27 research outputs found
Current and vorticity auto correlation functions in open microwave billiards
Using the equivalence between the quantum-mechanical probability density in a
quantum billiard and the Poynting vector in the corresponding microwave system,
current distributions were studied in a quantum dot like cavity, as well as in
a Robnik billiard with lambda=0.4, and an introduced ferrite cylinder. Spatial
auto correlation functions for currents and vorticity were studied and compared
with predictions from the random-superposition-of-plane-waves hypothesis. In
addition different types of vortex neighbour spacing distributions were
determined and compared with theory.Comment: PTP-LaTeX, 10 pages with 6 figures submitted to Progress of
Theoretical Physics Supplemen
Experimental Observation of a Fundamental Length Scale of Waves in Random Media
Waves propagating through a weakly scattering random medium show a pronounced
branching of the flow accompanied by the formation of freak waves, i.e.,
extremely intense waves. Theory predicts that this strong fluctuation regime is
accompanied by its own fundamental length scale of transport in random media,
parametrically different from the mean free path or the localization length. We
show numerically how the scintillation index can be used to assess the scaling
behavior of the branching length. We report the experimental observation of
this scaling using microwave transport experiments in quasi-two-dimensional
resonators with randomly distributed weak scatterers. Remarkably, the scaling
range extends much further than expected from random caustics statistics.Comment: 5 pages, 5 figure
Experimental observation of the mobility edge in a waveguide with correlated disorder
The tight-binding model with correlated disorder introduced by Izrailev and
Krokhin [PRL 82, 4062 (1999)] has been extended to the Kronig-Penney model. The
results of the calculations have been compared with microwave transmission
spectra through a single-mode waveguide with inserted correlated scatterers.
All predicted bands and mobility edges have been found in the experiment, thus
demonstrating that any wanted combination of transparent and non-transparent
frequency intervals can be realized experimentally by introducing appropriate
correlations between scatterers.Comment: RevTex, 4 pages including 4 Postscript figure
Experimental Observation of the Spectral Gap in Microwave n-Disk Systems
Symmetry reduced three-disk and five-disk systems are studied in a microwave
setup. Using harmonic inversion the distribution of the imaginary parts of the
resonances is determined. With increasing opening of the systems, a spectral
gap is observed for thick as well as for thin repellers and for the latter case
it is compared with the known topological pressure bounds. The maxima of the
distributions are found to coincide for a large range of the distance to radius
parameter with half of the classical escape rate. This confirms theoretical
predictions based on rigorous mathematical analysis for the spectral gap and on
numerical experiments for the maxima of the distributions.Comment: 5 pages, 4 figure
Coupling of polarization and spatial degrees of freedom of highly divergent emission in broad-area square vertical-cavity surface-emitting lasers
The polarization of highly divergent modes of broad-area square vertical-cavity surface-emitting lasers is shown to be only marginally affected by material anisotropies but determined by an interplay of the polarization properties of the Bragg cavity mirrors and of the transverse boundary conditions. This leads to a locking of the polarization direction to the boundaries and its indeterminacy for wave vectors oriented along the diagonal. We point out a non-Poissonian character of nearest-neighbor frequency spacing distribution and the impossibility of single-wave number solutions
Microwave realization of quasi one-dimensional systems with correlated disorder
A microwave setup for mode-resolved transport measurement in
quasi-one-dimensional (quasi-1D) structures is presented. We will demonstrate a
technique for direct measurement of the Green's function of the system. With
its help we will investigate quasi-1D structures with various types of
disorder. We will focus on stratified structures, i.e., structures that are
homogeneous perpendicular to the direction of wave propagation. In this case
the interaction between different channels is absent, so wave propagation
occurs individually in each open channel. We will apply analytical results
developed in the theory of one-dimensional (1D) disordered models in order to
explain main features of the quasi-1D transport. The main focus will be
selective transport due to long-range correlations in the disorder. In our
setup, we can intentionally introduce correlations by changing the positions of
periodically spaced brass bars of finite thickness. Because of the equivalence
of the stationary Schr\"odinger equation and the Helmholtz equation, the result
can be directly applied to selective electron transport in nanowires,
nanostripes, and superlattices.Comment: 11 pages, 9 figure