High order waveguide modes are nowadays of great interest for the development of new functionalities in photonics. Because of this, efficient mode couplers are required. In this thesis a new strategy for mode coupling is investigated, based on the interference arising from two coherent tilted beams superimposed in a star-coupler. Handling the high order modes allows to explore new processes within the photonics platform, as the intermodal four wave mixing. Intermodal four wave mixing is a new nonlinear optical process in waveguide, and it is here demonstrated on a silicon chip. Via intermodal four wave mixing it is possible to achieve a large and tunable frequency conversion, with the generation of photons spanning from the near to the mid infrared. The broadband operation of this process is of interest for the field of quantum photonics. Single photon sources are the main building block of quantum applications, and they need to be pure and efficient. Via intermodal four wave mixing, it is here demonstrated the generation of single photons above 2000 nm heralded by the idler at 1260 nm. Thanks to the discrete band phase matching of this nonlinear process, high purity single photons without narrow band spectral filters are demonstrated. Intermodal four wave mixing enables a new class of classical and quantum sources, with unprecedent flexibility and spectral tunability. This process is particularly useful for the developing field of mid infrared photonics, where a viable integrated source of light is still missing.

This thesis deals with the study of the yarn interlacing. The interlacing process is commonly employed by textile industries to impart cohesion points to a multi-filament yarn. Indeed, this work has been realized in the framework of a collaboration between the Department of Physics of the University of Trento (Italy) and Aquafil S.p.A., a company producing Nylon 6 yarn. The interlacing of the filaments into periodic knots is caused by their interaction with a turbolent flow, but the full dynamics is not well characterized. Additionally, one problem that textile industries need to face is the irregularity of the process, still difficult to improve. A regular knots distance is required to ensure the homogeneous appearance of the final fabric. Hence, it is interesting to understand which are the key parameters affecting and influencing interlacing, to improve its regularity. For this reason, the present work focuses on a deeper understanding of the process dynamics. Then, different on-line sensing techniques that measure the knots distance are investigated and compared. The evaluation of the process regularity during yarn production allows, as a further step, to change the machine parameters on-line, avoiding waste of time and material. In Chapter 1 is given the background knowledge about the yarn production process, starting from the raw material. The attention will be focused on interlacing, with an overview of the state of the art literature on that topic. In Chapter 2 the yarn-air interaction is investigated, with a high speed analysis of the yarn motion in an interlacer. A dynamics of interlacing is proposed, indicating the key role played by the turbolent pattern, observed by means of a tracer. Chapter 3 studies the vibrations close to the interlacer, to monitor a possible flow modulation caused by the yarn-air interaction. In Chapter 4 and Chapter 5 two sensing techniques have been approached, based on the use of a microphone and a photodiode. The issues related to those measurements have been investigated, for a final comparison of their performance in terms of capability of detecting the cohesion points distance on-line, on a running yarn.

Microresonators are fundamental building blocks in the growing field of integrated photonics and several resonator-based devices such as filters, switches and routers are currently used in common optical telecommunication networks. In order to exploit the peculiar features offered by integrated resonators, a complete and consistent comprehension of their physics and of the processes they can accommodate is needed. More specifically, coupling of light to and from a resonator represents a crucial point: a correct comprehension of the coupling dynamics, a proper model for the system and its validation through experimental procedure are all essential elements for a fruitful exploitation of the device. Among the different resonator-waveguide coupling schemes, the most widely used is the in-plane coupling and it consists of a waveguide placed near to a microresonator and laying on the same plane. However, an alternative approach is represented by the vertical coupling scheme, where the waveguide lays under the resonator edge. The peculiar position of the waveguide in this last configuration causes the device to show specific properties not present in other common coupling schemes: namely, a working range spanning from almost visible wavelengths (780nm) to the near IR domain (1600nm), the selective excitation of high order resonator radial modes and the possibility to fabricate wedge and free-standing resonators without any detrimental effect on the bus waveguide. In order to fully exploit these and other features of the vertical coupling scheme, a detailed investigation has been carried out throughout this thesis. The waveguide-microresonator system has been studied at different levels, from the general coupling dynamics to more specific and peculiar phenomena. In particular, the basic model proposed for the vertical coupling has been extended to consider wavelength dependences and an experimental validation has been carried out consequently. The reactive coupling model, which describes the internal dynamics of a vertically coupled resonator in the case of multimodal operation, has been experimentally proven. A general model considering the presence counterpropagating modes has been theoretically proposed and experimentally investigated. Finally, the bistable behaviour generated by thermo-optic effect when a large amount of power circulates in the microresonator has been experimentally studied. In order to better characterize the system response, a specific interferometric setup has been implemented. It consists in a Mach-Zehnder computer driven interferometer, whose peculiar characteristic is the ability to perform simultaneous pump and probe transmittance and phase measurements of any integrated photonic device provided with input and output ports. In this way, the information carried by the phase of the propagating optical signal is added to the one provided by its intensity and contributes to produce a more complete picture of the investigated system. In the case of microresonators this phase information becomes even more fundamental. Indeed, the phase response of a resonating structure is highly influenced by variations in the coupling strength, and the phase spectrum of a single resonance allows to clearly identify the resonator coupling regime for that specific resonance. This fact does not hold in the case of transmittance measurements, where single resonance spectrum carries information only on the total losses of the system. Finally, in order to exploit the combined information provided by this measurement procedure, a phasor plot representation is extensively used throughout the thesis work.

