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Light reflection from structured media
Citation Link: https://doi.org/10.15480/882.8896
Publikationstyp
Doctoral Thesis
Date Issued
2023
Sprache
English
Author(s)
Title Granting Institution
Hamburg University of Technology
Examination Date
2022-04-21
TORE-DOI
Citation
Technische Universität Hamburg (2023)
Peer Reviewed
false
The possibilities for material structuring and composition on nano and micrometer level have allowed new optical functionalities unavailable with bulk materials. For example, the combination of metals and dielectrics as alternating nanolayers provides a novel anisotropic medium with wave numbers approaching infinity in some directions, so called hyperbolic media. The properties of structured media are strongly dependent on geometry. If structural elements are much smaller than the wavelength of light in constituting materials, then the optical properties of the structured media can be described by effective medium parameters. In this case the structured medium represents a metamaterial. If structural elements are comparable to the wavelength, then the phase of light and interference effects should be considered. In the case of periodical structures, so-called photonic crystals, again effective propagation parameters can be defined for the so-called Bloch modes which propagate unperturbed through the periodic structure. Structures without periodicity are more difficult to describe, and approximate theories are applied to determine scattering. The structural elements much larger than the wavelength are in the realm of geometrical optics and are not considered here.
In this cumulative habilitation thesis, I discuss a particular effect of interaction with structured media, namely the reflection of light. In conventional media the reflection is observed at the boundary between two media, and it is described by the Fresnel equations. For metamaterials, the Fresnel equations can be also applied. In this case the reflection can be changed by the adjustment of the structure and thus the effective medium parameters. For photonic crystals and disordered media, the situation becomes more complex and Fresnel equations are not applicable anymore. Exact consideration of the boundary between structured medium and the input material should be considered. Reflection can build up via accumulation of scattering in the volume of the second medium or due to absence of propagating modes. A special case of reflection is considered when boundary between two media is moving, which leads not only to the change of direction of light but also the frequency. For each of the presented media special theoretical approaches were developed and applied to optimize the reflection properties for envisaged applications.
In this cumulative habilitation thesis, I discuss a particular effect of interaction with structured media, namely the reflection of light. In conventional media the reflection is observed at the boundary between two media, and it is described by the Fresnel equations. For metamaterials, the Fresnel equations can be also applied. In this case the reflection can be changed by the adjustment of the structure and thus the effective medium parameters. For photonic crystals and disordered media, the situation becomes more complex and Fresnel equations are not applicable anymore. Exact consideration of the boundary between structured medium and the input material should be considered. Reflection can build up via accumulation of scattering in the volume of the second medium or due to absence of propagating modes. A special case of reflection is considered when boundary between two media is moving, which leads not only to the change of direction of light but also the frequency. For each of the presented media special theoretical approaches were developed and applied to optimize the reflection properties for envisaged applications.
Subjects
light reflection
optical metamaterials
scattering
structured media
photonic crystals
photonic glasses
effective medium model
DDC Class
620: Engineering
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