In this article a microscopic electronic non-equilibrium effect, highly nonlinear polaritonics, i... more In this article a microscopic electronic non-equilibrium effect, highly nonlinear polaritonics, is proposed to mediate an ultrafast all-optical switching. The electronic band structure within gold (Au) nano grains shall be modified by external laser light, namely the Franz-Keldysh effect, and the modified electronic density of states within the Au grains are coupled to a single mode photonic waveguide. Using this microscopic polaritonic coupling without ever including any macroscopic influences due to the geometric arrangement a strong transmission reduction originating from the established quantum interference is derived. The lifetime of the coupled states is heavily dependent on the Fano resonance type binding and the amplitude of the applied electric field. Besides the Fano signatures the microscopic coupling photon-electron-photon leads to a gaped electronic density of states within the Au nano-grains.
In this article a microscopic electronic non-equilibrium effect, highly nonlinear polaritonics, i... more In this article a microscopic electronic non-equilibrium effect, highly nonlinear polaritonics, is proposed to mediate an ultrafast all-optical switching. The electronic band structure within gold (Au) nano grains shall be modified by external laser light, namely the Franz-Keldysh effect, and the modified electronic density of states within the Au grains are coupled to a single mode photonic waveguide. Using this microscopic polaritonic coupling without ever including any macroscopic influences due to the geometric arrangement a strong transmission reduction originating from the established quantum interference is derived. The lifetime of the coupled states is heavily dependent on the Fano resonance type binding and the amplitude of the applied electric field. Besides the Fano signatures the microscopic coupling photon-electron-photon leads to a gaped electronic density of states within the Au nano-grains.
In the last decade Anderson Localization of Light and Random Lasing has attracted a variety of in... more 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. There is no need of an external feedback mechanism, like in the system of a conventional laser. Whereas several attempts try to enter the subject numerically by considering cavity approximations, this thesis is concerned with building a microscopically self-consistent theory of random lasing. Designing this method, we had to study light localization effects in random media including absorption and gain. Incorporating interference effects by means of Cooperon contributions we derived Anderson localized states for passive media. Mapping this 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, but the system is weakly localized, which is sufficient for population inversion and stimulated emission.
Bulletin of the American Physical Society, Mar 14, 2016
, Germany-The Anderson transition was originally proposed for electrons, however it has been soon... more , Germany-The Anderson transition was originally proposed for electrons, however it has been soon searched for all kinds of waves in disordered media. This physics became extremely interesting with the application of high amplitude excitations, where the medium is supposed to respond with non-linear effects. In theory it is ever since a challenge to treat large random ensembles numerically, even if the medium is completely non-resonant or passive. We discuss in this talk transport of light with respect to a quantum field theoretical approach and we explain through comparison to other existing theories, what the advantages of state of the art theory in that field is, and why it is exciting.
We consider a photonic waveguide in contact with metallic nano-grains which are exposed to extern... more We consider a photonic waveguide in contact with metallic nano-grains which are exposed to external laser irradiation. In this non-equilibrium system, we study the influence of the external laser light using Keldysh - Floquet Green's functions. We calculate the electronic density of states and extract from the observed quantum interference the photonic transmission through the waveguide as a function of external laser frequency and intensity. Our results demonstrate the successful operation of an ultrafast all-optical switch driven by an external laser.
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 in... more 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 t...
We present diagrammatic transport theory including self-consistent nonlinear enhancement and diss... more We present diagrammatic transport theory including self-consistent nonlinear enhancement and dissipation in the multiple scattering regime. Our model of Vollhardt-Wölfle transport of photons is fit-parameter-free and raises the claim that the results hold up to the closest packed volume of randomly arranged ZnO Mie scatterers. We find that a symmetry breaking caused by dissipative effects of a lossy underlying substrate leads to qualitatively different physics of coherence and lasing in granular amplifying media. According to our results, confined and extended mode and their laser thresholds can be clearly attributed to unbroken and broken spatial symmetry. The diameters and emission profiles of random laser modes, as well as their thresholds and the positional-dependent degree of coherence can be checked experimentally.
