Origin of optical nonlinearity in plasmonic semiconductor nanostructures

The development of nanoscale nonlinear elements in photonic integrated circuits is hindered by the physical limits to the nonlinear optical response of dielectrics, which requires that the interacting waves propagate in transparent volumes for distances much longer than their wavelength. Here we present experimental evidence that optical nonlinearities in doped semiconductors are due to free-electron and their efficiency could exceed by several orders of magnitude that of conventional dielectric nonlinearities. Our experimental findings are supported by comprehensive computational results based on the hydrodynamic modeling, which naturally includes nonlocal effects, of the free-electron dynamics in heavily doped semiconductors. By studying third-harmonic generation from plasmonic nanoantenna arrays made out of heavily n-doped InGaAs with increasing levels of free-carrier density, we discriminate between hydrodynamic and dielectric nonlinearities. As a result, the value of maximum nonlinear efficiency as well as its spectral location can now be controlled by tuning the doping level. Having employed the common material platform InGaAs/InP that supports integrated waveguides, our findings pave the way for future exploitation of plasmonic nonlinearities in all-semiconductor photonic integrated circuits

The STRIP instrument of the Large Scale Polarization Explorer: microwave eyes to map the Galactic polarized foregrounds

In this paper we discuss the latest developments of the STRIP instrument of the "Large Scale Polarization Explorer" (LSPE) experiment. LSPE is a novel project that combines ground-based (STRIP) and balloon-borne (SWIPE) polarization measurements of the microwave sky on large angular scales to attempt a detection of the "B-modes" of the Cosmic Microwave Background polarization. STRIP will observe approximately 25% of the Northern sky from the "Observatorio del Teide" in Tenerife, using an array of forty-nine coherent polarimeters at 43 GHz, coupled to a 1.5 m fully rotating crossed-Dragone telescope. A second frequency channel with six-elements at 95 GHz will be exploited as an atmospheric monitor. At present, most of the hardware of the STRIP instrument has been developed and tested at sub-system level. System-level characterization, starting in July 2018, will lead STRIP to be shipped and installed at the observation site within the end of the year. The on-site verification and calibration of the whole instrument will prepare STRIP for a 2-years campaign for the observation of the CMB polarization.Comment: 17 pages, 15 figures, proceedings of the SPIE Astronomical Telescopes + Instrumentation conference "Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX", on June 15th, 2018, Austin (TX

Detection chain and electronic readout of the QUBIC instrument

The Q and U Bolometric Interferometer for Cosmology (QUBIC) Technical Demonstrator (TD) aiming to shows the feasibility of the combination of interferometry and bolometric detection. The electronic readout system is based on an array of 128 NbSi Transition Edge Sensors cooled at 350mK readout with 128 SQUIDs at 1K controlled and amplified by an Application Specific Integrated Circuit at 40K. This readout design allows a 128:1 Time Domain Multiplexing. We report the design and the performance of the detection chain in this paper. The technological demonstrator unwent a campaign of test in the lab. Evaluation of the QUBIC bolometers and readout electronics includes the measurement of I-V curves, time constant and the Noise Equivalent Power. Currently the mean Noise Equivalent Power is ~ 2 x 10⁻¹⁶ W/√Hz

Detection chain and electronic readout of the QUBIC instrument

The Q and U Bolometric Interferometer for Cosmology (QUBIC) Technical Demonstrator (TD) aiming to shows the feasibility of the combination of interferometry and bolometric detection. The electronic readout system is based on an array of 128 NbSi Transition Edge Sensors cooled at 350mK readout with 128 SQUIDs at 1K controlled and amplified by an Application Specific Integrated Circuit at 40K. This readout design allows a 128:1 Time Domain Multiplexing. We report the design and the performance of the detection chain in this paper. The technological demonstrator unwent a campaign of test in the lab. Evaluation of the QUBIC bolometers and readout electronics includes the measurement of I-V curves, time constant and the Noise Equivalent Power. Currently the mean Noise Equivalent Power is ~ 2 x 10⁻¹⁶ W/√Hz

