Materials with nontrivial topological properties may also be found in standard optical systems like photonic crystals and waveguide arrays. Many of these systems are characterized by a well-defined topological winding number (also known as the Brouwer degree). We pick several interesting optical model systems to show that the winding number is a very simple topological concept, which can often be guessed intuitively.
However, even for minor modifications of the standard topological model systems the use of the simplest types of winding numbers is no longer justified. Thus, we also present ongoing research to employ other intuitive topological concepts.
We will discuss the use of some of the standard methods of computational materials science to predict the optical properties of glasses. Given the accuracy of state-of-the-art ab initio methods to simulate the dielectric properties of solids, some of these methods turn out to be a viable alternative to experimental studies, and they also allow for the prediction of dielectric properties in frequency ranges, which might not be easily accessible in a real experiment.
Density functional based linear response theory for example allows for the simulation of dielectric properties over a wide frequency range, related to the many-electron system of a solid. We will summarize the corresponding theoretical background, and discuss the predictions made by applying some of these theoretical and numerical approaches to a variety of glasses.
Beyond the modelling of one-particle excitations that contribute to the dielectric properties of a solid, we also point out the possibility to include contributions from particle-hole excitations based on the Bethe-Salpeter equation. We will summarize the corresponding theoretical background and show some numerical examples.
Additional contributions to the dielectric properties, which stem from the vibrational motion of ions in a solid, are less straightforward to implement. Therefore, our principal focus will be on a critical assessment of various theoretical and numerical approaches discussed in the literature.
With respect to novel types of technological applications based on thin glass films, we will focus on the implementation of up/down-conversion process in conventional types of solar cells as mediated by the deposition of glass layers containing rare earth ions. We will point out several possibilities, where numerical rather than experimental data may become the basis of a typical solar cell device simulation.
Finally, we will suggest possible methodological improvements, which also take advantage of the accuracy and the numerical efficiency of first principles approaches.
We present the main features of first principles numerical methods to describe plasmonic excitations in bulk and nanosized materials, and we apply these methods to a number of bulk and lower-dimensional nanosystems. Our main focus lies on graphene, which is an interesting numerical and experimental paradigm to study plasmonic excitations in a nanosystem with anisotropic and lossy dielectric functions. Beyond graphene we also discuss plasmonic excitations in similar two-dimensional nanosystems. In order to analyse more complex collective excitations of the electron gas in nanosystems, we take advantage of a fundamental relation between density fluctuations and the electron energy loss spectra (EELS), and suggest a general method to study noise in nanosystems.
The optical properties of photonic devices largely depend on the dielectric properties of the underlying materials. We apply modern ab initio methods to study crystalline SiO 2 phases, which serve as toy models for amorphous glass. We discuss the dielectric response from the infrared to the VIS/UV, which is crucial for glass based photonic applications. Low density silica, like cristobalite, may provide a good basis for high transmission optical devices.
Conference Committee Involvement (2)
Fiber Lasers and Glass Photonics: Materials through Applications II
6 April 2020 | Online Only, France
Fiber Lasers and Glass Photonics: Materials through Applications