1. |
- Allaria, E., et al.
(author)
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Highly coherent and stable pulses from the FERMI seeded free-electron laser in the extreme ultraviolet
- 2012
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In: Nature Photonics. - 1749-4885. ; 6:10, s. 699-704
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Journal article (peer-reviewed)abstract
- Free-electron lasers (FELs) are promising devices for generating light with laser-like properties in the extreme ultraviolet and X-ray spectral regions. Recently, FELs based on the self-amplified spontaneous emission (SASE) mechanism have allowed major breakthroughs in diffraction and spectroscopy applications, despite the relatively large shot-to-shot intensity and photon-energy fluctuations and the limited longitudinal coherence inherent in the SASE mechanism. Here, we report results on the initial performance of the FERMI seeded FEL, based on the high-gain harmonic generation configuration, in which an external laser is used to initiate the emission process. Emission from the FERMI FEL-1 source occurs in the form of pulses carrying energy of several tens of microjoules per pulse and tunable throughout the 65 to 20 nm wavelength range, with unprecedented shot-to-shot wavelength stability, low-intensity fluctuations, close to transform-limited bandwidth, transverse and longitudinal coherence and full control of polarization.
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2. |
- Finetti, P., et al.
(author)
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Pulse duration of seeded free electron lasers
- 2017
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In: Physical Review X. - 2160-3308. ; 7:2
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Journal article (peer-reviewed)abstract
- The pulse duration, and, more generally, the temporal intensity profile of free-electron laser (FEL) pulses, is of utmost importance for exploring the new perspectives offered by FELs; it is a nontrivial experimental parameter that needs to be characterized. We measured the pulse shape of an extreme ultraviolet externally seeded FEL operating in high-gain harmonic generation mode. Two different methods based on the cross-correlation of the FEL pulses with an external optical laser were used. The two methods, one capable of single-shot performance, may both be implemented as online diagnostics in FEL facilities. The measurements were carried out at the seeded FEL facility FERMI. The FEL temporal pulse characteristics were measured and studied in a range of FEL wavelengths and machine settings, and they were compared to the predictions of a theoretical model. The measurements allowed a direct observation of the pulse lengthening and splitting at saturation, in agreement with the proposed theory.
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3. |
- Finetti, P., et al.
(author)
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Optical setup for two-colour experiments at the low density matter beamline of FERMI
- 2017
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In: Journal of optics. - : IOP Publishing. - 0150-536X .- 2040-8978 .- 2040-8986. ; 19:11
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Journal article (peer-reviewed)abstract
- The low density matter beamline of the free electron laser facility FERMI is dedicated to the study of atomic, molecular and cluster systems, and here we describe the optical setup available for two-colour experiments. Samples can be exposed to ultrashort pulses from a Ti:Sapphire source (fundamental, or second or third harmonic), and ultrashort light pulses of FERMI in the EUV/soft x-ray region with a well-defined temporal delay, and negligible jitter (<10 fs) compared to the pulse durations (40–100 fs). Detection schemes available include electron, ion and optical spectroscopy. The majority of experiments using this apparatus are pump-and-probe, where either wavelength can be pump or probe, but the system is also useful for other techniques, such as multi-photon spectroscopy, cross-correlation measurements and alignment of molecules in space.
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4. |
- Lorusso, A., et al.
(author)
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Pulsed laser deposition of yttrium photocathode suitable for use in radio-frequency guns
- 2017
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In: Applied Physics A. - : SPRINGER. - 0947-8396 .- 1432-0630. ; 123:12
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Journal article (peer-reviewed)abstract
- Yttrium (Y) thin film was grown by pulsed laser deposition (PLD) on a copper (Cu) polycrystalline substrate. Ex situ morphological and structural characterisations of the circular Y film of 1.2 mu m thickness and 3 mm diameter have shown a very low droplet density on the film surface and a crystalline feature with a preferred orientation along the Y (100) plane. Moreover, Y thin film resulted in being very adherent to the Cu substrate and more scratch resistant than Cu bulk. A twin thin film was deposited also on a Cu backflange of a radio-frequency (RF) gun to test the suitability of the metallic thin film as photocathode. It was observed that the Y-coated photocathode was characterised by a quantum efficiency (QE) higher than that of the Cu bulk photocathode even if the presence of space charge effects didnt allow deriving the absolute maximum value of QE of Y photocathode.
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