In the wake of the erbium-doped fiber amplifier - functional fibers and their impact

There have been a number of laser developments in recent years that are quite staggering in their simplicity, that are so powerful in their operation that engineers and scientist have to rethink the laser future. One such is the high power fibre laser, born out of the optical telecoms revolution. It challenges currently held views on how to make things, how to repair things, and how to destroy things. With small size, maintenance-free operation, high thermal and electrical efficiency and outstanding beam quality, it has the potential to change every industry and discipline it encounters

Fibre lasers: the new wave in material processing

In the last few years, fibre lasers have established themselves as the preferred laser source in many applications. The combination of small size, maintenance-free operation, thermal and electrical efficiency combined with outstanding (diffraction-limited) beam quality have made the fibre laser an attractive alternative to more established technologies. In fact, in some processes the fiber laser is the enabling technology. Unique among high power lasers, the fiber laser is monolithic, the light being entirely confined to the fiber core. This gives immunity to thermal distortion of the beam, almost instant startup, very high stability and protection from the environment. Maintenance is minimal, since no realignment or cleaning of components is necessary

Multi-kilowatt single-mode ytterbium-doped large-core fiber laser

We have demonstrated a highly efficient cladding-pumped ytterbium-doped fiber laser, generating >2.1 kW of continuous-wave output power at 1.1 µm with 74% slope efficiency with respect to launched pump power. The beam quality factor (M2) was better than 1.2. The maximum output power was only limited by available pump power, showing no evidence of roll-over even at the highest output power. We present data on how the beam quality depends on the fiber parameter, based on our current and past fiber laser developments. We also discuss the ultimate power-capability of our fiber in terms of thermal management, Raman nonlinear scattering, and material damage, and estimate it to 10 k

Propagation characteristics of guided waves in stratified metallic optical waveguides

An eigenvalue equation is derived for stratified metallic optical slab waveguides with any number of layers. The equation is solved using the numerical zoom analysis (NZA) method. The analysis is applied to various metallic optical slabs and the propagation characteristics of the guided waves are determined, which may be useful for optimizing the design parameters. It is found possible, with proper optimization, to design a polarizer having hundreds of decibels of extinction ratio at the cost of a fraction of a decibel of insertion loss. Examples of optimizations with respect to wavelength, relative refractive indices, core/clad geometries, etc. are demonstrated for slabs with single or double metal layers. Guidelines for determining the metal film thickness have been formulated and tabulated for many useful metals

Ensemble density-functional theory for ab-initio molecular dynamics of metals and finite-temperature insulators

A new method is presented for performing first-principles molecular-dynamics simulations of systems with variable occupancies. We adopt a matrix representation for the one-particle statistical operator Gamma, to introduce a ``projected'' free energy functional G that depends on the Kohn-Sham orbitals only and that is invariant under their unitary transformations. The Liouville equation [ Gamma , H ] = 0 is always satisfied, guaranteeing a very efficient and stable variational minimization algorithm that can be extended to non-conventional entropic formulations or fictitious thermal distributions.Comment: 5 pages, two-column style with 2 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#nm_meta

Highly efficient L-band fibre-DFB lasers

A more than 12mW highly efficient fibre-DFB laser operating at 1618.3nm is fabricated and characterised. Its high-power, low-noise and single-polarisation characteristics make it very suitable WDM-source for L-band transmission

Kepler-432: a red giant interacting with one of its two long period giant planets

We report the discovery of Kepler-432b, a giant planet ($M_b = 5.41^{+0.32}_{-0.18} M_{\rm Jup}, R_b = 1.145^{+0.036}_{-0.039} R_{\rm Jup}$) transiting an evolved star $(M_\star = 1.32^{+0.10}_{-0.07} M_\odot, R_\star = 4.06^{+0.12}_{-0.08} R_\odot)$ with an orbital period of $P_b = 52.501129^{+0.000067}_{-0.000053}$ days. Radial velocities (RVs) reveal that Kepler-432b orbits its parent star with an eccentricity of $e = 0.5134^{+0.0098}_{-0.0089}$, which we also measure independently with asterodensity profiling (AP; $e=0.507^{+0.039}_{-0.114}$), thereby confirming the validity of AP on this particular evolved star. The well-determined planetary properties and unusually large mass also make this planet an important benchmark for theoretical models of super-Jupiter formation. Long-term RV monitoring detected the presence of a non-transiting outer planet (Kepler-432c; $M_c \sin{i_c} = 2.43^{+0.22}_{-0.24} M_{\rm Jup}, P_c = 406.2^{+3.9}_{-2.5}$ days), and adaptive optics imaging revealed a nearby (0\farcs87), faint companion (Kepler-432B) that is a physically bound M dwarf. The host star exhibits high signal-to-noise asteroseismic oscillations, which enable precise measurements of the stellar mass, radius and age. Analysis of the rotational splitting of the oscillation modes additionally reveals the stellar spin axis to be nearly edge-on, which suggests that the stellar spin is likely well-aligned with the orbit of the transiting planet. Despite its long period, the obliquity of the 52.5-day orbit may have been shaped by star-planet interaction in a manner similar to hot Jupiter systems, and we present observational and theoretical evidence to support this scenario. Finally, as a short-period outlier among giant planets orbiting giant stars, study of Kepler-432b may help explain the distribution of massive planets orbiting giant stars interior to 1 AU.Comment: 22 pages, 19 figures, 5 tables. Accepted to ApJ on Jan 24, 2015 (submitted Nov 11, 2014). Updated with minor changes to match published versio

