diffractive dipolar coupling in non bravais plasmonic lattices

Honeycomb plasmonic lattices are characterized by a 2-particle unit cell. The difference between the intrasublattice and intersublattice coupling is distinctive of non-Bravais lattices. Although the two particles are identical the two types of coupling may be different

Zero degree Cherenkov calorimeters for the ALICE experiment

International audienceThe collision centrality in the ALICE experiment will be determined by the Zero Degree Calorimeters (ZDCs) that will measure the spectator nucleons energy in heavy ion collisions. The ZDCs detect the Cherenkov light produced by the fast particles in the shower that cross the quartz fibers, acting as the active material embedded in a dense absorber matrix. Test beam results of the calorimeters are presented

Final results of the tests on the resistive plate chambers for the ALICE muon arm

Abstract The trigger for the ALICE muon spectrometer will be issued by single-gap, low resistivity bakelite resistive plate chambers (RPCs). The trigger system consists of four 5.5 × 6.5 m 2 RPC planes arranged in two stations, for a total of 72 detectors. One hundred and sixteen detectors have been assembled and tested in Torino. The tests have been performed with the streamer mixture developed for heavy ion data-taking. The tests include: the detection of gas leaks and parasitic currents; the measurement of the efficiency with cosmic rays, with particular regard to the uniformity of the efficiency throughout the whole active surface, with a granularity of about 2 × 2 cm 2 ; the measurement of the dark current and of the mean and localised noise rate. All the RPCs produced have been characterised. Among them, the detectors to be finally installed in ALICE and some spare have been selected; 17% of all the produced detectors have been discarded. A short description of the test set-up is given. The results of the tests are presented, with particular regard to the performance of the selected detectors

