arXiv subjects

Ramazan Sahin

Publications and source records attributed to Ramazan Sahin.

At least 19 recordsLinked to original sources

arXiv2026

All-optical switching of continuous-variable entanglement in an absorption-suppressed plasmonic nanodimer

A subwavelength quantum-photonic circuit element should simultaneously generate nonclassical light, suppress plasmonic loss, and remain dynamically tunable. We show that an orthogonal plasmonic nanorod dimer can satisfy all three requirements. A phase-locked control polarization induces plasmonic refractive-index enhancement, driving the probe response toward a near-zero-extinction regime while simultaneously tuning the local second-harmonic parametric interaction. The resulting nonlinear plasmonic source operates in an absorption-suppressed regime and enables all-optical control of quantum correlations. We demonstrate switchable logarithmic negativity and single-mode nonclassicality, establishing a route toward actively tunable quantum-plasmonic circuit elements operating well below the diffraction limit.

quant-ph↗

arXiv2025

Off resonant Fano enhanced single molecule resolution imaging with a CW source

Apertureless scanning near-field optical microscopy (a-SNOM) is typically limited to ~10 nm resolution by the tip apex size. We demonstrate that ~1-nm resolution can be achieved under continuous-wave (CW) illumination by exploiting Fano path interference. A defect center that naturally forms at the apex of a metal-coated AFM tip acts as a quantum object and induces Fano interference, forcing a stronger but normally off-resonant plasmonic mode (597 nm) to operate effectively on resonance at the driving wavelength (520 nm). Because this interference occurs only beneath the defect, a ~1-nm-wide, strongly enhanced near-field hotspot is created. Using this off-resonant Fano-enhanced field, we achieve single-molecule-resolution imaging based on exact three-dimensional Maxwell simulations.

physics.optics↗

arXiv2025

Electrical-control of third-order nonlinearity via Fano interference

Programmable photonic computers necessitate the integration of electrically-tunable compact components into the photonic devices. In the state-of-the-art photonic quantum computers~(PQCs), phase-shift and displacement gates can be implemented in an electrically-programmable way. An efficient PQC, however, necessitates also the tuning of third or higher order nonlinearity for implementing continuous-variable~(CV) gates at a shorter sequence. Here, we demonstrate that such an optical component can be designed using Fano interference and Stark effect in a nonlinear nano-plasmonic system. We study the coupling of a broadband bright plasmon mode to a narrow linewidth quantum object(s), QO(s). We show that by shifting the level-spacing of the QO via Stark effect, one can continuously tune the third-order nonlinearity gate within a picosecond response time. We also present finite-difference time domain~(FDTD) simulations that take the retardation effects into account. In addition, we also show that enhancement due to Fano interference degrades if the QOs are positioned randomly as each QO introduces different phases. This reveals the importance of the spatial extent of the QO-ensemble to be employed in the experiments.

physics.optics↗

arXiv2025

Dynamic control of dipole decay rate via graphene plexcitons

Active control of the radiative properties of quantum emitters through engineered light-matter interactions is a key challenge in nanophotonics and quantum optics. In this work, we demonstrate dynamic modulation of dipole's decay rate by exploiting the tunable plexcitonic modes (graphene plasmons and QD-excitons) in the strong coupling regime. By integrating a quantum dot inside a graphene spherical shell and tuning the local optical response of hybrid modes via voltage-bias, we achieve continuous and reversible control over the decay rate, leading to significant enhancement or suppression of dipole emission from near- to far-infrared regime. Furthermore, the plexcitonic peaks shows much sharper linewidths in contrast to bare graphene plasmons even in the off-resonant coupling which indicates higher sensitivity of the systems at tuned wavelengths. We demonstrate the phenomenon with the numerical solution of 3D Maxwell's equations using MNPBEM tool. Our approach demonstrate a versatile platform for programmable emission control and offer a promising pathway for developing reconfigurable quantum photonic devices, such as tunable single-photon sources and ultrafast optical switches.

