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II9.02 - Quasiperiodic Concentrator for Absorption Enhancement in Thin Films 
April 24, 2014   9:00am - 9:15am

Plasmonic concentrators (PCs) can be constructed by etching long-range arrays of shallow sub-wavelength holes on the surface of a noble metal, such as silver. Each hole in the array can couple incident light to surface plasmon polariton (SPP) modes that propagate along the dielectric / metal interface. If the holes are close enough, SPP modes generated by neighboring holes can constructively interfere, thus enhancing the electromagnetic fields at the metal / dielectric interface by several orders of magnitude. Due to the field enhancement, absorption in a thin film resting above a PC can therefore exhibit broadband, polarization-independent enhancement (compared to a flat surface) [1]. This is not solely due to the increased effective path length of the incident light. Indeed, the average hole-hole spacing and the order of rotational symmetry of the pattern used can play a significant role, which can largely be understood in terms of increased constructive interference between SPPs.In addition to the simple periodic 2D (e.g., honeycomb, square, hexagonal) and random arrays, here we include quasiperiodic (QP) arrays (e.g., Penrose) featuring higher levels of local and long-range order (specifically, rotational symmetry), and a higher surface density of point scatterers, despite lacking long-range translational symmetry. By generalizing a Penrose array generation algorithm [2], an entire spectrum of QP patterns can be created and studied. We demonstrate that QP plasmonic concentrators can provide higher field enhancements, and as a result better absorption enhancement, compared to periodic or random arrays [3-4].Aside from the immediate application to thin film photovoltaics and biochemical sensing, the results presented here help provide a deeper understanding of SPP generation, propagation, and interference, as well as shedding light on higher order scattering effects contributing to the overall broadband field enhancements.1. Ostfeld, A E, D Pacifici. Appl. Phys. Lett. 98, no. 113112 (2011)2. de Bruijn N G. Kon. Nederl. Akad. Wetensch. Proc. Ser. A 84 (1981): 39-663. Flanigan P W, A E Ostfeld, N G Serrino, Z Ye, D Pacifici. Opt. Express. 21, no. 3 (2013): 2757-27764. Flanigan P W, A E Ostfeld, Z Ye, N G Serrino, D Pacifici. "Quasiperiodic plasmonic concentrators for ultra-thin film solar cells", Optics of Aperiodic Structures: Fundamentals and Device Applications, ed. Luca Dal Negro (2013).

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