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Abstract: Advances in the development of lasers have led to a new class of radiation sources generating coherent, tunable, ultrashort light pulses in the spectral region ranging from infrared to soft X-rays. This includes high-order harmonics generation in gas (HHG), on which relies the CITIUS facility at University of Nova Gorica (Slovenia), and free-electron lasers (FELs), such as the facility FERMI at Elettra-Sincrotrone Trieste (Italy). The distinctive structure of HHG and FEL radiation paved the way to time-resolved experiments, which are performed to investigate events occurring on a short, or very short, temporal scale, from picoseconds to femtoseconds. This work focuses on the advantages and disadvantages of some experimental techniques based on using these novel light sources to investigate the microscopic and/or ultrafast dynamics of matter samples, which have been previously driven out of equilibrium. Advantages rely on the implementation of various applications based on two-color schemes and, more specifically, include the possibility of acquiring two-dimensional frequency maps, measuring electrons’ effective masses, or investigating electronic properties decoupled from the influence of the lattice. Particular focus will be put on experimental methods relying on photoelectric effect and photoelectron spectroscopy. In all experiments, we took advantage of one or more specific properties of HHG and FEL sources, such as controllable chirp, to study laser dressed states in helium, variable polarization, to study electronic properties of iron-based pnictides and ultrashort pulses (< 10 fs) to study the purely electronic dynamics in transition metal dichalcogenides. On the other hand, the study of the interface between a molecule and a topological insulator revealed some intrinsic limitations and physical drawbacks of the technique, such as spurious effects originating from the high power pulses, like multiphoton absorption and the space charge effect, or the reduction of experimental resolution when pushing for shorter and shorter pulse durations. Some disadvantages are also connected to the current state-of-the-art in the field of ultrashort laser systems, where a trade-off needs to be found between repetition rate and laser power. Finally, state-of-the-art experiments based on the ability to generate ultrashort pulses carrying orbital angular momentum in visible, near-infrared as well as extreme UV range will be presented. The use of these pulses opens the door to the investigation of new physical phenomena, such as probing magnetic vortices using extreme ultraviolet light from a free-electron laser or imprinting the spatial distribution of an ultrashort infrared pulse carrying orbital angular momentum onto a photoelectron wave packet.
Found in: ključnih besedah
Summary of found: ...ultrafast lasers, two-color experiments, photoemission, high-order harmonic generation, free-electron lasers, hot-electrons dynamics,...
Keywords: ultrafast lasers, two-color experiments, photoemission, high-order harmonic generation, free-electron lasers, hot-electrons dynamics, surface science, pump-probe photoemission, ultraviolet photoemission, orbital angular momentum
Published: 02.12.2020; Views: 2743; Downloads: 101
Fulltext (19,78 MB)

Found in: ključnih besedah
Summary of found: ...in nanoscale materials, magnetic properties of nanostructures, photoemission, photoelectron spectra, ...
Keywords: electron states in nanoscale materials, magnetic properties of nanostructures, photoemission, photoelectron spectra
Published: 06.05.2014; Views: 5080; Downloads: 30
Fulltext (0,00 KB)

Found in: ključnih besedah
Summary of found: ...nanowires, nanowire doping, GaAs, scanning photoemission electron spectroscopy, ...
Keywords: nanowires, nanowire doping, GaAs, scanning photoemission electron spectroscopy
Published: 06.05.2014; Views: 5307; Downloads: 144
Fulltext (0,00 KB)

Abstract: 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.
Found in: ključnih besedah
Keywords: angle-resolved photoemission spectroscopy, ARPES, high harmonic generation, ultrafast surface science
Published: 20.04.2017; Views: 4464; Downloads: 0
Fulltext (1,80 MB)

Found in: ključnih besedah
Summary of found: ...contact, growth mode, electronic properties, chemical properties, photoemission spectroscopy, microscopy...
Keywords: metal contact, topological insulator contact, growth mode, electronic properties, chemical properties, photoemission spectroscopy, microscopy
Published: 05.12.2018; Views: 2900; Downloads: 0
Fulltext (8,13 MB)