Light measurements are widely used in physics experiments and medical applications. It is possible to nd many of them in High{Energy Physics, Astrophysics and Astroparticle Physics experiments and in the PET or SPECT medical techniques. Two different types of light detectors are usually used: thermal detectors and photoelectric effect based detectors. Among the rst type detectors, the Bolometer is the most widely used and developed. Its invention dates back in the nineteenth century. It represents a good choice to detect optical power in far infrared and microwave wavelength regions but it does not have single photon detection capability. It is usually used in the rare events Physics experiments. Among the photoelectric effect based detectors, the Photomultiplier Tube (PMT) is the most important nowadays for the detection of low-level light flux. It was invented in the late thirties and it has the single photon detection capability and a good quantum efficiency (QE) in the near-ultraviolet (NUV) and visible regions. Its drawbacks are the high bias voltage requirement, the diculty to employ it in strong magnetic field environments and its fragility. Other widely used light detectors are the Solid-State detectors, in particular the silicon based ones. They were developed in the last sixty years to become a good alternative to the PMTs. The silicon photodetectors can be divided into three types depending on the operational bias voltage and, as a consequence, their internal gain: photodiodes, avalanche photodiodes (APDs) and Geiger-mode detectors, Single Photon Avalanche Diodes (SPADs). The first type detector does not have internal gain, thus its signal is proportional to the number of incoming photons that are converted in electron-hole pairs. The detector and the read-out circuit noises limit the detector sensitivity to, at least, some hundreds of photons. The APD exploits the impact ionisation effect to have an internal gain up to some hundreds or more. The internal gain allows the detector to improve the performance with respect to a similar area photodiode reducing the sensitivity limit to some tens of photons. Operating the APDs with a bias voltage larger than the breakdown one, the Geiger-mode operation range can be reached. In this case, the detectors have a very high gain, in the order of (10^5-10^7), but their signal is not proportional to the number of the incoming photons, it is always the same. The SPAD (or GM-APD) is a typical Geiger-mode silicon detector. It has the single photon detection capability as the PMT, due to the high gain, but its signal is digital: it is fired or not by the incoming photons. The capability to give a signal proportional to the number of photons is lost in a SPAD. To recover this property, a matrix of independent SPADs connected in parallel is built. These matrices are called Silicon Photomultipliers, SiPMs (or Multi-Pixel Photon Counters, MPPCs). In a typical SiPM, the output signal is the sum of the SPAD ones, thus, although the digital nature of the SPAD signal, it is analogue and ranges from zero to the maximum number of cells composing the matrix. The detector response can be considered linear if the number of incoming photons is much smaller than the total number of cells because the probability that two photons arrive on the same cell is negligible. Main features of the SiPMs are the low bias voltage (<100 V typically), a high Photo-Detection Efficiency (PDE) in NUV and visible range (usually larger than the PMT QE), compactness, insensitivity to magnetic elds and high internal gain. The noise sources are the Dark Count Rate (DCR), the optical Cross-talk (CT) and the Afterpulsing (AP). The first is called primary noise and mainly depends, at room temperature, on the thermal generation of electron-hole pairs that can travel to the high-field region triggering a cell. The others are collectively called correlated noise because they can happen only after a primary signal, caused both by a photon or by a spontaneous carrier generation. In this thesis, the focus is on the characterisation of one SiPM technology produced in Fondazione Bruno Kessler (FBK) in Trento, Italy, named NUV-SiPMs. This technology, implementing the p-on-n concept, showed, from the beginning, a high PDE spectrum peaked in the NUV to violet region exceeding the 30 %, a very low DCR, typically below 100 KHz/mm^2 in the operating voltage range, and a total correlated noise probability under the 50 %. In the last years, the technology was developed modifying the silicon wafer substrate properties, reducing the delayed correlated noise probabilities, and adopting the so-called High-Density concept. In this last version, named NUV-HD, a new layout, with a narrower border region around the cell active area and deep trenches to electrically and optically isolate the cells, is employed. The first improvement has a direct influence on the PDE because it increases the Fill Factor (FF), the