Study of payload technologies for future far-infrared space-based interferometers

Abstract

This thesis focuses on the study of three technologies that are strongly related to the development of payload instrumentation for a far-infrared space interferometer. Each of them tackles a different aspect that needs to be taken into account when designing such a mission, which specifically arise when observing in the wavelength range 25-400µm. In particular, attention is given to the following: how to best carry out high angular resolution interferometry using multiple telescopes; how to ensure the reliable and stable operation of a FIR instrument, used for both imaging and spectroscopy and how to avoid the contamination of the detected signal, caused by the self-emission of quasi-optical components at cryogenic temperatures. Firstly, the problem of designing and building a focal-plane interferometer is analysed both indirectly, through simulations of sparse-aperture systems, and directly, by carrying out feasibility studies with two optical experiments, designed to evaluate different technologies needed for its construction. Secondly, the design and build of a spectral-spatial calibration source for a far-IR, double-Fourier interferometer, is discussed. In particular, different suitable materials are reviewed by analysing their optical and thermal properties, through literature review and laboratory measurements. Then, two designs are described, by discussing their material composition and by carrying out finite-element simulations. Finally, the issues that can arise from the use of large, polymer-based, quasi-optical components, is analysed, in the context of cryogenic space applications. Specifically, the effect of their heating, and consequent re-irradiation at longer wavelength, is studied in the case of an instrument that operates on board a far-infrared space observatory and a sub-mm probe. In particular, a cryogenic model of the thermal and optical properties of these components is created and used to quantify this effect through finite-element analysis