Optical Studies of Periodic Microstructures in Polar Materials

The optical properties of matter are based on the coupling of the incident electromagnetic radiation to oscillators within the material. The oscillators could be electrons, ions or molecules. Close to a resonance the dielectric function indicates strong dispersion and might be negative. A negative dielectric function brings about a complex wave vector that is linked with no permitted states for photons, i.e. high extinction and bulk reflectance, plus the chance to support surface waves.It is possible to manufacture a dielectric material which produces a complex wave vector. This kind of materials are known as photonic crystals and they may demonstrate a frequency range without permitted states for photons, i.e. an energy gap. A photonic crystal features a regularly varying dielectric function and the lattice constant is of the same order of magnitude as the wavelengths of the gap.In this particular dissertation, 2 optical phenomena resulting in a complex wave vector are combined. Polar materials, that have lattice resonance in the thermal infrared leading to strong dispersion, are analyzed in combination with a periodic structure. The periodicity introduced is accomplished making use of another material, and also by structuring of the polar material. One, two and three dimensional structures are considered. The polar materials utilized are silicon dioxide and silicon carbide. It is demonstrated, both by calculations and experiments that the 2 optical phenomena can co-exist and interact, both constructively and destructively. A possible application for the combination of the 2 phenomena is explained: Selective emittance in the thermal infrared. Additionally it is demonstrated that a polar material can be periodically structured with a focused ion beam in such manner that it excites surface waves.


1. Introduction
2. Optical materials
2.1 Electromagnetic waves in matter
2.2 Dielectric materials
2.3 Polar materials
2.3.1 The Lorentz model
2.3.2 The polaritonic gap
2.4 Metals
3. Effect of periodicity
3.1 The light line and the Brillouin zone
3.2 The photonic band gap
3.2 Polaritonic photonic crystals
4. Surface polaritons
4.1 General theory
4.1.1 Coupling by periodic structure
4.1.2 Coupling by ATR and nano structures
4.2 Enhanced optical transmission
5. Experimental
5.1 Fabrication of periodic structures
5.1.1 One-dimensional structures
5.1.2 Two-dimensional structures
5.1.2 Two-dimensional structures
5.1.3 Three-dimensional structures
5.2 Optical analysis
5.2.1 One-dimensional structures
5.2.2 Two-dimensional structure
5.2.3 Three-dimensional structures
6. Signature management in the thermal infrared
6.1 Black-body radiation
6.2 Atmospheric windows
6.3 Infrared camouflage
6.4 Emittance determination
7. Conclusions and discussion…….

Source: Uppsala University Library

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