the possibility to combine the chemical sensitivity of intense tuneable X-rays pulses from a free electron laser, with the wide range of observables available in an ultrafast transmission electron microscope is discussed. The requirements for such experiments are quantified via estimates based on state of the art experiments and simulations, and it is proposed that ultrafast electron imaging, diffraction and spectroscopy experiments can be performed in combination with a chemically selective X-ray excitation of materials.
[Show abstract][Hide abstract] ABSTRACT: We present the first experimental demonstration of MEMS-based magnetic optics for control of charged particle beams. Combined function (steering and focusing) 4-pole electromagnets with a 600-µm bore and 55-µm yoke thickness (686-µm magnetic length) have been fabricated with a novel MEMS process. These 3D solenoidal multi-pole electromagnets have demonstrated hysteresis-free adjustable 2D steering and focusing of a pC-charge 34-keV electron beam with 24-mT field intensity, 220-T/m field gradient, and potential for pulsed operation beyond 100 kHz. Simple geometric optimizations promise a 4-fold improvement in both field intensity and gradient without further scaling.
Solid-state Sensors, Actuators and Microsystems Workshop (Hilton Head 2014), Hilton Head Isl., SC; 06/2014
[Show abstract][Hide abstract] ABSTRACT: Pushing the limits in temporal resolution for transmission electron
microscopy (TEM) requires a revolutionary change in the electron source
technology. In this paper we study the possibility of employing a
radiofrequency photoinjector as the electron source for a time-resolved TEM. By
raising the beam energy to the relativistic regime we minimize the space charge
effects which otherwise limit the spatio-temporal resolution of the instrument.
Analysis and optimization of the system taking into account the achievable beam
brightness, electron flux on the sample, chromatic and spherical aberration of
the electron optic system, and space charge effects in image formation are
presented and supported by detailed numerical modeling. The results demonstrate
the feasibility of 10 nanometer - 10 picosecond spatio-temporal resolution
single-shot MeV TEM.
[Show abstract][Hide abstract] ABSTRACT: Thin foils, 0.5–50 μm in thickness, have been irradiated in vacuum at Prague Asterix Laser System in Prague using 1015–16 W cm−2 laser intensity, 1315 nm wavelength, 300 ps pulse duration and different focal positions. Produced plasmas from metals and polymers films have been monitored in the forward and backward directions. Ion and electron accelerations have been investigated by using Thomson parabola spectrometer, x-ray streak camera, ion collectors and SiC semiconductor detectors, the latter employed in time-of-flight configuration. Ion acceleration up to about 3 MeV per charge state was measured in the forward direction. Ion and electron emissions were detected at different angles as a function of the irradiation conditions.
Physica Scripta 05/2014; 2014(T161):014027. DOI:10.1088/0031-8949/2014/T161/014027 · 1.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Silicon carbide (SiC) detectors have been employed to analyze the multi-MeV ions generated from laser plasma. The irradiation was performed with the iodine laser of Prague Asterix Laser System Laboratory operating at 10(16) Wcm(-2) pulse intensity. Thin metallic and polymeric targets were irradiated and the produced plasmas were monitored in the forward direction. The use of SiC detectors ensures the cutting of the visible and soft UV radiation emitted from plasma, enhancing the sensitivity to protons and very fast heavy ions. The time-of-flight spectra obtained by irradiating polymeric films with high laser pulse energy produce protons with energy in the range 1.0-2.5MeV and all the charge states of carbon ions. The metallic Al target allows achieving energy up to 3.0MeV for protons and 40MeV for Al ions. All the results reveal the high performances of these detectors in terms of resolution and response time.
Physica Scripta 05/2014; T161(T161). DOI:10.1088/0031-8949/2014/T161/014021 · 1.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The high energy ions produced with intense pulsed laser were analyzed with Silicon Carbide detectors. In order to realize high performances and radiation resistant detectors, high quality and thick epitaxial layer were grown on a substrate and a Schottky diodes were then realized. These detectors were employed to probe the plasma generated with a 300 ps laser at intensity of 1016 W/cm2 operating at Prague Asterix Laser System Laboratory. They show a fast response and a high sensitivity to high energy ions. Metallic and polymeric thin films were irradiated and the produced plasmas were monitored in forward and backward directions. The analysis of the time-of-flight spectra evidences the emission of protons and ions at different energies. The spectra were deconvolved with a shifted Maxwell Boltzmann distribution. In our experimental conditions we detected protons in the energy range 1.2 – 3.0 MeV and heavy ions between 1.0 MeV up to 40 MeV depending on the target and the laser energy. The results were compared with the ones obtained by Thompson Parabola Spectrometer.
Journal of Physics Conference Series 04/2014; 508(1):012009. DOI:10.1088/1742-6596/508/1/012009
[Show abstract][Hide abstract] ABSTRACT: We discuss a two-color SASE free-electron laser (FEL) amplifier where the time and energy separation of two separated radiation pulses are controlled by manipulation of the electron beam phase space. Two electron beamlets with adjustable time and energy spacing are generated in an RF photo-injector illuminating the cathode with a comb-like laser pulse followed by RF compression in the linear accelerator. We review the electron beam manipulation technique to generate bunches with time and energy properties suitable for driving two-color FEL radiation. Experimental measurements at the SPARC-LAB facility illustrate the flexibility of the scheme for the generation of two-color FEL spectra.
New Journal of Physics 03/2014; 16(3):033018. DOI:10.1088/1367-2630/16/3/033018 · 3.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gold nanoparticles (AuNPs) conjugated to DNA are widely used for biomedical targeting and sensing applications. DNA functionalization is easily reached on laser generated gold nanoparticles because of their unique surface chemistry, not reproducible by other methods. In this context, we present an extensive investigation concerning the attachment of DNA to the surface of laser generated nanoparticles using Dynamic Light Scattering and UV-Vis spectroscopy. The DNA conjugation is highlighted by the increase of the hydrodynamic radius and by the UV-Vis spectra behavior. Our investigation indicates that Dynamic Light Scattering is a suitable analytical tool to evidence, directly and qualitatively, the binding between a DNA molecule and a gold nanoparticle, therefore it is ideal to monitor changes in the conjugation process when experimental conditions are varied.
PLoS ONE 03/2014; 9(3):e89048. DOI:10.1371/journal.pone.0089048 · 3.23 Impact Factor