400 research outputs found
Theory and numerical modeling of photonic resonances: Quasinormal Modal Expansion -- Applications in Electromagnetics
The idea of the modal expansion in electromagnetics is derived from the
research on electromagnetic resonators, which play an essential role in
developments in nanophotonics. All of the electromagnetic resonators share a
common property: they possess a discrete set of special frequencies that show
up as peaks in scattering spectra and are called resonant modes. These resonant
modes are soon recognized to dictate the interaction between electromagnetic
resonators and light. This leads to a hypothesis that the optical response of
resonators is the synthesis of the excitation of each physical-resonance-state
in the system: Under the excitation of external pulses, these resonant modes
are initially loaded, then release their energy which contributes to the total
optical responses of the resonators. These resonant modes with complex
frequencies are known in the literature as the Quasi-Normal Mode (QNM).
Mathematically, these QNMs correspond to solutions of the eigenvalue problem of
source-free Maxwell's equations. In the case where the optical structure of
resonators is unbounded and the media are dispersive (and possibly anisotropic
and non-reciprocal) this requires solving non-linear (in frequency) and
non-Hermitian eigenvalue problems. Thus, the whole problem boils down to the
study of the spectral theory for electromagnetic Maxwell operators. As a
result, modal expansion formalisms have recently received a lot of attention in
photonics because of their capabilities to model the physical properties in the
natural resonance-state basis of the considered system, leading to a
transparent interpretation of the numerical results. This manuscript is
intended to extend the study of QNM expansion formalism, in particular, and
nonlinear spectral theory, in general. At the same time, several numerical
modelings are provided as examples for the application of modal expansion in
computations.Comment: PhD thesi
MAGNETIC PROPERTIES AND DOMAIN STRUCTURE OF CoFeB/Pd MULTILAYERS WITH PERPENDICULAR MAGNETIC ANISOTROPY
The magnetic properties and domain structure of (CoFeB/Pd)n (n = 2 – 10) multilayers with perpendicular magnetic anisotropy have been investigated systematically. The study has been carried out by using vibration sample magnetometer (VSM) and magneto-optical Kerr effect (MOKE) microscope. The results show clear changes of magnetic hysteresis and domain structure when increasing the number of bilayer (n) from 2 to 10. With increasing the number of bilayer, the multilayers’ hysteresis loops change from square-shaped to slanted, while domain structures change from circular-like to maze
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