physics.app-ph↗

arXiv2025

Active tuning of ENZ resonances in meta-antenna through phase modulation of optical pulse

Plasmonic nanoantennas offer new avenues to manipulate the propagation of light in materials due to their near field enhancement and ultrafast response time. Here we investigate the epsilon-near-zero (ENZ) response in an L-shaped nanoantenna structure under the phenomenon of plasmonic analog of enhancement in the index of refraction. Using a quantum mechanical approach, we analyze the modulation in the response of probe field and emergence of ENZ frequency region both in the linear and nonlinear plasmonic system. We also demonstrate the active tuning of ENZ frequency region in a nanoantenna structure by modulating the phase of control pulse. The analytical and 3D FDTD simulation results show a significant spectral shift in the ENZ modes. Our proposed method offers the possibility to design and control optical tunable ENZ response in plasmonic metasurfaces without the use of ENZ material. Such metasurfaces can be used in on-chip photonic integrated circuits, further localization of incident fields, slow light operations and various quantum technologies.

physics.app-ph↗

arXiv2025

Continuous and Reversible Electrical Tuning of Fluorescent Decay Rate via Fano Resonance

We demonstrate that the decay rates of a fluorescent molecule can be controlled by electrically shifting a transparency introduced by a Fano resonance. An auxiliary quantum object (QO), located at the hotspot of a plasmonic nanoparticle, suppresses plasmonic excitation at its level spacing ω_QO. As a result, the local density of states (LDOS) associated with the plasmonic spectrum is also suppressed at ω=ω_QO. By shifting ω_QO via an applied voltage, we continuously tune the radiative and nonradiative decay rates of the fluorescent molecule by up to two orders of magnitude. This mechanism offers a valuable tool for integrated quantum technologies, enabling on-demand entanglement and single-photon sources, voltage-controlled quantum gate operations, and electrical control of superradiant-like phase transitions. The approach also holds promise for applications in super-resolution microscopy and surface-enhanced Raman spectroscopy (SERS).

physics.optics↗

arXiv2025

Optically tunable linear and nonlinear enhancement of index of refraction

Control of optical properties of materials by tuning their refractive index can revolutionize the current state-of-the-art technology to manipulate light propagation in the high loss media. Here we demonstrate active optical tuning of the plasmonic analog of \textit{enhancement of index of refraction} (EIR) in both linear and nonlinear regimes using a quantum mechanical approach. By employing a pump-probe scheme, we investigate the tuning of refractive index of the probe field by varying amplitude and phase of the pump source. In contrast to classical approach used in \cite{Panahpour2019}, we formulate both first- and second-order quantization to analyze nonlinear enhancement in the refractive index by modulating the response function of probe field. This approach enables indirect tuning of nonlinear modes and coherent control of the probe pulse under the coupling of linear plasmonic modes supported by two L-shaped nano-ellipsoids. Varying the pump amplitude not only shows a significant enhancement in the EIR in both regimes but also effectively suppresses optical losses with zero dispersion at the system's resonance frequency. Additionally, tuning pump phase induces a spectral shift in the frequency of the probe field which open new ways for active tuning of epsilon-near-zero (ENZ) materials. Our approach offers all-optical tuning of nonlinear refractive index which is essential for quantum technological applications. It also provides coherent control of optical properties of plasmonic nanostructures with applications in loss-compensated propagation and zero-index to high-refractive-index plasmonic metamaterials, as well as photonic switches.

