Browsing by Author "Karademir, E."

Now showing 1 - 8 of 8

Open Access
Absorption enhancement of molecules in the weak plasmon-exciton coupling regime
(Optical Society of American (OSA), 2014) Balci, S.; Karademir, E.; Kocabas, C.; Aydınlı, Atilla
We report on the experimental and theoretical investigations of enhancing the optical absorption of organic molecules in the weak plasmon-exciton coupling regime. A metal-organic hybrid structure consisting of dye molecules embedded in the polymer matrix is placed in close vicinity to thin metal films. We have observed a transition from a weak coupling regime to a strong coupling one as the thickness of the metal layer increases. The results indicate that absorption of the self-assembled J-aggregate nanostructures can be increased in the weak plasmon-exciton coupling regime and strongly quenched in the strong coupling regime. A theoretical model based on the transfer-matrix method qualitatively confirms the experimental results obtained from polarization-dependent spectroscopic reflection measurements.
Open Access
Electrically switchable metadevices via graphene
(American Association for the Advancement of Science, 2018) Balcı, Osman; Kakenov, Nurbek; Karademir, E.; Balcı, S.; Çakmakyapan, S.; Polat, E. O.; Cağlayan, H.; Özbay, Ekmel; Kocabaş, Coşkun
Metamaterials bring subwavelength resonating structures together to overcome the limitations of conventional materials. The realization of active metadevices has been an outstanding challenge that requires electrically reconfigurable components operating over a broad spectrum with a wide dynamic range. However, the existing capability of metamaterials is not sufficient to realize this goal. By integrating passive metamaterials with active graphene devices, we demonstrate a new class of electrically controlled active metadevices working in microwave frequencies. The fabricated active metadevices enable efficient control of both amplitude (>50 dB) and phase (>90°) of electromagnetic waves. In this hybrid system, graphene operates as a tunable Drude metal that controls the radiation of the passive metamaterials. Furthermore, by integrating individually addressable arrays of metadevices, we demonstrate a new class of spatially varying digital metasurfaces where the local dielectric constant can be reconfigured with applied bias voltages. In addition, we reconfigure resonance frequency of split-ring resonators without changing its amplitude by damping one of the two coupled metasurfaces via graphene. Our approach is general enough to implement various metamaterial systems that could yield new applications ranging from electrically switchable cloaking devices to adaptive camouflage systems. Copyright
Open Access
Lasing in a Slow Plasmon Moiré Cavity
(American Chemical Society, 2015) Karademir, E.; Balci, S.; Kocabas, C.; Aydınlı, Atilla
We report on lasing from dye-based excitons coupled to slow plasmon states inside metallic Moiré cavities. Surface plasmon polaritons (SPPs) inside the cavity were slowed down to a maximum group velocity of 0.3c. Varying the modulation of the Moiré cavity, we tune the output wavelength of the plasmonic laser by varying the fast modulation period of the Moiré cavity. This work opens a new way to study SPP-matter interaction dynamics and plasmonic lasing with Bragg cavity confined slow plasmons.
Open Access
Plasmonic band gap engineering of plasmon-exciton coupling
(Optical Society of American (OSA), 2014) Karademir, E.; Balci, S.; Kocabas, C.; Aydınlı, Atilla
Controlling plasmon-exciton coupling through band gap engineering of plasmonic crystals is demonstrated in the Kretschmann configuration. When the flat metal surface is textured with a sinusoidal grating only in one direction, using laser interference lithography, it exhibits a plasmonic band gap because of the Bragg scattering of surface plasmon polaritons on the plasmonic crystals. The contrast of the grating profile determines the observed width of the plasmonic band gap and hence allows engineering of the plasmonic band gap. In this work, resonant coupling between the molecular resonance of a J-aggregate dye and the plasmonic resonance of a textured metal film is extensively studied through plasmonic band gap engineering. Polarization dependent spectroscopic reflection measurements probe the spectral overlap occurring between the molecular resonance and the plasmonic resonance. The results indicate that plasmon-exciton interaction is attenuated in the band gap region along the grating direction. © 2014 Optical Society of America.
