Erdem Öğüt

Circularly and elliptically polarized near-field radiation from nanoscale subwavelength apertures

With advances in nanotechnology, obtaining circularly and elliptically polarized optical spots beyond the diffraction limit is an emerging need for plasmonic applications. Two techniques are suggested to obtain circularly and elliptically polarized near-field radiation using subwavelength apertures. It is demonstrated that a square aperture can mediate diffraction limited circularly or elliptically polarized radiation into an optical spot with circular or elliptical polarization beyond the diffraction limit. Linearly polarized diffraction limited radiation is converted into a circularly or an elliptically polarized optical spot beyond the diffraction limit by creating asymmetry in the subwavelength aperture.

Poly(vinylidene fluoride)/Zinc Oxide Smart Composite Material

This work aimed at fabrication and electromechanical characterization of a smart material system composed of electroactive polymer and ceramic materials. The idea of composite material system is on account of complementary characteristics of the polymer and ceramic for flexibility and piezoelectric activity. Our preliminary work included Polyvinylidene Fluoride (PVDF) as the flexible piezoelectric polymer, and Zinc Oxide (ZnO) as the piezoelectric ceramic brittle, but capable to respond strains without poling. Two alternative processes were investigated. The first process makes use of ZnO fibrous formation achieved by sintering PVA/zinc acetate precursor fibers via electrospinning. Highly brittle fibrous ZnO mat was dipped into a PVDF polymer solution and then pressed to form pellets. The second process employed commercial ZnO nanopowder material. The powder was mixed into a PVDF/acetone polymer solution, and the resultant paste was pressed to form pellets. The free standing composite pellets with electrodes on the top and bottom surfaces were then subjected to sinusoidal electric excitation and response was recorded using a fotonic sensor. An earlier work on electrospun PVDF fiber mats was also summarized here and the electromechanical characterization is reported.

Integrating Magnetic Heads With Plasmonic Nanostructures in Multilayer Configurations

Heat-assisted magnetic recording (HAMR) is an emerging technology that has increased the areal density of conventional recording techniques for hard disc drives. Integrated heads have enabled this increase through localized heating of the recording media during the recording process. One of the problems in integrating magnetic heads with plasmonic nanotransducers is the resulting losses. In this study, multilayer configurations with gold thin-films near magnetic thin-films are investigated to minimize radiative and load-induced losses. The effect of load-induced damping of the magnetic film and evanescent coupling is identified with the intensity enhancement near the magnetic films. It is shown that a higher intensity enhancement can be obtained by minimizing radiative and load-induced losses through adjusting layer thicknesses in multilayer configurations.

Focusing short-wavelength surface plasmons by a plasmonic mirror

Emerging applications in nanotechnology, such as superresolution imaging, ultra-sensitive biomedical detection, and heat-assisted magnetic recording, require plasmonic devices that can generate intense optical spots beyond the diffraction limit. One of the important drawbacks of surface plasmon focusing structures is their complex design, which is significant for ease of integration with other nanostructures and fabrication at low cost. In this study, a planar plasmonic mirror without any nanoscale features is investigated that can focus surface plasmons to produce intense optical spots having lateral and vertical dimensions of λ/9.7 and λ/80, respectively. Intense optical spots beyond the diffraction limit were produced from the plasmonic parabolic mirror by exciting short-wavelength surface plasmons. The refractive index and numerical aperture of the plasmonic parabolic mirror were varied to excite short-wavelength surface plasmons. Finite-element method simulations of the plasmonic mirror and scanning near-field optical microscopy experiments have shown very good agreement.

Polarization Aspects of Near-Field Radiation from Nanoscale Subwavelength Apertures

It is demonstrated that a square nanoaperture can mediate polarized diffraction-limited radiation into nanoscale optical spots with the same polarization. A rectangular nanoaperture can convert linearly-polarized diffraction-limited radiation into circularly and elliptically-polarized nanoscale optical spots.

Obtaining Circularly Polarized Optical Spots Beyond the Diffraction Limit Using Plasmonic Nano-Antennas

With advances in nanotechnology, emerging plasmonic nano-optical applications, such as all-optical magnetic recording, require circularly-polarized electromagnetic radiation beyond the diffraction limit. In this study, a plasmonic cross-dipole nano-antenna is investigated to obtain a circularly polarized near-field optical spot with a size smaller than the diffraction limit of light. The performance of the nano-antenna is investigated through numerical simulations. In the first part of this study, the nano-antenna is illuminated with a diffraction-limited circularly-polarized radiation to obtain circularly polarized optical spots at nanoscale. In the second part, diffraction limited linearly polarized radiation is used. An optimal configuration for the nano-antenna and the polarization angle of the incident light is identified to obtain a circularly polarized optical spot beyond the diffraction limit from a linearly polarized diffraction limited radiation.