physics.optics↗

arXiv2025

QUPERS: Quantum Enhanced Raman Spectroscopy

We present experimental demonstration of a recently predicted path interference phenomenon [Nanophotonics 7, 1687 (2018)]. A SERS process becomes resonant when both incident and the converted frequencies match with two plasmon resonances -- a condition which is hard to satisfy experimentally. Yet, presence of a quantum dot~(QD) coupled to the lower-energy plasmon mode has been predicted to introduce interference effect in the conversion paths and to bring the SERS process into resonance. Here, we experimentally demonstrate a 7-fold additional enhancement factor~(EF) {\it multiplying} the conventional SERS enhancement owing to the presence of QDs in addition to metal nanoparticles~(MNPs). We eliminate influence of alternative enhancement mechanisms and show that observed additional EF of 7 is solely because of the path interference~(Fano) effect taking place in the presence of the QDs. As the most significant evidence: we observe that when QD/MNP ratio exceeds $1$, EF starts to decrease. Two or more QDs sitting at different~(random) positions on a nanostar MNP surface starts to degrade the path interference effect. Even though the theoretically predicted maximum EFs of $\sim$100--1000 when QD is in the MNP hotspot are not always experimentally feasible in stochastic nature of large area SERS substrate, still, observation of a 7-fold overall increase in such a setting is significant for fabricating Raman-based sensor applications. More importantly, our scheme allows for designing selective SERS substrates. As the QD resonances can actively be shifted by external factors, such as by applying an electric field (Stark effect), it provides a previously-not-existing tool: active selective enhancement of Raman bands via an applied voltage.

physics.optics↗

arXiv2025

Tunable extraordinary optical transmission for integrated photonics

The propagation of light through opaque materials, served by periodic arrays of subwavelength holes, has revolutionized imaging and sensor technology with a breakthrough of extraordinary optical transmission (EOT). The enhanced optical transmission assisted by surface plasmon resonances (SPR) has become the most ingenious phenomenon in the field of light-matter interaction. Active tuning of SPR presents a new and simple way to control spectral features of the EOT signal (without the need to change the geometrical structure of the device). This provides a new possibility to integrate an active EOT device with tunable operational frequencies on a single chip of photonic integrated circuits (PIC)- a new scalable instrument in the optoelectronic industry, and quantum technology for improving subwavelength optical imaging and biomedical sensing. In this review, we discuss the fundamentals of EOT, the role of SPR, and how the active quantum plasmonic control of the EOT device makes it a feasible on-chip electro-optic programmable element for integrated photonics.

physics.optics↗

arXiv2024

Stark Control of Plexcitonic States in Incoherent Quantum Systems

Electro-optic control of quantum dots embedded in the plasmonic nanocavities enables active tuning of photonic devices for emerging applications in Quantum optics such as quantum information processing, entanglement and ultrafast optical switching. Here, we demonstrate the coherent control of plexcitonic states in (i) an off-resonant and (ii) a resonant coupled quantum systems through optical Stark effect (OSE). We analyze a hybrid plasmon-emitter system which exhibits tunable Fano resonance, Stark induced transparency (SIT) and vacuum Rabi splitting due to quadratic Stark shift in the degenerate states of quantum emitter (QE). In addition, a resonantly coupled system shows the signature of double Fano resonance due to Stark-induced splitting in a two-level QE. Our study shows that Stark tuning of plexcitons not only mitigates decoherence in the quantum system but it also stimulates on/off switching of spontaneous photon emission in the visible regime. Such tunable systems can be used to operate photonic integrated circuits (PIC) for applications in quantum computing and information processing.

physics.optics↗

arXiv2024

Voltage-controlled extraordinary optical transmission in the visible regime

Control of components in integrated photonic circuits is crucial in achieving programmable devices. Operation bandwidth of a plasmonic device cannot be generally tuned once it is manufactured, especially in the visible regime. Here, we demonstrate the electrical control of such a device for extraordinary optical transmission~(EOT) in the visible regime. (i) Operation frequency of the EOT device can be tuned via a bias voltage applied through nanowires. (ii) Or, at a given frequency, the EOT signal (normalized to the incident field) can be tuned continuously, e.g., between $10^{-4}$ and $0.4$. This corresponds to a 3-orders of magnitude modulation depth. We utilize Fano resonances induced by a quantum emitter~(QE) that is embedded into the nanoholes. The external bias-voltage tunes QE's resonance. We also discuss the lifetime extensions of surface plasmon polaritons as a response to an ultra-short optical pulse. Our proposed method provides the active electronic control of EOT signal which makes it a feasible and compact element in integrated photonic circuits, for bio-sensing, high resolution imaging, and molecular spectroscopy applications.

