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33.
Coherent THz Emission Enhanced by Coherent Synchrotron Radiation Wakefield
Primož Rebernik Ribič, Giovanni De Ninno, 2018, izvirni znanstveni članek

Opis: We demonstrate that emission of coherent transition radiation by a ∼1 GeV energy-electron beam passing through an Al foil is enhanced in intensity and extended in frequency spectral range, by the energy correlation established along the beam by coherent synchrotron radiation wakefield, in the presence of a proper electron optics in the beam delivery system. Analytical and numerical models, based on experimental electron beam parameters collected at the FERMI free electron laser (FEL), predict transition radiation with two intensity peaks at ∼0.3 THz and ∼1.5 THz, and extending up to 8.5 THz with intensity above 20 dB w.r.t. the main peak. Up to 80-µJ pulse energy integrated over the full bandwidth is expected at the source, and in agreement with experimental pulse energy measurements. By virtue of its implementation in an FEL beam dump line, this work promises dissemination of user-oriented multi-THz beamlines parasitic and self-synchronized to EUV and x-ray FELs.
Ključne besede: terahertz radiation, free-electron lasers, coherent transition radiation
Objavljeno v RUNG: 12.01.2020; Ogledov: 2857; Prenosov: 0
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34.
A detailed investigation of single-photon laser enabled Auger decay in neon
Primož Rebernik Ribič, Giovanni De Ninno, 2019, izvirni znanstveni članek

Opis: 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.
Ključne besede: laser enabled Auger decay, free-electron lasers, neon
Objavljeno v RUNG: 12.01.2020; Ogledov: 2717; Prenosov: 0
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35.
Complete Characterization of Phase and Amplitude of Bichromatic Extreme Ultraviolet Light
Primož Rebernik Ribič, Giovanni De Ninno, 2019, izvirni znanstveni članek

Opis: Intense, mutually coherent beams of multiharmonic extreme ultraviolet light can now be created using seeded free-electron lasers, and the phase difference between harmonics can be tuned with attosecond accuracy. However, the absolute value of the phase is generally not determined. We present a method for determining precisely the absolute phase relationship of a fundamental wavelength and its second harmonic, as well as the amplitude ratio. Only a few easily calculated theoretical parameters are required in addition to the experimental data.
Ključne besede: free-electron lasers, coherence, phase, attosecond
Objavljeno v RUNG: 12.01.2020; Ogledov: 2817; Prenosov: 0
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36.
Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser
Primož Rebernik Ribič, Giovanni De Ninno, 2019, izvirni znanstveni članek

Opis: 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.
Ključne besede: free electron laser, coherence, x-rays
Objavljeno v RUNG: 07.05.2019; Ogledov: 3331; Prenosov: 0
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37.
Ultra-Fast-VUV Photoemission Study of UV Excited 2-Nitrophenol
A. Ciavardini, Marcello Coreno, Carlo Callegari, C. Spezzani, Giovanni De Ninno, Barbara Ressel, Cesare Grazioli, Monica de Simone, Antti Kivimak̈i, Paolo Miotti, Fabio Frassetto, Luca Poletto, Petra Rudolf, Simona Fornarini, Marco Pezzella, Enrico Bodo, Susanna Piccirillo, 2019, izvirni znanstveni članek

Opis: The initial deactivation pathways of gaseous 2-nitrophenol excited at 268 nm were investigated by time-resolved photoelectron spectroscopy (TRPES) with femtosecond-VUV light, produced by a monochromatized high harmonic generation source. TRPES allowed us to obtain new, valuable experimental information about the ultrafast excited-state dynamics of 2-nitrophenol in the gas phase. In accord with recent ab initio on-the-fly nonadiabatic molecular dynamic simulations, our results validate the occurrence of an ultrafast intersystem crossing leading to an intermediate state that decays on a subpicosecond time scale with a branched mechanisms. Two decay pathways are experimentally observed. One probably involves proton transfer, leading to the most stable triplet aci-form of 2-nitrophenol; the second pathway may involve OH rotation. We propose that following intersystem crossing, an ultrafast fragmentation channel leading to OH or HONO loss could also be operative.
Ključne besede: Ultrafast photoemission, nitrophenol
Objavljeno v RUNG: 12.02.2019; Ogledov: 3547; Prenosov: 0
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38.
Orbital-dependent electron dynamics in Fe-pnictide superconductors
Ganesh Adhikary, Barbara Ressel, Primož Rebernik Ribič, Jurij Urbančič, Giovanni De Ninno, Damjan Krizmancic, A. Thamizhavel, Kalobaran Maiti, Matija Stupar, 2018, izvirni znanstveni članek

Opis: We report on orbital-dependent quasiparticle dynamics in EuFe 2 As 2, a parent compound of Fe-based superconductors, and a way to experimentally identify this behavior using time-and angle-resolved photoelectron spectroscopy across the spin density wave transition. We observe two different relaxation timescales for photoexcited d x z/d y z and d x y electrons. While the itinerant d x z/d y z electrons relax faster through the electron-electron scattering channel, d x y electrons form a quasiequilibrium state with the lattice due to their localized character, and the state decays slowly. Our findings suggest that electron correlation in Fe pnictides is an important property, which should carefully be taken into account when describing the electronic properties of both parent and carrier-doped compounds, and therefore establish a strong connection with cuprates
Ključne besede: photoelectron dynamics, Fe based superconductors
Objavljeno v RUNG: 29.11.2018; Ogledov: 3469; Prenosov: 0
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39.
Extreme-ultraviolet vortices from a free-electron laser
Primož Rebernik Ribič, Giovanni De Ninno, 2017, izvirni znanstveni članek

Objavljeno v RUNG: 27.02.2018; Ogledov: 3828; Prenosov: 195
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40.
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