Ultrawideband electromagnetic metamaterial absorber utilizing coherent absorptions and surface plasmon polaritons based on double layer carbon metapatterns

An ultrawideband electromagnetic metamaterial absorber is proposed that consists of double-layer metapatterns optimally designed by the genetic algorithm and printed using carbon paste. By setting the sheet resistance of the intermediate carbon metapattern to a half of that of the top one, it is possible to find an optimal intermediate metapattern that reflects and absorbs the EM wave simultaneously. By adding an absorption resonance via a constructive interference at the top metapattern induced by the reflection from the intermediate one, an ultrawideband absorption can be achieved without increasing the number of layers. Moreover, it is found that the metapatterns support the surface plasmon polaritons which can supply an additional absorption resonance as well as boost the absorption in a broad bandwidth. Based on the simulation, the $$90\%$$ 90 % absorption bandwidth is confirmed from 6.3 to 30.1 GHz of which the fractional bandwidth is 130.77$$\%$$ % for the normal incidence. The accuracy is verified via measurements well matched with the simulations. The proposed metamaterial absorber could not only break though the conventional concept that the number of layers should be increased to extend the bandwidth but also provide a powerful solution to realize a low-profile, lightweight, and low cost electromagnetic absorber.

Resonances of electromagnetic-induced transparency and electromagnetic-induced absorption at the transition with level momenta J=1/2 in unidirectional wave spectroscopy

The physical processes that form the saturated absorption resonance spectra on the atomic transition with level momenta J= 1/2 in the field of unidirectional waves of arbitrary intensities are investigated both analytically and numerically. It is shown that the narrow structures of the nonlinear resonance spectra (resonances of electromagnetic-induced transparency and absorption) and the processes forming them are determined by the direction of the light wave polarizations, degree of openness of the atomic transition, and the saturating wave intensity. The conditions under which the nonlinear resonance is exclusively coherent, due to the magnetic coherence of transition levels, are revealed.

Characterization of GeSbSe based slot optical waveguides

Background: Among various chalcogenides, GeSbSe shows a good transmittance in the visible, NIR and, midIR spectrum from 1-20 μm and also demonstrates excellent moldability. <P> Objective: In current work, we have characterized GeSbSe glass for use in sensor mechanism and for adaptive polarization control. <P> Methods: After analysing an earlier work regarding GeSbSe based Silicon on insulator optical waveguide, we have implemented GeSbSe in low refractive index slot region of SOI slot optical waveguide. Change in waveguide geometry can cause a shift in the dispersion profile, but a relatively distinct pattern has been observed. T-slot waveguide structure has also been analysed, where GeSbSe has been implemented in low refractive index slot regions with Graphene layer beneath the horizontal slot region for enhancement in tailoring ability of the birefringence parameters. <P> Results: Literature review led to the presence of absorption resonance wavelength in SOI slot optical waveguide with our proposed composition, which is attributed to the single average harmonic oscillator property of the chalcogenides. In T-slot waveguide structure, it was found that shift in Fermi energy and Mobility values can bring a change in birefringence, even with constant waveguide geometry and operating wavelength. <P> Conclusion: Absorption resonance wavelength in GeSbSe slot optical waveguide has been exploited for proposing the refractive index dispersion sensor. Our design approach regarding T-slot waveguide may lead to provision of automated polarization management sources for the light on chip circuits

Tunable Perfect THz Absorber Based on a Stretchable Ultrathin Carbon-Polymer Bilayer

By exploring the Salisbury screen approach, we propose and demonstrate a thin film absorber of terahertz (THz) radiation. The absorber is comprised of a less than 100 nm thick layer of pyrolytic carbon deposited on a stretchable polydimethylsiloxane (PDMS) film followed by the metal film. We demonstrate that being overall less than 200 microns thick, such a sandwich structure absorbs resonantly up to 99.9%of the incident THz radiation, and that the absorption resonance is determined by the polymer thickness, which can be adjusted by stretching.

pH-Dependent chromogenic properties of an orthogonal metal-C (aryl) bonded azobenzene-rhodium(III) porphyrin conjugate

An orthogonally arranged conjugate comprised of two rhodium(III) tetrakis-4-tolyporphyrins linked with an azobenzene moiety through a covalent Rh-C (aryl) bond has been facilely synthesized and characterized. Although photochemical isomerization of the azobenzene component was not observed, addition of trifluoroacetic acid (TFA) to the conjugate in a toluene solution causes significant colorimetric changes. UV-vis absorption, resonance light scattering (RLS), [Formula: see text]H-NMR and IM-MS spectra were employed to investigate the pH-dependent chromogenic behavior of the triad, which gives a new pathway for construction of pH-dependent assemblies of porphyrin-azobenzene complexes.