ratio between the active to the total cell area. The second layout change reduces the probability that a secondary photon can travel from a cell to a neighbouring one, reducing the cross-talk probability. Possible applications of the NUV-HD devices are: medical application (e.g. the Time of Flight PET, ToF-PET, scanners), the rare events Physics experiments (e.g. NEXT and DarkSide) and Astroparticle Physiscs experiments (e.g. the Cherenkov Telescope Array Observatory, CTA). The ToF-PET scanners are promising medical techniques with the goal of improving the spatial resolution of the classical PET scanners measuring the gamma rays time of flight. For this reason, these scanners require very fast photodetectors with coincidence time resolution (CTR) less or equal to 100 ps. NEXT and DarkSide are low temperature experiments with the main goal of observe rare events as the neutrinoless double beta decay and the Dark Matter particles. Due to the signal rarity, the detector noise requirements are very stringent. CTA will be a future ground-based Imaging Atmospheric Cherenkov Telescope (IACT) observatory, with the goal to track very high energy cosmic gamma rays, up to hundreds of TeV, to their galactic sources. It will consist of two matrices of telescopes of different type and size, each one having a camera. In the small size telescopes, the possibility to use the SiPMs to build the camera is under investigation. Since the cosmic gamma rays are detected through the secondary Cherenkov photons, produced by the accelerated electrons in the Earth atmosphere, the camera photosensors must have a very high detection efficiency from 300 nm to 600 nm, and, possibly, a low sensitivity in the NIR region to reject the night sky background. In addition, they must have good timing properties and high granularity. To fully characterise the SiPM, measurements of signal properties, noise parameters and PDE are needed. The set-ups and analysis of the characterisation procedure are fully described. In particular, the optical set-up, with its calibration procedures, and the analysis methods, with the definition of the possible uncertainty sources, are the central point of this work. During the dark characterisation, the SiPM is enclosed in a light-tight climatic chamber. An oscilloscope acquires and sends to a PC software millisecond-long SiPM waveforms. The software implements a Differential Leading Edge Discriminator (DLED) algorithm to better distinguish the SiPM pulses with time separation larger than a few nanoseconds. This analysis allows to count the primary pulses, due to the thermal/tunnelling excitations, obtaining the DCR, and measure the correlated noise probabilities. In addition, signal parameters as amplitude, gain and cell recharge time are measured. The PDE measurements require a set-up in which the number of impinging photons to the device is precisely known. For this reason, a compact set-up, consisting of an integrating sphere inside a light-tight box, a series of LEDs with peak wavelength ranging from NUV to NIR, fully characterised before use, a monochromator, equipped with a tungsten lamp, and a transparent optical fibre, was developed. Along with the set-up, a light calibration procedure, taking into account different uncertainty sources (LED wavelength shift, light uniformity at the device position, etc.), was also developed. Three different analysis techniques can be used to obtain the technology PDE. Each technique has its own benets and error sources. The equivalence among the different methods is shown. Moreover, measuring the PDE on SPADs with the same layout of single SiPM cells, identical results are obtained. This fact shows the equivalence between the single cell device and its larger counterpart, opening the possibility to measure the PDE of a new technology on SPADs. This is a very important result because the SPAD is a simpler device, with lower correlated noise, because it has no CT, and negligible primary one, often less than 1 kHz. Measurements are more precise, faster and it is possible to apply larger bias voltage, obtaining more information on the technology in such conditions at which no SiPM can be tested any more. A rst version NUV-HD technology characterisation is shown. In this version, the NUV-HD SiPMs have cell pitch ranging from 25 um to 40 um. A typical primary noise lower than 100 KHz/mm^2 and a delayed correlated noise probability less than 5 % are measured, up to 10 V of overvoltage. In the same bias voltage range, a direct CT probability lower than 45 % is measured in the largest cell devices (25 % in the smallest ones). The PDE spectrum has the expected shape with the maximum in the NUV-violet region. A maximum value exceeding the 60 % is measured in the largest cell devices (45 % in the smallest ones). To investigate possible variations of the measured features on the wafer, devices taken from different wafer points are measured and compared finding