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Holographic technologies have the potentiality to impact our everyday life in many sectors including science, education, entertainment, art, and healthcare. Although holographic screens and projectors are part of common imagination since long time, they are still at initial stages of development and integration. Recent achievements of metasurface and flat optics research gave an unprecedented strength to this field, overcoming critical aspects as efficiency, size and flexibility of conventional optics and liquid crystal technologies. However, although diffractive and metasurface holographic projectors with advanced functionalities and improved efficiencies are continuously reported, they are static devices, requiring demanding, burdensome, and irreversible manufacturing processes. Here we report an all-optical and single-step lithographic framework for the fabrication of diffractive holographic projectors directly on the surface of a photo-morphable polymer film. Real-time optimization during the accurate surface patterning and fully structural reconfigurability allowed for the first prototype of a fully reprogrammable pixel-less morphological projector, opening new routes for holographic image displaying and optical data sharing. more...

Air quality monitoring is traditionally performed using fixed monitoring stations in controlled environments. The instrumentation used in these stations, is often complex, bulky, very expensive, and it requires frequent maintenance works. Recently, the advancements in the field of digital technology and network communication made it possible to imagine a new paradigm of monitoring based on low-cost gas sensors. This latter is a very emerging technological area that offers considerable practical application. In this work, the performance evaluation of a low-cost O3 outdoor gas sensor was analysed by means of a comparative infield test. At this scope, we collected data in a strongly urbanized coastal zone, using both a commercial O3 monitoring station and a prototype station based on low-cost metaloxidesemiconductors (MOX) gas sensors. Finally, the performance and reliability of the low-cost prototype sensor versus the commercial one was evaluated through direct comparison between the acquired data., Il monitoraggio della qualità dell’aria è tradizionalmente eseguito utilizzando stazioni di monitoraggio fisse in ambienti controllati. La strumentazione utilizzata in queste unità è spesso complessa, ingombrante, molto costosa e richiede frequenti lavori di manutenzione. Recentemente, i progressi nel campo delle tecnologie digitali e delle comunicazioni hanno permesso di immaginare un nuovo paradigma di monitoraggio basato su reti di sensori di gas a basso costo. Quest’ultima è un’area tecnologica molto emergente che offre una notevole praticità applicativa. In questo lavoro, la valutazione delle prestazioni di un sensore low-cost di O3 atmosferico in ambiente outdoor è stata analizzata attraverso un test comparativo sul campo. A tal scopo, abbiamo raccolto i dati in una zona costiera fortemente urbanizzata, utilizzando sia una stazione di monitoraggio O3 commerciale sia una stazione prototipale basata su sensori di gas a basso costo di ossidi metallici a semiconduttori (MOX). Infine, è stato valutato il livello di prestazioni e l’affidabilità del sensore prototipale a basso costo attraverso il confronto diretto tra i dati acquisiti dai due sistemi. more...

Graphite intercalation compounds (GIC), i.e., graphite flakes embedding small molecules or ions, have been described in the literature since 1851 by Schafheutl. These extraordinary materials can be exploited for a number of technological applications, in different industrial �elds (for example, they have been used for the industrial preparation of expanded graphite, novel superconductors, catalysts, anode materials, etc.). Some GICs (e.g., graphite nitrate and graphite bisulfate) are able to expand remarkably by thermal heating, and the achieved expanded graphite can be used to prepare graphite nanoplatelets (GNP), Few Layer Graphene (FLG), and graphene monolayer. Here an expandable graphite (graphite bisulfate) is prepared by intercalation of graphite with sulfuric acid, in presence of an oxidizing agent. In this study, different chemical formulations for the synthesis of highly intercalated graphite bisulfate have been tested. In particular, nitric acid, potassium nitrate, potassium dichromate, potassium permanganate, sodium periodate, sodium chlorate, and hydrogen peroxide have been used in this synthesis scheme as the auxiliary reagent (oxidizing agent). The intercalation reaction was performed in a glass-flask reactor (placed in a thermostatic bath), using air bubbling as homogenizing approach. The reaction time always was 1h and the H2SO4: oxidizing agent ratio was 9 : 1 by volume for all reactive mixtures. Graphite flakes were placed in the glass reactor and then the oxidizing compound, dissolved in absolute H2SO4, was added. The reactions were stopped by adding deionized water to the systems. In order to evaluate the presence of delamination, and pre-expansion phenomena, and the achieved intercalation degree in the prepared samples, the obtained graphite intercalation compounds have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), infrared spectroscopy (FT-IR), micro-Raman spectroscopy (µ=RS) and thermal analysis (TGA). Delamination and pre-expansion phenomena were observed only for nitric acid, potassium dichromate and hydrogen peroxide, while the presence of strong oxidizers (KMnO4; NaIO4) led to stable graphite intercalation compounds. The largest content of intercalated bisulfate is achieved in the GICs obtained from NaIO4 and NaClO3. more...

