Intensity profile in a distributed feedback fibre laser characterised by a green fluorescence scanning technique

We report on an experimental technique for investigating the intensity profile in distributed feedback fibre lasers. By scanning along the laser length and monitoring the side green fluorescence, the intensity distribution in the laser can be inferred. With this approach, we experimentally verify the sharply peaked intensity distribution predicted for lambda/4 phase-shifted distributed feedback lasers

High performance optical fibre polarisers based on long period gratings in birefringent optical fibres

We have demonstrated the feasibility of achieving high performance fibre polarisers (insertion loss 30 dB), based on polarisation mode dispersion in a long period grating. Chirped operation with 100 nm bandwidth has also been achieved, showing the possibility of a broadband device

1.2dB/cm gain in an erbium:lutecium co-doped Al/P silica fibre

We report a peak gain of 1.2dB/cm at 1535nm in an Erbium:Lutecium codoped Al/P/Si fibre fabricated using a standard MCVD and solution doping technique. This is the highest gain per unit length yet reported in an erbium doped fiber amplifier. The incorporation of lutetium into the glass is shown to reduce the erbium ion clustering within the fiber

Non-photorefractive cw Tm-indiffused Ti:LiNbO₃ waveguide laser operating at room temperature

We report laser operation at 1.81µm and 1.85µm in a Tm3+:LiNbO3 Ti-diffused waveguide doped by thermal indiffusion at high temperature. We believe this is the first time lasing has been seen in Tm:LiNbO3 at room temperature. Continuous-wave operation was achieved at room temperature with a threshold of ~42 mW absorbed power. The output power was observed to be stable, without any sign of photorefractive damage

Spectra and energy levels of the trivalent ytterbium ion doped into lithium niobate by thermal indiffusion

An x-cut LiNbO3 substrate has been doped with Yb3+ ions by thermal diffusion from an Yb metal film of thickness 7nm. Polarised absorption and fluorescence spectra of the dopant ion have been measured using Ti-diffused y-propagating channel waveguides prepared in the doped region. Yb is a diode- pumpable laser ion with characteristics which can be compared favourably with those of Nd in some respects; for example the small energy difference between pump and laser photons reduces thermal load facilitating high power operation. A waveguide laser geometry is particularly advantageous for Yb due to the quasi-3-level nature of the laser transition. The simple fabrication technique described here has been used to produce a system which may have the potential to operate as an Yb waveguide laser in an electro-optic host crystal

Thermally indiffused Tm³⁺:LiNbO₃ waveguide lasers

Rare earth doped LiNbO3 is an interesting laser host as it has nonlinear, electro-optic and acousto-optic properties. Low-loss waveguides can also be made in this material and then combined with thermal indiffusion of the laser dopant. LiNbO3 can also be periodically poled for quasi-phase matching and/or reduced photorefraction. We report the first room temperature lasing of Tm3+:LiNbO3, and the first periodically poled Ti waveguides formed by electric field poling. Lasing was observed at 1.85µm in a Ti-indiffused waveguide with rare earth doping performed by thermal indiffusion

Cold atoms in space: community workshop summary and proposed road-map

We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies.publishedVersio

Multiwavelength observations of a TeV-Flare from W comae

We report results from an intensive multiwavelength campaign on the intermediate-frequency-peaked BL Lacertae object W Com (z = 0.102) during a strong outburst of very high energy gamma-ray emission in 2008 June. The very high energy gamma-ray signal was detected by VERITAS on 2008 June 7-8 with a flux F(>200 GeV) =(5.7 0.6) × 10-11 cm-2 s -1, about three times brighter than during the discovery of gamma-ray emission from W Com by VERITAS in 2008 March. The initial detection of this flare by VERITAS at energies above 200 GeV was followed by observations in high-energy gamma rays (AGILE; E γ≥ 100 MeV), X-rays (Swift and XMM-Newton), and at UV, and ground-based optical and radio monitoring through the GASP-WEBT consortium and other observatories. Here we describe the multiwavelength data and derive the spectral energy distribution of the source from contemporaneous data taken throughout the flare. © 2009. The American Astronomical Society. All rights reserved