11. Element-resolved study on the influence of a magnetic dopant on the exchange interaction in FePt on ultrashort timescalesJurij 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: 4382; Downloads: 0 |
12. The role of non-equilibrium dynamics in photo-induced phase transitions of correlated materialsJurij Urbančič, 2015, published scientific conference contribution abstract Abstract: We use femtosecond extreme-ultraviolet time- and angle-resolved photoelectron spectroscopy to study the ultrafast photo-induced suppression of the charge-density wave (CDW) in 1T-TiSe2. In the following non-equilibrium electron dynamics after femtosecond laser excitation, we see that hot-carrier multiplication is the primary driver for the ultrafast CDW suppression. As soon as the optically excited carriers have relaxed to a quasi-equilibrium hot Fermi-distribution electron gas, the CDW suppression stops. Theoretical calculations of the hot-carrier scattering processes and the screening properties further link the carrier multiplication to the observed CDW gap dynamics.
Keywords: Correlated Materials, High Harmonic Generation, ARPES
Published in RUNG: 22.05.2020; Views: 4250; Downloads: 0 |
13. Towards ultrafast X-ray condensed matter physics with MHz repetition rate HHG sourcesJurij Urbančič, 2015, published scientific conference contribution abstract Abstract: In recent years, an increasing number of ultrafast material science experiments are based on the use of table-top high-harmonic generation (HHG) lightsources [1,2]. Despite the huge success of these first experiments, a major drawback has been the limited repetition rate of these lightsources, in particular with respect to all types of photoemission experiments. Here, we combine newly developed high-repetition rate HHG sources [3,4] with state-of-the-art element-specific magneto-optical Kerr experiments. The chances and prospects for future ultrafast materials science experiments with these lightsources will be discussed.
Keywords: High Harmonic Generation, X-Rays, Condensed Matter
Published in RUNG: 22.05.2020; Views: 4799; Downloads: 0 |
14. Ultrafast Element-Specific Demagnetization in AlloysJurij Urbančič, doctoral dissertation Abstract: The study of magnetism has long been an active area of interest for the scientific research, while also providing vast technological applications such as information storage. It was first observed in the middle of the 90s that irradiating a ferromagnetic material with an intense femtosecond laser pulse can result in a loss of magnetization occurring below one picosecond. Since then, the study of magnetism on these femtosecond timescales has been a field of growing interest, addressing the question of how fast can the magnetization modification occurs and what presents the fundamental limit of this speed. For the understanding of these experimental observations, a number of different models were proposed, although the responsible microscopic mechanisms are still under discussion. According to one group of models, the change in magnetic moment is due to the spin-flip mechanism occurring during scattering events between electrons and (quasi-)particles. An example of this is the so-called Microscopic Three-Temperature Model (M3TM). A different approach is employed by the Superdiffusive Spin Current Model, where the loss of magnetization is attributed to a flow of chargeless spin particles taking place after the laser excitation.
With the purpose to explore the magnetic characteristic of materials, a range of investigation methods has been developed. One of them relies on the exploitation of the Magneto-Optical Kerr Effect (MOKE) and an incorporation of femtosecond laser pulses in pump-probe configuration. In this way, part of the beam from the same laser system is used to optically excite the system (the pump), while another part takes a snapshot of it (the probe), thus allowing us to investigate the magnetization dynamics with a femtosecond temporal resolution. In the experimental part of the thesis, we apply this MOKE technique to explore the demagnetization dynamics of a ferromagnetic alloy consisting of iron and nickel, also called Permalloy. It is observed that the magnetization is suppressed (quenched) in the first few hundred femtoseconds. Part of the experiments were performed using visible light with different fluences of the pump. The most notable observation is that this alloy exhibits different demagnetization dynamics at lower and higher fluence. What we see is a transition from one-step (demagnetization followed by a recovery on a much longer timescale) to a two-step (demagnetization followed by another slower demagnetization step) magnetization process occurring with the increment of pump fluence. This behavior is predicted and reproduced by the M3TM, which is applied for a comparison between experiments and theory.
Keywords: High Harmonic Generation, Magnetism, Ultrafast, Materials
Published in RUNG: 08.05.2020; Views: 4711; Downloads: 0
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15. Status and perspectives of the FERMI FEL facility (2019)Luca Giannessi, Enrico Allaria, Laura Badano, S. Bassanese, Filippo Bencivenga, Carlo Callegari, Flavio Capotondi, Davide Castronovo, F. Cilento, Paolo Cinquegrana, Giovanni De Ninno, Primož Rebernik Ribič, 2019, published scientific conference contribution Keywords: free-electron lasers, harmonic generation
Published in RUNG: 15.01.2020; Views: 4289; Downloads: 97
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17. First lasing of a free electron laser in the soft x-ray spectral range with echo enabled harmonic generationEnrico Allaria, Alessandro Abrami, Laura Badano, Maurizio Bossi, Flavio Capotondi, Davide Castronovo, Marco Cautero, Paolo Cinquegrana, Ivan Cudin, M. B. Danailov, Primož Rebernik Ribič, Giovanni De Ninno, 2019, published scientific conference contribution Keywords: free-electron lasers, harmonic generation
Published in RUNG: 15.01.2020; Views: 4434; Downloads: 93
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19. Pulse duration of seeded free-electron lasersPaola Finetti, Hauke Höppner, Enrico Allaria, Carlo Callegari, Flavio Capotondi, Paolo Cinquegrana, Marcello Coreno, Riccardo Cucini, Miltcho Bojanov Danailov, Alexander Demidovich, Giovanni De Ninno, Primož Rebernik Ribič, 2017, original scientific article Keywords: free-electron lasers, harmonic generation, pulse duration
Published in RUNG: 14.01.2020; Views: 4341; Downloads: 15
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20. Generation and applications of extreme-ultraviolet vorticesCarlos Hernández-García, Jorge Vieira, Jose T. Mendonça, Laura Rego, Julio San Román, Luis Plaja, Primož Rebernik Ribič, David Gauthier, Antonio Picón, 2017, original scientific article Keywords: XUV/X-ray vortices, orbital angular momentum of photons, high-harmonic generation, free-electron lasers, plasma physics
Published in RUNG: 13.01.2020; Views: 4524; Downloads: 16
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