Recordings of rare events require detection strategy in single-shot. It is also of crucial interest for recordings of terahertz waveforms in terahertz spectroscopy of irreversible processes. The time-domain spectroscopy usually requires scanning techniques that prevent the applications of very low repetition rate sources such as strong THz pulse sources based on table-top high power lasers or accelerators.
We present a strategy allowing complex electric fields to be recorded in single-shot using the chirped pulse electro-optic sampling technique at 1550 nm with signal processing techniques based on DEOS (Diversity Electro-Optic Sampling).
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.
L. Badano, E. Ferrari, E. Allaria, S. Bassanese, D. Castronovo, M. Danailov, A. Demidovich, G. De Ninno, S. Di Mitri, B. Diviacco, W. Fawley, L. Frohlich, G. Gaio, L. Giannessi, G. Penco, S. Spampinati, C. Spezzani, M. Trovò, M. Veronese
FERMI is the first user facility based upon an externally seeded free-electron laser (FEL) that delivers a coherent and tunable UV radiation (down to 4 nm at the fundamental) in a number of different configurations. A microbunching instability (MBI) developing in the bunch compressors and in the rest of the linac can degrade the quality of the high brightness electron beam sufficiently to reduce the FEL output intensity and spectral brightness. A laser heater installed in the low energy (100 MeV) part of the FERMI accelerator increases the local energy spread to provide Landau damping against this instability. In this paper we summarize the main results obtained with the FERMI laser heater since it commissioning in 2012. We present the measurement of the reduction of the incoherent energy spread at the linac exit induced by the heating of the electron beam at the beginning of the linac. We also discuss the positive effects of such heating upon the emission of coherent optical transition radiation and the FEL performances both in terms of intensity and spectrum. Moreover, we report about results that have been used to experimentally demonstrate that for transversely uniform heating the local energy spread augmentation is characterized by a non-Gaussian distribution that can be preserved up to the FEL undulator entrance with a significant impact on the performance of high-gain harmonic generation (HGHG) FELs, especially at soft x-ray wavelengths.
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.
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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