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Optical theorems and physical bounds on absorption in lossy media
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).ORCID-id: 0000-0002-3928-6064
Lund University, Sweden.ORCID-id: 0000-0003-4362-5716
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).ORCID-id: 0000-0002-7018-6248
2019 (Engelska)Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, nr 23, s. 34323-34342Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Two different versions of an optical theorem for a scattering body embedded inside a lossy background medium are derived in this paper. The corresponding fundamental upper bounds on absorption are then obtained in closed form by elementary optimization techniques. The first version is formulated in terms of polarization currents (or equivalent currents) inside the scatterer and generalizes previous results given for a lossless medium. The corresponding bound is referred to here as a variational bound and is valid for an arbitrary geometry with a given material property. The second version is formulated in terms of the T-matrix parameters of an arbitrary linear scatterer circumscribed by a spherical volume and gives a new fundamental upper bound on the total absorption of an inclusion with an arbitrary material property (including general bianisotropic materials). The two bounds are fundamentally different as they are based on different assumptions regarding the structure and the material property. Numerical examples including homogeneous and layered (core-shell) spheres are given to demonstrate that the two bounds provide complimentary information in a given scattering problem.

Ort, förlag, år, upplaga, sidor
Optical Society of America, 2019. Vol. 27, nr 23, s. 34323-34342
Nyckelord [en]
Material properties; Mie theory; Photon counting; Radiative transfer; Refractive index; Scattering
Nationell ämneskategori
Annan fysik
Forskningsämne
Fysik, Vågor och signaler
Identifikatorer
URN: urn:nbn:se:lnu:diva-89962DOI: 10.1364/OE.27.034323ISI: 000495871300120OAI: oai:DiVA.org:lnu-89962DiVA, id: diva2:1368831
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF), AM13-0011Tillgänglig från: 2019-11-08 Skapad: 2019-11-08 Senast uppdaterad: 2019-12-17Bibliografiskt granskad
Ingår i avhandling
1. Optimization and Physical Bounds for Passive and Non-passive Systems
Öppna denna publikation i ny flik eller fönster >>Optimization and Physical Bounds for Passive and Non-passive Systems
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Physical bounds in electromagnetic field theory have been of interest for more than a decade. Considering electromagnetic structures from the system theory perspective, as systems satisfying linearity, time-invariance, causality and passivity, it is possible to characterize their transfer functions via Herglotz functions. Herglotz functions are useful in modeling of passive systems with applications in mathematical physics, engineering, and modeling of wave phenomena in materials and scattering. Physical bounds on passive systems can be derived in the form of sum rules, which are based on low- and high-frequency asymptotics of the corresponding Herglotz functions. These bounds provide an insight into factors limiting the performance of a given system, as well as the knowledge about possibilities to improve a desired system from a design point of view. However, the asymptotics of the Herglotz functions do not always exist for a given system, and thus a new method for determination of physical bounds is required. In Papers I–II of this thesis, a rigorous mathematical framework for a convex optimization approach based on general weighted Lp-norms, 1≤p≤∞, is introduced. The developed framework is used to approximate a desired system response, and to determine an optimal performance in realization of a system satisfying the target requirement. The approximation is carried out using Herglotz functions, B-splines, and convex optimization. 

Papers III–IV of this thesis concern modeling and determination of optimal performance bounds for causal, but not passive systems. To model them, a new class of functions, the quasi-Herglotz functions, is introduced. The new functions are defined as differences of two Herglotz functions and preserve the majority of the properties of Herglotz functions useful for the mathematical framework based on convex optimization. We consider modeling of gain media with desired properties as a causal system, which can be active over certain frequencies or  frequency intervals.  Here, sum rules can also be used under certain assumptions.

In Papers V–VII of this thesis, the optical theorem for scatterers immersed in lossy media is revisited. Two versions of the optical theorem are derived: one based on internal equivalent currents and the other based on external fields in terms of a T-matrix formalism, respectively. The theorems are exploited to derive fundamental bounds on absorption by using elementary optimization techniques. The theory has a potential impact in applications where the surrounding losses cannot be neglected, e.g., in medicine, plasmonic photothermal therapy, radio frequency absorption of gold nanoparticle suspensions, etc.  In addition to this, a new method for detection of electrophoretic resonances in a material with Drude-type of dispersion, which is placed in a straight waveguide, is proposed.

Ort, förlag, år, upplaga, sidor
Växjö, Sweden: Linnaeus University Press, 2019. s. 217
Serie
Linnaeus University Dissertations ; 373/2019
Nyckelord
Convex optimization, physical bounds, Herglotz functions, quasi-Herglotz functions, passive systems, non-passive systems, approximation, absorption in lossy media
Nationell ämneskategori
Annan elektroteknik och elektronik
Forskningsämne
Fysik, Vågor och signaler
Identifikatorer
urn:nbn:se:lnu:diva-90223 (URN)978-91-89081-23-9 (ISBN)978-91-89081-24-6 (ISBN)
Disputation
2019-12-13, Newton, Hus C, Växjö, 09:15 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF), AM13-0011
Tillgänglig från: 2019-11-22 Skapad: 2019-11-21 Senast uppdaterad: 2019-11-22Bibliografiskt granskad

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Ivanenko, YevhenNordebo, Sven

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