Nanoparticelle fluorescenti per applicazioni biomediche

Fluorescence plays a key role in a growing number of disciplines, from molecular biology, to analytical chemistry, to optoelectronics. Its high spatial and temporal resolution and excellent signal-to-noise ratio make fluorescence an ideal tool for studying the structure and dynamics of matter and living systems on a molecular and nanometric scale. The most common fluorophores, organic molecules or metal complexes, are plagued by low brightness and photostability. These limitations can be overcome by embedding in ceramic or polymeric nanoparticles. Inclusion of organic fluorophores in silica nanoparticles, in particular, offers several advantages. Silica is an ideal matrix, transparent to visible light and relatively inert to photophysical processes. The embedded fluorophores, protected from the environment, enjoy a high resistance to photobleaching, while their presence in large numbers inside each nanoparticle makes for a much higher brightness. Silica nanoparticles are also extremely versatile. The ease of synthesis allows for the creation of complex structures through core-shell architectures with multiple layers, each doped with a different species. The surface can in turn be functionalized with molecules or macromolecules, which can control the chemical interactions of the nanoparticels with the environment and their colloidal stability in various solvents, or act as multivalent scaffold for the realization of supramolecular systems. These systems find application especially in the fields of drug delivery, intracellular imaging and sensing. Their intense and stable emission allows for the trafficking of nanoparticles in the intracellular environment to be easily tracked by fluorescence microscopy. Dye-doped silica nanoparticles are therefore ideally suited as vehicles for the delivery of therapeutic payloads, acting at the same time as tracers for in vivo imaging, or as fluorescent probes for in vitro imaging applied to fundamental biological problems. This thesis, in particular, deals with the development of vehicles for the delivery of an antitumor drug and with novel synthetic strategies paving the way for the realization of more complex vehicles. Chapter 1 presents the properties, synthesis and some applications of dye-doped silica nanoparticles. Special attention is given to biological applications. Chapter 2 briefly introduces photodynamic therapy (PDT), a non-invasive modality for the treatment of various diseases. Its clinical potential has been known for more than a century, but its use in oncological therapy is relatively recent. The treatment is administered in two stages: administration of a photoactive drug (a photosensitizer) which accumulates in the target tissues, and selective irradiation of the target area with focalized light. The photoactivation of the drug triggers a cascade of events leading to the destruction of the irradiated tissues. Chapter 3 describes the synthesis and characterization of silica-based carriers for covalently-linked photosensitizers. Conjugation with molecules capable of endowing the carrier with the desired functionality is one of the key advantages of using nanoparticels in photodynamic therapy. In order to make this kind of modification easier and more versatile, a modular carrier was conceived, its surface decorated with grafting sites for molecules bearing a complementary functionality. This functionalization strategy was tested by coating the nanoparticles with a poly(ethylene glycol) derivative. Chapter 4 reports the preparation of organically modified silica nanoparticles (ORMOSIL) doped non-covalently with meta-tetra(hydroxyphenyl)chlorin (mTHPC), a second generation photosensitizer. The investigation of the fate of these nanocarriers and of the embedded molecule after exposure to biological fluids and living cells yielded unexpected results. These results suggest that the delivery of drugs embedded in nanosystems may be more complex than it seems. A fluorimetric assay is presented, based on intraparticle energy trasfer processes, which can be used to tell unambiguously whether a physically embedded drug is delivered into living cells still associated with the nanosystem or follows a different path. Chapter 5 presents some peculiar features of mesoporous silica nanoparticles and the problems associated with their synthesis. Some ingenuous applications in the fields of controlled release and sensing are also shown. Chapter 6 describes an alternative carrier, based on mesoporous silica nanoparticles. A novel synthetic route was conceived, where the templating agent is a hydrolytically unstable inorganic phase, and the template removal treatment is a simple solvent exchange with water at room temperature. The proposed synthesis is an adaptation on a nanometric scale of a process that has been known for decades: the production of silica glasses with nanometric pores starting from borosilicates melts, obtained by inducing a phase separation and hydrolytically removing the boron-rich phase. Chapter 7 collects the experimental procedures related to the research reported in this thesis.Le applicazioni della fluorescenza rivestono un ruolo chiave in un numero crescente di discipline, dalla biologia molecolare, alla chimica analitica, all'optoelettronica. L'elevata risoluzione spaziale e temporale, insieme a un eccellente rapporto segnale-rumore, rendono la fluorescenza un metodo ideale per lo studio della struttura e della dinamica della materia e dei sistemi viventi su scala molecolare e nanometrica. I fluorofori più comunemente usati, molecole organiche o complessi metallici, presentano di frequente problemi di luminosità e fotostabilità. Questi limiti possono essere superati attraverso l’incapsulazione in nanoparticelle ceramiche o polimeriche. L'inclusione di fluorofori organici in nanoparticelle di silice, in particolare, offre numerosi vantaggi. La silice rappresenta una matrice ideale, trasparente alla luce visibile e relativamente inerte rispetto ai processi fotofisici. I fluorofori, protetti dall’ambiente esterno, godono di una elevata resistenza al photobleaching, mentre