Radiometry of an Integrating Sphere for Telescopes with a Fibre-Fed Spectrograph

Domingos, Andreia Guerreiro

http://hdl.handle.net/10451/58213

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Authors

Domingos, Andreia Guerreiro

Advisor(s)

Cabral, Alexandre Pereira, 1968-

Abstract(s)

Astronomical instrumentation is one of the areas were optics have seen recently a considerable evolution, and spectroscopic observations of astronomical objects is one of the key subjects. The goal of this thesis is to study integrating spheres, within the scope of astronomical instrumentation, an optical component that will enable the integration of sunlight for further injection into a spectrograph, by means of an optical fibre. For this study, it is fundamental to define a model that can describe the properties of an integrating sphere. Resulting in a radiometric model of the sphere, which allows to determine the order of magnitude of the attenuation and the uniformity thus obtained. Several Monte Carlo methods were studied bibliographically, however, it was verified that they were complex and very time consuming, resulting in an accuracy that was not required for this application. In order to create a simplified model, equations and the calibrated tables of irradiance uniformity and radiance sphere were used by the manufacture of integrating spheres, Labsphere[1]. Another important goal the main goals was to characterize the integrating spheres experimentally, so as to validate the selected model. Several step-ups and experimental tests were performed that it allowed to verify and characterize the behaviour of integrating spheres in terms of uniformity, radiance, influence of the incident angle of the source, influence of the incident f-number of the source, and varying the distance from the detector to the sphere. Overall, the experimental results demonstrate that the simplified model is valid for the intended application, with an accuracy of 10% for the uniformity, and the tests validated the use of an integrating sphere for astronomical spectrography.