Two-Dimensional Nanostructure Arrays for Plasmonic Nanolasers

The interest for plasmonic nanolasers has been growing in the last ten years, since they are one of the most promising ways to reach the miniaturization of lasers. In fact, these devices could break the limit of physical confinement of light thanks to the virtual cavity given by plasmonic nanostructures which substitutes the current macroscopic optical cavities. These plasmonic devices can also support high speed operation mode, low lasing threshold and a narrow directional emission. For this reason, during this project, we focused on the design, the synthesis and the characterization of plasmonic nanolasers based on Au nanodome arrays and Ag nanodisk arrays. In order to synthesize highly ordered nanostructure arrays, we used Nanosphere Lithography (NSL), which is a cost effective and high throughput technique based on the self-assembling of polystyrene nanospheres. Thanks to the versatility of NSL, we have developed different nanofabrication protocols, combining NSL with Reactive Ion Etching (RIE) and Physical Vapor Deposition (PVD). Therefore, we investigated the optical properties of our synthesized arrays, recreating the optical band structure along the high symmetry directions of the reciprocal space. Suitable dye emitters (Pyridine 2 and Styryl 9M) were selected in order to couple their emission with the optical modes of the nanoarrays, on the basis of optical band structure information. In addition, in order to optimize the plasmonic properties and the local field enhancement of the metallic nanostructures, numerical simulations by COMSOL Multiphysics were performed. The interaction between dye and plasmonic structure generated an amplified emission. In particular, for Au nanodome arrays coupled with Pyridine 2 dissolved in ethanol, an amplification on the emission arises at 720 nm with a threshold behavior at 0.9 mJ/cm^2 and the FWHM of 14 nm. Furthermore, a highly directional emission was obtained at 17° with an angular divergence of 3° which takes place along the Rayleigh anomaly mode. By comparing the results of Au nanodome arrays and silica nanodome arrays, we concluded that lattice modes give a contribution to the emission directionality, while plasmonic modes provide a reduced lasing threshold overcoming the energy loss. Ag hexagonal nanodisk array showed a similar behavior to the Au nanodome arrays: we found a lasing threshold at 1.6 mJ/cm^2 , with also a similar FWHM. In this case, the emission is directed at 65° and presents an angular divergence of about 14° . Moreover, we investigated a nanolaser with a solid-state gain medium for the interest in applications and for the device integration on a chip. The Styryl 9M laser dye is embedded in a PMMA film and coupled with an Au nanodome array. This solid-state system presents an amplified emission at 795 nm with a threshold of 1.2 mJ/cm^2 and a FWHM of about 26 nm. The sample shows also a directional emission at 24° and with an angular divergence of 6° . Further investigations have shown the possibility to eliminate the substrate, creating a self-standing device, which exhibits an amplified emission with similar properties of that with the substrate. Finally, in order to discern the spontaneous or stimulated nature of the emission, we performed coherence measurements of the emitted beam. By a modified Michelson interferometer, a coherence length of about 29 um was determined for Au nanodome arrays above threshold. This result demonstrated that a coherent, low-threshold and highly directional emission can be obtained by coupling a suitable fluorescent dye to a properly designed virtual cavity realized by an ordered array of plasmonic nanostructures.Nell'ultima decina di anni, l'interesse per i nanolaser plasmonici è cresciuto siccome sono uno tra i modi più promettenti per la miniaturizzazione dei laser. Infatti, questi dispositivi possono superare il limite di confinamento fisico della luce, grazie alla cavità virtuale data dalle nanostrutture plasmoniche che sostituiscono la convenzionale cavità ottica macroscopica. Inoltre, questi dispositivi plasmonici possono supportare modalità di funzionamento ad alta velocità, bassa soglia di emissione laser e una direzionalità ben definita. Per questa ragione, durante questo progetto, ci siamo concentrati sulla progettazione, la sintesi e la caratterizzazione di nanolasers plasmonici basati su array di nanocupole di oro e array di nanodischi di argento. Al fine di sintetizzare reticoli di nanoparticelle con un ordine elevato, abbiamo utilizzato la Nanosphere Lithography (NSL), una tecnica economica e ad alta produttività basata sull'autoassemblaggio di nanosfere di polistirene. Grazie alla versatilità della NSL, abbiamo sviluppato diversi protocolli di nanofabbricazione, combinando la NSL con i processi di Reactive Ion Etching (RIE) e deposizione fisica da vapore (PVD). Successivamente, abbiamo studiato le proprietà ottiche dei campioni sintetizzati, ricostruendo la struttura a bande ottica lungo le direzioni di alta simmetria dello spazio reciproco. Abbiamo selezionato due adeguati emettitori coloranti, la Pyridine 2 e lo Styryl 9M, al fine di accoppiare la loro emissione con le modalità ottiche dei reticoli nanostrutturati, sulla base delle informazioni della struttura a bande ottica. Inoltre, per ottimizzare le proprietà plasmoniche e l'amplificazione del campo locale delle nanostrutture metalliche, delle simulazioni numeriche sono state effettuate tramite il software COMSOL Multiphysics. L'interazione tra il colorante e la struttura plasmonica ha generato un'emissione amplificata. In particolare, nel reticolo di nanocupole di oro accoppiato alla piridina 2 disciolta in etanolo, un'amplificazione dell'emissione si presenta a720nm con un comportamento a soglia a 0.9 mJ/cm^2 . Inoltre, è stata ottenuta un'emissione direzionale a 17° con una divergenza angolare di 3° che avviene lungo l'anomalia di Rayleigh. Confrontando i risultati dei reticoli di nanocupole di oro con quelli dei reticoli di nanocupole di silice, abbiamo concluso che i modi di reticolo danno un contributo alla direzionalità dell'emissione, mentre i modi plasmonici forniscono una riduzione della soglia laser superando così la perdita di energia. Il reticolo esagonale di nanodischi di argento mostra un comportamento simile a quello con le nanocupole di oro: abbiamo trovato una soglia laser a 1.6 mJ/cm^2 , con anche una simile FWHM. In questo caso, questo fascio è diretto a 65° e presenta una divergenza angolare di circa 14° . Inoltre, abbiamo studiato anche un nanolaser con un mezzo di guadagno a stato solido per l'interesse nelle applicazioni e nell'integrazione di dispositivi su chip. Il colorante laser Styryl 9M è incorporato in un film di PMMA e accoppiato con un reticolo di nanocupole di oro. Questo sistema a stato solido presenta un'emissione amplificata a 795 nm con una soglia di 1.2 mJ/cm^2 e una FWHM di circa 26 nm. Questo campione manifesta anche un'emissione direzionale a 24° con una divergenza angolare di 6° . Ulteriori ricerche hanno dimostrato la possibilità di eliminare il substrato, creando un dispositivo autoportante, che presenta un'emissione amplificata con proprietà simili a quella con il substrato. Infine, per discernere la natura spontanea o stimolata dell'emissione, abbiamo misurato la coerenza del raggio emesso. Tramite un interferometro di Michelson dedicato, la lunghezza di coerenza è stimata a circa 29 um per i reticoli di nanocupole d'oro sopra la soglia. Questo risultato ha dimostrato che è possibile ottenere un'emissione coerente, a bassa soglia e altamente direzionale, accoppiando un colorante fluorescente adeguato con una cavità virtuale opportunamente progettata e realizzata da una reticolo ordinato di nanostrutture plasmoniche

