An efficient three-step sequence to afford a valuable class of spirocyclic pyrrolidines is reported. A reductive cleavage/Horner-Wadsworth-Emmons cascade facilitates the spirocyclisation of a range of isoxazolines bearing a distal beta-ketophosphonate. The spirocyclisation precursors are elaborated in a facile and modular fashion,viaa [3 + 2]-cycloaddition followed by the condensation of a phosphonate ester, introducing multiple points of divergence. The synthetic utility of this protocol has been demonstrated in the synthesis of a broad family of 1-azaspiro[4,4]nonanes and in a concise formal synthesis of the natural product (+/-)-cephalotaxine.

Bombardment damage produced by Si+ ions in AlxGa1_xAs/GaAs layer structures has been studied using transmission electron microscopy and ion channeling and backscattering spectrometry. The damage resistance of A1xGa1_xAs alloy layers increases with Al concentration. In particular, by comparison of complementary Si+ ion doses yielding similar nuclear displacement densities at 150keV and 2MeV bombardment energies, it is demonstrated for the first time that the local concentration of implanted Si impurity is likely to be a significant factor in controlling lattice damage build-up, especially for the highest Si+ ion implantation doses. It is also shown that, in a manner analogous to A1As, the alloy layers can confer a significant protection from ion damage upon adjacent, epitaxially-bonded narrow zones of crystalline GaAs.

Testicular pain can be a particularly challenging problem to manage in primary care, with potential pitfalls for the unwary. The most important acute diagnosis to consider is testicular torsion, as ischaemia, infarction and subsequent loss of function can occur within a few hours of onset. This article considers a range of different conditions that may present with testicular pain, sometimes with other accompanying symptoms. An accurate history is important in assessing testicular pain, and GPs should be aware of the perceived embarrassing nature of testicular symptoms. Examination skills are essential when considering the different causes of testicular pain. This article describes how to assess patients presenting with testicular pain in primary care, the different conditions causing testicular pain and when to refer to secondary care.

In the past two decades, alkene metathesis has risen in prominence to become a significant synthetic strategy for alkene formation. Many total syntheses of natural products have used this transformation. We review the use, from 2003 to 2015, of ring-closing alkene metathesis (RCM) for the generation of dihydrofurans or -pyrans in natural product synthesis. The strategies used to assemble the RCM precursors and the subsequent use of the newly formed unsaturation will also be highlighted and placed in context.

[57] ABSTRACT Many prior art bistable optical devices require resonant optical cavities and are therefore limited in their opera tion due to the long lifetimes associated with their high fmesse cavities. A bistable optical device that does not use a resonant cavity is disclosed wherein a nonlinear medium whose index of refraction increases with in creased light intensity is arranged to have input and output faces into which and out of which a laser beam having a nonuniform spatial pro?le can be propagated. A mirror having a predetermined area of reflectivity is positioned with respect to the output face of a nonlinear medium so as to re?ect only the light energy that propa gates in an area at the output face that is approximately equal to the area which the beam presents at this face when the beam is propagating at a critical power level, that is, when the beam is self-trapped.

Infrared transmittance and hemispherical-directional reflectance data from 2.5 to 25 microm on microstructured silicon surfaces have been measured, and spectral emissivity has been calculated for this wavelength range. Hemispherical-total emissivity is calculated for the samples and found to be 0.84 before a measurement-induced annealing and 0.65 after the measurement for the sulfur-doped sample. Secondary samples lack a measurement-induced anneal, and reasons for this discrepancy are presented. Emissivity numbers are plotted and compared with a silicon substrate, and Aeroglaze Z306 black paint. Use of microstructured silicon as a blackbody or microbolometer surface is modeled and presented, respectively.

We report on z-scan characterization of the two-photon absorption properties of crystalline potassium niobate at 430 nm. The value of the two-photon absorption coefficient was found to be similar to 4.3 cm/GW. Furthermore, we demonstrate efficient (> 60%) noncritically-phase-matched second harmonic generation at 430 nm with subpicosecond pump pulses.[GRAPHICS]High pulse energy SH generation. Connection lines are a guide for the eye only(C) 2009 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA

Laser beam shaping is an important subject in industrial and medical applications of lasers since different applications may require different laser intensity distributions. Recently we demonstrated successfully an all-fiber laser beam shaping device that could transform a Gaussian shaped laser beam into a uniform or ring-shaped beam in 1.5 mu m wavelength region. In this paper we present the work of the beam shaping in 1.0 mu m wavelength region to make it compatible to Yb-doped high power fiber laser. The device uses a long-period grating to couple a portion of core-mode, LP01 into a low-order m(th)-radial cladding mode LP0m. Interference of the two modes could reduce field at the centre and enhance the field in the first or second ring of the cladding mode to transform the Gaussian-shaped laser beam to an intensity uniform beam. The design parameters that affect the beam shaping will be discussed and the results of the interference from two cladding modes, LP03 and LP04 will be presented.

We report transient absorption saturation measurements on lead sulfide colloidal nanocrystals at the first and second exciton energies and fit the results to a model incorporating intraband and interband relaxation processes. We study in detail the Auger recombination from the first excited state, which takes place when more than one electron-hole pair is excited in a dot. We find an Auger coefficient of 4.5 x 10(-30) cm6/s for dots of 5.5 nm diameter, and observe saturation of the absorption bleaching when the (8-fold degenerate) first level is filled. We develop a model for the absorption dynamics using Poisson statistics and find a good fit with our experimental measurements.

