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Studies for the commissioning of FERMI@Elettra
Jurij Urbančič, 2011, magistrsko delo

Najdeno v: osebi
Ključne besede: laser na proste elektrone, sinhrotron, sinhrotronska svetloba, ultra-relativistični snop elektronov, ultraviolična svetloba, magistrske naloge
Objavljeno: 15.10.2013; Ogledov: 3408; Prenosov: 23
URL Polno besedilo (0,00 KB)
Gradivo ima več datotek! Več...

3.
Self-amplified photo-induced gap quenching in a correlated electron material
Jurij Urbančič, Eich Steffen, Mathias Stefan, 2016, izvirni znanstveni članek

Opis: Capturing the dynamic electronic band structure of a correlated material presents a powerful capability for uncovering the complex couplings between the electronic and structural degrees of freedom. When combined with ultrafast laser excitation, new phases of matter can result, since far-from-equilibrium excited states are instantaneously populated. Here, we elucidate a general relation between ultrafast non-equilibrium electron dynamics and the size of the characteristic energy gap in a correlated electron material. We show that carrier multiplication via impact ionization can be one of the most important processes in a gapped material, and that the speed of carrier multiplication critically depends on the size of the energy gap. In the case of the charge-density wave material 1T-TiSe 2 , our data indicate that carrier multiplication and gap dynamics mutually amplify each other, which explains—on a microscopic level—the extremely fast response of this material to ultrafast optical excitation. Self-amplified photo-induced gap quenching in a correlated electron material. Available from: https://www.researchgate.net/publication/308804379_Self-amplified_photo-induced_gap_quenching_in_a_correlated_electron_material [accessed Apr 20, 2017].
Najdeno v: osebi
Ključne besede: high harmonic generation, charge-density wave material, 1T-TiSe2, non-equilibrium electron dynamics, ultrafast surface science
Objavljeno: 20.04.2017; Ogledov: 2159; Prenosov: 0
.pdf Polno besedilo (1,10 MB)

4.
Time- and angle-resolved photoemission spectroscopy with optimized high-harmonic pulses using frequency-doubled Ti:Sapphire lasers
Steffen Eich, Jurij Urbančič, 2014, izvirni znanstveni članek

Opis: Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet 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 400 nm 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 to <150 meV while preserving excellent time resolution of about 30 fs.
Najdeno v: osebi
Ključne besede: angle-resolved photoemission spectroscopy, ARPES, high harmonic generation, ultrafast surface science
Objavljeno: 20.04.2017; Ogledov: 2096; Prenosov: 0
.pdf Polno besedilo (1,80 MB)

5.
PHYSICS II - Exercises
Jurij Urbančič, drugo učno gradivo

Opis: The following script is the first part of selected exercises and examples from the topics of Hydrostatics and Hydrodynamics. They were collected during the academic year 2019/20 when I was holding Physics II tutorials for the study program Physics and Astrophysics I. level within the School of Science at the University of Nova Gorica. The source material I used is given in the Bibliography at the end. Hopefully, these exercise fill help in providing a more in-depth understanding of physical phenomena discussed during the lectures.
Najdeno v: osebi
Ključne besede: Hydrostatics, Hydrodynamics, Physics 2
Objavljeno: 07.05.2020; Ogledov: 308; Prenosov: 0
.pdf Polno besedilo (404,17 KB)

6.
Ultrafast Element-Specific Demagnetization in Alloys
Jurij Urbančič, doktorska disertacija

Opis: 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.
Najdeno v: osebi
Ključne besede: High Harmonic Generation, Magnetism, Ultrafast, Materials
Objavljeno: 08.05.2020; Ogledov: 353; Prenosov: 0
.pdf Polno besedilo (12,06 MB)

7.
Narrowband high harmonic pulses for trARPES using frequency-upconverted Ti:Sapphire lasers
Jurij Urbančič, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: 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.
Najdeno v: osebi
Ključne besede: HHG, ARPES, Laser
Objavljeno: 22.05.2020; Ogledov: 217; Prenosov: 0

8.
Towards ultrafast X-ray condensed matter physics with MHz repetition rate HHG sources
Jurij Urbančič, 2015, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: 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.
Najdeno v: osebi
Ključne besede: High Harmonic Generation, X-Rays, Condensed Matter
Objavljeno: 22.05.2020; Ogledov: 215; Prenosov: 0

9.
The role of non-equilibrium dynamics in photo-induced phase transitions of correlated materials
Jurij Urbančič, 2015, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: 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.
Najdeno v: osebi
Ključne besede: Correlated Materials, High Harmonic Generation, ARPES
Objavljeno: 22.05.2020; Ogledov: 233; Prenosov: 0

10.
Element-resolved study on the influence of a magnetic dopant on the exchange interaction in FePt on ultrashort timescales
Jurij Urbančič, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: 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.
Najdeno v: osebi
Ključne besede: FePt, High Harmonic Generation, Laser, Magnetic Materials
Objavljeno: 22.05.2020; Ogledov: 242; Prenosov: 0

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