Characterisation and Modelling of the UV-Vis/IR Transmission of Multilayer Thin Film Filters for Applications in High Energy Astrophysics

This M.Sc. in Physics thesis may be of interest to all of those who want to: get started in the science of the future ESA Athena mission, with its science goals and its payload being described as of the first semester of 2022; be introduced to the use of thin film optical blocking filters in X-ray missions, both in the used materials, scientific reasons, and history; understand the basics of UV-Vis-IR transmittance modelling of thin film multilayer structures; see a detailed introduction to some optical models for metals and dielectric materials; and finally, see a first-hand experimental investigation and modelling of samples of nanometric filters made of aluminized polyimide. This work deals with the experimental investigation and modelling of the UV-Vis-IR transmission of multilayer thin film filters (MTFFs) designed for Athena, the large space mission selected in 2014 by the European Space Agency (ESA) to study the Cosmic Vision theme ‘Hot and Energetic Universe’. The mission is composed of a large effective area X-ray telescope and two focal plane detectors, the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager (WFI). Both detectors need filters to block non-X-ray radiation while ensuring a high X-ray transmission. At the moment the mission is in the B1 definition phase; thus, along with all the satellite systems, the filters need to be properly studied by experimental tests to consolidate their preliminary design. In collaboration with UNIPA (Università degli Studi di Palermo) and INAF (Instituto Nazionale di AstroFisica), samples of the designed multi-layered thin film filters are analysed and modelled in the UV-Vis-IR radiation bands, to verify their shielding properties from electromagnetic radiation coming from the environment, from the astrophysical sources within the telescope field-of-view and, particularly for the X-IFU, IR emitted by warm surfaces inside the instrument cryostat. The main objective is to experimentally measure the transmission of the samples with FTIR-MIR (Fourier Transformed InfraRed spectroscopy) and UV/Vis/NIR spectroscopy techniques, to characterise them and to develop a proper transmission model in the electromagnetic band of interest, for ultimately assessing the instruments’ compliance with the mission’s requirements. An optical n-k model was developed for the polyimide layers, and a discussion of the possible improvements is available in the concluding paragraphs.All of the references are available in the thesis on page 102. I will publish a second version in the future, reworking aspects that were highlighted in the concluding paragraphs