FERMI@Elettra is a free electron-laser (FEL)-based user facility that, after two years of commissioning, started preliminary users' dedicated runs in 2011. At variance with other FEL user facilities, ...FERMI@Elettra has been designed to deliver improved spectral stability and longitudinal coherence. The adopted scheme, which uses an external laser to initiate the FEL process, has been demonstrated to be capable of generating FEL pulses close to the Fourier transform limit. We report on the first instance of FEL wavelength tuning, both in a narrow and in a large spectral range (fine- and coarse-tuning). We also report on two different experiments that have been performed exploiting such FEL tuning. We used fine-tuning to scan across the 1s-4p resonance in He atoms, at 23.74 eV (52.2 nm), detecting both UV-visible fluorescence (4p-2s, 400 nm) and EUV fluorescence (4p-1s, 52.2 nm). We used coarse-tuning to scan the M4,5 absorption edge of Ge (∼29.5 eV) in the wavelength region 30-60 nm, measured in transmission geometry with a thermopile positioned on the rear side of a Ge thin foil.
Synchrotron radiation time structure is becoming a common tool for studying dynamic properties of materials. The main limitation is often the wide time domain the user would like to access with ...pump–probe experiments. In order to perform photoelectron spectroscopy experiments over time scales from milliseconds to picoseconds it is mandatory to measure the time at which each measured photoelectron was created. For this reason the usual CCD camera‐based two‐dimensional detection of electron energy analyzers has been replaced by a new delay‐line detector adapted to the time structure of the SOLEIL synchrotron radiation source. The new two‐dimensional delay‐line detector has a time resolution of 5 ns and was installed on a Scienta SES 2002 electron energy analyzer. The first application has been to characterize the time of flight of the photoemitted electrons as a function of their kinetic energy and the selected pass energy. By repeating the experiment as a function of the available pass energy and of the kinetic energy, a complete characterization of the analyzer behaviour in the time domain has been obtained. Even for kinetic energies as low as 10 eV at 2 eV pass energy, the time spread of the detected electrons is lower than 140 ns. These results and the time structure of the SOLEIL filling modes assure the possibility of performing pump–probe photoelectron spectroscopy experiments with the time resolution given by the SOLEIL pulse width, the best performance of the beamline and of the experimental station.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Advances in laser and Synchrotron Radiation instrumentation are continuously boosting fundamental research on the electronic structure of matter. At Elettra the collaboration between several groups ...active in the field of atomic, molecular and cluster physics and the Instrumentation and Detector Laboratory has resulted in an experimental set-up that successfully tackles the challenges posed by the investigation of the electronic structure of isolated species in the gas phase. The use of Synchrotron Radiation (SR) and Free Electron Laser (FEL) light, allows to cover a wide spectrum of targets from energetic to dynamics. We developed a Velocity Map Imaging (VMI) spectrometer that allows to perform as well SR as FEL experiments, just by changing part of the detection system.
In SR experiments, at the Gasphase beamline of Elettra, a cross delay line detector is used, coupled to a 4-channel time-to-digital converter that reconstructs the position of the electrons. Simultaneously, a Time-of-Flight (TOF) mass spectrometer is used to acquire photoion spectra. Such a system allows PhotoElectron-PhotoIon-Coincidence (PEPICO) spectroscopy of atoms, molecules and clusters. In FEL experiments (notably differing from SR experiments in the much higher rate of events produced and detected, which forces one to forfeit coincidence detection), at the Low Density Matter (LDM) beamline of FERMI, a Micro Channel Plate (MCP) a phosphor screen and a CCD camera are used instead, capable of shot-by-shot collection of practically all events, albeit without time resolution.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
5.
A beam-shaping system for TIMEX beamline Svetina, C.; Sostero, G.; Sergo, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2011, Volume:
635, Issue:
1
Journal Article
Peer reviewed
FERMI@Elettra is a Free Electron Laser (FEL) user facility currently under construction at Sincrotrone Trieste in Italy. It will provide a spatially coherent and transform-limited photon beam in the ...sub-ps regime, covering the VUV/Soft X-ray range (from 100 down to 1.33
nm). Thanks to its high fluence this 4th generation light source will be able to create and probe warm dense matter (WDM) inside the TIMEX end-station. Since the WDM state has a short lifetime (a few ps), measurement of basic physical quantities, such as temperature and density, is a challenge and new approaches are needed. For this reason a new method has been proposed for measuring temperature using a slowly responding pyrometric probe (Principi et al., 2010
1). However, the technique does require the spatial photon beam profile to be properly shaped at the sample. This can be done using an active optic (i.e. a deformable plane mirror) placed before the elliptical focusing mirror. Ray-tracing simulations and metrology measurements on a prototype have been performed and the results are presented here.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A new photoelectron imaging spectrometer has been used to measure the photoelectron angular distributions in pump-probe experiments where the VUV radiation of the synchrotron is used to prepare an ...aligned state of the target and the radiation of a Ti:sapphire laser ionizes it. The new set-up and its use to study the photoionization of the He 1s3p (1P1) and Ne 2p5nd (1P1) states are described.
We present a new bidimensional detector setup, based on cross delay line technology, specifically developed for time resolved experiments and particularly suited to work in conjunction with ...pump-and-probe systems. Thanks to the particular architecture of the acquisition electronics, the detector is able to correlate each event with the time it occurred in a way which preserves the picoseconds time resolution of pump-and-probe techniques and, more generally, can perform time resolved acquisition in the nanosecond or picoseconds scale. The acquisition setup count rate, up to more than 4
Mcounts/s in time resolved mode, exceeds the performances of the best two-dimensional detectors working in counting mode presently available on electron analysers.
First experimental results, obtained both on bench tests and in UHV conditions, where the detector has been mounted on an electron analyser, confirm the validity of the approach and show the potentiality of time resolved acquisition applied to electron spectroscopy analysis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The utilization of time-based approaches in modern physics experiments, has seen continuous growth thanks to the increasing performance of modern time-interval-meters (TIMs). In this context, ...Time-to-Digital Converters (TDCs), that are fully-digital TIMs, play a fundamental role. The digital approach makes the integration into measurement setups easier, while giving the possibility to investigate time-events with picosecond resolution over extended dynamic-ranges. Cross Delay-Lines (CDL) detectors are remarkably valuable, due to the fact that the position of the event can be detected by measuring the time of arrival, obtaining both information at once. With the purpose of achieving both fast parallel computing and time precision, the conventional acquisition systems usually count on 4-channel Application Specific Integrated Circuit (ASIC) Time-to-Digital Converters (TDCs) preceding a Field Programmable Logic Array (FPGA), reaching state-of-the-art performance in time resolved experiments. In this kind of architecture, the lack of reconfigurability, given by the ASIC, is a tightly limiting factor when customization of the setup is required, even more so at present day, where state-of-the-art TDCs with performance similar to ASICs can be fully implemented on FPGAs; for this reason, we propose a fully-FPGA based approach to this problem, in order to obtain a complete real-time system that can be completely reconfigured in function of the experimental setup. With the aim of improving the accuracy of the experiments, the time correlation between the CDL and the arrival time of other events occurring in conjunction is essential. For this reason, auxiliary TDC channels are needed. In this contribution, we present a compact, powerful and fully-configurable FPGA-based solution, where an 8-channel TDC with a precision of 12 ps r.m.s. and the related real-time image reconstruction algorithm are performed on two different FPGA devices. In this sense, a spatial resolution on the CDL of 50/60 µm FWHM is achieved.
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