In this paper we present a simple and novel method to maximize on-axis coupling efficiency to radially symmetric fibers without the need for extra free space optical elements. The method is based on inserting a segment of step-index multimode fiber (MMF), cleaved to a particular length, between the input fiber and the output fiber (OF). The MMF segment modifies the input field to match the guided modes in the OF. Using this technique we show that, by inserting an appropriate length MMF segment, it is theoretically possible to obtain a coupling coefficient as high as −0.8 dB between a single mode fiber and a graded index ring-shaped fiber and −0.32 dB for a multi-shell fiber. Our experimental measurements showed good agreement with theoretical predictions for the ring fiber.

We report time-resolved measurements of the linewidth enhancement factors (-factors) , and , associated with the adiabatic carrier recovery, carrier heating, and two-photon absorption dynamical processes, respectively, in semiconductor optical amplifiers (SOAs) with different degrees of dimensionality-one InAs/InGaAsP/InP quantum dot (0-D), one InAs/InAlGaAs/InP quantum dash (1-D), and a matching InGaAsP/InGaAsP/InP quantum well (2-D)-all operating near 1.55- wavelengths. We find the lowest values in the QD SOA, 2-10, compared to 8-16 in the QW, and values of and that are also lower than in the QW. In the QD SOA, the -factors exhibit little wavelength dependence over the gain bandwidth, promising for wide-bandwidth all-optical applications. We also find significant differences in the -factors of lasers with the same structure, due to the differences between gain changes that are induced optically or through the electrical bias. For the lasers we find the QW structure instead has the lower -factor, having implications for directly modulated laser applications.

A 10-Gb/s transmission experiment has been performed on multishell multimode fiber Bragg gratings. The device can simultaneously serve as wavelength filter and mode selector and is compatible with conventional graded refractive index multimode fiber (MMF) components. This could be a promising technology for wavelength-division multiplexing and mode diversity in practical MMF-based optical access networks.

We demonstrate a simple all-fiber device that can transform a Gaussian-shaped laser beam into a uniform intensity beam. The device is based on the interaction of a core mode and a cladding mode partially coupled out by a long-period grating. We have achieved good beam uniformity (<4% intensity variation) and reduced beam divergence (1.5deg of half divergence angle) while keeping the insertion loss to 0.1 dB. The measured beam uniformity matches well with simulated results. The device can also change the beam shape from a Gaussian to a donut, to top hat, and back to a Gaussian, dynamically by tuning the laser wavelength.

Demonstrated is 40 Gbit/s multiple-fibre-channel wavelength conversion using a passive ultrafast reflective switch, and a 2D Fresnel lens array aligned to a fibre array. Input pulses of 1-2 ps duration and 0.3 nJ energy are wavelength converted to multiple channels with a tunable wavelength range of 20 nm and an extinction ratio better than 6 dB. Simultaneous 1-to-N conversion is also demonstrated...

We measure linear and quadratic dispersion parameters (beta 1 and beta 2 ) on a 6-mm twin- hole fiber using a single-arm interferometric technique. Furthermore, beta 0 is extracted from the measured beta 1 and beta 2 through an optimization algorithm.

We present a simple fiber-based single-arm spectral interferometer to measure directly the second-order dispersion parameter of short lengths of fiber (< 50 cm). The standard deviation of the measured dispersion on a 39.5-cm-long SMF28(TM) fiber is 1x10(-4) ps/nm, corresponding to 1% relative error, without employing any curve fitting. Our technique measures the second-order dispersion by examining the envelope of the interference pattern produced by three reflections: two from the facets of the test fiber and one from a mirror placed away from the fiber facet at a distance that introduces the same group delay as the test fiber at the measured wavelength. The operational constraints on system parameters, such as required bandwidth, wavelength resolution, and fiber length, are discussed in detail. Experimental verification of this technique is carried out via comparison of measurements of single mode fiber (SMF28(TM)) with published data and via comparison of measurements of a dispersion compensating fiber with those taken using conventional techniques. Moreover, we used this new technique to measure the dispersion coefficient of a 45-cm-long twin-hole fiber over a 70 nm bandwidth. It is the first time dispersion measurement on this specialty fiber is reported.

We measured linear and quadratic dispersion on millimeter-length fibers, waveguides, and nanowires based on common-path spectral interferometry. We obtained the linear dispersion parameter, beta', with a relative precision of 1.45 x 10(-4), and extracted the quadratic dispersion parameter, beta'', from the Taylor expansion of beta' x beta'' values show a discrepancy of < 1% when compared with simulation as well as with measurement results obtained by a conventional Michelson interferometer. Using this method, we experimentally confirmed the sign inversion of the group velocity dispersion of AlGaAs nanowires for what is believed to be the first time.

We assess the influence of the degree of quantum confinement on the carrier recovery times in semiconductor optical amplifiers (SOAs) through an experimental comparative study of three amplifiers, one InAs-InGaAsP-InP quantum dot (0-D), one InAs-InAlGaAs-InP quantum dash (1-D), and one InGaAsP-In-GaAsP-InP quantum well (2-D), all of which operate near 1.55-mum wavelengths. The short-lived (around ...

We compare the alpha-factor of a QD amplifier operating at 1.55 mum to a quantum dash and quantum well amplifier at 1.55 mum. The QD has the lowest alpha-factor with a minimum alpha of 1.

There are no requirements in the selection process for inclusion of specific topical areas. When a large number of submissions are received for a specific area, this is taken as evidence that the topic has been fertile ground for activity and research over the course of the preceding year. OPN strives to ensure that engineering, science, and technology are all represented. The number of papers accepted overall is limited by space. With 33 papers accepted, 2000 has proven to be another successful year. OPN and OSA would like to thank the hundreds of researchers from all over the world who submitted summaries to Optics in 2000.