1. New achievements in orbital angular momentum beam characterization using a Hartmann wavefront sensor and the Kirkpatrick-Baez active optical system KAOSLuka Novinec, Matteo Pancaldi, Flavio Capotondi, Giovanni De Ninno, Francesco Guzzi, George Kourousias, Emanuele Pedersoli, Barbara Ressel, Benedikt Rösner, Alberto Simoncig, 2024, original scientific article Abstract: Advances in physics have been significantly driven by state-of-the-art technology, and in photonics and X-ray science this calls for the ability to manipulate the characteristics of optical beams. Orbital angular momentum (OAM) beams hold substantial promise in various domains such as ultra-high-capacity optical communication, rotating body detection, optical tweezers, laser processing, super-resolution imaging etc. Hence, the advancement of OAM beam-generation technology and the enhancement of its technical proficiency and characterization capabilities are of paramount importance. These endeavours will not only facilitate the use of OAM beams in the aforementioned sectors but also extend the scope of applications in diverse fields related to OAM beams. At the FERMI Free-Electron Laser (Trieste, Italy), OAM beams are generated either by tailoring the emission process on the undulator side or, in most cases, by coupling a spiral zone plate (SZP) in tandem with the refocusing Kirkpatrick–Baez active optic system (KAOS). To provide a robust and reproducible workflow to users, a Hartmann wavefront sensor (WFS) is used for both optics tuning and beam characterization. KAOS is capable of delivering both tightly focused and broad spots, with independent control over vertical and horizontal magnification. This study explores a novel non-conventional `near collimation' operational mode aimed at generating beams with OAM that employs the use of a lithographically manufactured SZP to achieve this goal. The article evaluates the mirror's performance through Hartmann wavefront sensing, offers a discussion of data analysis methodologies, and provides a quantitative analysis of these results with ptychographic reconstructions.
Keywords: tailored photonics beams, orbital angular momentum of light, wavefront sensing, ptychography
Published in RUNG: 19.08.2024; Views: 629; Downloads: 3
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3. Light-Induced Magnetization at the NanoscaleJonas Wätzel, Primož Rebernik Ribič, Marcello Coreno, Miltcho Danailov, Christian David, Alexander Demidovich, Michele Di Fraia, Luca Giannessi, Klavs Hansen, Špela Krušič, Michele Manfredda, Michael Meyer, Andrej Mihelič, Najmeh Mirian, Oksana Plekan, Barbara Ressel, Benedikt Rosner, Alberto Simoncig, Simone Spampinati, Matija Stupar, Matjaž Žitnik, Marco Zangrando, Carlo Callegari, Jamal Berakdar, Giovanni De Ninno, 2022, original scientific article Keywords: FEL, orbital angular momentum, magnetisation
Published in RUNG: 16.01.2023; Views: 1629; Downloads: 0
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4. Advantages and disadvantages of experiments with ultrashort two-color pulsesMatija Stupar, 2020, doctoral dissertation 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.
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 in RUNG: 02.12.2020; Views: 4853; Downloads: 138
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5. 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: 3870; Downloads: 15
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6. Tunable orbital angular momentum in high-harmonic generationDavid Gauthier, Primož Rebernik Ribič, Ganesh Adhikari, A Camper, C Chappuis, LF Dimauro, G Dovillaire, Fabio Frassetto, R Geneaux, Paolo Miotti, Luca Poletto, Barbara Ressel, C. Spezzani, Matija Stupar, T Ruchon, Giovanni De Ninno, 2017, original scientific article Keywords: Angular orbital momentum, High harmonic generation
Published in RUNG: 05.02.2018; Views: 4837; Downloads: 764
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