The control of structured waves has recently opened innovative scenarios in the perspective of radiation propagation, advanced imaging, and light-matter interaction. In information and communication technology, the spatial degrees of freedom offer a wider state space to carry many channels on the same frequency or increase the dimensionality of quantum protocols. However, spatial decomposition is much more arduous than polarization or frequency multiplexing, and very few practical examples exist. Among all, beams carrying orbital angular momentum gained a preeminent role, igniting a variety of methods and techniques to generate, tailor, and measure that property. In a more general insight into structured-phase beams, we introduce here a new family of wave fields having a multipole phase. These beams are devoid of phase singularities and described by two continuous spatial parameters which can be controlled in a practical and compact way via conformal optics. The outlined framework encompasses multiplexing, propagation, and demultiplexing as a whole for the first time, describing the evolution and transformation of wave fields in terms of conformal mappings. With its potentialities, versatility, and ease of implementation, this new paradigm introduces a novel playground for space division multiplexing, suggesting unconventional solutions for light processing and free-space communications.

The main purpose of this study is to introduce a semi-classical model describing betting scenarios in which, at variance with conventional approaches, the payoff of the gambler is encoded into the internal degrees of freedom of a quantum memory element. In our scheme, we assume that the invested capital is explicitly associated with the quantum analog of the free-energy (i.e. ergotropy functional by Allahverdyan, Balian, and Nieuwenhuizen) of a single mode of the electromagnetic radiation which, depending on the outcome of the betting, experiences attenuation or amplification processes which model losses and winning events. The resulting stochastic evolution of the quantum memory resembles the dynamics of random lasing which we characterize within the theoretical setting of Bosonic Gaussian channels. As in the classical Kelly Criterion for optimal betting, we define the asymptotic doubling rate of the model and identify the optimal gambling strategy for fixed odds and probabilities of winning. The performance of the model are hence studied as a function of the input capital state under the assumption that the latter belongs to the set of Gaussian density matrices (i.e. displaced, squeezed thermal Gibbs states) revealing that the best option for the gambler is to devote all their initial resources into coherent state amplitude.

This study discusses lighting devices in Etruria and the comparison with similar tools in Greece, focusing on social and cultural differences. Greeks did not use candlestick-holders; objects that have been improperly identified as candelabra should more properly be classified as lamp/utensil stands. The Etruscans, on the other hand, preferred to use torchlight for illumination, and as a result, the candelabrum--an upright stand specifically designed to support candles -- was developed in order to avoid burns to the hands, prevent fires or problems with smoke, and collect ash or melting substances. Otherwise they also used utensil stands similar to the Greek lamp holders, which were placed near the kylikeion at banquets. Kottaboi in Etruria were important utensils used in the context of banquets and symposia, while in Greece, they were interchangeable with lamp/utensil stands.

Halide ion mobility in metal halide perovskites remains an intriguing phenomenon, influencing their optical and photovoltaic properties. Selective injection of holes through electrochemical anodic bias has allowed us to probe the effect of hole trapping at iodide (0.9 V) and bromide (1.15 V) in mixed halide perovskite (CH3NH3PbB1.5I1.5) films. Upon trapping holes at the iodide site, the iodide gradually gets expelled from the mixed halide film (as iodine and/or triiodide ion), leaving behind re-formed CH3NH3PbBr3 domains. The weakening of the Pb-I bond following the hole trapping (oxidation of the iodide site) and its expulsion from the lattice in the form of iodine provided further insight into the photoinduced segregation of halide ions in mixed halide perovskite films. Transient absorption spectroscopy revealed that the iodide expulsion process leaves a defect-rich perovskite lattice behind as charge carrier recombination in the re-formed lattice is greatly accelerated. The selective mobility of iodide species provides insight into the photoinduced phase segregation and its implication in the stable operation of perovskite solar cells.

We show that converting the surfaces of lead halide perovskite to water-insoluble lead (II) oxysalt through reaction with sulfate or phosphate ions can effectively stabilize the perovskite surface and bulk material. These capping lead oxysalt thin layers enhance the water resistance of the perovskite films by forming strong chemical bonds. The wide-bandgap lead oxysalt layers also reduce the defect density on the perovskite surfaces by passivating undercoordinated surface lead centers, which are defect-nucleating sites. Formation of the lead oxysalt layer increases the carrier recombination lifetime and boosts the efficiency of the solar cells to 21.1%. Encapsulated devices stabilized by the lead oxysalt layers maintain 96.8% of their initial efficiency after operation at maximum power point under simulated air mass (AM) 1.5 G irradiation for 1200 hours at 65 degrees C.

