Nanoplasmonic Pyramidal Metamaterial Absorber at Optical Frequencies

A pyramidal shaped metamaterial absorber (PMA) supports broadband and polarization independent resonant absorption at optical frequencies. The PMA is designed by stack of alternative plasmonic/dielectric multilayers. These nanoplasmonic pyramids offers resonant absorption characteristics at wide range of optical frequencies. The optimized PMA structure allows 76% spectral absorption and nearly perfect absorption (over 90%) at several bands between range of 400 nm – 1500 nm wavelength. These light absorption characteristics of PMA are useful for photodetection, thermal imaging, thermal emitters, and solar cells etc.

Optical properties of plasmonic metal nanoparticles on GaN surface

Effect of the plasmonic resonant absorption in metal nanoparticles formed on the GaN surface on optical properties of samples is studied. Silver and gold nanoparticles are formed by solid-state dewetting on epitaxial GaN grown by molecular beam epitaxy (MBE) on c-sapphire substrate. Theoretical and experimental optical characteristics show the appearance characteristic absorption of the surface plasmon resonance. The results of the work show the possibility of increasing the efficiency of GaN-based optoelectronic devices.

Weak Damping of Propagating MHD Kink Waves in the Quiescent Corona

Propagating transverse waves are thought to be a key transporter of Poynting flux throughout the Sun’s atmosphere. Recent studies have shown that these transverse motions, interpreted as the magnetohydrodynamic kink mode, are prevalent throughout the corona. The associated energy estimates suggest the waves carry enough energy to meet the demands of coronal radiative losses in the quiescent Sun. However, it is still unclear how the waves deposit their energy into the coronal plasma. We present the results from a large-scale study of propagating kink waves in the quiescent corona using data from the Coronal Multi-channel Polarimeter (CoMP). The analysis reveals that the kink waves appear to be weakly damped, which would imply low rates of energy transfer from the large-scale transverse motions to smaller scales via either uniturbulence or resonant absorption. This raises questions about how the observed kink modes would deposit their energy into the coronal plasma. Moreover, these observations, combined with the results of Monte Carlo simulations, lead us to infer that the solar corona displays a spectrum of density ratios, with a smaller density ratio (relative to the ambient corona) in quiescent coronal loops and a higher density ratio in active-region coronal loops.

Effects of substrate phonon absorption on the resonance behavior of metal-insulator-metal metamaterial terahertz absorbers

We have investigated effects of substrate phonon absorption on the resonance behavior of metal-insulator-metal double layer metamaterial absorbers in the terahertz frequency range. A sharp resonant absorption dip is clearly observed for a metamaterial-on-ground-plane structure fabricated on a GaAs substrate when THz radiation is incident from the surface metamaterials side. However, when the THz is incident from the substrate side to the ground-plane-on-metamaterial structures fabricated on a GaAs substrate, the resonance dip is almost merged into the broad background of acoustic phonon absorption. The resonant absorption is recovered when the GaAs substrate is replaced with a high-resistivity Si substrate.

Design of hybrid narrow-band plasmonic absorber based on chalcogenide phase change material in the infrared spectrum

Structures absorbing electromagnetic waves in the infrared spectral region are important optical components in key areas such as biosensors, infrared images, thermal emitters, and special attention is required for reconfigurable devices. We propose a three-dimensional metal-dielectric plasmonic absorber with a layer of PCM’s (Phase Change Materials). The phase shift effects of PCMs are numerically analyzed, and it is possible to obtain a shifting control of the resonant absorption peaks between the amorphous and crystalline states using the Lorentz–Lorenz relation. By using this empirical relation, we analyzed the peak absorption shift at intermediate phases between the amorphous and the crystalline. The geometric parameters of the structure with the PCM layer in the semi-crystalline state were adjusted to exhibit strong absorption for normal incidence. The effects of the oblique incidence on the absorption for the TM and TE polarization modes were also analyzed. Our results demonstrate that PCMs have great potential for reconfigurable nanophotonic devices.