Open Access
Plexcitonic crystals: A tunable platform for light-matter interactions
(Optical Society of American (OSA), 2014) Karademir, E.; Balci, S.; Kocabas, C.; Aydınlı, Atilla
Coupled states of surface plasmon polaritons (SPPs) and excitons are collectively called plexcitons [Nano Lett. 8, 3481 (2008)]. Plexcitonics is an emerging field of research aiming to control light-matter interaction at the nanometer length scale using coupled pairs of surface-plasmons and excitons. Ability to control the interaction between localized excitons and propagating surface-plasmons is important for realization of new photonic devices. In this letter, we report plexcitonic crystals that yield direction-dependent plasmon-exciton coupling. We have fabricated one- and two-dimensional plexcitonic crystals on periodically corrugated silver surfaces, which are loaded with J-aggregate complexes. We show that plasmon-exciton coupling is blocked for some crystal directions when exciton energy falls inside the plasmonic band gap of the periodically corrugated metallic surface. ©2014 Optical Society of America.
Open Access
Slow plasmons in grating cavities
(SPIE, 2016) Aydınlı, Atilla; Karademir, E.; Balcı, S.; Kocabaş, Coşkun
Recent research on surface plasmon polaritons and their applications have brought forward a wealth of information and continues to be of interest to many. In this report, we concentrate on propagating surface plasmon polaritons (SPPs) and their interaction with matter. Using grating based metallic structures, it is possible to control the electrodynamics of propagating SPPs. Biharmonic gratings loaded with periodic Si stripes allow excitation of SPPs that are localized inside the band gap with grating coupling, [1]. The cavity state is formed due to periodic effective index modulation obtained by one harmonic of the grating and loaded Si stripes. More complicated grating structures such as metallic Moiré surfaces have also been shown to form a localized state inside the band gap when excited with Kretschmann configuration, [1-6].
Open Access
Strong coupling between localized and propagating plasmon polaritons
(OSA - The Optical Society, 2015) Balci, S.; Karademir, E.; Kocabas, C.
We investigate plasmon-plasmon (PP) coupling in the strongly interacting regimes by using a tunable plasmonic platform consisting of triangular Ag nanoprisms placed nanometers away from Ag thin films. The nanoprisms are colloidally synthesized using a seed-mediated growth method and having size-tunable localized surface plasmon polariton (SPP) resonances immobilized on Si3N4 films. The PP coupling between the localized SPPs of metal nanoprisms and the propagating SPPs of the metal film is controlled by the nanoprism concentration and the plasmon damping in the metal film. Results reveal that Rabi splitting energy determining the strength of the coupling can reach up to several hundreds meV, thus demonstrating the ultrastrong coupling occurring between localized and propagating SPPs. The metal nanoparticle-metal thin film hybrid system over the square-centimeter areas presented here provides a unique configuration to study PP coupling all the way from the weak to ultrastrong coupling regimes in a broad range of wavelengths.
Open Access
Tuning surface plasmon-exciton coupling via thickness dependent plasmon damping
(American Physical Society, 2012) Balci, S.; Kocabas, C.; Ates, S.; Karademir, E.; Salihoglu, O.; Aydınlı, Atilla
In this paper, we report experimental and theoretical investigations on tuning of the surface plasmon-exciton coupling by controlling the plasmonic mode damping, which is defined by the plasmonic layer thickness. The results reveal the formation of plasmon-exciton hybrid state characterized by a tunable Rabi splitting with energies ranging from 0 to 150 meV. Polarization-dependent spectroscopic reflection measurements were employed to probe the dispersion of the coupled system. The transfer matrix method and analytical calculations were used to model the self-assembled J-aggregate/metal multilayer structures in excellent agreement with experimental observations. © 2012 American Physical Society.