no difference but the primary noise. This parameter shows a variation by a factor up to about three on the wafer level. To compare the different cell devices, all the measured parameters are plotted as a function of the peak PDE, about 400 nm. During this comparison, the smallest device reveals worse than the others having a larger noise, both primary and correlated, at the same PDE value. The other three devices are comparable within the measurement errors. From the PDE measurements, a comparison between the measured FF and the expected one, as dened by the design, is obtained. In the smallest cell device, this comparison shows an unexpected discrepancy leading to the possibility that the expected FF is larger than the effective one. This possibility is investigated in the last part of this thesis in which a complete study of the factors contributing to the PDE is shown. This study is performed on a new NUV-HD version employing a photodiode with equal dopant prole of the SiPMs, a circular SPAD having 100 % FF and a square one with 35 um cell size and a nominal FF equal to 81 %. A developed box model is used to describe the electric eld inside the cell. The calculated effective FF is always different from the expected one. The reason of the measured difference is the electric field transition from the constant high value to zero occurring at the active area border region. This partially efficient region has an effect similar to an added completely ineffective region of 1-1.5 um size inside the expected active area. The transition region effect is critical for the smallest cells because it strongly reduces the effective FF with respect to the design one. The study of the factors contributing to the PDE of the NUV-HD SiPMs is very important. Through the obtained results, it is confirmed that the technology QE is just maximised in the wavelength range of interest, NUV to blue, and, at the same wavelengths, the triggering probability saturation rate is very small allowing the detectors to reach the maximum PDE when biased with a few volts of overvoltage. This operating condition has also the effect to employ the detector having low noise, both primary and correlated one. The best solution to further improve the technology PDE is a redesign of the electric field border region to reduce the gap between the expected FF and the effective one. This is more important for the smallest cell devices in which the actual transition region effect reduces the PDE performance to about the 50-60 % of the expected values.

Proton therapy is a recent type of radiotherapy that uses high-energy proton beams, and more recently carbon ion beams, to benefit of their physical selectivity. The energy deposited by these particle beams is inversely proportional to their velocity. Therefore they release most of the energy at the end of their path into the tissue. The energy is deposited in a few millimeters, in a zone called the Bragg peak. Before and after the Bragg peak the energy deposition is minimal. The depth and the width of the Bragg peak depends on the beam energy and on the density of tissues located along the beam path. By setting the beam energy, the Bragg peak can be positioned in the tumor site, avoiding the healthy tissues. Because of the sharpness of the Bragg peak zone, proton therapy is advantageous for tumors located near to important body part, such as the brain, spine, and neck. The drawback is that small uncertainties on particle range can have a serious impact on treatment and limit the efficiency of the proton therapy. To obtain more effective treatments in proton therapy real-time range verifications are necessary to perform on-line corrections of the delivered treatment. Among different techniques presented in the literature, positron emission tomography (PET) and prompt gamma imaging (PGI) are the most promising methods for in vivo range verification. PET and PGI are indirect approaches to measure protons penetration depth inside patients because they aim to detect secondary particles resulting from the interaction between proton beams and tissue nuclei. PET imaging detects coincidence gamma rays due to the production of positron emitters and requires some minutes to achieve enough statistics to have a sufficient signal to noise ratio. PGI instead uses prompt gamma rays generated by de-excitation of target nuclei; the quantity of these rays and their temporal emission (few nanoseconds) allow to perform a range verification during treatment with the PGI. Several research groups are evaluating different approaches to realize a prompt gamma imaging system suitable for the use in clinical condition and the optimization of a gamma-ray detector for PGI is still ongoing. The Gammarad project works in this direction and aims to develop an high-performance and solid-state gamma ray detection module (GDM) with a slit camera design. The project is based on a collaboration among Fondazione Bruno Kessler (FBK, Trento, Italy), Politecnico di Milano (Milano, Italy), the Trento Institute for Fundamental Physics and Applications (TIFPA, Trento, Italy ), and the Proton Therapy Center of Trento (Italy). The project is divided into two parts. The first part focuses on the technological development of a gamma-ray imaging module. This module is composed by a gamma-ray detector, based on a solid-state silicon sensor, and an integrated circuit. They are assembled into a compact module with data and control systems. The second part of the project will be dedicated to the experimental validation of the system both in laboratory with radioactive sources and in a real environment, that of proton therapy. The most innovative part of the gamma-ray detector developed for the project is the photo-sensor used for the scintillation light readout. In traditional applications it is a photomultiplier tube (PMT). However, in recent years, Silicon Photomultiplier (SiPM) has become increasingly popular in a variety of applications for its promising characteristics. Among them, current-generation SiPMs offer high gain, high Photon Detection Efficiency (PDE), excellent timing performance, high count-rate capability and good radiation hardness. Due to these characteristics they are used as PMTs replacement in several applications, such as in nuclear medicine (PET), in high-energy physics (calorimeters), astrophysics (Cherenkov telescopes) and in others single-photon or few-photon applications. For its characteristics, the SiPM is also very promising for the scintillator readout in prompt gamma imaging and in high energy gamma-ray spectroscopy. Detectors for these applications must be compact, robust, and insensitive to the magnetic field. They have to provide high performance in terms of spatial, temporal, and energy resolution. SiPMs can satisfy all these requirements but typically they have been used with relatively low energy gamma rays and low photon flux, so manufacturers have optimized them for these conditions. Because of the limited number of micro-cells in a standard SiPM, 625 cells/mm^2 with 40 μm cells, the detector response is non-linear in high energies condition. Increasing the cell density is extremely important to improve the linearity of the SiPM and to avoid the compression of the energy spectrum at high energies, which worsens the energy resolution and makes difficult the calibration of the detector. On the other hand, small cells provide a lower Photon Detection Efficiency (PDE) because of the lower Fill Factor (FF) and as a consequence a lower energy resolution. Summarizing, the energy resolution at high energies is a trade-off between the excess noise factor (ENF) caused by the non-linearity of the SiPM and the PDE of the detector. Moreover, the small cell size provides an ultra-fast recovery time, in the order of a few of nanosecond for the smallest cells. A short recovery time together with a fast scintillator such a LYSO, reduces pile-up in high-rate applications, such as PGI. Based on the above considerations, the aim of this thesis is to develop an optimized gamma-ray detector composed of SiPMs for high-dynamic-range application, such as the scintillation light readout in prompt gamma imaging and in high-energy gamma-ray spectroscopy. SiPMs evaluated for the detector are High-Density (HD) and Ultra-High-Density (UHD) SiPM technologies recently produced at Fondazione Bruno Kessler (FBK). Instead of standard SiPMs, HD and UHD SiPMs have a very small micro-cell pitch, from 30 μm down to 5 μm with a cell density from 1600 cells/mm^2 to 46190 cells/mm^2, respectively. HD SiPMs are produced using a lithography technology with smaller critical dimensions and designed with trenches among SPADs. Small cells have a lower gain which helps to reduce correlated noise, such as After-Pulse and Cross-Talk. Trenches provide an optical and electrical cell isolation, and a smaller dead border around cells which increase the FF limiting PDE losses. UHD SiPMs push the limits of the HD technology even further, by reducing all the feature sizes, such as contacts, resistors and border region around cells. UHD SiPMs have hexagonal cells in a honeycomb configuration which generate a circular active area and a dead border around cells lower than 1 μm. The reduction of this dead boarder can improve the FF in smaller cells although it usually decrease with cell sizes. It is necessary understand how these significant layout changes affect the optical properties of SiPMs to evaluate which SiPM technology provides best performance in high-energy gamma-ray applications. In the first part of the thesis, I presents the characterization of HD and UHD SiPM technologies in terms of PDE, gain, Dark Count Rate, and correlated noise for the cell sizes between 30 and 7.5 μm. The most important markers of SiPMs performance in gamma-ray spectroscopy are however the energy resolution and the linearity when coupled to the scintillator