A new limit on the resonant absorption of solar axions obtained via 169Tm-containing bolometer

A newly developed experimental technique based on 169Tm-containing cryogenic bolometer detector was employed in order to perform the search for solar axions. The inclusion of target material into the active detector volume allowed for significant increase in sensitivity to axion parameters. A short 6.6 days measurement campaign with 8.18 g detector crystal yielded the following limits on axion couplings: | g A γ ( g A N 0 + g A N 3 ) ≤ 1.44 × 10 − 14 GeV − 1 and | g A e ( g A N 0 + g A N 3 ) ≤ 2.81 × 10 − 16 . The achieved results demonstrate high scalability potential of presented experimental approach.

Determining the optimal parameters of ultra-high-frequency treatment of chickpeas for the production of gluten-free flour

This paper describes the materials and results of studying the properties of such a leguminous crop as the chickpea variety Miras 07 of Kazakhstan selection in order to obtain gluten-free flour and further process it to produce confectionery products. The research involved the ultra-high-frequency (UHF) treatment of chickpea grain to improve quality indicators and reduce anti-alimentary factors. A change in the protein fraction of chickpeas was determined under exposure to ultra-high-frequency processing. The study has proven the effectiveness of ultra-high-frequency treatment of chickpea for 180 seconds. Based on chemical analysis, it was found that the exposure to ultra-high-frequency treatment fully preserved the vitamin and mineral complex, compared with untreated chickpeas. When chickpea grain is heated for 180 seconds, up to 20 % of the starch contained in the grain passes into dextrin, which is easily absorbed by humans while the toxic substances are destroyed. The change in the protein fraction of chickpeas during ultra-high-frequency processing was determined. With ultra-high-frequency treatment of chickpea flour at 180 seconds of exposure, the protein fraction content remains unchanged at 79.8 %. The result based on the IR spectrum data indicates that ultra-high-frequency processing did not affect the protein-amino acid composition of the examined Miras 07 chickpea variety. The current study has confirmed the effectiveness of ultra-high-frequency chickpea treatment, which leads to the intensification of biochemical processes in the processed product due to the resonant absorption of energy by protein molecules and polysaccharides. Under the influence of ultra-high-frequency treatment, there is a decrease in the microbiological contamination of raw materials while the organoleptic indicators improve. According to the microbiological indicators of chickpea flour, the content of microorganisms was 1×103 CFU/g, which meets the requirements for sanitary and hygienic safety

Paving the Way for Tunable Graphene Plasmonic THz Amplifiers

This study reviews recent advances in room-temperature coherent amplification of terahertz (THz) radiation in graphene, electrically driven by a dry cell battery. Our study explores THz light–plasmon coupling, light absorption, and amplification using a current-driven graphene-based system because of its excellent room temperature electrical and optical properties. An efficient method to exploit graphene Dirac plasmons (GDPs) for light generation and amplification is introduced. This approach is based on current-driven excitation of the GDPs in a dual-grating-gate high-mobility graphene channel field-effect transistor (DGG-GFET) structure. The temporal response of the DGG-GFETs to the polarization-managed incident THz pulsation is experimentally observed by using THz time-domain spectroscopy. Their Fourier spectra of the transmitted temporal waveform through the GDPs reveals the device functions 1) resonant absorption at low drain bias voltages below the first threshold level, 2) perfect transparency between the first and the second threshold drain bias levels, and 3) resonant amplification beyond the second threshold drain bias voltage. The maximal gain of 9% is obtained by a monolayer graphene at room temperatures, which is four times higher than the quantum limit that is given when THz photons directly interact with electrons. The results pave the way toward tunable graphene plasmonic THz amplifiers.

Design of Hybrid Narrow-Band Plasmonic Absorber Based on Chalcogenide Phase Change Material in the Infrared Spectrum

Structures absorbing electromagnetic waves in the infrared spectral region are important optical components in key areas such as biosensors, infrared images and thermal emitters, and require special attention from reconfigurable devices. We propose a three-dimensional metal-dielectric plasmonic absorber with a layer of PCM's (Phase Change Materials). The phase shift effects of PCMs are analyzed, and it is possible to obtain a displacement control in the resonant absorption peaks between the amorphous and crystalline states using the Lorentz-Lorenz relation. Aided in this empirical relation, we analyzed the absorption shift in the intermediate phases between them. The geometric parameters of the structure with the pcm material layer in the semi-crystalline state were optimized to present strong absorption for normal incidence. The effects of the oblique incidence for the TM and TE polarization modes were also analyzed. Our results demonstrate that PCMs have great potential for reconfigurable nanophotonic devices.