Temporal interfaces and metamaterial response enabled by boundaries

10.36227/techrxiv.14579253 ◽

2021 ◽

Author(s):

Luca Stefanini ◽

Davide Ramaccia ◽

Filiberto Bilotti ◽

Alessandro Toscano

Keyword(s):

Refractive Index ◽

Sudden Change ◽

Wave Impedance ◽

Optical Devices ◽

Anomalous Scattering ◽

Scattering Coefficients ◽

Boundary Properties ◽

Actual Material ◽

Scattering Response ◽

Novel Devices

In the last years, temporal metamaterials have been exploited as a novel platform for conceiving several electromagnetic and optical devices based on the anomalous scattering response achieved at a single or multiple sudden change of their medium properties, which however is difficult to carry out in a realistic scenario In this letter we investigate on the possibility to emulate the scattering response of a temporal metamaterial without acting on the medium properties, but on the effective refractive index and wave impedance perceived by the wave during the propagation within a guiding structure rather than the actual material, by acting on its boundaries. The work presents in closed form the scattering coefficients achieved when the boundary properties are suddenly modified for inducing an effective temporal interface. In this framework, temporally controlled metasurfaces can be used to implement the proposed concept, giving an easier path also to the design and realization of novel devices at microwave and optical frequencies.

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Sensitivity Analysis of Bistatic Scattering for Soil Moisture Retrieval

Remote Sensing ◽

10.3390/rs13020188 ◽

2021 ◽

Vol 13 (2) ◽

pp. 188

Author(s):

Tingting Li ◽

Irena Hajnsek ◽

Kun-Shan Chen

Keyword(s):

Sensitivity Analysis ◽

Soil Moisture ◽

Quality Index ◽

High Sensitivity ◽

Bare Soil ◽

Sensitivity Index ◽

Scattering Coefficients ◽

Observation Systems ◽

Bistatic Scattering ◽

Scattering Response

Soil moisture is one of the vital environmental variables in the land–atmosphere cycle. A study of the sensitivity analysis of bistatic scattering coefficients from bare soil at the Ku-band is presented, with the aim of deepening our understanding of the bistatic scattering features and exploring its potential in soil moisture retrieval. First, a well-established advanced integral method was adopted for simulating the bistatic scattering response of bare soil. Secondly, a sensitivity index and a normalized weight quality index were proposed to evaluate the effect of soil moisture on the bistatic scattering coefficient in terms of polarization and angular diversity, and the combinations thereof. The results of single-polarized VV data show that the regions with the maximum sensitivity and high quality index, simultaneously, to soil moisture are in the forward off-specular direction. However, due to the effect of surface roughness and surface autocorrelation function (ACF), the single-polarized data have some limitations for soil moisture inversion. By contrast, the results of two different polarization combinations, as well as a dual-angular simulation of one transmitter and two receivers, show significant estimation benefits. It can be seen that they all provide better ACF suppression capabilities, larger high-sensitivity area, and higher quality indices compared to single-polarized estimation. In addition, dual polarization or dual angular combined measurement provides the possibility of retrieving soil moisture in backward regions. These results are expected to contribute to the design of future bistatic observation systems.

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Novel optical devices based on the tunable refractive index of magnetic fluid and their characteristics

Journal of Magnetism and Magnetic Materials ◽

10.1016/j.jmmm.2011.06.025 ◽

2011 ◽

Vol 323 (23) ◽

pp. 2987-2996 ◽

Cited By ~ 43

Author(s):

Yong Zhao ◽

Yuyan Zhang ◽

Riqing Lv ◽

Qi Wang

Keyword(s):

Refractive Index ◽

Magnetic Fluid ◽

Optical Devices ◽

Tunable Refractive Index

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Generalized Kerker effect in PT-symmetric nanoantenna array

Journal of Optics ◽

10.1088/2040-8986/ac486f ◽

2022 ◽

Author(s):

Jinal Tapar ◽

Saurabh Kishen ◽

Naresh Kumar Emani

Keyword(s):