Lead halide perovskites have demonstrated outstanding performance in photovoltaics, photodetectors, radiation detectors and light-emitting diodes. However, the electromechanical properties, which are the main application of inorganic perovskites, have rarely been explored for lead halide perovskites. Here, we report the discovery of a large electrostrictive response in methylammonium lead triiodide (MAPbI(3)) single crystals. Under an electric field of 3.7 mu m(-1), MAPbI(3) shows a large compressive strain of 1%, corresponding to a mechanical energy density of 0.74 J cm(-3), comparable to that of human muscles. The influences of piezoelectricity, thermal expansion, intrinsic electrostrictive effect, Maxwell stress, ferroelectricity, local polar fluctuation and methylammonium cation ordering on this electromechanical response are excluded. We speculate, using density functional theory, that electrostriction of MAPbI(3) probably originates from lattice deformation due to formation of additional defects under applied bias. The discovery of large electrostriction in lead iodide perovskites may lead to new potential applications in actuators, sonar and micro-electromechanical systems and aid the understanding of other field-dependent material properties.

We suggest and demonstrate a tomographic method to characterise homodyne detectors at the quantum level. The positive operator measure associated with the detector is expanded in a quadrature basis and probed with a set of coherent states. The coefficients of the expansion are then retrieved using a least squares algorithm. Our model is general enough to describe different implementations of the homodyne setup, and it has proven capable of effectively describing the detector response to different tomographic sets. We validate the reconstructed operator measure on nonclassical states and exploit results to estimate the overall quantum efficiency of the detector.

New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 mu eV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown & Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths.

Earth-abundant, non toxic and cheap Fe2O3 can be used as photocatalyst for sustainable hydrogen production from bio-ethanol aqueous solutions, under sunlight irradiation and without the application of any external electrical bias. To this aim, supported materials are not only technologically more appealing than powders, but also of key importance to develop photoactive and stable Fe2O3-based nanostructured photocatalysts. Here we demonstrated that, while bulk Fe2O3 is unsuitable for solar hydrogen evolution, nanostructured iron(III) oxide polymorphs show promising photoactivity. In particular, a hydrogen yield of 20 mmol h(-1) m(-2) was obtained on epsilon-Fe2O3 nanorod arrays supported on Si(100) under simulated sunlight irradiation, mainly due to UV solar photon absorption. The functionalization with partially oxidized Ag nanoparticles resulted in a positive performance improvement upon selective irradiation with the UV portion of the solar spectrum. Conversely, the incorporation of Au nanoaggregates into epsilon-Fe2O3 enabled to obtain a significant H-2 production even under sole Vis light.

The apparatus exploited in this work is composed of an optical cable linked to a portable FieldSpec UV/VNIR that records the spectral downwelling radiance in underwater environment, allowing us to calculate the shortwave attenuation coefficient in water. Results for three inland water bodies are presented under different atmospheric conditions (sun zenith angle and wind speed) and water composition (chlorophyll a concentration and turbidity). We show that the spectral downwelling zenith radiance profiles under high sun elevations present a positive slope in the upper layers due to relatively high scattering of direct sunlight compared to attenuation. For deeper layers, attenuation overcomes the scattering of sunlight leading to a constant negative logarithmic slope. For low sun elevations, a negative slope is observed in the entire water column since the scattering of direct sunlight is always lower than attenuation. Whenever a negative logarithmic constant slope is observed, the attenuation coefficient was computed. A relation was observed between attenuation coefficient in the photosynthetically active radiation (PAR) spectral region and water turbidity, for the three water bodies under study.

New strategies are requested for the preparation of bioinspired host-guest complexes to be employed in technologically relevant applications, as sensors and optoelectronic devices. We report here a new approach employing a single monomeric protein as host for the strongly fluorescent rhodamine dye. The selected protein, belonging to the intracellular lipid binding protein family, fully encapsulates one rhodamine molecule inside its cavity forming a host-guest complex stabilized by H and pi-hydrogen bonds, a salt bridge, and favorable hydrophobic contacts, as revealed by the NMR derived structural model. The protein-dye solutions are easily processable and form homogeneous thin films exhibiting excellent photophysical and morphological properties, as derived from photoluminescence and AFM data. The obtained results represent the proof of concept of the viability of this bio host-guest system for the development of bioinspired optoelectronic devices.