Polarized coherent emission outside high-symmetry points of dye-coupled plasmonic lattices

Developing intense, coherent and ultra-fast light sources with nanoscale dimensions is a crucial issue for many applications in nanophotonics. To date, plasmonic nanolasers represent one of the most promising nanophotonic devices capable of this remarkable feature. In the present work we report on the emission properties of two-dimensional Au hexagonal nanodome arrays, fabricated by nanosphere lithography, coupled with a dye liquid solution used as the gain medium. Low-threshold stimulated emission at room temperature is demonstrated by spectral and angle-resolved photolu- minescence measurements performed as a function of the pump fluence. The emission arises with narrow angular divergence in off-normal direction, out of high-symmetry points of the plasmonic lattice. The polarization properties of the stimulated emission are investigated, revealing a strong linear polarization character controlled by the polarization orientation of the pumping beam, while the first-order temporal coherence properties are measured by using a tilted-mirrors Michelson interferometer. Finally, by comparing the results obtained for the plasmonic Au nanodomes arrays with those of purely dielectric nanoarrays, the role of the plasmonic modes and the photonic lattice modes in the emission process is highlighted

Double-Langmuir model for optimized nanohole array-based plasmonic biosensors

The sensing mechanism of plasmonic nanohole arrays is investigated and a novel model is proposed to interpret their optical response over a wide dynamic range of concentrations (10^-13 - 10^-5 M), based on a double- Langmuir model. This model describes the signal response of the analyte binding as the sum of two independent contributions which are related to two different surface regions of the biosensor, namely the top gold surface of the nanohole array and the lateral gold area inside the nanoholes. Numerical simulations highlight the different near-field behaviour of these two regions and their very different refractive index sensitivities, which both support the double-Langmuir model. This is corroborated by experimental biosensing measurements with gold nanohole arrays with hexagonal symmetry, synthesized by nanosphere lithography. Their sensing performances are optimized by numerical simulations by changing their geometrical parameters (i.e., lattice constant, nanohole diameter and height) in order to achieve a maximum sensitivity. For the biosensing experiments, the biotin-streptavidin complex is used as a benchmark test for the optimized nanohole array and a robust calibration is provided by the double-Langmuir model obtaining a limit of detection of 0.3 ng/mL, which corresponds to an absolute analyte quantity of 0.02 fmol

Where Brain, Body and World Collide

The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < pt < 8 Gev/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy sqrt{s} = 7 TeV using an integrated luminosity of 2.2 nb^{-1}. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs

Final results of the tests on the resistive plate chambers for the ALICE muon arm

International audienceThe trigger for the ALICE muon spectrometer will be issued by single-gap, low resistivity bakelite resistive plate chambers (RPCs). The trigger system consists of four 5.5x6.5 m2 RPC planes arranged in two stations, for a total of 72 detectors. One hundred and sixteen detectors have been assembled and tested in Torino. The tests have been performed with the streamer mixture developed for heavy ion data-taking. The tests include: the detection of gas leaks and parasitic currents; the measurement of the efficiency with cosmic rays, with particular regard to the uniformity of the efficiency throughout the whole active surface, with a granularity of about 2x2 cm2; the measurement of the dark current and of the mean and localised noise rate. All the RPCs produced have been characterised. Among them, the detectors to be finally installed in ALICE and some spare have been selected; 17% of all the produced detectors have been discarded. A short description of the test set-up is given. The results of the tests are presented, with particular regard to the performance of the selected detectors