Mohammed Nadhim Abbas

Wide-angle polarization independent infrared broadband absorbers based on metallic multi-sized disk arrays

Two-dimensional metallic broadband absorbers on a SiO(2)/Ag/Si substrate were experimentally studied. The absorptivity of such structure can be increased by tailoring the ratio of disk size to the unit cell area. The metallic disk exhibits a localized surface plasmon polariton (LSPP) mode for both TE and TM polarizations. A broadband thermal emitter can be realized because the LSPP mode is independent of the periodicities. By manipulating the ratios and disk sizes, a high-performance, wide-angle, polarization-independent dual band absorber was experimentally achieved. The results demonstrated a substantial flexibility in absorber designs for applications in thermal photovoltaics, sensors, and camouflage.

T-shaped plasmonic array as a narrow-band thermal emitter or biosensor

A T-shaped plasmonic array is proposed for application as an effective thermal emitter or biosensor. The reflection and thermal radiation properties of a T-shaped array are investigated theoretically. The angular dependent reflectance spectrum shows a clear resonant dip at 0.36 eV for full polar angles. No other significant localized resonant mode is found in the investigated spectral range from 0.12 eV to 0.64 eV. According to the Kirchhoffs law, the thermal radiation of the proposed structure can lead to a sharp peak at 3.5 microm with low sideband emission. We have also found that the T-shaped structure filled with organic material such as PMMA with different thicknesses (10 nm -50 nm) can lead to significant shift of the resonance wavelength. Thus, the T-shaped structure can also be used as a good sensor for organic materials.

Angle-independent plasmonic infrared band-stop reflective filter based on the Ag/SiO 2 /Ag T-shaped array

A plasmonic infrared (IR) filter assisted by localized surface plasmon polaritons (LSPPs) in a Ag/SiO₂/Ag T-shaped array was theoretically and experimentally investigated. By using a Fourier transform infrared (FTIR) spectrometer, an angle-independent LSPP resonant mode caused by a Fabry-Pérot resonance in the structure was observed in agreement with the prediction from the rigorous coupled-wave analysis (RCWA) simulation. The resonant wavelength of the mode can also be controlled by modifying the geometry of the T-shaped structure. Such LSPP property can be used as an IR reflection-type band-stop filter with a single spectral bandwidth and an ultrahigh immunity to incident angles.

Plasmon-polariton band structures of asymmetric T-shaped plasmonic gratings.

It is shown that asymmetric T-shaped plasmonic gratings can display plasmon-polariton band structures with wide range of band gaps and tunable group velocities. A structure gap is introduced in the post of Tshaped plasmonic gratings and it is found that the size of this gap plays an important role in controlling the plasmon-polariton band gap and group velocities. We obtained variation of energy band gap ranging from 0.4 eV to 0.0323 eV by changing the size of the structure gap from 0 to 250 nm. The plasmon-polariton band structures were obtained by using Rigorous Coupled Wave Analysis. We studied the difference between symmetric and asymmetric T-shaped gratings and found that the symmetric structure has a momentum gap in the photonic band structure, which can be avoided in the asymmetric structure. Furthermore, by varying the post and spacer (made of SiO2) thicknesses we can tune the energy band gap from 0.1 eV to 0.148 eV and from 0.183 eV to 0.19 eV, respectively. In this device, we obtain tunable group velocities ranging from one to several orders of magnitude smaller than the speed of light in the vacuum. This asymmetric T-shaped plasmonic grating is expected to have applications in surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for applications requiring large photonic band gap.

Characterization of the surface plasmon polariton band gap in an Ag/SiO 2 /Ag T-shaped periodical structure

In this study, the localized surface plasmon polariton (LSPP) band gap of an Ag/SiO(2)/Ag asymmetric T-shaped periodical structure is demonstrated and characterized. The Ag/SiO(2)/Ag asymmetric T-shaped periodical structure was designed and fabricated to exhibit the LSPP modes in an infrared wavelength regime, and its band gap can be manipulated through the structural geometry. The LSPP band gap was observed experimentally with the absorbance spectra and its angle dependence characterized with different incident angles. Such a T-shaped structure with a LSPP band gap can be widely exploited in various applications, such as emitters and sensors.

Using off-specular ellipsometry spectra of dielectric grating-coupled plasmon mode for biosensing

We performed spectroscopic ellipsometry measurements of the specular and off-specular reflections of a one-dimensional polymethyl methacrylate grating on a Au-coated glass substrate and analyzed the data with efficient theoretical modeling. Very good agreement is obtained between calculation and experiment for both specular and off-specular reflections. It is found that the resonance peak of the off-specular reflection is much sharper than specular reflection at a wavelength that matches the condition for exciting the interface (surface plasmon) mode. When different media are used as the ambient, we found that the off-specular reflection near the surface-plasmon resonance can give significant enhancement in detection sensitivity compared with the corresponding specular reflection. This study may open a new way for biosensing. To analyze the data, we also developed a method to compute quasi-photonic band structures for periodic structures with frequency-dependent complex dielectric constants.

Localized Surface Plasmon Polarition (LSPP) Based Sensor Made of a Round-Shaped Metal Array for Applications in Biosensing

Two-dimensional metallic round-shaped disk structure on a SiO2/Au/Si substrate was experimentally studied. By using a Fourier transform infrared spectrometer, an angle and polarization independent localized surface plasmon polariton mode caused by a Fabry-Perot-like resonance was observed. Such structure has the ability to sense changes in refractive index from 1 to 1.39. Because of its large incident angle tolerance and local sensing ability, the structure can potentially be utilized for applications in biomedical diagnostics, food safety monitoring, and environmental detection.

Plasmonic thermal emitter using perfect absorber made of metallic disk on SiO 2

It is shown that the metallic disk structure can be used as an efficient narrow-band thermal emitter in the IR region. The absorption spectra of such structure are investigated both theoretically and experimentally. Calculations of thermal radiation properties of the metallic disk show that the metallic disk is a perfect emitter at a specific wavelength. The metallic disk exhibits only one significant localized surface plasmon polariton mode for both TM and TE polarizations simultaneously.