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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246 records were found.
In recent years, ultra-violet laser direct writing has been recognized as a technique that provides a powerful way of creating integrated optical devices. We will describe the developments in this field, concentrating on the use of two-beam writing to create Bragg gratings in planar integrated format. In this paper we will show how our UV writing technique can be used to fabricate structures required in a wide range of applications, from the creation of wide-band couplers, through to highly sensitive integrated sensor devices. The direct computer control in UV direct writing removes many of the constraints that normally limit planar integrated optics. In particular, it dispenses with the photolithography and etching steps traditionally required to make low-loss waveguide devices. The work reported will show how this flexibility of UV w...
Nonlinear conversion of diode based sources using MgO doped PPLN provides a viable route to watt level power visible laser wavelength systems with high electrical efficiency and offer a low cost solution for applications in laser projection and bio-optics. Recent developments of superior nonlinear materials together with brighter and more powerful diode sources provide an excellent opportunity for optical technology over the coming decade.
We have found that the application of light to strontium barium niobate (SBN) during electrical repoling stabilises the newly formed domains. This stabilisation becomes apparent when repoling the crystal back into its original domain direction as a change in the distribution of displacement current as a function of voltage. This appears to be the process underlying the other recent work in the area of optical control of domain structures for quasi phase-matching of nonlinear processes. We present an explanation for this effect in terms of the micro-domain structure of SBN. This model should aid in the search for new materials for optical periodic poling
We present a theoretical and experimental study of the line shape of resonant four-wave mixing induced by broad-bandwidth laser radiation that revises the theory of Meacher, Smith, Ewart, and Cooper (MSEC) [Phys. Rev. A 46, 2718 (1992)].
We adopt the same method as MSEC but correct for an invalid integral used to average over the distribution of atomic velocities. The revised theory predicts a Voigt line shape composed of a homogeneous, Lorentzian component, defined by the collisional rate Gamma, and an inhomogeneous, Doppler component, which is a squared Gaussian. The width of the inhomogeneous component is reduced by a factor of (root)2 compared to the simple Doppler width predicted by MSEC. In the limit of dominant Doppler broadening, the width of the homogeneous component is predicted to be 4Gamma, whereas in the limit of domi...
We report the first demonstration of a bulk optical Bragg deflector based on an electro-optically induced grating in z-cut periodically poled LiNbO3 (PPLN) operating at a wavelength of at 1.064 micron. Discussions on the reduction of photorefractive damage by control of the grating period are presented.
The performance of a coupler/Bragg grating interferometric OADM is studied theoretically at 40Gb/s. Employment of such filters with typically degraded spectral responses can result in at least 0.15 dB higher Eye-Opening Penalty compared to fully optimized OADMs.
Many solutions exist for making laser modulators including acousto-optic (AO) and bulk electro-optic (EO) devices. However, another class of modulators based on Bragg diffraction in periodically poled materials offers the potential to overcome disadvantages inherent in the more conventional types, such as low efficiency in the infra-red and high drive voltages. These devices are an extension of early work on grating based EO devices, for example those by Hammer [1] and Barros & Wilson [2], but by making use of periodic poling they allow additional design freedom. This in turn allows fast switching, high efficiency and simple construction as demonstrated in periodically poled lithium niobate at 633nm [3, 4].
