High Power Laser-Grating Interaction

A system which presents a periodic optical structure is usually referred to as a photonic structure, for its light manipulation capabilities. The most simple one dimensional photonic structure that can be made of metallic material is a diffraction grating, which is known for its "light splitting" properties: an incident wave will be split and diffracted at different angles. Because of this, gratings are commonly used as monochromators and spectrometers. However, for p-polarised incident light and particular ratios of light wavelength over grating pitch, a diffraction grating can behave like an optical cavity, i.e. all the incident light can be confined in the proximity of the grating surface and converted into a surface wave, a kind of wave that propagates parallel to the metallic surface and is evanescent away from it. In the present work, since SPR provides a local enhancements of the e.m. field, we investigate an application of this phenomenon to the field of high power laser matter interaction. Today’s laser amplification technology is such that, during the interaction, ordinary matter is rapidly ionized and forms an overdense plasma in front of the (typically solid) target. This means that laser light cannot propagate inside the material, therefore making difficult the transfer of the laser energy. The most efficient heating mechanisms are based on the acceleration of electrons that are dragged in the vacuum and re-injected into the plasma with supra thermal velocities. This is usually referred as "vacuum heating", and a crucial role is played by the fields near the plasma-vacuum interface. Thus, the concept we investigate in this thesis work is the introduction of a periodic modulation to the target surface, which is maintained during the interaction process. The aim is to excite a SPR and confine the laser energy in proximity of the target surface, in order to enhance the absorption process. The interest in this work is in the availability in the near future of high contrast laser pulses, which allows the conservation of the target periodic structure, that until now tends to be erased by the the laser pre-pulse (high pre-pulse = low contrast). Clearly, the grating depth cannot be as small as in usual gratings, where the depth over pitch ratio is h/d = 1/100 and throughout our work we set the parameter range as h/d = 0,05-0,2. In these conditions we have observed numerically that the SPR is red-shifted at increasing h/d. To account for this fact, we have used a non-perturbative formalism to perform an original analytic calculation which enables us to predict the shifting of the resonant frequencies. The idea of absorption enhancement via SPR excitation has already been investigated by means of self-consistent particle-in-cell (PIC) simulations, showing that when a modulated target replace a flat one, the absorption increases from 20% to 70%. However, because of the intrinsic noise of PIC methods, it is not evident the actual contribution of the surface modes to the absorption process. Therefore, in order to clarify the surface plasmon contribution to electrons acceleration, we simplify the self-consistent numerical problem by splitting it in two steps: at first the surface fields produced by a modulated surface are studied with a FDTD electromagnetic code, assuming fot the plasma a Drude dielectric constant. Then the electrons motion in the surface fields is studied by a test particle approach. With this numerical scheme we are able to show that the electrons dynamics is greatly sensitive to SPR excitation. In particular, the average kinetic energy acquired by the electrons in the resonant fields is much greater than in the not resonant case, and the energy distribution of the accelerated electrons shows an extended "plateau" region, that is absent when the resonance is not excited. This confirms our hypothesis that the major effect in electrons acceleration grating driven enhancement is due to the possibility to excite collective surface electrons modes, and cannot be explained as a consequence of "hot spot" creation in the field pattern, because of the field lines bending caused by the modulation of the surface. Consequently the energy absorption enhancement observed in PIC simulations has to be considered an effect of the collective surface electron mode excitation

Plasmonische Generation von Attosekundenpulsen und Attosekundenabbildung von Oberflächenplasmonen

