Report on geophysical and geological surveys at Blackmount, Argyllshire

Blackmount, on the southern fringe of Rannoch Moor is largely drift covered but, where exposed, the underlying Precambrian Moine psammite contains granitic veins which probably stem from the adjacent (Devonian) Moor of Rannoch granite. These veins are generally pyritiferous and, at one locality, carry small amounts of molybdenite. Blackmount is also traversed by the Ericht-Laidon Fault, which, in theory, and by analogy with a similar fault to the south-east (the Tyndrum Fault), could be a site of significant sulphide mineralisation. Magnetic, very low frequency electro-magnetic (VLF EM), slingram EM and induced polarisation measurements carried out in the area of the veins suggest that the mineralisation has little or no lateral or depth continuation. Similar surveys were successful in locating the Ericht-Laidon Fault beneath drift, but suggest no associated mineralisation down to the\ud greatest depth investigated

Representativeness of samples from general practice lists in epidemiological studies: case-control study

Ethical constraints often prevent epidemiological studies from evaluating the impact of non-participation. Particular problems may arise when subjects fail to respond to an approach by researchers or when they cannot be contacted because of inaccurate contact details or a doctor's refusal to give permission for their patient to be approached. If these subjects differ from those subjects who agree or decline to participate then the validity and generalisability of the study may be compromised. We investigated these issues in a case-control study of acute leukaemia in England

Planar micromachined glass cantilevers utilising integrated Bragg Fabry-Perot cavities

Here we demonstrate a glass cantilever based on a unique micromachining and etching approach, combined with UV written Bragg gratings. We shall also discuss the increase in sensitivity by using two Bragg gratings to form Fabry-Pérot cavity. Cantilevers are in ultra sensitive force sensors used in applications such as Atomic Force Microscopy, mass sensing and acoustic transducers

Lateral groove geometry for planar UV written evanescent devices - new flexibility new devices

Conventional evanescent optical devices have made use of etched windows to allow access of an optical field to a material of interest. Such devices are a route to accurate refractive index sensors and to realising modulators, however, the geometry of etching the cladding to give the fluid access to a pre-defined core waveguide mode is limiting. In this work, we present an alternative approach in which a groove is cut using a polishing saw blade to give a vertical, high optical quality trench. Optical waveguides are then UV written to allow evanescent lateral access of the mode to a fluid placed in the trench. This seemingly subtle change in geometry provides greatly increased flexibility to tailor the interaction between the optical mode and the surrounding material, by, for example, changing the mode size and the allowing couplers or tapers to be used

New geometry for planar UV written refractive index sensors

We shall present some of our recent results from our work on UV written planar waveguide refractive index sensors. Refractive index of an analyte is measured through the perturbation of an optical mode, interrogation of the modal index is achieved via the reflected spectra from a Bragg grating defined in the same process as the channel waveguide. Here we introduce a new geometry which embraces the benefits of planar technology to realise new integrated devices. The geometry allows several different sensors to be defined on the same substrate each offering complementary information. Such information may include index as a function of penetration depth for surface binding analytes, interrogation wavelength for dispersion analysis, enhanced sensitivity in specific index ranges and temperature compensation. We shall also outline the inherent fabrication advantages and device feature benefits, including a reduction in return loss, spectral artefacts and a suggested reduction in stress induced birefringence. The silica sensing surface opposed to gold used in SPR devices opens new avenues to exploit surface binding. With a marked reduction in complexity and cost these devices may have significant impact in future sensor markets

Anisotropic focusing characteristics of micro-domain structures within crystalline Sr_0.61Ba_0.39Nb₂O₆ : the crystal ball

We report the anisotropic focusing characteristics of a spherically configured region of micro-domains that have been induced within a cubic shaped crystal of Ce:doped Sr0.61Ba0.39Nb2O6. The internal spherical structure focuses extraordinary polarised light, but not ordinary polarised. The spherical region, which is easily observed via scattering, is formed as the crystal cools down, after a repoling cycle through the Curie temperature, with an applied field. Analytic modelling of the thermal gradients that exist within the crystal during cooling reveals a small (< 1°) temperature difference between the central and outside regions. The similarity in shape between these temperature profiles and the observed scattering region suggests a possible mechanism for the growth of this spherical micro-domained structure

Gouy phase compensation in quasi-phase matching

In any focussed nonlinear interaction the focus induced phase shift, known as the Gouy phase shift, provides an imperfection in phase matching for any linearly invariant material. However, using an appropriately designed quasi-phase matched structure it is theoretically possible to compensate for the deleterious effects of the Gouy phase shift, allowing a symmetric frequency response and tighter optimal focussing than in a uniform material

Flat-top temperature tuning response in periodically-poled nonlinear crystals

Second harmonic generation via periodically-poled nonlinear materials offers an efficient means of generating high-quality visible light that would be otherwise unattainable with traditional laser sources. While this technology has the potential for implementation in many mass-industrial applications, temperature stability requirements of 0.1 deg.C can make packaging with a pump source problematic. Using our high fidelity poling technique we have achieved precise placement of poled domains in Lithium Niobate based on the resulting mathematical models. These initial devices provide more than 4 deg.C flat-top temperature stability, albeit with a corresponding loss in operational efficiency. Our aim is to implement improved designs in magnesium-doped Lithium Niobate for packaging with near-room temperature diode-based pump sources, as could be applied towards RGB TV and projector applications