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The work presented in this thesis is derived from experimentation in the field of polymeric photorefractive materials. Low T(_g) polymeric composites were prepared, based on the well-known photoconductive polymer PVK (maximum 50% w/w), sensitized with TNF (2% w/w) and C(_60) (0.2% w/w), plasticized with ECZ (maximum 49.3% w/w) and doped with the nonlinear optical materials NPP (50% w/w), DAN (20% w/w), DED (5% w/w), DCNQI (0.5% w/w), ULTRA-DEMI (5% w/w) and DI-DEMI (2% w/w), and their dielectric, linear and non linear optical properties were investigated. All the materials, except DCNQI, exhibited good solubility and sample processibility. The dielectric properties of the composites at 1 KHz and 1 MHz were determined using a parallel-plate capacitance bridge. The dielectric constant and loss at 10 GHz were measured using a novel adaptation of the resonant cavity technique, which was designed for measurements at ambient and elevated temperatures. The method was used to measure of the dielectric constant and loss of two novel, high T(_g), electro-optic polymers at temperatures up to 100 ºC. The dielectric properties measured were typical of polymeric materials. The absorption coefficient and the refractive index at different wavelengths were measured using a spectrophotometer. For the refractive index, an interference fringe analysis was used. The nonlinear measurements consisted of second harmonic generation, to prove the nonhnearity of the composites, two-beam coupling measurements, to prove their photorefractivity and degenerate four-wave mixing to measure their diffraction efficiency. The NPP, DAN, DED and ULTRA-DEMI doped investigated composites exhibited second order nonlinearity with highest the one of ULTRA-DEMI, at 292 pm/V for 19 kV of corona poling field. The photorefractivity of the NPP, DAN and DED doped composites was proven at 632.8 nm, while ULTRA-DEMI doped composites photooxidized before any measurements were possible. The two-beam coupling coefficients measured were lower than 20 cm(^-3), while net gain was observed only in the NPP doped composite. The diffraction efficiencies of the NPP, DAN and DED doped composites were measured at 632.8 nm, and were found to be l0(^-5)-l0(^-6).

This work describes the preparation and use of the Plessey linear photodiode array in the observation of some stellar spectral features. An outline of the principles of the construction and operation of the diode array, along with some preliminary laboratory test results, form the initial part of this thesis. A suitable xy-movement control was designed and constructed, as well as the cryostat which was used to house the array at the coude focus of the telescope. Constraints at the telescope imposed several limitations, all of which had to be taken into consideration. The general experimental operation, signal processing, and control logic are all described, along with the data acquisition and storage techniques. Data reduction and analysis methods were developed to deal with difficulties peculiar to this type of photodiode array system. A theoretical investigation into the effects of the array geometry on the collection of spectra is described. On the astronomical side, observations of the neutral oxygen triplet at A7774 form the major set of results obtained. The equivalent width of A7774 can give information about the temperature absolute magnitude, and luminosity of many types of stars. The role of non-LTE is discussed, as well as its effect on the measurements of line widths. Finally, the phenomenon of stellar mass loss is outlined. Unfortunately, few results were obtained in this investigation. However, a description of the reasons behind the loss of matter from stars is given, along with probable mass loss mechanisms, features, and detection. A brief word on mass loss rates is included, but the lack of sufficient results in this region pre-empted any quantitative comparisons.

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