1,721,289 research outputs found
Ultracompact low-pass modal filters based on shortcuts to adiabaticity
No full textA versatile approach to the design of photonic ultracompact low-pass modal filters is proposed. The idea stems from the shortcut to adiabaticity protocol, originally developed for quantum-mechanical systems and recently introduced in full-wave optics. This method allows one to achieve efficient rejection of higher order modes in a broad wavelength range for any two-dimensional multimode optical waveguide in an ultracompact configuration of the filter. A study case, corroborated by finite-element method numerical simulations, is reported for slab waveguides
Modeling Optical Rectification In Doubly-Resonant Dielectric Nanostructures: Effective Nonlinear Response And THz Emission Control
No full textFrequency-conversion is one of the many applications that has benefited from the rapid development of the field of nonlinear nanophotonics. In this work we theoretically study the difference-frequency generation process between two NIR pump fields in Mie-resonant nanoscatterers, which via the χ(2)(ω 3 ω 1, -ω 2) susceptibility emit a THz-signal. The key features responsible for enhancing the conversion-efficiency are disentangled and a comparison is reported between the numerical results yielded by pillars made of Al 0.18 Ga0.82 As and LiNbO3. These are complemented with a reduced effective model for the down-conversion process, together with an analysis of the radiation pattern dependence on crystal orientation
On the limits of quasi-static theory in plasmonic nanostructures
Full text linkThe approximated analytical approach of quasi-static theory (QST) is widely used in modelling the optical response of plasmonic nanoparticles. It is well known that its accuracy is remarkable provided that the particle is much smaller than the wavelength of the interacting radiation and that the field induced inside the structure is approximately uniform. Here, we investigate the limits of QST range of validity for gold nanostructures freestanding in air. First, we compare QST predictions of scattering spectra of nanospheres and cylindrical nanowires of various sizes with the exact results provided by Mie scattering theory. We observe a non-monotonic behaviour of the error of QST as a function of the characteristic length of the nanostructures, revealing a non-trivial scaling of its accuracy with the scatterer size. Second, we study nanowires with elliptical section upon different excitation conditions by performing finite element numerical analysis. Comparing simulation results with QST estimates of the extinction cross-section, we find that QST accuracy is strongly dependent on the excitation conditions, yielding good results even if the field is highly inhomogeneous inside the structure
Validazione di metodologie del calcolo dell'energia di deformazione conseguente alla collisione di autovetture
No full textCanine Seventh Lumbar Vertebra Fracture: A Systematic Review
Full text link(1) Background: Lumbosacral traumatic injuries are reported as 39% of canine vertebral lesions. This area is prone to fracture and luxation. Several surgical techniques were described from 1975 to 2021 to stabilize the traumatic injuries of the lumbosacral junction. This report aims to critically review the available literature focused on clinical presentation, surgical techniques, and follow-up of the lumbar vertebra fracture. (2) Methods: Three bibliographic databases: PubMed, Google Scholar, and Scopus were used with a board search of Lumbosacral junction fracture AND, of L7 fracture AND (canine OR dog). The Joanna Briggs Institute (JBI) Critical Appraisal Checklist for case reports and case series was applied for the studies included. (3) Results: A total of 432 reports yielded only nine that met the inclusion criteria. Non-ambulatory paraparesis/plegia, sciatic nerve involvement, faecal/urinary incontinence, and severe back lumbar pain were the most reported signs. Survey radiographs were the most reported technique to confirm the diagnoses. The surgical treatment was reported in all reports examined with a good long-term prognosis. (4) Conclusions: The seventh lumbar vertebra fracture, despite the different surgical techniques performed, had a favourable prognosis for long-term outcome and neurological recovery
Ultrafast hot electron dynamics in plasmonic nanostructures: Experiments, modelling, design
Full text linkMetallic nanostructures exhibit localized surface plasmons (LSPs), which offer unprecedented opportunities for advanced photonic materials and devices. Following resonant photoexcitation, LSPs quickly dephase, giving rise to a distribution of energetic ‘hot’ electrons in the metal. These out-of-equilibrium carriers undergo ultrafast internal relaxation processes, nowadays pivotal in a variety of applications, from photodetection and sensing to the driving of photochemical reactions and ultrafast all-optical modulation of light. Despite the intense research activity, exploitation of hot carriers for real-world nanophotonic devices remains extremely challenging. This is due to the com- plexity inherent to hot carrier relaxation phenomena at the nanoscale, involving short-lived out-of-equilibrium electronic states over a very broad range of energies, in interaction with thermal electronic and phononic baths. These issues call for a comprehensive understanding of ultrafast hot electron dynamics in plasmonic nanostructures. This paper aims to review our contribution to the field: starting from the fundamental physics of plasmonic nanostructures, we first describe the experimental techniques used to probe hot electrons; we then introduce a numerical model of ultrafast nanoscale relaxation processes, and present examples in which experiments and modelling are combined, with the aim of designing novel optical functionalities enabled by ultrafast hot-electron dynamics
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