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The quasi-stationary state characterizing the saturation of a single-pass free-electron laser is governed by the Vlasov equation obtained by performing the continuum limit of the Colson-Bonifacio model. By means of a statistical treatment, this approach allows to predict analytically the saturated laser intensity as well as the final electron-beam energy distribution. In this paper we consider the
The optical klystron installed on the Elettra storage-ring is normally used as interaction region for an oscillator free-electron laser, but, removing the optical cavity and using an external seed laser, one obtains an effective scheme for single-pass harmonic generation. In this configuration the high-power external laser is synchronized with the electron beam entering the first undulator of the
UV absorption from carbon nanoparticles is a very interesting astrophysical topic. The prominent hump centred at 217.5 nm is the most dominant feature in the interstellar extinction curve and also the most controversial and a long-standing problem in astrophysics. At the University of Milano an experimental set-up based on a Pulsed Microplasma Cluster Source has been developed for the investigatio
In a Storage-Ring Free-Electron Laser (SRFEL) giant pulses can be produced by the interaction between the light stored in the optical cavity and an electron beam with low energy-spread (cold beam). This interplay produces the heating of the beam. After the generation of a single giant pulse the overlap between electrons and radiation is periodically prevented for a time necessary to dump the energ
In a storage-ring free-electron laser (FEL), the onset and growth of intra-cavity power at the resonator wavelength can be naturally accompanied by coherent emission at higher harmonics. Contrary to what happens in singlepass linac-based devices, the electron beam is re-circulated in the storage ring and, while the microbunching becomes "thermalized" from turn to turn, the evolution of other bunch
Single-pass free-electron lasers constitute an example of systems with long-range interactions. The light-particle interplay leading to the power growth and successive relaxation towards a quasi-stationary state is governed by the Vlasov equation. A maximum entropy principle inspired to Lynden-Bell's theory of "violent relaxation" for the Vlasov equation can be invoked to analytically characterize
Coherent radiation from a relativistic electron beam is a valuable way to overcome the present limitations of conventional lasers and synchrotron radiation light sources. The typical scheme has electrons, directly from a linac, in a single-pass interaction with a laser pulse in the presence of a static undulator magnetic field. We demonstrate that a storage-ring free-electron laser can also achiev
We present an experimental characterization of the process of coherent harmonic generation in single-pass free electron lasers. The harmonic radiation is obtained by seeding the electron beam stored in the Elettra storage ring with a Ti:sapphire laser. Different methods for generating harmonics are compared between them, and a detailed characterization of the emitted light is performed for differe
We demonstrate for the first time that seeded harmonic generation on electron storage rings can produce coherent optical pulses in the vacuum ultraviolet spectral range. The experiment is performed at Elettra, where coherent pulses are generated at 132nm, with a duration of about 100fs. The light source has a repetition rate of 1kHz and adjustable polarization; it is very bright, with a peak power
Taking advantage of the storage ring free electron laser beamline at Elettra, we have implemented an experimental setup for the generation of sub-picosecond (ps) coherent optical pulses in the VUV range. The setup is based on the frequency up-conversion of a high-power external signal (provided by a Ti:Sapphire laser) and makes use of a relativistic electron bunch as resonating medium. The produce
The Free-electron-laser at Hamburg (FLASH) operates in the Self-Amplified Spontaneous Emission (SASE) mode, delivering to users photons in the XUV wavelength range. The FEL seeding schemes promise to improve the properties of the generated radiation in terms of stability in intensity and time. Such an experiment using higher harmonics of an optical laser as a seed is currently under construction a
The free-electron laser facility FLASH at DESY (Hamburg) was upgraded during a five month shutdown in winter 2009 [1]. Part of this upgrade was the installation of a direct seeding experiment in the XUV spectral range. Beside all components for transport and diagnostics of the photon beam in and out of the accelerator environment, a new 10 m long variable gap undulator was installed upstream of th
Recently, the Free electron LASer in Hamburg (FLASH) at DESY has been upgraded considerably [1]. Besides increasing the maximum energy to about 1.2 GeV and installation of a third-harmonic rf cavity linearizing the longitudinal phase space distribution of the electron bunch, an FEL seeding experiment at wavelengths of about 35 nm has been installed. The goal is to establish direct FEL seeding empl
The sFLASH-experiment has been built at the Free-Electron Laser in Hamburg (FLASH) to study the high-gain-FEL amplification of a laser seed from a high harmonic generation (HHG) source. Ideally, the HHG-seed can be amplified up to a GW-power level, improving both the shot-to-shot stability and the longitudinal coherence of the FEL-pulse. In 2010/2011 the sFLASH-components and sub-systems have been
The sFLASH-experiment has been built at the Free- Electron Laser in Hamburg (FLASH) to study the highgain- FEL amplification of a laser seed from a high harmonic generation (HHG) source. Ideally, the HHG seed can be amplified up to a GW-power level, improving both the shot-to-shot stability and the longitudinal coherence of the FEL-pulse. In 2010/2011 the sFLASH-components and sub-systems have bee
The shear plate dowel joint (SPDJ) is a novel connection design for heavy timber structures. The connection uses a single large diameter dowel and glued-on steel plates to transfer loads between members. Consequently, the design of the dowel is of great influence for the global performance of the connection. This paper presents an experimental and numerical investigation of the influence of the ge
The large stocks of soil organic carbon (SOC) in soils and deposits of the northern permafrost region are sensitive to global warming and permafrost thawing. The potential release of this carbon (C) as greenhouse gases to the atmosphere does not only depend on the total quantity of soil organic matter (SOM) affected by warming and thawing, but it also depends on its lability (i.e., the rate at whi
Octopus vulgaris, well-known from temperate waters of the Mediterranean Sea and a well-cited model species among the cephalopods, has large eyes with which it scans its environment actively and which allow the organism to discriminate objects easily. On cursory examination, the single-chambered eyes of octopus with their spherical lenses resemble vertebrate eyes. However there are also apparent di
Intergroup changes occur often between subgroups who are asymmetric in status (e.g., size, power, prestige), with important consequences for social identification, especially among the members of lower-status groups. Mergers offer an example of such changes, when subgroups (merger partners) merge into a common, superordinate group (post-merger group). Lower-status subgroups frequently perceive the
