The effect of anisotropy on cross section spectra of uniaxial spherical particles small compared to the wavelength

Höfer, Sonja; Mutschke, H.; Mayerhöfer, Th.G.

doi:10.1016/j.jqsrt.2020.106909

Cited by 4 publications

(2 citation statements)

References 30 publications

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“…It is smallest for setups 1_2p and 1_1o, for which the c-axis is parallel to the long particle axis and the wave is incident along a short axis of the particle; while it is largest for setups 1_1p and 1_2o, where the opposite is true. As we showed in Höfer et al (2020a), the bulk mode of an isolated oscillator gets shifted to higher wavenumbers, explaining the shift of band 7, while band 11 is strongly influenced by the bulk mode 4 at nearly the same wavenumber position.…”

Section: Resultssupporting

confidence: 62%

Effects of anisotropy on absorption cross-section spectra of medium-sized spheroidal corundum particles

Höfer

Mutschke

Mayerhöfer

2021

A&A

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Context. It has been widely accepted that corundum particles condense in the atmospheres of oxygen-rich asymptotic giant branch stars and effectively produce an infrared emission feature at 13 μm. Laboratory experiments have predicted that these particles have the shape of oblate spheroids. Aims. We investigate the influence of the material anisotropy of uniaxial corundum on absorption cross section spectra of medium sized spheroidal particles in the infrared spectral region. Methods. We compared absorption cross-section spectra of the anisotropic corundum particles gained by finite-difference time-domain simulations to spectra calculated by a weighted sum approximation of the according fictive isotropic materials, with one material having the dielectric function of the a–b-plane and the other having the dielectric function of the c-axis of corundum. We carried out investigations for different axes ratios of the spheroids, particles volumes, and different geometries of the dielectric axes to the particle axes as well as to the polarization and propagation direction of the incident light. Results. We observed several effects attributed to anisotropy that are non-additive, so that they cannot be reproduced with the combined spectra of the isotropic materials. Conclusions. Care should be taken when calculating the corundum infrared spectrum with simpler approaches. When particle sizes above 1 μm are to be considered, the T-matrix formalism delivers correct band shifts and bulk modes for many, but not all bands. This remains true in orientation-averaged spectra and for particles in the 0.1 μm size range.

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Section: Resultssupporting

confidence: 62%

Effects of anisotropy on absorption cross-section spectra of medium-sized spheroidal corundum particles

Höfer

Mutschke

Mayerhöfer

2021

A&A

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“…The above-discussed interest in hyperbolic nanoantennas and potential use in optical devices makes it necessary to understand, at the fundamental level, the behavior of optical modes of these structures. While discussion on basic properties of anisotropic resonators can be found in literature [32,33] and is relevant to the topic at hand, hyperbolic nanoparticles need separate treatment. Here, we contribute to this topic by discussing basic electromagnetic properties of hyperbolic nanospheres.…”

Section: Introductionmentioning

confidence: 99%

Polarization-dependent mode coupling in hyperbolic nanospheres

Czajkowski,

Bancerek,

Korneluk

et al. 2021

Preprint

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Hyperbolic materials offer a much wider freedom in designing optical properties of nanostructures than ones with isotropic and elliptical dispersion, both metallic or dielectric. Here, we present a detailed theoretical and numerical study of the unique optical properties of spherical nanoantennas composed of such materials. Hyperbolic nanospheres exhibit a rich modal structure that, depending on the polarization and direction of incident light, can exhibit either a full plasmonic-like response with multiple electric resonances, a single, dominant electric dipole or one with mixed magnetic and electric modes with an atypical reversed modal order. We derive resonance conditions for observing these resonances in the dipolar approximation and offer insight into how the modal response evolves with the size, material composition, and illumination. Specifically, the origin of the magnetic dipole mode lies in the hyperbolic dispersion and its existence is determined by two diagonal permittivity components of different sign. Our analysis shows that the origin of this unusual behavior stems from complex coupling between electric and magnetic multipoles, which leads to very strongly scattering or absorbing modes. These observations assert that hyperbolic nanoantennas offer a promising route towards novel light-matter interaction regimes.

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The effect of anisotropy on cross section spectra of quartz, calcite and corundum spheres of moderate size

Höfer

Mutschke

Mayerhöfer

2020

Journal of Quantitative Spectroscopy and Radiative Transfer

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The effect of anisotropy on cross section spectra of uniaxial spherical particles small compared to the wavelength

Cited by 4 publications

References 30 publications

Effects of anisotropy on absorption cross-section spectra of medium-sized spheroidal corundum particles

Effects of anisotropy on absorption cross-section spectra of medium-sized spheroidal corundum particles

Polarization-dependent mode coupling in hyperbolic nanospheres

The effect of anisotropy on cross section spectra of quartz, calcite and corundum spheres of moderate size

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