Mesoscopic light transport by very strong collective multiple scattering in nanowire mats

Under the extreme condition of the scattering length being much shorter than the wavelength, light transport in random media is strongly modified by mesoscopic interference, and can even be halted in an effect known as Anderson localization. Anderson localization in three dimensions has recently been realized for acoustic waves and for cold atoms. Mats of disordered, high-refractive-index semiconductor nanowires are one of the strongest three-dimensional scattering materials for light, but localization has not been shown. Here, we use statistical methods originally developed for microwave waveguides to demonstrate that transport of light through nanowire mats is strongly correlated and governed by mesoscopic interference contributions. Our results confirm the contribution of only a few open modes to the transmission

Inherent regulation of EAL domain-catalyzed hydrolysis of second messenger c-di-GMP

The universal second messenger cyclic di-GMP (cdG) is involved in the regulation of a diverse range of cellular processes in bacteria. The intracellular concentration of the dinucleotide is determined by the opposing actions of diguanylate cyclases (DGCs) and cdG specific phosphodiesterases (PDEs). While most PDEs have accessory domains that are involved in the regulation of their activity, the regulatory mechanism of this class of enzymes has remained unclear. Here, we use biophysical and functional analyses to show that the isolated EAL domain of a PDE from E. coli (YahA) is in a fast thermodynamic monomer - dimer equilibrium, and that the domain is active only in its dimeric state. Furthermore, our data indicate thermodynamic coupling between substrate binding and EAL dimerization with the dimerization affinity being increased about 100-fold upon substrate binding. Crystal structures of the YahA-EAL domain determined under various conditions (apo, Mg(2+), c-di-GMP/Mg(2+) complex) confirm structural coupling between the dimer interface and the catalytic center. The in-built regulatory properties of the EAL domain probably facilitates its modular, functional combination with the diverse repertoire of accessory domains

Measurements on the optical transmission matrices of strongly scattering nanowire layers

\u3cp\u3eLight incident on a scattering medium is redistributed over transport channels that either transmit through or reflect from the medium. We perform experiments aiming at finding individual transport channels of extremely strongly scattering materials. A small number of transport channels in a scattering sample are open with transmission coefficient close to 1; field transmission mainly takes place through these channels [1-3]. This means that, even if two very different incident fields are sent to the sample, the corresponding transmitted fields are correlated. As the scattering becomes stronger, these correlations become more pronounced.\u3c/p\u3

Controlling a Nanowire Quantum Dot Band Gap Using a Straining Dielectric Envelope

We tune the emission wavelength of an InAsP quantum dot in an InP nanowire over 200 meV by depositing a SiO₂ envelope using plasma-enhanced chemical vapor deposition without deterioration of the optical quality. This SiO₂ envelope generates a controlled static strain field. Both red and blue shift can be easily achieved by controlling the deposition conditions of the SiO₂. Using atomistic empirical tight-binding calculations, we investigate the effect of strain on a quantum dot band structure for different compositions, shape, and crystal orientations. From the calculations, we estimate the applied strain in our experiment. This enables engineering of the band gap in nanowires with unprecedented possibilities to extend the application range of nanowire devices