for the detection of high-energy gamma-rays. A typical characterization of the energy resolution of SiPMs, coupled to scintillator crystals, is performed with radioactive source up to 1.5 MeV. However, PGI features gamma ray-energies up to 15 MeV which are not easily provided by the usual laboratory calibration sources. Extrapolating the behaviour of the detector from the "low" energy data is not correct and leads to unreliable data for calibration and performance estimation. Therefore, I developed a novel setup that simulates the LYSO light emission in response to gamma photons up to 30 MeV. A LED (emitting at 420 nm) is driven by a pulse generator, emulating the light emitted by a LYSO scintillator when excited by gamma rays. The pulse generator parameters (amplitude, duration, rise and fall time constants) are adjusted so that the LED emitted photons match the intensity and time distribution of the LYSO emission. The photon number in each light pulse is calibrated from the measurements at 511 keV obtained with a ^(22)Na source and a LYSO crystal coupled to the SiPMs. Using this LED setup I characterized the energy resolution and non-linearity of HD and UHD SiPMs in high-energy gamma-ray conditions. The second part of the thesis provides a detailed description of the scintillator setup and of the setup for the simulation of high-energy gamma-ray response, followed by the results of the characterization performing with these setups. Summarizing the results, the lowest non-linearity is provided by the technology with highest cell density, the RGB-UHD. For the 10 and 12.5 μm-cells we obtained values of 4.5% and 5% respectively at 5 MeV and 6 V over-voltage. On the other hand, we measured the best energy resolution of 2.6% and 2.3% at 5 MeV for the largest SiPM cells of 20 and 25 μm respectively, without the intrinsic term of the scintillator crystal and at 6 V over-voltage. This is due to the dependence of the energy resolution on the photon detection efficiency, which increases with the size of the SiPM cell. The optimal performance of the detector in high-dynamic-range applications, which depends on the several SiPM parameters, such as excess noise factor, photon detection efficiency, and cell sizes of the SiPM, is a trade off between non-linearity and energy resolution. At 5 MeV, the best trade-off for prompt gamma imaging application is reached by the 15 μm-cell. At 10 MeV the 12.5 μm-cell provides the best trade-off, because of the higher number of photons emitted by the scintillator. Furthermore, I distinguish the different components of the energy resolution (intrinsic, statistical, detector and electronic noise) as a function of cell sizes, over-voltage and energy, thanks to the combination of the scintillator and LED setups. The estimation of the intrinsic contribution of the scintillator crystal, coupled to the HD SiPMs, getting consistent results among the several cell sizes. On the basis of previous characterization, HD SiPMs with dimensions of 4x4 mm^2 and 15 μm-cell were chosen to produce the photo-detector module of the gamma camera, optimized for an energy range between 2 and 8 MeV. This module is a 8x8 array of SiPMs which is called tile. The production of the tile requires research on packaging techniques to solve two main challenges: the maximization of the photo-sensitive area and the application of a protective resin, transparent in the near UV to maximize light collection from the LYSO. After some R&D on packaging, I obtained a fully functional tile with 64 SiPMs with a fill factor, ratio between the photo-sensitive area and the total area, of about 86%. This fill factor is comparable to the values obtained when a Through Silicon Vias (TSVs) technique is used to connect SiPMs but without the high production cost and the additional fabrication process complexity of the TSV. It should be highlighted that packaging operations is very critical because it is necessary to produce a tile with all working SiPMs, since defective items can not be replaced in the tile. The last part of the thesis presents the packaging procedure that I have defined to produce photo-detector modules and the characterization of the photo-detector array in terms of energy resolution, position sensitive and non-linearity. The measurements on the tile were carried out jointly with the Gammarad partner of Politecnico di Milano, which provided the ASIC and DAQ for the readout. In conclusion, the R&D activity carried out during this thesis has provided to Gammarad project the final photo-detection module with state of the art performance for high-energy gamma-ray spectroscopy. The characterization of the module shows also a position sensitivity that matches with the SiPM dimensions, and a proper acquisition of high-energy gamma-ray events from 800 keV to 13 MeV. This module will be tested on beam in an experimental treatment room at the Proton therapy facility in Trento by the Gammarad project partners.

