1,720,963 research outputs found
Design and characterization of resonant devices for optical applications
Full text linkPeriodic structures have attracted huge research interest over the past many years due to their interesting electromagnetic properties. There are lots of useful applications in the fields of photonics and microwave engineering that come from periodic structures. Examples of periodic structures include diffraction gratings, photonic crystals, phased array antennas, frequency selective surfaces, and metamaterials. A diffraction grating is composed of diffracting elements arranged periodically. The spacing between these elements is comparable to the wavelength of the incident light. The amplitude, or phase, or both, of the diffracted electromagnetic radiation from a diffraction grating, can be modified in a controlled and predictable manner. Another interesting phenomenon is the presence of sharp resonant features in the optical spectra of the gratings such as Guided-Mode Resonances (GMR). GMR gratings have been employed in wide-ranging applications such as sensors for biosensing, optical absorbers, efficient photodetectors and tunable filters for optical communication systems, reflection mirrors for lasers, and spectrometers.
The first part of this work focuses on the design, fabrication, and characterization of resonant pillar gratings. This is further split into two parts. The first part describes the graphene-based pillar grating for optical absorber applications. The performance of the proposed periodic structure is investigated through numerical simulations. The proposed design exploits the guided mode resonances of the structure to achieve enhanced absorption in the monolayer graphene. In the second part, a phase change material vanadium-dioxide (VO2) is integrated with the pillar grating structure to achieve the thermal tuning of the optical response exploiting the phase change properties of VO2. The grating has been fabricated utilizing a nanoimprint lithography system exploiting a silicon mold. VO2 nano-powders have been deposited by spin-coating. In addition to the experimental tests, the proposed structure is simulated using the RCWA method. Next, plasmonic grating structures on planar as well curved surfaces are designed and analyzed through numerical simulations for sensing and Surface Enhanced Raman Spectroscopy (SERS) applications. The work related to plasmonic structures has also been further split into two parts. In the first part, a planar plasmonic grating is designed and synthesized for sensing applications in the transmission domain exploiting Extraordinary Transmittance (EOT) properties of the plasmonic modes as well as the sensitivity of these modes to the changes in the refractive index of the surrounding media. A Finite Difference Time Domain (FDTD) model of the finite set of nanoplatelets has been developed to theoretically investigate and optimize the nanostructure as well as validate the experimental results. Plasmonic modes can concentrate light to much smaller locations creating field hotspots. This makes plasmonic structures a suitable platform for SERS. In the second part of the work, plasmonic gratings on planar and curved surfaces are investigated as SERS platforms
Tunable Nanoislands Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection
No full text: Creating plasmonic nanoparticles on a tapered optical fiber (TF) tip enables a remote surface-enhanced Raman scattering (SERS) sensing probe, ideal for challenging sampling scenarios like biological tissues, site-specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Ultimately, this limits the design of the best-performance remote SERS sensing probe. Here we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands with varied geometric parameters in direct contact with the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark molecule, rhodamine 6G (R6G), and serotonin, a highly relevant neurotransmitter for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, we observed a different behavior for serotonin linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provides new clues to discover and understand intricate plasmonic-driven chemical reactions
Plasmonic brain implants for the next generation of nano-optical neural interfaces
No full textWe propose a new class of plasmonic neural implants for harnessing nanoscale light-matter interactions in the brain using highly curved nanostructures on tapered optical fiber
High transmission from 2D periodic plasmonic finite arrays with sub-20 nm gaps realized with Ga focused ion beam milling
Full text linkFabricating plasmonic nanostructures with good optical performances often requires lengthy and challenging patterning processes that can hardly be transferred to unconventional substrates, such as optical fiber tips or curved surfaces. Here we investigate the use of a single Ga focused ion beam process to fabricate 2D arrays of gold nanoplatelets for nanophotonic applications. While observing that focused ion beam milling of crossing tapered grooves inherently produces gaps below 20 nm, we provide experimental and theoretical evidence for the spectral features of grooves terminating with a sharp air gap. We show that transmission near 10% can be obtained via two-dimensional nano-focusing in a finite subset of 2D arrays of gold nanoplatelets. This enables the application of our nanostructure to detect variations in the refractive index of thin films using either reflected or transmitted light when a small number of elements are engaged
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Plasmonic Nanostructures on Curved Surfaces for Fiber-Based Sensors
No full textPlasmonic devices on a curved surface can open exciting new possibilities for guiding, focusing, deflecting, and controlling the propagation of plasmonic waves. Propagation on curved surfaces can be designed to mimic optical fiber-based plasmonic devices, for example, advanced optical probes for biological sensing applications. However, there is limited progress in this field due to technological limitations especially the fabrication of subwavelength structures on curved substrates is quite challenging. In this paper, we discuss the perspectives and challenges that lie in the design and simulation of plasmonic devices with a special focus on curvature induced effects and implications. We present numerical studies of gold films on a curved surface that resemble a fiber-based sensor. The results from this study can be helpful in the analysis and design of plasmonic devices involving optical fiber and other flexible substrates
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Optical Properties of Finite Subsets of FIB-Milled 2D Periodic Arrays of Gold Nanoplatelets with Sub-20-nm Gaps
No full textWe theoretically and experimentally investigate the optical properties arising from the illumination of a subset of elements in FIB-milled 2D-periodic arrays of gold nanoplatelets with sub-20-nm gaps
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