A gas of ultracold interacting quantum degenerate Fermions is considered in a three-dimensional o... more A gas of ultracold interacting quantum degenerate Fermions is considered in a three-dimensional optical lattice which is externally modulated in the frequency and the amplitude. This theoretical study utilizes the Keldysh formalism to account for the system being out of thermodynamical equilibrium. A dynamical mean field theory, extended to non-equilibrium, is presented to calculate characteristic quantities such as the local density of states and the non-equilibrium distribution function. A dynamic Franz-Keldysh splitting is found which accounts for the non-equilibrium modification of the underlying bandstructure. The found characteristic Floquet-fan like bandstructure accounts for the quantized nature of the effect over all frequency space.
We present photonic transport in D=3 dimensional granular dissipative semiconductor media. Our se... more We present photonic transport in D=3 dimensional granular dissipative semiconductor media. Our self-consistent diagrammatic approach of the Bethe-Salpeter equation including the Cooperon predicts a spatially dependent correlation volume within the disordered medium that is equivalent to the laser's mode extent inside the sample. Our results are relevant for the construction of disordered complex semiconductor micro-lasers and active Mie sphere samples. They define concrete critical parameters for the phase transition to lasing in disordered non-linear random media.
A generalized non-equilibrium dynamical mean field theory (DMFT) for graphene is presented. The N... more A generalized non-equilibrium dynamical mean field theory (DMFT) for graphene is presented. The NE-DMFT describes graphene in the presence of an external field coupling to the electrons and thus changing in a severe but controllable way the elecronic properties of graphene. The nonequilibrium DMFT derives properties such as electronic density of states (LDOS) and occupation numbers of the optically driven system. It fully characterizes the system in its time dependent state. It is demonstrated, how such a setup may be employed in order to realize all-optical switching processes. Results for relevant time scales in setups as well as wave-mixing influences are presented.
We implement externally excited ZnO Mie resonators in a framework of a generalized Hubbard Hamilt... more We implement externally excited ZnO Mie resonators in a framework of a generalized Hubbard Hamiltonian to investigate the lifetimes of excitons and exciton-polaritons out of thermodynamical equilibrium. Our results are derived by a Floquet-Keldysh-Green’s formalism with Dynamical Mean Field Theory (DMFT) and a second order iterative perturbation theory solver (IPT). We find that the Fano resonance which originates from coupling of the continuum of electronic density of states to the semiconductor Mie resonator yields polaritons with lifetimes between 0.6 ps and 1.45 ps. These results are compared to ZnO polariton lasers and to ZnO random lasers. We interpret the peaks of the exciton-polariton lifetimes in our results as a sign of gain narrowing which may lead to stable polariton lasing modes in the single excited ZnO Mie resonator. This form of gain may lead to polariton random lasing in an ensemble of ZnO Mie resonators in the non-equilibrium.
Spatially uniform optical excitations can induce Floquet topological band structures within insul... more 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.
Spatially uniform excitations can induce Floquet topological bandstructures within insulators whi... more 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.
The spatial formation of coherent random laser modes in strongly scattering disordered random med... more The spatial formation of coherent random laser modes in strongly scattering disordered random media is a central feature in the understanding of the physics of random lasers. We derive a quantum field theoretical method for random lasing in disordered samples of complex amplifying Mie resonators which is able to provide self-consistently and free of any fit parameter the full set of transport characteristics at and above the laser phase transition. The coherence length and the correlation volume respectively is derived as an experimentally measurable scale of the phase transition at the laser threshold. We find that the process of stimulated emission in extended disordered arrangements of active Mie resonators is ultimately connected to time-reversal symmetric multiple scattering in the sense of photonic transport while the diffusion coefficient is finite. A power law is found for the random laser mode diameters in stationary state with increasing pump intensity.
We present diagrammatic transport theory including self-consistent nonlinear enhancement and diss... more We present diagrammatic transport theory including self-consistent nonlinear enhancement and dissipation in the multiple scattering regime. Our model of Vollhardt-Wölfle transport of photons is fit-parameter-free and raises the claim that the results hold up to the closest packed volume of randomly arranged ZnO Mie scatterers. We find that a symmetry breaking caused by dissipative effects of a lossy underlying substrate leads to qualitatively different physics of coherence and lasing in granular amplifying media. According to our results, confined and extended mode and their laser thresholds can be clearly attributed to unbroken and broken spatial symmetry. The diameters and emission profiles of random laser modes, as well as their thresholds and the positional-dependent degree of coherence can be checked experimentally.
We report a quantum field theoretical description of light transport and random lasing. The Bethe... more 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 semiconductor Mie scatterers.
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Papers by Regine Frank