The work presents the recent developments in Quantum Monte Carlo calculations for nuclear systems including strange degrees of freedom. The Auxiliary Field Diffusion Monte Carlo algorithm has been extended to the strange sector by the inclusion of the lightest among the hyperons, the Λ particle. This allows to perform detailed calculations for Λ hypernuclei, providing a microscopic framework for the study of the hyperon-nucleon interaction in connection with the available experimental information. The extension of the method for strange neutron matter, put the basis for the first Diffusion Monte Carlo analysis of the hypernuclear medium, with the derivation of neutron star observables of great astrophysical interest.

In conventional silicon solar cell, the collection probability of light generated carries shows a drop in the high energy range 280-400nm. One of the methods to reduce this loss, is to implement nanometre sized semiconductors on top of a solar cell where high energy photons are absorbed and low energy photons are re-emitted. This effect, called luminescence down-shifter (LDS), modifies the incident solar spectrum producing an enhancement of the energy conversion efficiency of a cell. We investigate this innovative effect using silicon nanoparticles dispersed in a silicon dioxide matrix as active material. In particular, I proposed to model these structures using a transfer matrix approach to simulate its optical properties in combination with a 2D device simulator to estimate the electrical performance. Based on the optimized layer sequences, high efficiency cells were produced within the european project LIMA characterized by silicon quantum dots as active layer. Experimental results demonstrate the validity of this approach by showing an enhancement of the short circuit current density with up to 4%. In addition, a new configuration was proposed to improve the solar cell performances. Here the silicon nanoparticles are placed on a cover glass and not directly on the silicon cells. The aim of this study was to separate the silicon nanocrystals (Si-NCs) layer from the cell. In this way, the solar device is not affected by the Si-NCs layer during the fabrication process, i.e. the surface passivation quality of the cell remains unaffected after the application of the LDS layer. Using this approach, the downshifting contribution can be quantified separately from the passivation effect, as compared with the previous method based on the Si-NCs deposition directly on the solar devices. By suitable choice of the dielectric structures, an improvement in short circuit current of up 1% due to the LDS effect is demonstrated and simulated.

Introduction In this thesis I report the work of my PhD; it treated two different topics, both related by a third one, that is the computational method that I use to solve them. I worked on EFT-theories for nuclear systems and on Hypernuclei. I tried to compute the ground state properties of both systems using Monte Carlo methods. In the first part of my thesis I briefly describe the Monte Carlo methods that I used: VMC (Variational Monte Carlo), DMC (Diffusion Monte Carlo), AFDMC (Auxiliary Field Diffusion Monte Carlo) and AFQMC (Auxiliary Field Quantum Monte Carlo) algorithms. I also report some new improvements relative to these methods that I tried or suggested: I remember the fixed hypernode extension (§ 2.6.2) for the DMC algorithm, the inclusion of the L2 term (§ 3.10) and of the exchange term (§ 3.11) into the AFDMC propagator. These last two are based on the same idea used by K. Schmidt to include the spin-orbit term in the AFDMC propagator (§ 3.9). We mainly use the AFDMC algorithm but at the end of the first part I describe also the AFQMC method. This is quite similar in principle to AFDMC, but it was newer used for nuclear systems. Moreover, there are some details that let us hope to be able to overcome with AFQMC some limitations that we find in AFDMC algorithm. However we do not report any result relative to AFQMC algorithm, because we start to implement it in the last months and our code still requires many tests and debug. In the second part I report our attempt of describing the nucleon-nucleon interaction using EFT-theory within AFDMC method. I explain all our tests to solve the ground state of a nucleus within this method; hence I show also the problems that we found and the attempts that we tried to overcome them before to leave this project. In the third part I report our work about Hypernuclei; we tried to fit part of the ΛN interaction and to compute the Hypernuclei Λ-hyperon separation energy. Nevertheless we found some good and encouraging results, we noticed that the fixed-phase approximation used in AFDMC algorithm was not so small like assumed. Because of that, in order to obtain interesting results, we need to improve this approximations or to use a better method; hence we looked at AFQMC algorithm aiming to quickly reach good results.

