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The generation of electron pulses of high peak current and low emittance in a 3-GHz radio-frequency electron gun requires the illumination of the photocathode by a rectangular-shaped 10-ps light beam with a rise time of less than 1 ps. The generation of this kind of laser pulse needs the insertion of a programmable pulse shaper into a femtosecond laser system. The shaping system that we discuss is a spectral phase-only filter. A genetic algorithm, in conjunction with a proper cost function, is used to determine the phase filter function for the desired square-pulse generation. Simulations show that the system is highly sensitive to the properties of the input signal and to alignment. Third-harmonic generation, as required by photoemission, leads to some relaxation in the settings of the system.

SPARC and SPARX are two different initiatives toward an Italian Free Electron Laser (FEL) source operating in the Self Amplified Spontaneous Emission (SASE) mode, in which several national research institutions are involved. SPARC is a high gain FEL project devoted to provide a source of visible and VUV radiation while exploiting the SASE mechanism. An advanced Photo-Injector system, emittance compensating RF-gun plus a 150 MeV Linac, will inject a high quality e-beam into the undulator to generate high brilliance FEL radiation in the visible region at the fundamental wavelength, (∼500 nm). The production of flat top drive laser beams, high peak current bunches, and emittance compensation scheme will be investigated together with the generation of higher harmonic radiation in the VUV region. SPARX is the direct evolution of such a high gain SASE FEL toward the 13.5 and 1.5 nm operating wavelengths, at 2.5 GeV. To get the required value for the bunch peak current, Ipeak ≈ 2.5 kA, the “hybrid” scheme, RF-compression stage plus magnetic chicane, is analyzed and compared with the more standard double stage of magnetic compression. The two options are reviewed considering the tolerance to the drive laser pulse phase jitter.

Abstract: The possibility of building free-electron lasers and masers with quasi-circular undulators is considered. The two-mirror cavity is replaced by a suitable waveguide. The magnetic field along the orbit has a continuous component superimposed on the alternating one. Besides allowing large freedom for electron guiding and focusing, the structure allows effective negative mass conditions, which may enhance the electron beam modulation when space charge effect are important. Furthermore the radiation frequency can be higher than that in a linear undulator with the same electron energy, and long interaction times are possible in a compact structure.

We present an analytical expression for the small-signal gain of a Free Electron Laser (FEL) in the presence of a Gaussian mode. To describe the electron beam evolution we use the one-dimensional (1-d) Vlasov equation. Our perturbation result, valid for small values of the parameterq (length of the undulatorL divided by the Rayleigh rangeZR), can be extrapolated to values ofq˜4÷5.

We give the exact analytical solution of the evolution equation of an electron beam interacting in a wiggler with an electromagnetic wave. The initial energy distribution is assumed both monochromatic and gaussian. Furthermore, the evolution in a drift space is considered. Some basic characteristics of the FEL and TOK are derived from the mathematical properties of the solution.

In this paper the free-electron laser (FEL) experiment SEAFEL in progress at the Legnaro (Padova) INFN laboratory is presented. The accelerator characteristics and FEL parameters are discussed. The laser could sweep the millimeter region up to 2 mm with a power around 15 kW. The main goal is the continuous-wave operation. An existing electron device with some small modifications is used for the experiment.

The coherent radiation from a relativistic electron beam in transverse, plane-polarized, spatially periodic magnetic fields is calculated by taking into account anharmonic effects. Coherent radiation is interpreted in classical terms,i.e.as the effect of bunching of the beam. The treatment is made with the assumption that the beam interacts with the input radiation in a first undulator (buncher) and radiates then in a separate one (radiator). The formulae predict the radiated spectrum and show that frequency multiplication is possible together with power amplification.

A comparison between three possible cavity configurations, the confocal cavity, the ring cavity and the Bragg cavity is presented for a millimeter FEL set within the high voltage head of an electrostatic accelerator. A simple mechnical design to make the Bragg cavity tunable is proposed. The usual theory of the sinusoidal Bragg corrugation, in cylindrical geometry, is extended to the rectangular corrugation and, further, the theory of the Bragg mirror is extended to rectangular geometry. The features of a Bragg mirror in cylindrical and rectangular geometry are compared.

In this letter paper we analyse the effect of electron-beam qualities (namely, energy spread and emittances) on both spontaneous emission and gain of an Optical Klystron (OK).

A CH3OH FIR system has been developed for plasma diagnostics. A CO2 laser devoted to pump the CH3OH molecule has been studied. Different internal diameters of FIR cavity, input coupling holes and focusing lenses have been experimented.

The gas flow rate has resulted very important to get high power in a CO2diffusion-cooled laser. Some measurements suggest that the power dependence on the flow is connected with the chemical dissociation of the components of the gas mixture. Four different gas circuits have been experimented. La potenza emessa da un laser a CO2è risultata strettamente dipendente dalla velocità del flusso di gas. Alcune misure suggeriscono che questa dipendenza sia legata alla dissociazione chimica delle molecole componenti la miscela di gas. Sono stati anche sperimentati quattro diversi assetti del circuito del gas. Величина потока газа очень сильно влияет на получение большой мощности в CO2лазера. Измерения предполагают, что степенная зависимость от потока связана с химической диссоциацией компонент газовой смеси. Проводятся эксперименты для четырех различных газовых контуров.

In this paper we present a survey of the classical theory of the coherent emission of radiation in the optical and submillimetre range from a relativistic electron beam in a transverse, plane-polarized, spatially periodic magnetic field. Two kinds of lay-outs are proposed: the converter and the transverse optical klystron (TOK) in the reflex version.

A 352-MHz one-cell photocathode electron gun is studied. The simulations with PARMELA are done with two values of peak accelerating fields: 21 and 10 MV/m. Three cavity profiles are compared. The results are also discussed in view of the previous analytic theory. The space-charge effect with peak current greater than 300 A covers the RF effect. The beam qualities are not sensitive to cavity design.<>

Aim: To evaluate late suine surfactant therapy for the pulmonary disease in extremely low birth weight infants (ELBW).Methods: A retrospective study of all ELBW admitted in the NICU of Vicenza during 2007-2009. Patients were divided into three groups: early surfactant for respiratory distress syndrome (Group 1), late surfactant for postsurfactant slump (respiratory failure after six days of life) (Group 2) and no surfactant (Group 3). A respiratory severity score (RSS) was used to measure the severity of lung disease and response to surfactant therapy. In group 2 ventilatory parameters before, after 12 and 24 hours the administration of late surfactant were also evaluated.Results: Over three years, 58 ELBW were analyzed, 36 of group 1, 14 of group 2 and 8 of group 3. Patients of group 2 had lower gestational age and birth weights compared to patients of group 1 and 3 (EGA 25 +/- 1.27 in group 2 vs 26 +/- 1.92 and 30 +/- 3.06; birth weight 670 grams +/- 155 vs 732 +/- 136 and 884 +/- 104). More prenatal steroids were used in group 1 than in group 2 (72% vs 57%). Patients of group 2 had an improvement of their lung disease showed by a reduction of their RSS for 48 hours. PCO2, pH, MAP improved at both 12 and 24 hours after surfactant administration.Conclusions: Late surfactant therapy led to a short-term improvement of lung disease in ELBW with postsurfactant slump. These patients were more premature and with lower birth weight.