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21.
Slow interatomic Coulombic decay of multiply excited neon clusters
Denis Iablonskyi, Giovanni De Ninno, 2016, original scientific article

Abstract: Ne clusters (∼ 5000 atoms) were resonantly excited (2 p→ 3 s) by intense free electron laser (FEL) radiation at FERMI. Such multiply excited clusters can decay nonradiatively via energy exchange between at least two neighboring excited atoms. Benefiting from the precise tunability and narrow bandwidth of seeded FEL radiation, specific sites of the Ne clusters were probed. We found that the relaxation of cluster surface atoms proceeds via a sequence of interatomic or intermolecular Coulombic decay (ICD) processes while ICD of bulk atoms is additionally affected by the surrounding excited medium via inelastic electron scattering. For both cases, cluster excitations relax to atomic states prior to ICD, showing that this kind of ICD is rather slow (picosecond range). Controlling the average number of excitations per cluster via the FEL intensity allows a coarse tuning of the ICD rate.
Keywords: Clusters, low-denisty matter, free-electron laser
Published in RUNG: 27.10.2020; Views: 2017; Downloads: 0
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22.
Element-resolved study on the influence of a magnetic dopant on the exchange interaction in FePt on ultrashort timescales
Jurij Urbančič, 2017, published scientific conference contribution abstract

Abstract: In this study, we investigate the optically induced ultrafast demagnetization dynamics of a FePt alloy doped with Mn atoms on the characteristic timescale of the exchange interaction of a few femtoseconds. We use high harmonic generation with photon energies in the XUV to gain elemental resolution in a femtosecond magneto-optical Kerr-effect experiment [1] in transversal geometry. Following up on earlier experiments, which showed the importance of the exchange interaction in the demagnetization process in alloys [2,3], we see clear differences in the dynamical responses of the three elements Fe, Pt, and Mn. Our results suggest, that the exchange coupling between the magnetic moments of the FePt alloy and the Mn dopant changes on ultrashort timescales.
Keywords: FePt, High Harmonic Generation, Laser, Magnetic Materials
Published in RUNG: 22.05.2020; Views: 2951; Downloads: 0

23.
Narrowband high harmonic pulses for trARPES using frequency-upconverted Ti:Sapphire lasers
Jurij Urbančič, published scientific conference contribution abstract

Abstract: trARPES using femtosecond XUV high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800 nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that shorter wavelength driven high harmonic extreme-ultraviolet trARPES is superior to using 800 nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution while preserving excellent time resolution.
Keywords: HHG, ARPES, Laser
Published in RUNG: 22.05.2020; Views: 2594; Downloads: 0

24.
Shaping FEL radiation : from multipulse/multicolor emission to generation of twisted light
Primož Rebernik Ribič, 2016, published scientific conference contribution abstract (invited lecture)

Keywords: radiation, synchrotron, free-electron laser
Published in RUNG: 16.01.2020; Views: 2757; Downloads: 11
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A detailed investigation of single-photon laser enabled Auger decay in neon
Primož Rebernik Ribič, Giovanni De Ninno, 2019, original scientific article

Abstract: 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.
Keywords: laser enabled Auger decay, free-electron lasers, neon
Published in RUNG: 12.01.2020; Views: 2717; Downloads: 0
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28.
Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser
Primož Rebernik Ribič, Giovanni De Ninno, 2019, original scientific article

Abstract: X-ray free-electron lasers (FELs), which amplify light emitted by a relativistic electron beam, are extending nonlinear optical techniques to shorter wavelengths, adding element specificity by exciting and probing electronic transitions from core levels. These techniques would benefit tremendously from having a stable FEL source, generating spectrally pure and wavelength-tunable pulses. We show that such requirements can be met by operating the FEL in the so-called echo-enabled harmonic generation (EEHG) configuration. Here, two external conventional lasers are used to precisely tailor the longitudinal phase space of the electron beam before emission of X-rays. We demonstrate high-gain EEHG lasing producing stable, intense, nearly fully coherent pulses at wavelengths as short as 5.9 nm (~211 eV) at the FERMI FEL user facility. Low sensitivity to electron-beam imperfections and observation of stable, narrow-band, coherent emission down to 2.6 nm (~474 eV) make the technique a prime candidate for generating laser-like pulses in the X-ray spectral region, opening the door to multidimensional coherent spectroscopies at short wavelengths.
Keywords: free electron laser, coherence, x-rays
Published in RUNG: 07.05.2019; Views: 3331; Downloads: 0
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29.
Energy enhancement of the target surface electron by using a 200 TW sub-picosecond laser
J. Y. Mao, 2018, original scientific article

Abstract: One order of magnitude energy enhancement of the target surface electron beams with central energy at 11.5 MeV is achieved by using a 200 TW, 500 fs laser at an incident angle of 72° with a prepulse intensity ratio of 5×10−6. The experimental results demonstrate the scalability of the acceleration process to high electron energy with a longer (sub-picosecond) laser pulse duration and a higher laser energy (120 J). The total charge of the beam is 400±20 pC(
Keywords: Strong field laser physics, Plasmas, Particles, Femtosecond phenomena, Surface dynamics.
Published in RUNG: 07.08.2018; Views: 4075; Downloads: 0
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30.
Studies in the atmospheric monitoring at the Pierre Auger Observatory using the upgraded Central Laser Facility
Carlos Medina-Hernandez, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, published scientific conference contribution

Abstract: The Fluorescence Detector (FD) at the Pierre Auger Observatory measures the intensity of the scattered light from laser tracks generated by the Central Laser Facility (CLF) and the eXtreme Laser Facility (XLF) to monitor and estimate the vertical aerosol optical depth (τ(z,t)). This measurement is needed to obtain unbiased and reliable FD measurements of the arrival direction and energy of the primary cosmic ray, and the depth of the maximum shower development. The CLF was upgraded substantially in 2013 with the addition of a solid state laser, new generation GPS, a robotic beam calibration system, better thermal and dust isolation, and improved software. The upgrade also included a back-scatter Raman LIDAR to measure τ(z,t). The new features and applications of the upgraded instrument are described. These include the laser energy calibration and the atmospheric monitoring measurements. The first τ(z,t) results and comparisons after the upgrade are presented using different methods. The first method compares the FD hourly response to the scattered light from the CLF (or XLF) against a reference hourly profile measured during a clear night where zero aerosol contents are assumed. The second method simulates FD responses with different atmospheric parameters and selects the parameters that provide the best fit to the actual FD response. A third method uses the new Raman LIDAR receiver in-situ to measure the back-scatter light from the CLF laser. The results show a good data agreement for the first and second methods using FD stations located at the same distance from the facilities. Preliminary results of τ(z,t) using the Raman LIDAR are presented as well.
Keywords: Pierre Auger Observatory, extensive air showers, the Fluorescence Detector, atmospheric monitoring, vertical aerosol optical depth, the Central Laser Facility, the eXtreme Laser Facility
Published in RUNG: 03.03.2016; Views: 4820; Downloads: 182
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