Solid-state autocatalysis and oscillatory reactions in silicate glass systems

We report the first demonstration of autocatalysis and oscillatory behaviour in the solid-state where no decomposition process is involved. Our material system is solid-state silica glass impregnated with hydrogen. It is at the heart of photosensitivity in glass-based optical waveguides and devices, which have many applications including telecommunication devices, fibre lasers, and optical sensors. Consequently, the results reported here extend the engineering of chemical complexity to a previously uncharted area in materials science of particular relevance to photonic applications. Diagnosis is carried out optically, opening up a new approach to characterisation of such catalytic processes generally.     

The reflection-absorption infrared spectrum of the dioxygen species adsorbed on platinum recorded by FT-IR spectroscopy

The reflection-absorption infrared spectrum of oxygen adsorbed on a recrystallized Pt foil at 80K shows a single band at 875 cm^?1 at saturation coverage. The spectrum produced by an equilibrated mixture of oxygen isotopes confirms that the adsorbate is molecular. The apparent effective charge, e*, calculated from the RAIR spectrum is in good agreement with that calculated from the electron energy loss (EEL) spectrum reported previously. The coverage dependent frequency shift can be accounted for by dipole-dipole coupling. The large inherent bandwidth is probably due to enhanced vibrational relaxation via electron-hole pair formation.     

Thermal regenerated type IIa fiber Bragg gratings for ultra-high temperature operation

Thermally regenerated fiber Bragg gratings written in photosensitive fibers with nanosecond laser pulses without hydrogen loading have been shown to become temperature stable up to 600 °C. In this paper, we give an experimental analysis of the refractive index development for fabricating the gratings and for the thermal regeneration process. Furthermore, we identify a thermal induced type IIa (type In) behavior of the refractive index to be responsible for the regeneration. The variation of refractive index modulation and the average index in the grating region is discussed. With additional annealing it is possible to improve the temperature stability beyond 1000 °C.     

Sensitivity enhancement of fiber Bragg gratings to transverse stress by using microstructural fibers

We present simulation and experimental results of fiber Bragg grating responses to transverse stress in microstructure fibers. The grating wavelength shifts and peak splits are studied as a function of external load and fiber orientation. Both simulation and measurement results indicate that the sensitivity of grating sensors to the transverse stress can be enhanced by a factor of eight in a two-hole fiber over that in a standard fiber.     

Photo-induced densification in Er<Superscript>3+</Superscript>/Al doped silica preform plates using 193-nm laser light

The growth rate of Bragg gratings written using 193-nm light from an ArF excimer laser is shown to be non-linear with the pulse energy density for Er³⁺ co-doped Al silica. This yields a refractive-index increase up to a few 10⁻³. We then use phase-shift interferometry to measure the sample surface topography following exposure. Subsequently, we formulate an inhomogeneous stress model to analyse the observed change of volume within the core material. Below pulse energies of 550 mJ/cm², the results show that refractive-index changes are primarily due to a densification process. At higher pulse energies material re-expansion occurs.     

Lattice gauge theories and motion in group space

We extend the SU(2) lattice gauge theory of Kogut and Susskind to a general non-Abelian gauge group. At the Lagrangian level, we find the theory to be related to the motion of a point in group space. We then quantise such a system using the natural geometric structure of group parameter space, and we apply our results to find the Hamiltonian for the general lattice gauge theory. We also discuss the large N behaviour of the theory.     

Correlation of ultraviolet-induced stress changes and negative index growth in type IIa germanosilicate waveguide gratings

The stress anisotropy in planar germanosilicate waveguides is used to follow the changes in stress, measured as a birefringence, with UV irradiation. Compressive stress increases with the growth of the negative index grating, saturating when the grating modulation saturates.     

355-nm hypersensitization of optical fibers

The intrinsic 244-nm photosensitivity of boron-codoped germanosilicate optical fibers is enhanced by 355-nm hypersensitization. Hypersensitization through standard polymer coating is also demonstrated.     

Using simulation modelling for evaluating screening services for diabetic retinopathy

In using discrete event simulation for planning services in the health sector, epidemiologists and clinicians were closely involved in model design, data collection, analysis, validation and experimentation. For patients with diabetes, loss of sight can be prevented by timely treatment if detected sufficiently early. Simulation models, using the patient oriented simulation technique, POST, have been developed to assist policy makers in the choice of screening strategy in terms of operator, equipment, frequency of screening and target population. The models describe the progress of a population of diabetic patients, including new arrivals, over 25 years. The initial population were given characteristics retrospectively and the parameters were derived from peer reviewed publications. The results from the models show that the interval between screening is more important than screening sensitivity. The simulation can determine the expected workload and the amount of vision loss prevented for any population group.