Bi-functional nonlinearities in monodisperse ZnO nano-grains - Self-consistent transport and random lasing

We report a quantum field theoretical description of light transport and random lasing. The Bethe-Salpeter equation is solved including maximally crossed diagrams and non-elastic scattering. This is the first theoretical framework that combines so called off-shell scattering and lasing in random media. We present results for the self-consistent scattering mean free path that varies over the width of the sample. Further we discuss the density dependent correlation length of self-consistent transport in disordered media composed of semi-conductor Mie scatterers.Comment: AIP (accepted

Microscopic Theory of Random Lasing and Light Transport in Amplifying Disordered Media

In the last decade Anderson Localization of Light and Random Lasing has attracted a variety of interest in the community of condensed matter theory. The fact that a system so inartificial as a thin layer consisting of dust particles, which have amplifying properties, can produce coherent laser emission, is of a simple elegance, which promises new insights in fundamental physics. The Random Laser consists of randomly distributed scatterers which have amplifying properties, embedded in an either amplifying or a passive medium. There is no need of an external feedback mechanism, like in the system of a conventional laser. Despite the striking chasteness of the effect, there are still vivid discussions about theory for the random laser, which has not been fully described yet. Whereas there are several attempts to enter the subject numerically by considering cavity approximations, this thesis is concerned with building a microscopically self-consistent theory of random lasing. In order to design this method we had to study light localization effects in random media including absorption and gain. We incorporated interference effects by calculating the Cooperon contributions and we found, that we reach Anderson localized states for passive media. Mapping this theory on a system which consists of laser active Mie-scatterers in a passive medium, we found that by incorporation of the Cooperon, we loose the Anderson localization again, but the system is still weakly localized, which is sufficient for the enhancement of population inversion and stimulated emission. The description of a random lasing system is completed by coupling the analytically derived microscopic transport theory to the laser rate equations of a four level laser and solving the system numerically self-consistent. Finally we develop a generalized method for describing light transport, multiple scattering and interference effects in a translationally non-invariant system of finite size analytically. The solution of this theory coupled to the rate equations gives us a closed theory to calculate transport and lasing properties of a random lasing slab geometry

Behavior of Floquet Topological Quantum States in Optically Driven Semiconductors

Spatially uniform optical excitations can induce Floquet topological band structures within insulators which can develop similar or equal characteristics as are known from three-dimensional topological insulators. We derive in this article theoretically the development of Floquet topological quantum states for electromagnetically driven semiconductor bulk matter and we present results for the lifetime of these states and their occupation in the non-equilibrium. The direct physical impact of the mathematical precision of the Floquet-Keldysh theory is evident when we solve the driven system of a generalized Hubbard model with our framework of dynamical mean field theory (DMFT) in the non-equilibrium for a case of ZnO. The physical consequences of the topological non-equilibrium effects in our results for correlated systems are explained with their impact on optoelectronic applications.Comment: Symmetry (accepted September 18, 2019). arXiv admin note: substantial text overlap with arXiv:1909.0692

Evolution of Floquet Topological Quantum States in Driven Semiconductors

Spatially uniform excitations can induce Floquet topological bandstructures within insulators which have equal characteristics to those of topological insulators. Going beyond we demonstrate in this article the evolution of Floquet topological quantum states for electromagnetically driven semiconductor bulk matter. We show the direct physical impact of the mathematical precision of the Floquet-Keldysh theory when we solve the driven system of a generalized Hubbard model with our framework of dynamical mean field theory (DMFT) in the non-equilibrium. We explain the physical consequences of the topological non-equilibrium effects in our results for correlated sysems with impact on optoelectronic applications.Comment: 9 Pages (accepted