Attosecond pulses are ultrashort radiation bursts produced via high harmonic generation (HHG) during a highly nonlinear excitation process driven by a near infrared (NIR) laser pulse. Attosecond pulses can be used to probe the electron dynamics in ultrafast processes via the attosecond streaking technique, with a resolution on the attosecond time scale. In this thesis it is shown that both the generation of attosecond (AS) pulses and the probing of ultrafast processes by means of AS pulses, can be extended to cases in which the respective driving and streaking fields are produced by surface plasmons excited on nanostructures at NIR wavelengths. Surface plasmons are optical modes generated by collective oscillations of the surface electrons in resonance with an external source. In the first part of this thesis, the idea of high harmonic generation (HHG) in the enhanced field of a surface plasmon is analyzed in detail by means of numerical simulations. A NIR pulse is coupled into a surface plasmon propagating in a hollow core tapered waveguide filled with noble gas. The plasmon field intensity increases for decreasing waveguide radius, such that at the apex the field enhancement is sufficient for producing high harmonic radiation. It is shown that with this setup it is possible to generate isolated AS pulses with outstanding spatial and temporal structure, but with an intensity of orders of magnitude smaller than in standard gas harmonic arrangements. In the second part, an experimental technique for the imaging of surface plasmonic excitations on nanostructured surfaces is proposed, where AS pulses are used to probe the surface field by means of photoionization. The concept constitutes an extension of the attosecond streak camera to ``Attosecond Photoscopy'', which allows space- and time-resolved imaging of the plasmon dynamics during the excitation process. It is numerically demonstrated that the relevant parameters of the plasmonic resonance buildup phase can be determined with subfemtosecond precision. Finally, the method used for the numerical solution of the Maxwell's equations is discussed, with particular attention to the problem of absorbing boundary conditions. New insights into the mathematical formulation of the absorbing boundary conditions for Maxwell's equations are provided.Attosekundenpulse sind ultrakurze extrem-ultraviolette (XUV) Pulse, die durch einen nicht-linearen, von einer nah-infraroten (NIR) Laserquelle stimulierten Anregungsprozess erzeugt werden. Attosekundenpulse können verwendet werden, um die Elektronendynamik eines ultraschnellen Prozesses durch die ``Attosecond Streaking'' Technik zu messen, mit einer Auflösung auf der Attosekundenskala. In dieser Dissertation wird gezeigt, dass sowohl die Erzeugung von Attosekundenpulsen als auch die Messung ultraschneller Prozesse mittels Attosekundenpulse auf Fälle erweitert werden können, bei denen die Anregungs- und Streakingsfelder von Oberflächenplasmonen generiert werden, welche bei nahinfraroten Wellenlängen auf Nanostrukturen angeregt werden. Oberflächenplasmonen sind optische Moden, die aus einer kollektiven Schwingung der Elektronen an der Oberfläche in Resonanz mit einer externen Quelle entstehen. Im ersten Abschnitt dieser Dissertation wird das Konzept der High Harmonic Generation (HHG) in plasmonisch erhöhten Feldern durch numerische Simulationen analysiert. Ein NIR Puls wird mit einem Oberflächenplasmon, das sich in einem konischen, mit Edelgas gefüllten, Hohlleiter ausbreitet, gekoppelt. Die Intensität des plasmonischen Feldes steigt mit der Verringerung des Durchmessers des Hohlleiters, sodass die Felderhöhung an seiner Spitze groß genug wird, um hohe harmonische Strahlung zu generieren. Es wird nachgewiesen, dass die Herstellung von isolierten Attosekundenpulsen mit außergewöhnlichen Zeit- und Raumstrukturen möglich ist. Trotzdem ist deren Intensität um mehrere Größenordnungen niedriger als die, die in Experimenten mit fokussierten Laserpulsen erreicht werden kann. Im zweiten Abschnitt wird eine experimentelle Technik für die Abbildung plasmonischer Oberflächenanregungen vorgeschlagen, wobei Attosekundenpulse verwendet werden, um das Feld an der Oberfläche mittels ``Momentum Streaking'' der photoionisierten Elektronen zu messen. Dieses Konzept ist eine Erweiterung der ``Attosecond Streak Camera'', welches ich ``Attosecond Photoscopy'' nenne. Es ermöglicht die Abbildung eines Plasmons in Zeit und Raum während des Anregungsprozesses. Anhand von numerischen Simulationen wird es gezeigt, dass die wesentlichen Parameter des plasmonischen Resonanzaufbaus mit subfemtosekunden-Präzision bestimmt werden können. Zuletzt wird die Methode für die numerische Lösung der Maxwell-Gleichungen diskutiert, mit Fokus auf das Problem der absorbierenden Randbedingungen. Neue Einsichten in die mathematische Formulierung der Randbedingungen der Maxwell-Gleichungen werden vorgestellt

Plasmonische Generation von Attosekundenpulsen und Attosekundenabbildung von Oberflächenplasmonen

