Multi-mode photonic crystal fibers for VCSEL based data transmission

Quasi error-free 10 Gbit/s data transmission is demonstrated over a novel type of 50 micron core diameter photonic crystal fiber with as much as 100 m length. Combined with 850$ nm VCSEL sources, this fiber is an attractive alternative to graded-index multi-mode fibers for datacom applications. A comparison to numerical simulations suggests that the high bit-rate may be partly explained by inter-modal diffusion.Comment: Accepted for Optics Expres

Shape complexity and fractality of fracture surfaces of swelled isotactic polypropylene with supercritical carbon dioxide

We have investigated the fractal characteristics and shape complexity of the fracture surfaces of swelled isotactic polypropylene Y1600 in supercritical carbon dioxide fluid through the consideration of the statistics of the islands in binary SEM images. The distributions of area $A$, perimeter $L$, and shape complexity $C$ follow power laws $p(A)\sim A^{-(\mu_A+1)}$, $p(L)\sim L^{-(\mu_L+1)}$, and $p(C)\sim C^{-(\nu+1)}$, with the scaling ranges spanning over two decades. The perimeter and shape complexity scale respectively as $L\sim A^{D/2}$ and $C\sim A^q$ in two scaling regions delimited by $A\approx 10^3$. The fractal dimension and shape complexity increase when the temperature decreases. In addition, the relationships among different power-law scaling exponents $\mu_A$, $\mu_B$, $\nu$, $D$, and $q$ have been derived analytically, assuming that $A$, $L$, and $C$ follow power-law distributions.Comment: RevTex, 6 pages including 7 eps figure

Nanometer-scale sharpness in corner-overgrown heterostructures

A corner-overgrown GaAs/AlGaAs heterostructure is investigated with transmission and scanning transmission electron microscopy, demonstrating self-limiting growth of an extremely sharp corner profile of 3.5 nm width. In the AlGaAs layers we observe self-ordered diagonal stripes, precipitating exactly at the corner, which are regions of increased Al content measured by an XEDS analysis. A quantitative model for self-limited growth is adapted to the present case of faceted MBE growth, and the corner sharpness is discussed in relation to quantum confined structures. We note that MBE corner overgrowth maintains nm-sharpness even after microns of growth, allowing the realization of corner-shaped nanostructures.Comment: 4 pages, 3 figure

IMS software developments for the detection of chemical warfare agent

Interference compounds like gasoline, diesel, burning wood or fuel, etc. are presented in common battlefield situations. These compounds can cause detectors to respond as a false positive or interfere with the detector's ability to respond to target compounds such as chemical warfare agents. To ensure proper response of the ion mobility spectrometer to chemical warfare agents, two special software packages were developed and incorporated into the Bruker RAID-1. The programs suppress interferring signals caused by car exhaust or smoke gases resulting from burning materials and correct the influence of variable sample gas humidity which is important for detection and quantification of blister agents like mustard gas or lewisite

Response of Multi-strip Multi-gap Resistive Plate Chamber

A prototype of Multi-strip Multi-gap Resistive Plate chamber (MMRPC) with active area 40 cm $\times$ 20 cm has been developed at SINP, Kolkata. Detailed response of the developed detector was studied with the pulsed electron beam from ELBE at Helmholtz-Zentrum Dresden-Rossendorf. In this report the response of SINP developed MMRPC with different controlling parameters is described in details. The obtained time resolution ($\sigma_t$) of the detector after slew correction was 91.5$\pm$3 ps. Position resolution measured along ($\sigma_x$) and across ($\sigma_y$) the strip was 2.8$\pm$0.6 cm and 0.58 cm, respectively. The measured absolute efficiency of the detector for minimum ionizing particle like electron was 95.8$\pm$1.3 $\%$. Better timing resolution of the detector can be achieved by restricting the events to a single strip. The response of the detector was mainly in avalanche mode but a few percentage of streamer mode response was also observed. A comparison of the response of these two modes with trigger rate was studiedComment: 19 pages, 26 figure

A numerical test of differential equations for one- and two-loop sunrise diagrams using configuration space techniques

We use configuration space methods to write down one-dimensional integral representations for one- and two-loop sunrise diagrams (also called Bessel moments) which we use to numerically check on the correctness of the second order differential equations for one- and two-loop sunrise diagrams that have recently been discussed in the literature.Comment: 11 pages, no figures, published versio

Surface Crystallization of Liquid Au-Si and Its Impact on Catalysis.

In situ transmission electron microscopy reveals that an atomically thin crystalline phase at the surface of liquid Au-Si is stable over an unexpectedly wide range of conditions. By measuring the surface structure as a function of liquid temperature and composition, a simple thermodynamic model is developed to explain the stability of the ordered phase. The presence of surface ordering plays a key role in the pathway by which the Au-Si eutectic solidifies and also dramatically affects the catalytic properties of the liquid, explaining the anomalously slow growth kinetics of Si nanowires at low temperature. A strategy to control the presence of the surface phase is discussed, using it as a tool in designing strategies for nanostructure growth

Large-scale Graphitic Thin Films Synthesized on Ni and Transferred to Insulators: Structural and Electronic Properties

We present a comprehensive study of the structural and electronic properties of ultrathin films containing graphene layers synthesized by chemical vapor deposition (CVD) based surface segregation on polycrystalline Ni foils then transferred onto insulating SiO2/Si substrates. Films of size up to several mm's have been synthesized. Structural characterizations by atomic force microscopy (AFM), scanning tunneling microscopy (STM), cross-sectional transmission electron microscopy (XTEM) and Raman spectroscopy confirm that such large scale graphitic thin films (GTF) contain both thick graphite regions and thin regions of few layer graphene. The films also contain many wrinkles, with sharply-bent tips and dislocations revealed by XTEM, yielding insights on the growth and buckling processes of the GTF. Measurements on mm-scale back-gated transistor devices fabricated from the transferred GTF show ambipolar field effect with resistance modulation ~50% and carrier mobilities reaching ~2000 cm^2/Vs. We also demonstrate quantum transport of carriers with phase coherence length over 0.2 $\mu$m from the observation of 2D weak localization in low temperature magneto-transport measurements. Our results show that despite the non-uniformity and surface roughness, such large-scale, flexible thin films can have electronic properties promising for device applications.Comment: This version (as published) contains additional data, such as cross sectional TEM image