Suppression of Intensity Fluctuations in Free Space High-Speed Optical Communication Based on Spectral Encoding of a Partially Coherent Beam

A new concept of a free-space, high-speed (Gbps) optical communication system based on spectral encoding of radiation from a broadband pulsed laser is developed. It is shown that, in combination with the use of partially coherent laser beams and a relatively slow photosensor, scintillations can be suppressed by orders of magnitude for distances of more than 10 km. We also consider the spectral encoding of radiation from a LED as a gigabit rate solution of the "last mile" problem and rapid-deployment systems for disaster recovery.Comment: 16 pages, 2 figure

A Discrete Two-Dimensional Model of a Loaded Cantilever Influenced by Time-Dependent Forces

We developed a discrete two-dimensional model of a cantilever which incorporates the effects of inhomogeneity, the geometry of an attached particle, and the influence of external time-dependent forces. We provide a comparison between the solutions for our discrete model and its continuous limit. The rotational-vibrational mode is studied in detail. The results of numerical simulations demonstrate usefulness of our model for many applications when a cantilever has a complicated geometry and is affected by time-depended and distributed external forces.Comment: Pages 15, Figures 1

Roughening transition as a driving factor in the formation of self-ordered one-dimensional nanostructures

Based on the Monte Carlo kinetic method, we investigated the formation mechanisms of periodical modulations arising along the length of one-dimensional structures. The evolution of initially cylindrical nanowires/slabs at temperatures lower than their respective melting temperatures can result either in breakup into single nanoclusters or in the formation of stable states with pronounced modulations of cross section. Such configurations, observed in a number of experiments, are excited at wavelengths that are below the critical value for the development of classical Rayleigh instability. We show that the modulation excited in the subcritical mode corresponds to the appearance of roughening transition on the quasi-one-dimensional surface of nanowires/slabs. Since the arise of roughening transition is possible only on certain facets of metals with a given crystal structure, the short-wavelength modulations of one-dimensional systems, as shown in our work, can be realized (i) with the proper orientation of the nanowire/slab axis providing spontaneous appearance of roughening transition on its lateral surface, (ii) by the method of activating the surface diffusion of atoms by external impact (irradiation with an electron beam or contact with a cold plasma), which stimulates roughening transition without significant heating of the nanowire. The results obtained for the cases of BCC and FCC lattices can be used in the controlled synthesis of ordered one-dimensional structures for use in optoelectronics and in ultra-large-scale integrated circuits

Formation of Nanoclusters and Nanopillars in Nonequilibrium Surface Growth for Catalysis Applications: Growth by Diffusional Transport of Matter in Solution Synthesis

Growth of nanoclusters and nanopillars is considered in a model of surface deposition of building blocks (atoms) diffusionally transported from solution to the forming surface structure. Processes of surface restructuring are also accounted for in the model, which then yields morphologies of interest in catalysis applications. Kinetic Monte Carlo numerical approach is utilized to explore the emergence of FCC-symmetry surface features in Pt-type metal nanostructures. Available results exemplify evaluation of the fraction of the resulting active sites with desirable properties for catalysis, such as (111)-like coordination, as well as suggest optimal growth regimes

Dynamics of quasi-one-dimensional structures under roughening transition stimulated by external irradiation

We studied the striking effect of external irradiation of nanowires on the dynamics of their surface morphology at elevated temperatures that do not destroy their crystal lattice. Numerical experiments performed on the basis of the Monte Carlo model revealed new possibilities for controlled periodic modulation of the cross-section of quasi-one-dimensional nanostructures for opto- and nanoelectronic elements. These are related to the fact that external irradiation stimulates the surface diffusion of atoms. On the one hand, such stimulation should accelerate the development of the well-known spontaneous thermal instability of nanowires (Rayleigh instability), which leads to their disintegration into nanoclusters. On the other hand, this leads to the forced development of the well-known roughening transition (RT) effect. Under normal circumstances, this manifests itself on selected crystal faces at a temperature above the critical one. The artificial stimulation of this effect on the lateral surface of quasi-one-dimensional structures determines many unpredictable scenarios of their surface dynamics, which essentially depend on the orientation of the nanowire axis relative to its internal crystal structure. In particular, the long-wave Rayleigh breakup observed in absence of external irradiation transforms into strongly pronounced short-wave metastable modulations of the cross-section (a chain of unduloids). The effect of the self-consistent relationship between the Rayleigh instability and RT is dimensional and can be observed only at relatively small nanowire radii. The fact is analyzed that, for the manifestation of this effect, it is very important to prevent significant heating of the nanowire when surface diffusion is stimulated. A number of developed theoretical concepts have already found confirmation in real experiments with Au and Ag nanowires irradiated by electrons and Ag+ ions, respectively