physics.optics↗

arXiv2023

All-Optical Control of Ultrafast Plasmon Resonances in the Pulse-Driven Extraordinary Optical Transmission

Understanding the ultrafast processes at their natural-time scale is crucial for controlling and manipulating nanoscale optoelectronic devices under light-matter interaction. Here, we demonstrate that ultrafast plasmon resonances, attributed to the phenomenon of Extraordinary Optical Transmission (EOT), can be significantly modified by tuning the spectral and temporal properties of the ultrashort light pulse. In this scheme, all-optical active tuning governs spatial and temporal enhancement of plasmon oscillations in the EOT system without device customization. We analyze the spectral and temporal evolution of the system through two approaches. First, we develop a theoretical framework based on the coupled harmonic oscillator model, which analytically describes the dynamics of plasmon modes in the coupled and uncoupled state. Later, we compare the evolution of the system under continuous wave and pulsed illumination. Further, we discuss time-resolved spectral and spatial dynamics of plasmon modes through 3D-FDTD simulation method and wavelet transform. Our results show that optical tuning of oscillation time, intensity, and spectral properties of propagating and localized plasmon modes yields a 3-fold enhancement in the EOT signal. The active tuning of the EOT sensor through ultrashort light pulses pave the way for the development of on-chip photonic devices employing high-resolution imaging and sensing of abundant atomic and molecular systems.

physics.optics↗

arXiv2022

Green Synthesis and the formation kinetics of silver nanoparticles in aqueous Inula Viscosa extract

In this study, we present the production of silver nanoparticles in aqueous Inula Viscosa extract by the green synthesis approach at room temperature. The structural, morphological properties as well as formation kinetics of the synthesized silver nanoparticles were characterized by UV-VIS, STEM, XRD, Raman and FTIR measurements. Mono-dispersed and very stable silver nanoparticles with size of 15$\pm$5 nm and face-centered cubic crystal structure were synthesized in aqueous Inula Viscosa extract. The kinetic studies of silver nanoparticles formation in Inula Viscosa extract show that silver nanoparticle formation reaction reached the equilibrium within 24 h and fit in the first-order reaction kinetics. The results clearly show that the size of fabricated nanoparticles is independent on the dynamical formation process since the reaction time and initial silver ion concentration did not affect on size and morphology of the produced particles.

physics.app-ph↗

arXiv2022

Silent-enhancement of multiple Raman modes via tuning optical properties of graphene nanostructures

Raman scattering signal can be enhanced through localization of incident field into sub-wavelength hot-spots through plasmonic nano-structures (Surface-enhanced Raman scattering-SERS). Recently, further enhancement of SERS signal via quantum objects are proposed by [1] without increasing the hot-spot intensity (\textit{silent-enhancement}) where this suggestion prevents the modification of vibrational modes or the breakdown of molecules. The method utilizes path interference in the non-linear response of Stokes-shifted Raman modes. In this work, we extend this phenomenon to tune the spectral position of \textit{silent-enhancement} factor where the multiple vibrational modes can be detected with a better signal-to-noise ratio, simultaneously. This can be achieved in two different schemes by employing either (i) graphene structures with quantum emitters or (ii) replacing quantum emitters with graphene spherical nano-shell in \cite{Postaci2018}. In addition, the latter system is exactly solvable in the steady-state. These suggestions not only preserve conventional non-linear Raman processes but also provide flexibility to enhance (silently) multiple vibrational Raman modes due to the tunable optical properties of graphene.

