Interfacing optical fibers with plasmonic nanoconcentrators

The concentration of light to deep-subwavelength dimensions plays a key role in nanophotonics and has the potential to bring major breakthroughs in fields demanding to understand and initiate interaction on nanoscale dimensions, including molecular disease diagnostics, DNA sequencing, single nanoparticle manipulation and characterization, and semiconductor inspection. Although planar metallic nanostructures provide a pathway to nanoconcentration of electromagnetic fields, the delivery/collection of light to/from such plasmonic nanostructures is often inefficient, narrow-band, and requires complicated excitations schemes, limiting widespread applications. Moreover, planar photonic devices reveal a reduced flexibility in terms of bringing the probe light to the sample. An ideal photonic-plasmonic device should combine (i) a high spatial resolution at the nanometre level beyond to what is state-of-the-art in near-field microscopy with (ii) flexible optical fibers to promote a straightforward integration into current near-field scanning microscopes. Here, we review the recent development and main achievements of nanoconcentrators interfacing optical fibers at their end-faces that reach entirely monolithic designs, including campanile probes, gold-coated fiber-taper nanotips, and fiber-integrated gold nanowires

Direct observation of modal hybridization in nanofluidic fiber [Invited]

Hybrid-material optical fibers enhance the capabilities of fiber-optics technologies, extending current functionalities to several emerging application areas. Such platforms rely on the integration of novel materials into the fiber core or cladding, thereby supporting hybrid modes with new characteristics. Here we present experiments that reveal hybrid mode interactions within a doped-core silica fiber containing a central high-index nanofluidic channel. Compared with a standard liquid-filled capillary, calculations predict modes with unique properties emerging as a result of the doped core/cladding interface, possessing a high power fraction inside and outside the nanofluidic channel. Our experiments directly reveal the beating pattern in the fluorescent liquid resulting from the excitation of the first two linearly polarized hybrid modes in this system, being in excellent agreement with theoretical predictions. The efficient excitation and beat of such modes in such an off-resonance situation distinguishes our device from regular directional mode couplers and can benefit applications that demand strong coupling between fundamentaland higher-order- modes, e.g. intermodal third-harmonic generation, bidirectional coupling, and nanofluidic sensing

Whetstones from Bronze Age hill forts of North Eastern Italy

A group of Bronze Age whetstones from Protohistoric hill forts, locally called Castellieri, of eastern Friuli Venezia Giulia (north eastern Italy) has been studied using different techniques, including non destructive methods such as X-ray computed micro-tomography and portable X-ray fluorescence, in order to characterize the raw material and define its origin. The obtained results suggest that small pebbles of reddish subarkose and quartz arenites collected from the gravel deposits of river Isonzo, perhaps deriving from Val Gardena Formation outcrops, were exploited for the production of the studied artefacts during the Bronze Age. These data complement our knowledge about the lithic raw materials exploitation strategies during the ancient phase of Castellieri culture, almost exclusively based on local rock type

Polished stone axes from Varna/Nössingbühel and Castelrotto/Grondlboden, South Tyrol (Italy)

A collection of polished stone axes from a late Neolithic site and an Early Bronze Age hill fort in South Tyrol (Italy) have been analysed through a multi-analytical approach, mainly based on non-destructive techniques (i.e. Raman spectroscopy, X-ray fluorescence and prompt gamma activation analysis) to identify the raw materials used in the same area during different periods and compare them with those in use in the surrounding territories. The analytical results suggest raw material exploitation strategies based on local or close sedimentary, metamorphic and magmatic rocks. Most of the artefacts are made from antigoritic serpentinite, whose origin is probably from Hohe Tauern (Austria) or related secondary deposits. These data confirm the importance of such raw material for the production of polished stone axes during recent prehistory and integrate the present knowledge about the distribution of antigoritic artefacts in north-eastern Italy and neighbouring countries

X-ray computed microtomography of late copper age decorated bowls with cross-shaped foots from central Slovenia and the Trieste Karst (North-Eastern Italy): technology and paste characterization.

About 20 Late Copper Age bowls with cross-shaped foots from Deschmann\u2019s pile dwellings (Ljubljansko barje, central Slovenia) and Trieste Karst (North-Eastern Italy) have been investigated using X-ray computed microtomography (microCT) in order to study the vessel-forming technique, to characterise their pastes and to test the hypothesis that some Karst bowls could have been imported from nowadays central Slovenia or even more distant regions. In three selected virtual slices per sample, clay, lithic inclusions and pores have been segmented and quantified. In addition, the area, maximum length and width of each lithic inclusion have been calculated. Then, the microCT-derived results have been statistically analysed by principal component analysis (PCA). The orientation of pores and disjunctions in microCT volumes show that the basins of the bowls were built using mainly the coiling technique, while the base was shaped starting from a central piece, to which a layer of clay was added and then reshaped in order to produce the foots. The Slovenian bowls include both medium/coarse-grained and very fine- or fine-grained vessels mainly tempered with carbonate inclusions. The pastes of the Karst bowls are considerably heterogeneous. One bowl was most likely imported to the Karst but not from central Slovenia as it shows peculiar components, shape and decoration. The other two imported vessels show a very fine-grained paste comparable to the one of several samples from Deschmann\u2019s pile dwellings. Such technological similarity is confirmed by PCA of microCT data and petrographic observations. Our study confirms the existence of strong cultural connections between central Slovenia and the northernmost Adriatic coast during the Late Copper Age

Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells.Alessandro Tuniz, Korbinian J. Kaltenecker, Bernd M. Fischer, Markus Walther, Simon C. Fleming, Alexander Argyros and Boris T. Kuhlme

High-accuracy methodology for the integrative restoration of archaeological teeth by using reverse engineering techniques and rapid prototyping

The reconstruction of the original morphology of bones and teeth after sampling for physicochemical (e.g., radiocarbon and uranium series dating, stable isotope analysis, paleohistology, trace element analysis) and biomolecular analyses (e.g., ancient DNA, paleoproteomics) is appropriate in many contexts and compulsory when dealing with fossil human remains. The reconstruction protocols available to date are mostly based on manual re-integration of removed portions and can lead to an imprecise recovery of the original morphology. In this work, to restore the original external morphology of sampled teeth we used computed microtomography (microCT), reverse engineering (RE), computer-aided design (CAD) and rapid prototyping (RP) techniques to fabricate customized missing parts. The protocol was tested by performing the reconstruction of two Upper Palaeolithic human teeth from the archaeological excavations of Roccia San Sebastiano (Mondragone, Caserta, southern Italy) and Riparo I of Grotte Verdi di Pradis (Clauzetto, Pordenone, north-eastern Italy) (RSS2 and Pradis 1, respectively), which were sampled for physicochemical and biomolecular analyses. It involved a composite procedure consisting in: a) the microCT scanning of the original specimens; b) sampling; c) the microCT scanning of the specimens after sampling; d) the reconstruction of the digital 3D surfaces of the specimens before and after sampling; e) the creation of digital models of the missing/sampled portions by subtracting the 3D images of the preserved portions (after the sampling) from the images of the intact specimens (before the sampling) by using reverse engineering techniques; f) the prototyping of the missing/sampled portions to be integrated; g) the painting and application of the prototypes through the use of compatible and reversible adhesives. By following the proposed protocol, in addition to the fabrication of a physical element which is faithful to the original, it was possible to obtain a remarkable correspondence between the contact surfaces of the two portions (the original and the reconstructed one) without having to resort to any manipulation/adaptation of either element