An Efficient Large-Area Grating Coupler for Surface Plasmon Polaritons

We report the design, fabrication and characterization of a periodic grating of shallow rectangular grooves in a metallic film with the goal of maximizing the coupling efficiency of an extended plane wave (PW) of visible or near-infrared light into a single surface plasmon polariton (SPP) mode on a flat metal surface. A PW-to-SPP power conversion factor > 45 % is demonstrated at a wavelength of 780 nm, which exceeds by an order of magnitude the experimental performance of SPP grating couplers reported to date at any wavelength. Conversion efficiency is maximized by matching the dissipative SPP losses along the grating surface to the local coupling strength. This critical coupling condition is experimentally achieved by tailoring the groove depth and width using a focused ion beam.Comment: The final publication is available at http://www.springerlink.com. http://dx.doi.org/10.1007/s11468-011-9303-

Acoustic cloak based on Bézier scatterers

[EN] Among the different approaches proposed to design acoustic cloaks, the one consisting on the use of an optimum distribution of discrete scatters surrounding the concealing object has been successfully tested. The feasibility of acoustic cloaks mainly depends on the number and shape of the scatterers surrounding the object to be cloaked. This work presents a method allowing the reduction of the number of discrete scatterers by optimizing their external shape, which is here defined by a combination of cubic Bézier curves. Based on scattering cancellation, a two-dimensional directional cloak consisting of just 20 Bézier scatters has been designed, fabricated and experimentally characterized. The method of fundamental solutions has been implemented to calculate the interaction of an incident plane wave with scatterers of arbitrary shape. The acoustic cloak here proposed shows a performance, in terms of averaged visibility, similar to that consisting of 120 scatterers with equal circular cross sections. The operational frequency of the proposed cloak is 5940 Hz with a bandwidth of about 110 Hz.J. Sanchez-Dehesa acknowledges the financial support by the Spanish Ministerio de Economia y Competitividad and the European Union Fondo Europeo para el Desarrollo Regional (FEDER) under Grant with Ref. TEC2014-53088-C3-1-R. Lu Zhimiao acknowledges the financial support from the program of China Scholarships Council (No. 201503170282), Wen Jihong, Cai Li and Lu Zhimiao acknowledge the support by National Natural Science Foundation of China (Grant Nos 51275519 and 11372346)Lu, Z.; Sanchis Martínez, L.; Wen, J.; Cai, L.; Bi, Y.; Sánchez-Dehesa Moreno-Cid, J. (2018). Acoustic cloak based on Bézier scatterers. Scientific Reports. 8. https://doi.org/10.1038/s41598-018-30888-7S8Cummer, S. A. & Schurig, D. One path to acoustic cloaking. 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L., Boisvert, J. E. & Howarth, T. R. Acoustic cloaking using layered pentamode materials. J. Acoust. Soc. Am. 127(5), 2856–2864 (2010).Chen, Y. et al. Broadband solid cloak for underwater acoustics. Phys. Rev. B 95, 180104 May (2017).Alù, A. & Engheta, N. Achieving transparency with plasmonic and metamaterial coatings. Phys. Rev. E 72(1), 016623 (2005).Guild, M. D., Alu, A. & Haberman, M. R. Cancellation of acoustic scattering from an elastic sphere. J. Acoust. Soc. Am. 129(3), 1355–1365 (2011).García-Chocano, V. M. et al. Acoustic cloak for airborne sound by inverse design. Appl. Phys. Lett. 99(7), 074102 (2011).Sanchis, L. et al. Three-Dimensional Axisymmetric Cloak Based on the Cancellation of Acoustic Scattering from a Sphere. Phys. Rev. Lett. 110, 124301 Mar (2013).Andkjær, J. & Sigmund, O. Topology optimized for Airborne sound. ASME J. Vib. Acoust. 135(2), 041011 (2013).Guild, M. D. Acoustic Cloaking of Spherical Objects Unsing Thin Elastic Coatings. Univ. of Texas at Austin (2012).Guild, M. D., Haberman, M. R. & Alú, A. Plasmonic-type Acoustic cloak made of a bilaminate shell. Phys. Rev. B 86(10), 104302 (2012).Rohde, C. A. et al. Experimental demonstration of underwater acoustic scattering cancellation. Sci. Rep. 5, 13175 (2015).Popa, B.-I. & Cummer, S. A. Cloaking with optimized homogeneous anisotropic layers. Phys. Rev. A 79, 023806 Feb (2009).Urzhumov, Y., Landy, N., Driscoll, T., Basov, D. & Smith, D. R. Thin low-loss dielectric coatings for freespace cloaking. Opt. Lett. 38(10), 1606–1608 (2013).Andkjaer, J. & Sigmund, O. Topology optimized low-contrast all-dielectric optical cloak. Appl. Phys. Lett. 98(2), 021112 (2011).Climente, A., Torrent, D. & Sánchez-Dehesa, J. Sound focusing by gradient index sonic lenses. Applied Physics Letters 97(10), 104103 (2010).Håkansson, A., Sánchez-Dehesa, J. & Sanchis, L. Acoustic lens design by genetic algorithms Phys. Rev. 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Optimized microwave illusion device

This work was funded by the Engineering and Physical Sciences Research Council (EPSRC), UK under a Programme Grant (EP/I034548/1) ‘The Quest for Ultimate Electromagnetics using Spatial Transformations (QUEST

Outlook for inverse design in nanophotonics

Recent advancements in computational inverse design have begun to reshape the landscape of structures and techniques available to nanophotonics. Here, we outline a cross section of key developments at the intersection of these two fields: moving from a recap of foundational results to motivation of emerging applications in nonlinear, topological, near-field and on-chip optics.Comment: 13 pages, 6 figure

Demographic, social, and environmental factors predicting Danish children’s greenspace use

BACKGROUND: Evidence suggest that greenspace use can be associated with children's physical, mental, social health, and well-being (Tillmann et al., 2018; Mygind et al., 2019; Mygind et al., 2021). Greenspace can facilitate a wide range of low-cost activities and the availability of greenspace is frequently linked to increased levels of recreational physical activity. Accordingly, contemporary children's declining greenspace use prompts a need to understand the factors that affect frequency of use. METHODS: Aiming to determine to what extent demographic, environmental and social factors predict greenspace use for school-aged (6-15-year-old) children in Denmark, a national online survey was distributed to parents of 10.000 0-15-year-old children. From a total of 4772 responses a sub-sample of 3171 responses from parents of school-aged children was included in the analysis for this study. The aim was addressed by answering the following research questions: 1) How often do Danish children use greenspaces? 2) What demographic differences in greenspace use are present? 3) How do social and environmental factors predict greenspace use? RESULTS: Responses from the 3171 parents showed that 49.5% of the children used greenspace almost every day during the summer season. Multivariate binary logistic regression analysis showed that the number of types of greenspaces within walking or cycling distance from home was a strong predictor for daily use. Social factors (parental concern and encouragement) also predicted use, but less so. Geography and child age were the only demographic predictors for using greenspace almost every day. CONCLUSIONS: Findings from the present study suggest that providing opportunity for choosing between various types of greenspaces within walking or cycling distance might be an effective way to stimulate children's use of greenspace. Also, increased parental awareness of their role in children's outdoor spatial behaviours might further greenspace use among children