Theoretical Criteria for Scattering Dark States in Nanostructured Particles

Nanostructures with multiple resonances can exhibit a suppressed or even completely eliminated scattering of light, called a scattering dark state. We describe this phenomenon with a general treatment of light scattering from a multiresonant nanostructure that is spherical or nonspherical but subwavelength in size. With multiple resonances in the same channel (i.e., same angular momentum and polarization), coherent interference always leads to scattering dark states in the low-absorption limit, regardless of the system details. The coupling between resonances is inevitable and can be interpreted as arising from far-field or near-field. This is a realization of coupled-resonator-induced transparency in the context of light scattering, which is related to but different from Fano resonances. Explicit examples are given to illustrate these concepts.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Grant DMR-0819762

Generalized Fano lineshapes reveal exceptional points in photonic molecules

The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide. At this stage, fascinating phenomena are predicted, including electromagnetic-induced transparency and phase transitions. To experimentally observe the exceptional points, the near-field coupling to waveguide proposed so far was proved to work only in peculiar cases. Here, we extend the interference detection scheme, which lies at the heart of the Fano lineshape, by introducing generalized Fano lineshapes as a signature of the exceptional point occurrence in resonant-scattering experiments. We investigate photonic molecules and necklace states in disordered media by means of a near-field hyperspectral mapping. Generalized Fano profiles in material science could extend the characterization of composite nanoresonators, semiconductor nanostructures, and plasmonic and metamaterial devices

The optimization of multi-storey composite steel frames with genetic algorithm including dynamic constraints [Çok katli kompozit çelik çerçevelerin genetik algoritma ile dinamik sinirlayicin optimizasyonu]

Optimum design of the structures, in other words designing the structures with minimum weight is one of the major research areas in structural engineering. The priority during optimization process is to ensure whether the necessary conditions are satisfied or not. In this study, the optimization of steel frame systems is carried out for traditional and dynamic constraints by using a genetic algorithm that mimics the biological processes. The stress constraints are determined according to TS648-Turkish code for design and construction of steel structures. Furthermore, displacement constrains are considered in the optimization procedure. In addition, natural frequencies are incorporated as dynamic constraints. Optimum design of multi-story plane frames is obtained and comparisons with the results of previous studies are made. The same design processes are repeated for the case of frames with composite beams. A program is coded in MATLAB to carry out all these applications. Results obtained in the study for the frame systems are also verified by SAP2000. It is concluded that the weight of the frames with composite beams are fewer and the dynamic constraints affect the design

Multispectral Plasmon Induced Transparency in Coupled Meta-Atoms

We introduce an approach enabling construction of a scalable metamaterial media supporting multispectral plasmon induced transparency. The composite multilayered media consist of coupled meta-atoms with radiant and sub-radiant hybridized plasmonic modes interacting through the structural asymmetry. A perturbative model incorporating hybridization and mode coupling is introduced to explain the observed novel spectral features. The proposed scheme is demonstrated experimentally by developing a lift-off-free fabrication scheme that can automatically register multiple metamaterial layers in the transverse plane. This metamaterial which can simultaneously enhance nonlinear processes at multiple frequency domains could open up new possibilities in optical information processing

Integrated Plasmonic NanoBiosensors

We will demonstrate plasmonic and metamaterial based integrated nano-biosensors and ultrasensitive infrared absorption spectroscopy. These systems by enabling monitoring of molecular-protein interactions in real-time within aqueous solutions can be important for biomedical sciences and pharmacology

U-Shaped Nano-Apertures for Enhanced Optical Transmission and Resolution

The subject of light transmission through optically thin metal films perforated with arrays of subwavelength nanoholes has recently attracted significant attention. In this work, we present experimental and calculated results on optical transmission/reflection of the U-shaped nanoapertures for enhanced optical transmission and resolution. We propose different structure designs in order to prove the effect of geometry on resonance and enhanced fields. Theoretical calculations of transmission/reflection spectra and field distributions of U-shaped nano-apertures are performed by using 3-dimensional finite-difference time-domain method. The results of these numerical calculations show that transmission through the apertures is indeed concentrated in the gap region. Added to theoretical calculations we also performed a liftoff free plasmonic device fabrication technique based on positive resist electron beam lithography and reactive ion etching in order to fabricate U-shaped nanostructures. After transferring nanopattern on 80 nm thick suspended SiNx membrane using EBL followed by dry etching, a directional metal deposition processes is used to deposit 5 nm thick Ti and 30 nm thick Au layers. Theoretical calculations are supported with experimental results to prove the tunability of resonances with the geometry at the mid-infrared wavelengths which could be used for infrared detection of biomolecules