la loro presenza in numero elevato all'interno di ogni particella conferisce a queste un’elevata luminosità. Le nanoparticelle di silice sono anche sistemi estremamente versatili. La facilità della sintesi consente la realizzazione di strutture complesse attraverso architetture core-shell a strati multipli, ciascuno drogato con una specie diversa. La superficie, a sua volta, può essere funzionalizzata con molecole o macromolecole che ne controllino l'interazione chimica con l'ambiente e la stabilità colloidale in diversi solventi, o fungere da piattaforma multivalente per la realizzazione di sistemi supramolecolari. Questi sistemi trovano applicazione soprattutto nei campi del drug delivery, dell’imaging cellulare e della sensoristica. L’emissione di fluorescenza intensa e stabile consente infatti di seguire il movimento delle nanoparticelle nell'ambiente intracellulare tramite microscopia ottica. Queste si prestano quindi ad essere sfruttate, ad esempio, come vettori per il trasporto di carichi terapeutici che fungano allo stesso tempo da traccianti per l'imaging dei tessuti malati, oppure come sonde fluorescenti per l’imaging cellulare in vitro, applicato allo studio di problemi biologici di base. Questo lavoro di tesi tratta, in particolare, dello sviluppo di vettori per un farmaco antitumorale e di nuove strategie sintetiche che aprono la strada alla realizzazione di vettori più complessi. Nel capitolo 1 sono illustrate le proprietà, i metodi di sintesi e alcune applicazioni delle nanoparticelle di silice drogate con specie fluorescenti. Particolare attenzione è dedicata alle applicazioni biologiche. Nel capitolo 2 viene introdotta la terapia fotodinamica (o PDT, acronimo di photodynamic therapy), un trattamento non invasivo per la cura di una varietà di malattie tumorali e di altra natura. Le sue potenzialità cliniche sono note da più di un secolo, ma l’uso in terapia oncologica è relativamente recente. Il trattamento si articola in due fasi: la somministrazione di un farmaco fotoattivo (un fotosensibilizzatore) che si accumula nei tessuti malati, e l’irraggiamento selettivo di questi con luce focalizzata. La fotoattivazione del farmaco innesca una cascata di eventi che conduce alla distruzione dei tessuti irraggiati. Nel capitolo 3 vengono descritti la sintesi e la caratterizzazione di vettori per fotosensibilizzatori basati su nanoparticelle di silice nelle quali il farmaco è legato covalentemente alla matrice. La coniugazione con molecole che conferiscano al vettore le funzionalità desiderate è uno dei vantaggi chiave dell’uso di nanoparticelle in terapia fotodinamica. Per facilitare queste modifiche e renderle il più possibile versatili, è stato progettato un vettore modulare la cui superficie fosse decorata con siti di ancoraggio per molecole recanti una funzionalità complementare. Questa strategia di funzionalizzazione è stata messa alla prova funzionalizzando le nanoparticelle con un derivato del polietilenglicole. Nel capitolo 4 viene descritta la preparazione di nanoparticelle di silice modificate con gruppi organici (ORMOSIL) drogate con meta-tetra(idrossifenil)clorina (mTHPC), un fotosensibilizzatore di seconda generazione. Lo studio del destino di questi nanovettori e della molecola incapsulata al loro interno in seguito all’esposizione a fluidi biologici e cellule viventi ha fornito risultati inattesi. I risultati ottenuti suggeriscono che il trasporto di farmaci incapsulati in nanosistemi possa essere più complesso di come appare. Viene presentato un saggio fluorimetrico basato sul trasferimento energetico che può essere utile per determinare senza ambiguità se un farmaco intrappolato fisicamente venga trasportato nelle cellule ancora associato al nanosistema o segua una strada diversa. Nel capitolo 5 vengono illustrate le caratteristiche salienti delle nanoparticelle di silice mesoporose e i problemi legati alla loro sintesi. Vengono inoltre presentate alcune applicazioni nel campo del drug delivery e della sensoristica. Nel capitolo 6 viene presentato un vettore alternativo, basato su nanoparticelle di silice mesoporose. È stata concepita una strategia sintetica innovativa, nella quale l’agente templante è una fase inorganica idroliticamente instabile, e il trattamento di rimozione del templante consiste nel semplice scambio di solvente con acqua a temperatura ambiente. La sintesi proposta è la trasposizione su scala nanometrica di un processo noto da decenni: la produzione di vetri di silice con pori di dimensioni nanometriche a partire da vetri borosilicati, ottenuta inducendo una separazione di fase e rimuovendo selettivamente la fase ricca di boro per idrolisi. Nel capitolo 7 sono raccolte le procedure sperimentali relative all’attività di ricerca descritta in questo lavoro di tesi

Origin of optical nonlinearity in plasmonic semiconductor nanostructures

The development of nanoscale nonlinear elements in photonic integrated circuits is hindered by the physical limits to the nonlinear optical response of dielectrics, which requires that the interacting waves propagate in transparent volumes for distances much longer than their wavelength. Here we present experimental evidence that optical nonlinearities in doped semiconductors are due to free-electron and their efficiency could exceed by several orders of magnitude that of conventional dielectric nonlinearities. Our experimental findings are supported by comprehensive computational results based on the hydrodynamic modeling, which naturally includes nonlocal effects, of the free-electron dynamics in heavily doped semiconductors. By studying third-harmonic generation from plasmonic nanoantenna arrays made out of heavily n-doped InGaAs with increasing levels of free-carrier density, we discriminate between hydrodynamic and dielectric nonlinearities. As a result, the value of maximum nonlinear efficiency as well as its spectral location can now be controlled by tuning the doping level. Having employed the common material platform InGaAs/InP that supports integrated waveguides, our findings pave the way for future exploitation of plasmonic nonlinearities in all-semiconductor photonic integrated circuits