M.E. Couprie

Surface states and space charge layer dynamics on Si(111)2×1: A free electron laser-synchrotron radiation study

Combining the use of a UV storage ring free electron laser and of synchrotron radiation, a time resolved core level spectroscopy study has been performed on photoexcited Si(111)2×1 surfaces with subnanosecond resolution. This enabled us to measure band bending fluctuations, caused by surface carrier dynamics, during the first nanosecond after photoexcitation; differences in the Si2p core level lineshape, dependent on the pump-probe time delay, were also observed. The presence of defects was found to reduce the fluctuations and make the carrier recombination process faster.

A longitudinal feedback for the Super-ACO free electron laser stability in the UV

Abstract To take complete benefit of the FELs features, longitudinal feedback has been developed for operating the FEL at perfect tuning without jitter. The laser micropulse temporal position is detected and compared to a reference position corresponding to perfect tuning. The time difference is converted into a correcting voltage, which is applied to the RF frequency pilot to adjust the synchronism condition. When the feedback is established, the micropulse jitter is reduced, the intensity fluctuations on the ms scale are damped and wavelength drift is suppressed. It has thus significantly improved the FEL operation at perfect tuning, and provides a stable laser with all its parameters optimized for the users.

Operation of the European storage ring FEL at ELETTRA down to 190 nm

Abstract Recent improvements in the performance of the European storage ring FEL at ELETTRA including shorter wavelength operation (190xa0nm), wider tunability and increased power are described. We report briefly also on initial use for experimental studies.

First lasing and initial performance of the European UV/VUV storage ring FEL at ELETTRA

Abstract An overview of the European storage ring FEL project is presented, including a description of the main components, details of initial lasing at 350 and 220xa0nm and future prospects.

European project to develop a UV/VUV free-electron laser facility on the ELETTRA storage ring☆

Abstract The main features and novel technical aspects of a new European project to integrate a free-electron laser on an existing “third generation” synchrotron radiation user facility are described, including the design of the optical cavity and undulator, the electron beam characteristics and a first assessment of the predicted laser performance.

Mirror degradation and heating in storage ring FELs

Abstract Storage Ring Free Electrons Lasers (SRFELs) in the UV are now utilized as laser facilities for time-resolved fluorescence experiments or two-colour experiments with synchronized FEL and synchrotron radiations. Such experiments set new requirements for the laser and, consequently, for the optics such as long duration lasing, high laser power and short wavelengths. As these features imply operation of the storage ring at higher energies, cavity mirrors are subjected to radiation from undulator harmonics under more drastic conditions: increased power leading to heating of the front mirror, and degradation induced by undulator radiation extending towards X-rays. Also, for short λ operation, new difficulties arise: some materials become more absorbant and scattering losses increase.

The UV European FEL at ELETTRA: towards compatibility of storage ring operation for FEL and synchrotron radiation

Abstract The European Free Electron Laser (FEL) at ELETTRA has recently increased its maximum operating energy up to 1.5 GeV , the highest electron-beam energy used so far for an FEL. This is an important improvement in the performance of the source, increasing the extracted power at wavelengths around 200 nm and providing better beam stability and lifetime. Furthermore, this development represents a first step towards the solution of a crucial issue—the compatibility of FEL and normal synchrotron radiation operation at a user facility like ELETTRA. In this paper we discuss the most important aspects of this issue; in particular, we show that the properties of the electron beam in FEL mode can match the needs of normal synchrotron radiation experiments that require a few bunch filling of the storage ring.

Operation and performance of a free electron laser oscillator down to 190 nm

We present recent results obtained by the European Free Electron Laser (FEL) project at the ELETTRA storage ring. Coherent and tunable light was produced in the ultraviolet down to below 190 nm, the shortest lasing wavelength obtained so far with a FEL oscillator. The performance of the FEL is described, together with a series of technical solutions that have been adopted on it. These solutions increase its validity as a source for applications, and demonstrate the potential of FEL oscillators to become sources with features in the vacuum ultraviolet.

Electron beam properties and impedance characterization for storage rings used for free electron lasers

Abstract Good electron beam qualities and stability are the crucial features of Storage Rings dedicated to synchrotron radiation sources or to Free Electron Laser. Most of these characteristics depend on the coupling of the e-beam with the machine environment, which can be in turn modelled in terms of a characteristic impedance, whose absolute value and structure can be used to specify both the stability (longitudinal and transverse) of the beam and its qualities (energy spread, bunch length, peak current, etc.). In this paper we consider two specific examples of Storage Rings used for FEL operation and analyze their performances by means of semianalytical and numerical methods. The analysis is aimed at clarifying the dependence of beam energy spread and bunch length on beam current and at providing a set of parameters useful for the optimization of Free Electron Laser or synchrotron radiation sources.

Study of the transverse modes on the Super-ACO FEL

Abstract Experimentally, the Super-ACO free electron laser (FEL) is usually observed on a main TEM 0 n mode, with n ranging between 0 and 5, depending on the adjustments. In addition a large tail is present, resulting from higher-order modes. A theoretical analysis is presented. Consequences are derived concerning the laser power and the cavity losses.