Attosecond pulses are ultrashort radiation bursts produced via high harmonic generation (HHG) during a highly nonlinear excitation process driven by a near infrared (NIR) laser pulse. Attosecond pulses can be used to probe the electron dynamics in ultrafast processes via the attosecond streaking technique, with a resolution on the attosecond time scale. In this thesis it is shown that both the generation of attosecond (AS) pulses and the probing of ultrafast processes by means of AS pulses, can be extended to cases in which the respective driving and streaking fields are produced by surface plasmons excited on nanostructures at NIR wavelengths. Surface plasmons are optical modes generated by collective oscillations of the surface electrons in resonance with an external source. In the first part of this thesis, the idea of high harmonic generation (HHG) in the enhanced field of a surface plasmon is analyzed in detail by means of numerical simulations. A NIR pulse is coupled into a surface plasmon propagating in a hollow core tapered waveguide filled with noble gas. The plasmon field intensity increases for decreasing waveguide radius, such that at the apex the field enhancement is sufficient for producing high harmonic radiation. It is shown that with this setup it is possible to generate isolated AS pulses with outstanding spatial and temporal structure, but with an intensity of orders of magnitude smaller than in standard gas harmonic arrangements. In the second part, an experimental technique for the imaging of surface plasmonic excitations on nanostructured surfaces is proposed, where AS pulses are used to probe the surface field by means of photoionization. The concept constitutes an extension of the attosecond streak camera to ``Attosecond Photoscopy'', which allows space- and time-resolved imaging of the plasmon dynamics during the excitation process. It is numerically demonstrated that the relevant parameters of the plasmonic resonance buildup phase can be determined with subfemtosecond precision. Finally, the method used for the numerical solution of the Maxwell's equations is discussed, with particular attention to the problem of absorbing boundary conditions. New insights into the mathematical formulation of the absorbing boundary conditions for Maxwell's equations are provided.Attosekundenpulse sind ultrakurze extrem-ultraviolette (XUV) Pulse, die durch einen nicht-linearen, von einer nah-infraroten (NIR) Laserquelle stimulierten Anregungsprozess erzeugt werden. Attosekundenpulse können verwendet werden, um die Elektronendynamik eines ultraschnellen Prozesses durch die ``Attosecond Streaking'' Technik zu messen, mit einer Auflösung auf der Attosekundenskala. In dieser Dissertation wird gezeigt, dass sowohl die Erzeugung von Attosekundenpulsen als auch die Messung ultraschneller Prozesse mittels Attosekundenpulse auf Fälle erweitert werden können, bei denen die Anregungs- und Streakingsfelder von Oberflächenplasmonen generiert werden, welche bei nahinfraroten Wellenlängen auf Nanostrukturen angeregt werden. Oberflächenplasmonen sind optische Moden, die aus einer kollektiven Schwingung der Elektronen an der Oberfläche in Resonanz mit einer externen Quelle entstehen. Im ersten Abschnitt dieser Dissertation wird das Konzept der High Harmonic Generation (HHG) in plasmonisch erhöhten Feldern durch numerische Simulationen analysiert. Ein NIR Puls wird mit einem Oberflächenplasmon, das sich in einem konischen, mit Edelgas gefüllten, Hohlleiter ausbreitet, gekoppelt. Die Intensität des plasmonischen Feldes steigt mit der Verringerung des Durchmessers des Hohlleiters, sodass die Felderhöhung an seiner Spitze groß genug wird, um hohe harmonische Strahlung zu generieren. Es wird nachgewiesen, dass die Herstellung von isolierten Attosekundenpulsen mit außergewöhnlichen Zeit- und Raumstrukturen möglich ist. Trotzdem ist deren Intensität um mehrere Größenordnungen niedriger als die, die in Experimenten mit fokussierten Laserpulsen erreicht werden kann. Im zweiten Abschnitt wird eine experimentelle Technik für die Abbildung plasmonischer Oberflächenanregungen vorgeschlagen, wobei Attosekundenpulse verwendet werden, um das Feld an der Oberfläche mittels ``Momentum Streaking'' der photoionisierten Elektronen zu messen. Dieses Konzept ist eine Erweiterung der ``Attosecond Streak Camera'', welches ich ``Attosecond Photoscopy'' nenne. Es ermöglicht die Abbildung eines Plasmons in Zeit und Raum während des Anregungsprozesses. Anhand von numerischen Simulationen wird es gezeigt, dass die wesentlichen Parameter des plasmonischen Resonanzaufbaus mit subfemtosekunden-Präzision bestimmt werden können. Zuletzt wird die Methode für die numerische Lösung der Maxwell-Gleichungen diskutiert, mit Fokus auf das Problem der absorbierenden Randbedingungen. Neue Einsichten in die mathematische Formulierung der Randbedingungen der Maxwell-Gleichungen werden vorgestellt

