The Low Density Matter (LDM) beamline at FERMI: optical layout and first commissioning

Svetina, Cristian; Grazioli, Cesare; Mahne, Nicola; Raimondi, Lorenzo; Fava, C.; Zangrando, Marco; Gerusina, Simone; Alagia, Michele; Avaldi, L.; Cautero, G.; Simone, Monica de; Devetta, M.; Fraia, Michele Di; Drabbels, Marcel; Feyer, Vitaliy; Finetti, P.; Katzy, R.; Kivimäki, A.; Lyamayev, V.; Mazza, Tommaso; Moise, A.; Möller, Thomas; O’Keeffe, Patrick; Ovcharenko, Yevheniy; Piseri, P.; Plekan, Oksana; Prince, Kevin C.; Sergo, R.; Stienkemeier, F.; Stranges, Stefano; Coreno, Marcello; Callegari, Carlo

doi:10.1107/s1600577515005743

Cited by 50 publications

(42 citation statements)

References 23 publications

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“…This, however, would require using a much longer wavelength of radiation of about 12 nm (100 eV) to assure sufficiently strong scattering at large angles. This long wavelength regime is not available at LCLS, but is common at the FLASH and FERMI free electron lasers [37][38]. A recent XFEL based wide angle x-ray scattering study of Ag nano-particles enabled the reconstruction of their three-dimensional shapes [36].…”

Section: Oblate and Prolate Shapes Of Rotating Dropletsmentioning

confidence: 99%

Shapes of rotating superfluid helium nanodroplets

et al. 2017

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Rotating superfluid He droplets of approximately 1 μm in diameter were obtained in a free nozzle beam expansion of liquid He in vacuum and were studied by single-shot coherent diffractive imaging using an x-ray free electron laser. The formation of strongly deformed droplets is evidenced by large anisotropies and intensity anomalies (streaks) in the obtained diffraction images. The analysis of the images shows that, in addition to previously described axially symmetric oblate shapes, some droplets exhibit prolate shapes. Forward modeling of the diffraction images indicates that the shapes of rotating superfluid droplets are very similar to their classical counterparts, giving direct access to the droplet angular momenta and angular velocities. The analyses of the radial intensity distribution and appearance statistics of the anisotropic images confirm the existence of oblate metastable superfluid droplets with large angular momenta beyond the classical bifurcation threshold.3

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Section: Oblate and Prolate Shapes Of Rotating Dropletsmentioning

confidence: 99%

Shapes of rotating superfluid helium nanodroplets

et al. 2017

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“…The pulse energies, calculated intensity, and intensity ratios, are given in appendix. For strong ω and weak 2ω, the average intensities were 2×10 13 and 4.6×10 11 W cm −2 respectively, while for weak ω and strong 2ω, the average intensities were 6.3×10 11 and 3×10 13 W cm −2 respectively.…”

Section: Experimental Methodsmentioning

confidence: 97%

“…The intensity at the sample was calculated from the measured pulse energies at the exit of the FERMI radiators, the measured spot area and the calculated transmission of the transport optics [13]. At 26.85 eV (ω), the theoretical transmission is 0.6, and at 53.7 eV (2ω) it is 0.77.…”

Section: Experimental Methodsmentioning

confidence: 99%

A detailed investigation of single-photon laser enabled Auger decay in neon

et al. 2019

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Single-photon laser enabled Auger decay (spLEAD) is an electronic de-excitation process which was recently predicted and observed in Ne. We have investigated it using bichromatic phase-locked free electron laser radiation and extensive angle-resolved photoelectron measurements, supported by a detailed theoretical model. We first used separately the fundamental wavelength resonant with the Ne + 2s-2p transition, 46.17 nm, and its second harmonic, 23.08 nm, then their phase-locked bichromatic combination. In the latter case the phase difference between the two wavelengths was scanned, and interference effects were observed, confirming that the spLEAD process was occurring. The detailed theoretical model we developed qualitatively predicts all observations: branching ratios between the final Auger states, their amplitudes of oscillation as a function of phase, the phase lag between the oscillations of different final states, and partial cancellation of the oscillations under certain conditions.

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“…The experiment was performed at the Low Density Matter (LDM) beamline [9] at FERMI FEL-1 [2]. The EUV pulses had an average energy of 16 µJ, duration estimated between 60 and 80 fs FWHM, circular polarization, focal size 30 µm FWHM, and were tuned to the wavelength resonant with the two-photon doubly excited target state, 75.65 nm.…”

Section: Methodsmentioning

confidence: 99%

Application of Matched-Filter Concepts to Unbiased Selection of Data in Pump-Probe Experiments with Free Electron Lasers

et al. 2017

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Pump-probe experiments are commonly used at Free Electron Lasers (FEL) to elucidate the femtosecond dynamics of atoms, molecules, clusters, liquids and solids. Maximizing the signal-to-noise ratio of the measurements is often a primary need of the experiment, and the aggregation of repeated, rapid, scans of the pump-probe delay is preferable to a single long-lasting scan. The limited availability of beamtime makes it impractical to repeat measurements indiscriminately, and the large, rapid flow of single-shot data that need to be processed and aggregated into a dataset, makes it difficult to assess the quality of a measurement in real time. In post-analysis it is then necessary to devise unbiased criteria to select or reject datasets, and to assign the weight with which they enter the analysis. One such case was the measurement of the lifetime of Intermolecular Coulombic Decay in the weakly-bound neon dimer. We report on the method we used to accomplish this goal for the pump-probe delay scans that constitute the core of the measurement; namely we report on the use of simple auto-and cross-correlation techniques based on the general concept of "matched filter". We are able to unambiguously assess the signal-to-noise ratio (SNR) of each scan, which then becomes the weight with which a scan enters the average of multiple scans. We also observe a clear gap in the values of SNR, and we discard all the scans below a SNR of 0.45. We are able to generate an average delay scan profile, suitable for further analysis: in our previous work we used it for comparison with theory. Here we argue that the method is sufficiently simple and devoid of human action to be applicable not only in post-analysis, but also for the real-time assessment of the quality of a dataset.

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The Low Density Matter (LDM) beamline at FERMI: optical layout and first commissioning

Cited by 50 publications

References 23 publications

Shapes of rotating superfluid helium nanodroplets

Shapes of rotating superfluid helium nanodroplets

A detailed investigation of single-photon laser enabled Auger decay in neon

Application of Matched-Filter Concepts to Unbiased Selection of Data in Pump-Probe Experiments with Free Electron Lasers

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