The seeded FEL FERMI has completed the commissioning of both the FEL lines, and it is now providing the user community with a coherent and tunable UV radiation (from 100 nm to 4 nm) in a number of different configurations. These also include original FEL-pump - FEL-probe schemes with twin-seeded FEL pulses. Among the key systems for the operation of FERMI, there is the femtosecond optical timing system and dedicated longitudinal diagnostics, specifically developed for FERMI. In this paper, after a short review of the FERMI optical timing system and of its routinely achieved performances, we focus on the results obtained from the suite of longitudinal diagnostics (Bunch Arrival Monitor, Electro Optical sampling station and RF deflectors) all operating in single shot and with 10s fs resolution which demonstrate the FERMI achieved performances. The longitudinal diagnostics measurements are compared between these device and other device on shot-to-shot basis, looking for correlations between machine parameters. Finally future challenges in terms of improvement of existing diagnostics, planned installations and possible upgrades are discussed.
The goal of this work is to prove the feasibility of building a laser system that can generate mid-infrared radiation with
the parameters required for the measurement of the hyperfine splitting in the ground state of the mounic hydrogen
spectroscopy.
The first experimental results of a very straightforward scheme that, to our knowledge, has not been considered in the
literature, are presented. We study a laser test bench system emitting nanosecond pulses of infrared tunable radiation in
the spectral range 6.78 μm with high energy and narrow line-width, based on direct difference frequency generation
(DFG), in non-oxide nonlinear crystals, using as pump lasers a single-mode Nd:YAG laser and tunable narrowbandwidth
Cr:forsterite laser.
The investigated system is based on lithium thioindate (LiInS2) and silver thiogallate (AgGaS2) crystals cut for type II difference frequency generation. The pulses of the Nd:YAG laser (1,064 μm) are combined with the pulses at ~ 1.262 μm of the Cr:forsterite laser through a dichroic mirror and sent to the nonlinear crystals in different optical geometries.
The generated radiation reaches an output energy up to 80 μJ in a single pass optical geometry, has 10 ns long pulses at
50 Hz frequency repetition rate and is tunable in the range 6595 – 6895 nm. These first results prove the suitability of
such an approach for building the laser system for the muonic-hydrogen experiment.
Cristian Svetina, Nicola Mahne, Lorenzo Raimondi, Luca Rumiz, Marco Zangrando, Enrico Allaria, Filippo Bencivenga, Carlo Callegari, Flavio Capotondi, Davide Castronovo, Paolo Cinquegrana, Paolo Craievich, Ivan Cudin, Massimo Dal Forno, Miltcho Danailov, Gerardo D'Auria, Raffaele De Monte, Giovanni De Ninno, Alexander Demidovich, Simone Di Mitri, Bruno Diviacco, Alessandro Fabris, Riccardo Fabris, William Fawley, Mario Ferianis, Eugenio Ferrari, Lars Froehlich, Paolo Furlan Radivo, Giulio Gaio, Luca Giannessi, Maya Kiskinova, Marco Lonza, Benoit Mahieu, Claudio Masciovecchio, Ivaylo Nikolov, Fulvio Parmigiani, Emanuele Pedersoli, Giuseppe Penco, Mauro Predonzani, Emiliano Principi, Fabio Rossi, Claudio Scafuri, Claudio Serpico, Paolo Sigalotti, Simone Spampinati, Carlo Spezzani, Michele Svandrlik, Mauro Trovo, Alessandro Vascotto, Marco Veronese, Roberto Visintini, Dino Zangrando
FERMI@Elettra is the first seeded VUV/soft X-ray FEL source. It is composed of two undulatory chains: the low energy branch (FELl) covering the wavelength range from 20 nm up to 100 nm, and the high energy branch (FEL2, employing a double stage cascade), covering the wavelength range from 4 nm up to 20 nm. At the end of 2012 FELl has been opened to external users while FEL2 has been turned on for the first time having demonstrated that a double cascade scheme is suitable for generating high intensity coherent FEL radiation. In this paper we will share our experience and will show our most recent results for both FERMI FELl and FEL2 sources. We will also present a brand new machine scheme that allows to perform two-colour pump and probe experiments as well as the first experimental results.
Modern VUV and X-ray Free Electron Laser (FEL) facilities contain a number of ultrafast lasers (like photoinjector, seed and pump-probe lasers) whose performance is crucial for the generated FEL light quality as well as for the accuracy of the time resolved measurements performed using the FEL pulses. One of the very important laser related aspects, especially at seeded FELs, is the ability to precisely lock the ultrafast laser systems to the master clock signal, keeping the timing jitter and drifts of the generated pulses with respect to the machine timing as low as possible. The aim of this work is to review the main sources of timing jitter and drifts and present the schemes and solutions developed at FERMI for their characterization and compensation. The paper will first introduce a general scheme showing the architecture of the laser locking system developed for FERMI. Both the radio-frequency (RF) locking and the advanced balanced optical cross correlator electronics and optical setup design are described, together with data on the laser oscillator locking performance obtained in different modalities. Cross correlation measurements indicating the contribution of the ultrafast regenerative amplifier and optical beam transport part to the overall temporal jitter of the amplified ultrashort pulses arriving at destination are presented. The paper also includes examples of the influence of improved laser timing jitter and drifts on the seeded FEL performance and discusses foreseen future developments.
S. Di Mitri, E. Allaria, P. Cinquegrana, P. Craievich, M. Danailov, A. Demidovich, G. De Ninno, B. Diviacco, W. Fawley, L. Froelich, L. Giannessi, R. Ivanov, M. Musardo, I. Nikolov, G. Penco, P. Sigalotti, S. Spampinati, C. Spezzani, M. Trovò, M. Veronese
After less than two years of commissioning the FERMI@Elettra free electron laser is now entering into the operation
phase and is providing light to the first user experiments. To reach the final ambitious goals of providing high power
coherent pulses with fundamental wavelengths down to 4 nm, the system will need further studies and additional
commissioning time in 2011 when fine tuning of the major systems such as the electron gun and the main accelerator
will take place. Nevertheless, FERMI is already able to provide light with unique characteristics allowing Users to
perform experiments not possible with other facilities. Based on a 1.5 GeV electron linear accelerator, FERMI@Elettra
has two seeded FEL lines that cover the whole spectral range from 100 nm down to 4 nm with fully coherent pulses. The
use of the high gain harmonic generation scheme initiated by a tunable laser in the UV allows FERMI to produce light
characterized by both transverse and full temporal coherence. The use of specially designed undulators allows full
control of the FEL polarization and can be continuously varied from linear to circular in any orientation or ellipticity.
Here we will report about the first results and the future plans for FERMI@Elettra.
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