Photothermally responsive supramolecular polymers containing azobenzene units have been synthesised and employed as dispersants for multi-walled carbon nanotubes (MWCNTs) in organic solvents. Upon triggering the trans-cis isomerisation of the supramolecular polymer intermolecular interactions between MWCNTs and the polymer are established, reversibly affecting the suspensions of the MWCNTs, either favouring it (by heating, i.e. cis -> trans isomerisation) or inducing the CNTs' precipitation (upon irradiation, trans -> cis isomerisation). Taking advantage of the chromophoric properties of the molecular subunits, the solubilisation/precipitation processes have been monitored by UV-Vis absorption spectroscopy. The structural properties of the resulting MWCNT-polymer hybrid materials have been thoroughly investigated via thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and atomic force microscopy (AFM) and modelled with molecular dynamics simulations.

We present a theoretical and experimental study aimed at characterizing statistical regimes in a random laser. Both the theoretical simulations and the experimental results show the possibility of three regions of fluctuations increasing the pumping energy. An initial Gaussian regime is followed by Lévy statistics, and Gaussian statistics is recovered again for high pump pulse energy.These different statistical regimes are possible in a weakly diffusive active medium, while the region of Lévy statistics disappears when the medium is strongly diffusive presenting always a Gaussian regime with smooth emission spectrum. Experiments and theory agree in identification of the key parameters determining the statistical regimes of the random laser.

LIGHT, la notte dei ricercatori del CNR, consiste in un evento di divulgazione scientifica basato su un inedito format che coniuga performance scientifiche e sperimentali e pratiche sportive. Antonio Tintori, responsabile scientifico di LIGHT dal 2008, descrive in questo contributo la proficua relazione esistente tra scienza e arti marziali.

We demonstrate the feasibility of coherent spectroscopy experiments in alkali vapors at room temperature by using an automatic all-optical atomic dispenser. The reliability of the system is proved by observing electromagnetically induced transparency (EIT) resonances in siloxane-coated cells where large and stable K densities are achieved by light-controlled atomic desorption from the cell coating. The experimental results prove that this technique preserves the orientation of the atomic system, and, at the same time, allows a fine, continuous, and rapid control of the vapor density also suitable for magnetic-sensitive applications. (c) 2012 Optical Society of America

In a random laser (RL), a system possessing in itself both resonator and amplifying medium while lacking a macroscopic cavity, the feedback is provided by the scattering, which forces light to travel very long random paths. Here, we demonstrate that RL properties may be tuned by the topology of the scattering system retaining unchanged scattering strength and gain efficiency. This is possible in a system based on sparse clusters, possessing two relevant structural lengths: the macroscopic inter cluster separation and the mesoscopic intra-cluster mean free path.

A prolonged reverse bias (RB) stress forcing a short-circuit current through a dye solar cell, corresponding to the harshest test a shadowed cell may experience in real conditions, can cause the RB operating voltage V-RB to drift with time, initially slowly but accelerating for V-RB<(-1.65 +/- 0.15)V when gas bubbles, identified as H-2 (gas chromatography), are produced inside the cell, leading to breakdown. A close connection between VRB, cell performance, and stability was established. Contributions to RB degradation include triiodide depletion and impurities, in particular water. Acting upon these components and setting up protection strategies is important for delivering long-lasting modules.

We theoretically and numerically investigate the effect of focusing and defocusing nonlinearities on Anderson localization in highly nonlocal media. A perturbative approach is developed to solve the nonlocal nonlinear Schrödinger equation in the presence of a random potential, showing that nonlocality stabilizes Anderson states.

The spectrum of a random laser (RL) may appear either as a set of sharp resonances or as a smooth line superimposed on the fluorescence. Recently, Leonetti, Conti, and Lopez [Nat. Photonics 5, 615 (2011)] accounted for this duality with the onset of a mode-locked regime that is triggered by the increase of both the number of activated modes and of the intermode interaction and is accompanied by a pulse shortening. Here we report an extensive review of the experimental approach used by Leonetti et al., including the sample preparation and the particulars of the setup. Here we describe also the way in which our approach allows us either to set the degree of interaction between modes or to have a certain degree of control over the effective set of resonances brought to lasing. Moreover we report an investigation on the spatial properties of the RL which brings further confirmation of the synchronization picture, whose physical origin is deepened.

Spiral twisting offers additional opportunities for controlling the loss, dispersion, and polarization state of light in optical fibers with noncircular guiding cores. Here, we report an effect that appears in continuously twisted photonic crystal fiber. Guided by the helical lattice of hollow channels, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal fiber has potential applications in, for example, band-rejection filters and dispersion control.