Scattered Field ◽

Far Field ◽

Low Loss ◽

Spectral Singularity ◽

Scattering Coefficients ◽

Scattering Response ◽

Nanophotonic Structures ◽

Different Order ◽

Lattice Modes ◽

Nanoantenna Arrays

Abstract All-dielectric nanophotonics is a rapidly developing and practical alternative to plasmonics for nanoscale optics. The electric and magnetic Mie resonances in high-index low-loss dielectric nanoresonators can be engineered to exhibit unique scattering response. Recently, nanophotonic structures satisfying parity-time (PT) symmetry have been shown to exhibit novel scattering responses beyond what can be achieved from the conventional nanoresonators. The complex interference of the magnetic and electric Mie resonances and lattice modes excited in PT-symmetric nanoantenna arrays give rise to a scattering anomaly called lasing spectral singularity (SS), where the scattering coefficients tend to infinity. In our previous work [1], we demonstrated the existence of lasing spectral singularities in vertically stacked 2D GaInP PT-symmetric metasurface. In this paper, we analyze the direction-sensitive scattering response of the PT-symmetric GaInP metasurface by decomposing the total scattered field into the electric and magnetic multipoles. The far-field scattering response at the singularity is highly asymmetric for incidence from either the gain or loss side and can be tuned by changing the geometry. By analyzing the phase of even- and odd-parity higher order multipoles, we explain the observed scattering response over a broad parameter space in terms of generalized Kerker effect. The interference between the direction-dependent excitation of different order multipoles and the overall 2D-lattice resonance opens a route towards designing a special class of tunable sources exhibiting direction-sensitive emission properties.

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Optical Properties of Electrically Active Gold Nanoisland Films Enabled with Interfaced Liquid Crystals

Nanomaterials ◽

10.3390/nano10020290 ◽

2020 ◽

Vol 10 (2) ◽

pp. 290 ◽

Cited By ~ 1

Author(s):

Hung-Chi Yen ◽

Tsung-Rong Kuo ◽

Chun-Ta Wang ◽

Jia-De Lin ◽

Chia-Chun Chen ◽

...

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Liquid Crystal ◽

Active Control ◽

Resonance Wavelength ◽

Hybrid Structure ◽

Optical Devices ◽

Nanostructured Surface ◽

Wavelength Tunability ◽

Nanoisland Film

A system comprising a gold nanoisland film (Au NIF) covered with a liquid crystal (LC) material is introduced. By applying a voltage across the LC bulk, we demonstrate that changes in the refractive-index and orientation significantly modified the hybrid plasmonic–photonic resonances of the Au NIF. The hybrid structure enabled active control of the spectrum of the resonance wavelength of the metallic nanoisland by means of an externally applied electric field. Our modeling supports the observed results in LC/Au NIF. In a combination of the nanostructured surface with birefringent LCs, nonpolarized wavelength tunability of ~15 nm and absorbance tunability of ~0.024 were achieved in the visible wavelength, opening the door to optical devices and nanoscale sensors.

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On the crystallization of potash-alum

Mineralogical Magazine and Journal of the Mineralogical Society ◽

10.1180/minmag.1906.014.65.03 ◽

1906 ◽

Vol 14 (65) ◽

pp. 134-142 ◽

Cited By ~ 1

Author(s):

Jacques Chevalier

Keyword(s):

Refractive Index ◽

Sudden Change ◽

Supersaturated Solution ◽

Metastable Condition ◽

Preceding Communication

As has been mentioned in the preceding communication, a supersaturated solution, which is cooling or evaporating, passes successively into the metastable condition, in which an introduced crystal can grow in it, and then into the labile condition, in which it may crystallize spontaneously. The transition is indicated by a sudden change in the refractive index of the solution. It seems possible that in these two distinct states of the solution there may be a difference in the mode of growth of the crystals. In the following experiments an attempt was made to find evidence of such a difference by the examination of thin drops of solution crystallizing under the microscope: and potash-alum was found to be a convenient substance for the purpose.

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