639 research outputs found

    Absorption-emission cross-section ratio for Er<sup>3+</sup> doped fibres at 1.5µm

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    The ratio of absorption to emission cross-section is determined for Er3+ doped fibres. This parameter, essential in modelling optical amplifiers, is found to be significantly different from previously published values. Reasons for this are discussed

    Optical control of photon tunneling through an array of nanometer scale cylindrical channels

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    We report first observation of photon tunneling gated by light at a different wavelength in an artificially created array of nanometer scale cylindrical channels in a thick gold film. Polarization properties of gated light provide strong proof of the enhanced nonlinear optical mixing in nanometric channels involved in the process. This suggests the possibility of building a new class of "gated" photon tunneling devices for massive parallel all-optical signal and image processing.Comment: 4 pages, 4 figure

    Scattering mechanism in a step-modulated subwavelength metal slit: a multi-mode multi-reflection analysis

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    In this paper, the scattering/transmission inside a step-modulated subwavelength metal slit is investigated in detail. We firstly investigate the scattering in a junction structure by two types of structural changes. The variation of transmission and reflection coefficients depending on structural parameters are analyzed. Then a multi-mode multi-reflection model based on ray theory is proposed to illustrate the transmission in the step-modulated slit explicitly. The key parts of this model are the multi-mode excitation and the superposition procedure of the scatterings from all possible modes, which represent the interference and energy transfer happened at interfaces. The method we use is an improved modal expansion method (MEM), which is a more practical and efficient version compared with the previous one [Opt. Express 19, 10073 (2011)]. In addition, some commonly used methods, FDTD, scattering matrix method, and improved characteristic impedance method, are compared with MEM to highlight the preciseness of these methods.Comment: 25 pages, 9 figure

    A diode-laser-pumped, Er<sup>3+</sup>-doped fibre laser operating at 1.57µm

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    Erbium-doped fibers show promise as stable narrow-linewidth laser sources and optical amplifiers operating in the third telecommunications window around 1.55µm Diode laser pumping is possible using the weak pump-band located at 807nm, although this band suffers severely from excited-state absorption (ESA), which reduces gain and pump efficiency. At the low pump power available from diode lasers the Er3+ behaves as a quasi four-level system. However, by codoping the core glass heavily with Yb3+, it is possible to excite the Er3+ ions indirectly using energy transfer. The Yb3+ provides an intense broad pump-band centered at 900nm, which reduces the effect of ESA. As a consequence of the resulting higher pump efficiency, the laser will oscillate at the required shorter wavelengths

    Classical Cepheids: Yet another version of the Baade-Becker-Wesselink method

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    We propose a new version of the Baade--Becker--Wesselink technique, which allows one to independently determine the colour excess and the intrinsic colour of a radially pulsating star, in addition to its radius, luminosity, and distance. It is considered to be a generalization of the Balona approach. The method also allows the function F(CI) = BC + 10 log (Teff) for the class of pulsating stars considered to be calibrated. We apply this technique to a number of classical Cepheids with very accurate light and radial-velocity curves and with bona fide membership in open clusters (SZ Tau, CF Cas, U Sgr, DL Cas, GY Sge), and find the results to agree well with the reddening estimates of the host open clusters. The new technique can also be applied to other pulsating variables, e.g. RR Lyrae and RV Tauri.Comment: 6 pages, 2 figures, 1 table; Submitted to Astrophysical Bulletin, 201

    Engineering the Photonic Density of States with metamaterials

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    The photonic density of states (PDOS), like its' electronic coun- terpart, is one of the key physical quantities governing a variety of phenom- ena and hence PDOS manipulation is the route to new photonic devices. The PDOS is conventionally altered by exploiting the resonance within a device such as a microcavity or a bandgap structure like a photonic crystal. Here we show that nanostructured metamaterials with hyperbolic dispersion can dramatically enhance the photonic density of states paving the way for metamaterial based PDOS engineering

    +21dBm erbium power amplifier pumped by a diode-pumped Nd:YAG laser

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    Efficient energy transfer has been demonstrated in an Er/Yb co-doped phosphorus doped silica fiber for the first time. This has indirectly allowed the use of reliable, high-power AlGaAs diode laser arrays as the semiconductor pump source through the use of a diode-pumped Nd:YAG (DPL) laser operating at 1064 nm. Small signal gains of 42 dB and output powers of 71 mW (+18.5 dBm) have been observed with a single DPL. Bidirectional pumping with two DPLs has yielded an output power of 130 mW (+21 dBm)

    Young and Intermediate-age Distance Indicators

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    Distance measurements beyond geometrical and semi-geometrical methods, rely mainly on standard candles. As the name suggests, these objects have known luminosities by virtue of their intrinsic proprieties and play a major role in our understanding of modern cosmology. The main caveats associated with standard candles are their absolute calibration, contamination of the sample from other sources and systematic uncertainties. The absolute calibration mainly depends on their chemical composition and age. To understand the impact of these effects on the distance scale, it is essential to develop methods based on different sample of standard candles. Here we review the fundamental properties of young and intermediate-age distance indicators such as Cepheids, Mira variables and Red Clump stars and the recent developments in their application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in Space Science Reviews (Chapter 3 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age

    Analytical solutions to zeroth-order dispersion relations of a cylindrical metallic nanowire

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    Zeroth-order complex dispersion relations of a cylindrical metallic nanowire have been solved out analytically with approximate methods. The analytical solutions are valid for the sections of the dispersion relations whose frequencies are close to the Surface Plasmon frequency. The back bending of the Surface Plasmon-Polaritons(SPPs) can be well described by the analytical solutions, confirming that the back bending is originated from the metal Ohmic loss. The utility of the back bending point in the dispersion relation for the measurement of the metallic Ohimc loss has also been suggested.Comment: 6pages, 3figure

    Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits

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    The WWgamma triple gauge boson coupling parameters are studied using p-pbar -> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were collected with the DO detector from an integrated luminosity of 162 pb^{-1} delivered by the Fermilab Tevatron Collider. The cross section times branching fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum) pb. The one-dimensional 95% confidence level limits on anomalous couplings are -0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.Comment: Submitted to Phys. Rev. D Rapid Communication
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