The laser driven ion acceleration is a burgeoning field of resarch and is attracting a growing number of scientists since the first results reported in 2000 obtained irradiating thin solid foils by high power laser pulses. The growing interest is driven by the peculiar characteristics of the produced bunches, the compactness of the whole accelerating system and the very short accelerating length of this all-optical accelerators. A fervent theoretical and experimental work has been done since then. An important part of the theoretical study is done by means of numerical simulations and the most widely used technique exploits PIC codes (“Particle In Cell'”). In this thesis the PIC code AlaDyn, developed by our research group considering innovative algorithms, is described. My work has been devoted to the developement of the code and the investigation of the laser driven ion acceleration for different target configurations. Two target configurations for the proton acceleration are presented together with the results of the 2D and 3D numerical investigation. One target configuration consists of a solid foil with a low density layer attached on the irradiated side. The nearly critical plasma of the foam layer allows a very high energy absorption by the target and an increase of the proton energy up to a factor 3, when compared to the ``pure'' TNSA configuration. The differences of the regime with respect to the standard TNSA are described The case of nearly critical density targets has been investigated with 3D simulations. In this case the laser travels throughout the plasma and exits on the rear side. During the propagation, the laser drills a channel and induce a magnetic vortex that expanding on the rear side of the targer is source of a very intense electric field. The protons of the plasma are strongly accelerated up to energies of 100 MeV using a 200PW laser.

La visualizzazione scientifica è la resa in forma visuale di dati, al fine di meglio comprenderli per sé e più facilmente illustrarli ad altri. I dati visualizzati sono informazioni quantitative frutto di osservazione, astrazione o calcolo. Il processo di visualizzazione presuppone una serie di regole per la codifica e decodifica dell’informazione. Normalmente il codice rappresentativo è articolato, per gestire al meglio il compromesso tra la fedeltà di rappresentazione e i limiti del mezzo usato per rappresentarla; non di rado però è sottointeso. Nei casi in cui la rappresentazione visuale è densamente figurativa, cioè imita espressamente la realtà, questo può portare a una confusione tra significante e significato oppure a un’interpretazione errata da parte dell’utente guidata dall’analogia con la memoria e l’esperienza vissuta. Questo fraintendimento può dimostrarsi particolarmente rischioso nei casi in cui la rappresentazione visuale ha come oggetto qualcosa di fisicamente esistente ma, per cause legate alla natura fisica dell’oggetto, inaccessibile alla vista e agli strumenti ottici. Abbiamo argomentato come nel caso di rappresentazioni della realtà più arbitrarie e scarsamente figurative, la corrispondenza con il contenuto informativo è più cosciente nell’utilizzatore, permettendo di superare alcuni dei limiti cognitivi delle rappresentazioni visuali. Ci siamo quindi chiesti se non fosse possibile, e magari anche conveniente, realizzare rappresentazioni sensoriali che non fanno uso della vista e ne abbiamo studiato le potenzialità. Lo studio ha guidato la realizzazione di una resa in forma tattile e uditiva dell’emissione di onde radio da parte di oggetti celesti in una regione di cielo, attraverso parametri tattili e uditivi arbitrari e non necessariamente corrispondenti ad analoghi visuali. La sperimentazione, effettuata anche con l’aiuto di utenti non vedenti, ha evidenziato una notevole efficacia in termini di trasferimento di informazione e di coinvolgimento di un pubblico diversamente abile, mostrando interessanti spunti di ricerca futuri in ambito didattico, museale e sociale. / Scientific visualization is the visual representation of data, in order to better understand and illustrate them. The displayed data is any quantitative information, resulting from observation, abstraction or calculation. The display process implies a set of rules for encoding information in a visual form. Normally the code is complex, in order to better compromise between the fidelity of representation and the limits of the medium used to represent it; not infrequently, however, it is tacit. In cases where the visual representation is densely figurative (i.e. a clear imitation of reality), this can lead to mistake signifier for signified, or to misinterpret the represented data, due to the analogy of the representation with real experience. This misunderstanding may be particularly risky in cases where the object of the visual representation is something physical, but inaccessible to the eye and to optical instruments. We argue that in the case of more arbitrary and less figurative representations, the fruition is more conscious, also allowing to overcome some of the cognitive limits of visual representations. We investigate whether it is possible, and maybe even more suitable, to create sensorial representations that do not use the view, therefore we studied the potential of such representations. This study led to the realization of a tactile and acoustic map of radio waves emitted from celestial objects in a region of the sky, using tactile and auditory parameters not necessarily corresponding to visual analogues. The experiment, carried out also with visually impaired users, showed a significant effect in terms of transfer of information and involvement of a disabled audience, presenting interesting cues for future research in education, implementations for science centers and creation of integrations projects about sensory impairment.