Browsing by Author "Çağlayan, H."

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Open Access
Connection of collimation, asymmetric beaming, and independent transmission-reflection processes in concentric-groove gratings supporting spoof surface plasmons
(Springer, 2019) Habib, Mohsin; Serebryannikov, A. E.; Çağlayan, H.; Vandenbosch, G. A. E.; Özbay, Ekmel
Transmission through subwavelength apertures enables separation of the incidence half-space and the exit half-space, which leads to that the spatial distribution of the field in the latter is not affected by the distribution in the former. The distribution in the exit half-space is mainly determined by the properties of surface plasmons (SPs) at the exit-side interface. In this paper, for the microwave structures with one-side concentric corrugations around a single annular hole, we demonstrate the possible connections between asymmetric transmission in the beaming regime and collimation of the waves incident at different angles, which can be considered as two sides of the same phenomenon occurring due to the common effect of such a separation and the radiation shaping effect being possible due to the spoof SPs at the corrugated exit interface. Collimation manifests itself in that the waves incident at different angles from a wide range contribute to the single outgoing beam so that a far-zone observer cannot distinguish between the contributions of different angles of arrival. Asymmetry in transmission manifests itself in that the spatial shaping of radiation (beaming) in the exit half-space appears only for one of the two opposite incidence directions. Moreover, even in the structures with the same corrugations on both sides, i.e., without asymmetric transmission, spatial separation of two wave processes, e.g., two symmetric or asymmetric collimation processes, can be obtained for a wide range of nonzero angles of incidence.
Open Access
Plasmon-modulated photoluminescence enhancement in hybrid plasmonic nano-antennas
(IOP Publishing, 2020) Rashed, A. R.; Habib, M.; Das, N.; Özbay, Ekmel; Çağlayan, H.
In this work, we performed a systematic study on a hybrid plasmonic system to elucidate a new insight into the mechanisms governing the fluorescent enhancement process. Our lithographically defined plasmonic nanodisks with various diameters act as receiver and transmitter nano-antennas to outcouple efficiently the photoluminescence of the coupled dye molecules. We show that the enhancement of the spontaneous emission rate arises from the superposition of three principal phenomena: (i) metal enhanced fluorescence, (ii) metal enhanced excitation and (iii) plasmon-modulated photoluminescence of the photoexcited nanostructures. Overall, the observed enhanced emission is attributed to the bi-directional near-field coupling of the fluorescent dye molecules to the localized plasmonic field of nano-antennas. We identify the role of exciton–plasmon coupling in the recombination rate of the sp-band electrons with d-band holes, resulting in the generation of particle plasmons. According to our comprehensive experimental analyses, the mismatch between the enhanced emission and the emission spectrum of the uncoupled dye molecules is attributed to the plasmon-modulated photoluminescence of the photoexcited hybrid plasmonic system.