A inteligibilidade da palavra em igrejas católicas, através de análises de carácter objectivo e subjectivo
Lencastre, Margarida Maria Mendes de Freitas de Queiroz e
1988-01-01
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223 records were found.
Fibre gratings can be written through the primary fibre coating using conventional UV exposure techniques. This leads to superior strength and yield and improved case of manufacturing.
Photorefractive fibre gratings are devices that are rapidly being taken up by the telecommunications and fibre sensor industries due to their wide range of uses. They can be thought of as one-dimensional holograms written directly into the core of a conventional optical fibre which have the capability of reflecting light of a specific wavelength back along the fibre. Like holograms, they are essentially permanent and are written using specialised lasers. They rely on the fact that the refractive index of the germania-doped silica fibre core can be changed by exposure to intense ultraviolet (UV) light, however the exact nature of the photorefractive change is not yet fully understood. In general, it is possible to produce an absolute refractive index change of 10−6 - 10−3 in most fibres, though it is necessary to use specially designed ...
Fibre Bragg gratings have been written through the fibre coating using a 248nm excimer laser for the first time. A standard off-the-shelf coating was used, and 92% reflectivity gratings were obtained with an index change of 2.4x10
Rare-earth-doped fibre lasers and amplifiers have been demonstrated at several wavelengths in the visible and near infrared regions. We describe recent advances in the field with particular attention to applications in telecommunications
Rare-earth doped single-mode fibre lasers and amplifiers will form the basis of all-fibre optical circuits. Recent advances in the field and some possible applications will be described.
We report the demonstration of waveguide lasers in lithium niobate into which the active element neodymium has been introduced by thermal diffusion. The waveguides were fabricated using conventional Ti indiffusion, and optical feedback was provided by the polished endfaces alone. The absorbed power threshold of one waveguide laser was estimated at 13±3 mW for pumping at 814 nm, and its slope efficiency in terms of total lasing output as a function of absorbed pump power was estimated to be 55±8%. Laser output powers in excess of 100 mW were observed.
We report the demonstration of waveguide lasers in LiNbO3 into which neodymium has been diffused. Optical feedback from the polished endfaces alone yielded an absorbed power threshold of 13±3 mW, and a slope efficiency of 55±8%.