Disentangling Blended K2 Photometry: Determining the Planetary Host Star

The presence of companion stars, whether bound or unbound, make correct identification of the planetary hosting star difficult when a planet has been detected through a photometrically blended transiting event. We present an approach that uses a combination of light curve analysis and stellar modeling to disentangle eight K2 photometrically blended binary systems that have either a confirmed or suspected planet to identify the probable host star. The key to our approach is the use of the mean stellar density, calculated using the transit geometry, as a discriminator. The approach is strongly dependent on the difference in magnitude between the stars and the observed transit depth, which is corrected by the flux ratio between the two stars. While our approach does not lead to a definitive result for all systems, we were able to determine the following for the eight systems in this case study: there are two systems where the primary was highly likely to be the planet-hosting star (>90% likelihood); three systems where the primary was likely to be the hosting star (>55% likelihood); one system where the secondary was likely to be the planet-hosting star (>55% likelihood); and two systems where we were uncertain which star was the planet-hosting star (≈50% likelihood to be either the primary or the secondary). Two systems, denoted by their EPIC number, EPIC 201546283 and EPIC 201862715, had confirmed planets, K2-27b and K2-94b, respectively, with radii of 4.0 ± 0.1 and 16.4 ± 2.9 R⊕, respectively

Effects of methylphenidate on cognition and behaviour in children with neurofibromatosis type 1:a study protocol for a randomised placebo-controlled crossover trial

INTRODUCTION: Dopamine dysregulation has been identified as a key modulator of behavioural impairment in neurofibromatosis type 1 (NF1) and a potential therapeutic target. Preclinical research demonstrates reduced dopamine in the brains of genetically engineered NF1 mouse strains is associated with reduced spatial-learning and attentional dysfunction. Methylphenidate, a stimulant medication that increases dopaminergic and noradrenergic neurotransmission, rescued the behavioural and dopamine abnormalities. Although preliminary clinical trials have demonstrated that methylphenidate is effective in treating attention deficit hyperactivity disorder (ADHD) symptoms in children with NF1, its therapeutic effect on cognitive performance is unclear. The primary aim of this clinical trial is to assess the efficacy of methylphenidate for reducing attention deficits, spatial working memory impairments and ADHD symptoms in children with NF1.METHODS AND ANALYSIS: A randomised, double-blind, placebo-controlled trial of methylphenidate with a two period crossover design. Thirty-six participants with NF1 aged 7-16 years will be randomised to one of two treatment sequences: 6 weeks of methylphenidate followed by 6 weeks of placebo or; 6 weeks of placebo followed by 6 weeks of methylphenidate. Neurocognitive and behavioural outcomes as well as neuroimaging measures will be completed at baseline and repeated at the end of each treatment condition (week 6, week 12). Primary outcome measures are omission errors on the Conners Continuous Performance Test-II (attention), between-search errors on the Spatial Working Memory task from the Cambridge Neuropsychological Test Automated Battery (spatial working memory) and the Inattentive and Hyperactivity/Impulsivity Symptom Scales on the Conners 3-Parent. Secondary outcomes will examine the effect of methylphenidate on executive functions, attention, visuospatial skills, behaviour, fine-motor skills, language, social skills and quality of life.ETHICS AND DISSEMINATION: This trial has hospital ethics approval and the results will be disseminated through peer-reviewed publications and international conferences.TRIAL REGISTRATION NUMBER: ACTRN12611000765921.</p