Shybo. An open-source low-anthropomorphic robot for children

This article presents Shybo: a novel low-anthropomorphic robot for children. The robot, resulted from the combination of open-source hardware and software, is able to perceive sounds and to react through two non-verbal behaviors: hat’s movement and lighting. By taking advantage of an open- source machine-learning software, the robot can be easily trained by children. This robot can be employed in research to support human-robot interaction studies with children, for investigating perceptual aspects of robot’s features or for investigating children’ cognitive abilities. It can also be used for applications in educational context to support playful learning experiences

Il rumore della parola nell'immagine. Traduzione e commento del volume Le complexe de Cyrano. La langue parlée dans les films francais di Michel Chion

Nella presente tesi, la traduzione del volume di Michel Chion,intitolato Le complexe de Cyrano. La langue parlée dans les films français e uscito in Francia nel 2008, si accompagna a un commento volto a sottolineare le principali difficoltà traduttive

Sviluppo di tecniche di analisi del segnale da sonde ottiche per il monitoraggio di sistemi di combustione stazionaria

Nel presente report è stata esaminata l’attività, condotta da ENEA (Agenzia nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenibile) ed in collaborazione con il Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali dell’Università di Pisa, volta allo sviluppo e messa a punto di sistemi diagnostici per lo studio delle principali variabili chimico-fisiche di processo, utili all’indagine fenomenologica di base sul processo ed alla validazione di codici di calcolo come strumenti di progettazione. Nello specifico, l’attività è stata rivolta all'analisi dei segnali delle sonde ottiche in sistemi di combustione stazionari

Shybo. Design of a research artifact for human-robot interaction studies.

This article discusses the role of Design Research in the field of Human-Robot Interaction (HRI). Notably, the Research through Design (RtD) approach is proposed as a valuable method to develop HRI research artefacts due to the importance of having a physical artefact, a robot, that enables direct interaction. Moreover, there is a growing interest in HRI for design methodologies as methods for investigation. The article presents an example of a design process, focused on hands-on activities, namely sketching, 3D modelling, prototyping, and documenting. These making practices were applied to the development of Shybo, a small sound-reactive robot for children. Particular attention has been given to the five prototypes that led to the definition of the current solution. Morphological, behavioral, and interaction aspects were investigated throughout the whole process. Each phase of the design process was then documented with the intent of sharing potentially replicable practices and contributing to the understanding of the role that RtD can play in HRI

In Vitro Susceptibility Tests in the Context of Antifungal Resistance: Beyond Minimum Inhibitory Concentration in Candida spp.

Abstract: Antimicrobial resistance is a matter of rising concern, especially in fungal diseases. Multiple reports all over the world are highlighting a worrisome increase in azole- and echinocandin-resistance among fungal pathogens, especially in Candida species, as reported in the recently published fungal pathogens priority list made by WHO. Despite continuous efforts and advances in infection control, development of new antifungal molecules, and research on molecular mechanisms of antifungal resistance made by the scientific community, trends in invasive fungal diseases and associated antifungal resistance are on the rise, hindering therapeutic options and clinical cures. In this context, in vitro susceptibility testing aimed at evaluating minimum inhibitory concentrations, is still a milestone in the management of fungal diseases. However, such testing is not the only type at a microbiologist’s disposal. There are other adjunctive in vitro tests aimed at evaluating fungicidal activity of antifungal molecules and also exploring tolerance to antifungals. This plethora of in vitro tests are still left behind and performed only for research purposes, but their role in the context of invasive fungal diseases associated with antifungal resistance might add resourceful information to the clinical management of patients. The aim of this review was therefore to revise and explore all Citation: Franconi, I.; Lupetti, A. In Vitro Susceptibility Tests in the Context of Antifungal Resistance: Beyond Minimum Inhibitory Concentration in Candida spp. J. Fungi 2023, 9, 1188. https:// doi.org/10.3390/jof9121188 Academic Editor: Michael A. Pfaller Received: 16 November 2023 Revised: 6 December 2023 Accepted: 7 December 2023 Published: 12 December 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). other in vitro tests that could be potentially implemented in current clinical practice in resistant and difficult-to-treat cases