Ultrafast Long-Distance Electron-Hole Plasma Expansion in GaAs Mediated by Stimulated Emission and Reabsorption of Photons.

Electron-hole plasma expansion with velocities exceeding c/50 and lasting over 10 ps at 300 K was evidenced by time-resolved terahertz spectroscopy. This regime, in which the carriers are driven over >30 µm is governed by stimulated emission due to low-energy electron-hole pair recombination and reabsorption of the emitted photons outside the plasma volume. At low temperatures a speed of c/10 was observed in the regime where the excitation pulse spectrally overlaps with emitted photons, leading to strong coherent light-matter interaction and optical soliton propagation effects.

Improving security in terahertz wireless links using beam symmetry of vortex and Gaussian beams.

We present an effective way to improve the security of a point-to-point terahertz wireless link on a physical layer supported by numerical calculations in the frame of Fourier optics. The improvement is based on original countermeasures which exploit three independent degrees of freedom of the carrier wave: its intensity and azimuthal and radial symmetry. When the transmission line is intercepted, the light beam is subject to changes in either of the three degrees of freedom. We propose a strategy to measure these changes and they are quantified by a single eavesdropping parameter that is shown to be correlated to the secrecy capacity of the transmission. Consequently, its excessive value serves as an indication of the beam interception. We consider the carrier wave in the form of Gaussian and vortex beams. Comparison between the two reveals that vortex beam ensures a even higher level of security.

Silver Nanoparticles with Liquid Crystalline Ligands Based on Lactic Acid Derivatives.

We have prepared and studied silver nanoparticles functionalized with ligands based on lactic acid derivatives. Several types of hybrid systems that differed in the size of silver nanoparticles as well as the length of surface ligands were analyzed. Transmission electron microscopy (TEM) observation provided information about the size and shape of nanoparticles and proved good homogeneity of studied systems. By dynamic light scattering (DLS) measurements, we have measured the size distribution of nanoparticle systems. Plasmonic resonance was detected at around 450 nm. For two hybrid systems, the mesomorphic behaviour has been demonstrated by x-ray measurements. The observed thermotropic liquid crystalline phases reveal lamellar character. We have proposed a model based on self-assembly of intercalated liquid crystalline ligands.

Surface-Adsorbed Long G-Quadruplex Nanowires Formed by G:C Linkages.

G-quadruplexes connected into long, continuous nanostructures termed G-wires show properties superior to dsDNA when applied in nanotechnology. Using AFM imaging, we systematically studied surface adsorption of a set of G-rich oligonucleotides with GC-termini for their ability to form long G-wires through G:C pairing. We investigated the effects of increasing sequence length, the type of nucleotide in the side loops, and removal of the CG-3' terminus. We found that sequences with adenine in the side loops most readily form G-wires. The role of magnesium as an efficient surface-anchoring ion was also confirmed. Conversely, as resolved from dynamic light scattering measurements, magnesium had no ability to promote G-quadruplex formation in solution. These insights may help in selecting prosperous candidates for construction of G-quadruplex based nanowires and to explore them for their electronic properties.

Programmed self-assembly of a quadruplex DNA nanowire.

The ability to produce, reproducibly and systematically, well-defined quadruplex DNA nanowires through controlled rational design is poorly understood despite potential utility in structural nanotechnology. The programmed hierarchical self-assembly of a long four-stranded DNA nanowire through cohesive self-assembly of GpC and CpG "sticky" ends is reported. The encoding of bases within the quadruplex stem allows for an uninterrupted π-stacking system with rectilinear propagation for hundreds of nanometers in length. The wire is mechanically stable and features superior nuclease resistance to double-stranded DNA. The study indicates the feasibility for programmed assembly of uninterrupted quadruplex DNA nanowires. This is fundamental to the systematic investigation of well-defined DNA nanostructures for uses in optoelectronic and electronic devices as well as other structural nanotechnology applications.