physics.optics↗

arXiv2021

Modulating the temporal dynamics of nonlinear ultrafast plasmon resonances

Spatio-temporal control of ultrafast plasmon resonances has gained research interest in recent years because of their tremendous implications in nonlinear optics and ultrafast quantum technology. In particular, the lifetime of ultrashort plasmon oscillations has become a debatable subject in recent experimental and theoretical studies to fulfill the future challenges concerning their effective employment in the vast applications of the plasmonic industry. Here, we examined the temporal properties of nonlinear plasmonic modes in metal nanostructures by interacting them with quantum objects in the weak coupling regime in order to distinguish it from the fundamental plasmonic mode. First of all, we present an analytical description of nonlinear ultrafast dynamics of localized surface plasmon resonances when the second harmonic plasmon mode interacts with long-lived dark mode or quantum emitter. Later, the coupled plasmonic system is realized in two different ways to control the lifetime of second harmonic mode by coupling, i) driven mode to dark mode (or long lifetime quantum emitter) ii)itself to dark mode (or long lifetime quantum emitter). The driven-dissipative dynamics are solved through a numerical technique governing the spatial and temporal changes in the second harmonic plasmonic response supported by AuNP. Finally, the lifetime enhancement of nonlinear plasmon mode is manifested by performing FDTD simulations for a nonlinear plasmonic system of Au nanoparticles coupled with a long lifetime quantum emitter.

physics.optics↗

arXiv2020

Ultra-large actively tunable photonic band gaps via plasmon-analog of index enhancement

We present a novel method for active continuous-tuning of a band gap which has a great potential to revolutionize current photonic technologies. We study a periodic structure of x and y-aligned nanorod dimers. Refractive index of a y-polarized probe pulse can be continuously-tuned by the intensity of an x-polarized auxiliary (pump) pulse. Order of magnitude index-tuning can be achieved with a vanishing loss using the plasmon-analog of refractive index enhancement [Phys. Rev. B 100, 075427 (2019)]. Thus, a large band gap can be created from a non-existing gap via the auxiliary pulse. We also present a "proof of principle" demonstration of the phenomenon using numerical solutions of Maxwell equations. The new method, working for any crystal dimensions, can also be utilized as a linear photonic switch operating at tens of femtoseconds.

physics.optics↗

arXiv2020

Single-molecule-resolution ultrafast near-field optical microscopy via plasmon lifetime extension

A recent study shows that: when a long lifetime particle is positioned near a plasmonic metal nanoparticle, lifetime of plasmon oscillations extends, but, "only" near that long-life particle [PRB 101, 035416 (2020)]. Here, we show that this phenomenon can be utilized for ultrahigh (single-molecule) resolution ultrafast apertureless (scattering) SNOM applications. We use the exact solutions of 3D Maxwell equations. We illuminate a metal-coated silicon tip, a quantum emitter (QE) placed on the tip apex, with a femtosecond laser. The induced near-field in the apex decays rapidly except in the vicinity of the sub-nm-sized QE. Thus, the resolution becomes solely limited by the size of the QE. As positioning of a QE on the tip apex is challenging, we propose the use of a newly-discovered phenomenon; stress-induced defect formation in 2D materials. When a monolayer, e.g., transition metal dichalcogenide (TMD) is transferred to the AFM tip, the tip indentation of 2D TMD originates a defect-center located right at the sharpest point of the tip; that is exactly at its apex. Moreover, the resonance of the defect is tunable via a voltage applied to the tip. Our method can equally be used for background-noise-free nonlinear imaging and for facilitating single-molecule-size chemical manipulation.

physics.optics↗

arXiv2020

A quantum emitter coated with graphene interacting in the strong coupling regime

We demonstrate the strong coupling of a quantum dot and a graphene spherical shell coating it. Our simulations are the exact solutions of 3D Maxwell equations. Interaction produces sharp hybrid modes, even when the two are off-resonant, which are voltage-tunable (continuously) in an 80 meV interval. Despite a voltage-tunable quantum dot, the coupling of the light to these "very sharp" plexcitonic resonances is an order of magnitude larger than its coupling to a quantum dot. Hence, our results are very attractive for sensing applications and graphene display technologies with sharper colors. Moreover, on a simple theoretical model, we explain why such sharp, highly tunable, resonances emerge.

physics.optics↗