DESIGN AND IMPLEMENTATION OF SPATIAL FILTERING AT COAST

By reducing the effects of wavefront phase corrugation caused by atmospheric turbulence, spa-tial filtering can redunce the uncertainties in visibility observations with optical/IR interferom-eters. The aim of the work described in this Thesis was to investigate the use of spatial filtering on astronomical optical interferometers and to construct an optimised filtering solution for the Cambridge Optical Aperture Synthesis Telescope (COAST). A numerical simulation was carried out to predict the performance of several different forms of spatial filtering. The results of this investigation led to the design of a pinhole spatial filtering system for use at COAST. This system used near-infrared achromatic lenses as the coupling optics and an array of different sized pinholes. All components were tested and a series of alignment schemes were devised for both the coupling optics and the pinholes. Tests of this system showed that the filters performed as expected, however inaccuracies in the tip-tilt wavfront correction at COAST limited the usefulness of the system in fast seeing conditions. This study demonstrated that pinhole spatial filtering is practical and effective way of introducing spatial filtering as an occasional instrumnet used for regular observing at a modern optical interferometer. The COAST spatial filtering system was used to investigate the separation and flux ratio of th