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Abstract: The influence of the adsorbed gases on the photoelectron performance of Mg thin film-based photocathodes was investigated. Mg thin films were deposited on Silicon and Copper substrates by pulsed laser ablation technique. The samples deposited on Silicon substrate were used to deduce the morphology, the structure and the thickness by using different diagnostic techniques. On the contrary, the samples deposited on Copper substrate were tested as photocathodes in a DC photodiode cell. The quantum efficiency of the Mg photocathodes was systematically improved by laser cleaning treatments, which appears to be necessary before any use of a metallic photocathode. The role of the hydrogen and oxygen absorption process on the emission properties is presented and discussed. [Copyright &y& Elsevier]

Abstract: Mg films deposited by pulsed laser ablation on a Cu substrate were tested as photocathodes in a DC diode. They showed features of robustness and a quantum efficiency of at low accelerating field when illuminated by 266nm light at normal incidence. A graphite protective layer of about 20nm thickness deposited by laser ablation just after the Mg deposition made the cathode stable and of easy handling. The cathodes could stay for several weeks in air before being inserted in the test chamber. The preparation procedure and the tests are presented. [Copyright &y& Elsevier]

The heating of the electronic distribution of a copper photocathode due to an intense drive laser pulse is calculated under the two-temperature model using fluences and pulse lengths typical in RF photoinjector operation. Using the finite temperature-extended relations for the photocathode intrinsic emittance and quantum efficiency, the time-dependent emittance growth due to the same photoemission laser pulse is calculated. This laser heating is seen to limit the intrinsic emittance achievable for photoinjectors using short laser pulses and low quantum efficiency metal photocathodes. A pump-probe photocathode experiment in a standard 1.6 cell S-band gun is proposed, in which simulations show the time dependent thermal emittance modulation within the bunch from laser heating can persist for meters downstream and, in principle, be measured using a slice emittance diagnostic. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we review the status of bright electron sources. High peak current (up to kA) low emittance (< 1 mm rad) electron beams have been one of the critical components in the development of XFELs. The outlook for the field is even more promising as progress in the understanding of photoemission physics, development of novel photocathode materials, gun and laser technology, enable further progress in advanced light sources as well as novel applications such as ultrafast electron diffraction and microscopy. We outline here the more recent research trends which pave the way for potentially orders of magnitude brightness improvements with respect to the current state-of-the-art. [ABSTRACT FROM AUTHOR]

Abstract: The advance in laser–plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular, the upcoming experiments with the 250TW laser at the FLAME facility of the INFN Laboratori Nazionali di Frascati, will enter the GeV regime with more than 100pC of electrons. At the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need for developing a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV), with still unknown angular divergences. Within the PlasmonX experiment at FLAME, a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence, present challenges in the design and construction of such a device. We present the design considerations for this spectrometer that lead to the use of scintillating fibers, multichannel photo-multipliers and a multiplexing electronics, a combination which is innovative in the field. We also present the experimental results obtained with a high intensity electron beam performed on a prototype at the LNF beam test facility. [Copyright &y& Elsevier]

Abstract: The advance in laser–plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular the upcoming experiments with the FLAME laser at LNF will enter the GeV regime with almost 1nC of electrons. From the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need to develop a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV) under still unknown angular divergences. Within the PlasmonX experiment at LNF a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence present unprecedented challenges in the design and construction of such a device. We will present the design considerations for this spectrometer and the first results from a prototype. [ABSTRACT FROM AUTHOR]

Abstract: In the framework of the DS4 EUROFEL collaboration, a research work plan at the SPARC free-electron laser (FEL) test facility aiming at the investigation of seeded and cascaded FEL configurations is under implementation. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher-order harmonics generated both in crystals (400 and 266nm) and in gases (266, 160, 114nm). The SPARC FEL can be configured to test several cascaded FEL configurations. In this paper we introduce SPARC and its main parameters and we analyze the superradiant cascade and the harmonic cascade seeded with a signal with the typical time structure of the harmonics generated in gas. [Copyright &y& Elsevier]

Abstract: A new technique, named “laser comb”, was tested during the last SPARC run. It is able to produce electron pulse trains with a charge of some hundreds pC, a repetition rate of some terahertz, and a sub-picosecond length. This technique is based on the velocity bunching configuration of the SPARC injector. It can be useful to drive pump and probe free-electron laser experiments, to generate coherent excitation of plasma waves in plasma accelerators, and to produce narrow band terahertz radiation. In this paper, we describe the experimental results achieved so far and provide a comparison with simulations. [Copyright &y& Elsevier]

Abstract: The PLasma Acceleration and MONochromatic X-ray generation (PLASMONX) project foresees the installation at LNF of a 0.3PW (6J, 20fs pulse) Ti:Sa laser system, named Frascati Laser for Acceleration and Multidisciplinary Experiments (FLAME), to operate in close connection with the existent SPARC electron photo-injector, allowing for advanced laser/e-beam interaction experiments. Among the foreseen scientific activities, a Thomson scattering experiment between the SPARC electron bunch and the high power laser will be performed. At the present time the linac has been tested and the electron beam characterized up to the maximum operating energy (150MeV). The beam lines transporting the beam to the interaction chamber with the laser have been designed. The electron final focusing system, featuring a quadrupole triplet and large radius solenoid magnet (ensuring an e-beam waist of 5–10μm) as well as the whole interaction chamber layout has been defined. The optical transfer line issues: transport up to the interaction; tight focusing; diagnostics and fine positioning; have been solved within the final design. The construction of the building hosting the laser has been completed; delivering and installation of the laser, as much of the beam lines elements will take place in the next months. [Copyright &y& Elsevier]