Holographic relief gratings can be fabricated directly on the surface of azobenzene-containing materials (or simply azomaterials) without additional development steps. Despite often being described to have ideal sinusoidal profiles, the developing surface morphology in large amplitude gratings can affect the light distribution of the writing interferogram, causing profile deformations and deviations in the expected diffraction behavior. In this work, we characterize the temporal evolution of the surface relief grating (SRG) morphology fabricated by means of interference lithography on azopolymer films, quantitatively relating the results of a Fourier analysis of their surface profiles to the accurate measurement of efficiencies in the transmitted diffraction orders. A reliable surface structuration dynamics is empirically extracted from the analysis and used to formulate a simple but detailed diffraction model that, within the scalar diffraction theory, exhaustively describes the diffraction behavior of real SRGs without the need of complex rigorous electromagnetic theories. Our results add a deeper insight in the quantitative description of the morphology and the diffraction behavior of SRGs, which can contribute to their adoption for operating high-performance, reconfigurable, compact, and lightweight diffractive optical devices. © 2022 The Authors. Published by American Chemical Society. more...

Real-time manipulation of light in a diffractive optical element made with an azomaterial, through the lightinduced reconfiguration of its surface based on mass transport, is an ambitious goal that may enable new applications and technologies. The speed and the control over photopatterning/ reconfiguration of such devices are critically dependent on the photoresponsiveness of the material to the structuring light pattern and on the required extent of mass transport. In this regard, the higher the refractive index (RI) of the optical medium, the lower the total thickness and inscription time can be. In this work, we explore a flexible design of photopatternable azomaterials based on hierarchically ordered supramolecular interactions, used to construct dendrimer-like structures by mixing specially designed sulfur-rich, high-refractive-index photoactive and photopassive components in solution. We demonstrate that thioglycolic-type carboxylic acid groups can be selectively used as part of a supramolecular synthon based on hydrogen bonding or readily converted to carboxylate and participate in a Zn(II)−carboxylate interaction to modify the structure of the material and fine-tune the quality and efficiency of photoinduced mass transport. Compared with a conventional azopolymer, we demonstrate that it is possible to fabricate high-quality, thinner flat diffractive optical elements to reach the desired diffraction efficiency by increasing the RI of the material, achieved by maximizing the content of high molar refraction groups in the chemical structure of the monomers. more...

Flat optical elements enable the realization of ultra-thin devices able to either reproduce or overcome the functionalities of standard bulky components. The fabrication of these elements involves the structuration of material surfaces on the light wavelength scale, whose geometry has to be carefully designed to achieve the desired optical functionality. In addition to the limits imposed by lithographic design-performance compromises, their optical behavior cannot be accurately tuned afterward, making them difficult to integrate in dynamic optical systems. Here we show the realization of fully reconfigurable flat varifocal diffractive lens, which can be in-place realized, erased and reshaped directly on the surface of an azopolymer film by an all-optical holographic process. Integrating the lens in the same optical system used as standard refractive microscope, results in a hybrid microscope capable of multi-depth object imaging. Our approach demonstrates that reshapable flat optics can be a valid choice to integrate, or even substitute, modern optical systems for advanced functionalities. more...